draft-ietf-taps-minset-00.txt   draft-ietf-taps-minset-01.txt 
TAPS M. Welzl TAPS M. Welzl
Internet-Draft S. Gjessing Internet-Draft S. Gjessing
Intended status: Informational University of Oslo Intended status: Informational University of Oslo
Expires: April 25, 2018 October 22, 2017 Expires: August 10, 2018 February 6, 2018
A Minimal Set of Transport Services for TAPS Systems A Minimal Set of Transport Services for TAPS Systems
draft-ietf-taps-minset-00 draft-ietf-taps-minset-01
Abstract Abstract
This draft recommends a minimal set of IETF Transport Services This draft recommends a minimal set of IETF Transport Services
offered by end systems supporting TAPS, and gives guidance on offered by end systems supporting TAPS, and gives guidance on
choosing among the available mechanisms and protocols. It is based choosing among the available mechanisms and protocols. It is based
on the set of transport features given in the TAPS document draft- on the set of transport features given in the TAPS document draft-
ietf-taps-transports-usage-08. ietf-taps-transports-usage-09.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 25, 2018. This Internet-Draft will expire on August 10, 2018.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The Minimal Set of Transport Features . . . . . . . . . . . . 5 3. The Minimal Set of Transport Features . . . . . . . . . . . . 5
3.1. Flow Creation . . . . . . . . . . . . . . . . . . . . . . 5 3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION . . . . . . . 5
3.2. Flow Connection and Termination . . . . . . . . . . . . . 7 3.2. MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Flow Group Configuration . . . . . . . . . . . . . . . . 8 3.3. DATA Transfer . . . . . . . . . . . . . . . . . . . . . . 9
3.4. Flow Configuration . . . . . . . . . . . . . . . . . . . 8 3.3.1. Sending Data . . . . . . . . . . . . . . . . . . . . 9
3.5. Data Transfer . . . . . . . . . . . . . . . . . . . . . . 9 3.3.2. Receiving Data . . . . . . . . . . . . . . . . . . . 10
3.5.1. The Sender . . . . . . . . . . . . . . . . . . . . . 9 4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5.2. The Receiver . . . . . . . . . . . . . . . . . . . . 10 4.1. ESTABLISHMENT, AVAILABILITY and TERMINATION . . . . . . . 11
4. An MinSet Abstract Interface . . . . . . . . . . . . . . . . 11 4.2. MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Specification . . . . . . . . . . . . . . . . . . . . . . 12 4.2.1. Connection groups . . . . . . . . . . . . . . . . . . 12
5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 17 4.2.2. Individual connections . . . . . . . . . . . . . . . 13
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 4.3. DATA Transfer . . . . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . 18 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 19 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
Appendix A. Deriving the minimal set . . . . . . . . . . . . . . 21 9.1. Normative References . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Deriving the minimal set . . . . . . . . . . . . . . 18
A.1. Step 1: Categorization -- The Superset of Transport A.1. Step 1: Categorization -- The Superset of Transport
Features . . . . . . . . . . . . . . . . . . . . . . . . 21 Features . . . . . . . . . . . . . . . . . . . . . . . . 19
A.1.1. CONNECTION Related Transport Features . . . . . . . . 23 A.1.1. CONNECTION Related Transport Features . . . . . . . . 20
A.1.2. DATA Transfer Related Transport Features . . . . . . 38 A.1.2. DATA Transfer Related Transport Features . . . . . . 36
A.2. Step 2: Reduction -- The Reduced Set of Transport A.2. Step 2: Reduction -- The Reduced Set of Transport
Features . . . . . . . . . . . . . . . . . . . . . . . . 43 Features . . . . . . . . . . . . . . . . . . . . . . . . 41
A.2.1. CONNECTION Related Transport Features . . . . . . . . 44 A.2.1. CONNECTION Related Transport Features . . . . . . . . 42
A.2.2. DATA Transfer Related Transport Features . . . . . . 45 A.2.2. DATA Transfer Related Transport Features . . . . . . 43
A.3. Step 3: Discussion . . . . . . . . . . . . . . . . . . . 46 A.3. Step 3: Discussion . . . . . . . . . . . . . . . . . . . 43
A.3.1. Sending Messages, Receiving Bytes . . . . . . . . . . 46 A.3.1. Sending Messages, Receiving Bytes . . . . . . . . . . 44
A.3.2. Stream Schedulers Without Streams . . . . . . . . . . 48 A.3.2. Stream Schedulers Without Streams . . . . . . . . . . 46
A.3.3. Early Data Transmission . . . . . . . . . . . . . . . 49 A.3.3. Early Data Transmission . . . . . . . . . . . . . . . 47
A.3.4. Sender Running Dry . . . . . . . . . . . . . . . . . 50 A.3.4. Sender Running Dry . . . . . . . . . . . . . . . . . 48
A.3.5. Capacity Profile . . . . . . . . . . . . . . . . . . 50 A.3.5. Capacity Profile . . . . . . . . . . . . . . . . . . 48
A.3.6. Security . . . . . . . . . . . . . . . . . . . . . . 51 A.3.6. Security . . . . . . . . . . . . . . . . . . . . . . 49
A.3.7. Packet Size . . . . . . . . . . . . . . . . . . . . . 51 A.3.7. Packet Size . . . . . . . . . . . . . . . . . . . . . 49
Appendix B. Revision information . . . . . . . . . . . . . . . . 52 Appendix B. Revision information . . . . . . . . . . . . . . . . 49
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
1. Introduction 1. Introduction
The task of any system that implements TAPS is to offer transport The task of any system that implements TAPS is to offer transport
services to its applications, i.e. the applications running on top of services to its applications, i.e. the applications running on top of
TAPS, without binding them to a particular transport protocol. TAPS, without binding them to a particular transport protocol.
Currently, the set of transport services that most applications use Currently, the set of transport services that most applications use
is based on TCP and UDP; this limits the ability for the network is based on TCP and UDP (and protocols running on top of them); this
stack to make use of features of other protocols. For example, if a limits the ability for the network stack to make use of features of
protocol supports out-of-order message delivery but applications other protocols. For example, if a protocol supports out-of-order
always assume that the network provides an ordered bytestream, then message delivery but applications always assume that the network
the network stack can never utilize out-of-order message delivery: provides an ordered bytestream, then the network stack can never
doing so would break a fundamental assumption of the application. utilize out-of-order message delivery: doing so would break a
fundamental assumption of the application.
By exposing the transport services of multiple transport protocols, a By exposing the transport services of multiple transport protocols, a
TAPS system can make it possible to use these services without having TAPS system can make it possible to use these services without having
to statically bind an application to a specific transport protocol. to statically bind an application to a specific transport protocol.
The first step towards the design of such a system was taken by The first step towards the design of such a system was taken by
[RFC8095], which surveys a large number of transports, and [TAPS2] as [RFC8095], which surveys a large number of transports, and [TAPS2] as
well as [TAPS2UDP], which identify the specific transport features well as [TAPS2UDP], which identify the specific transport features
that are exposed to applications by the protocols TCP, MPTCP, UDP(- that are exposed to applications by the protocols TCP, MPTCP, UDP(-
Lite) and SCTP as well as the LEDBAT congestion control mechanism. Lite) and SCTP as well as the LEDBAT congestion control mechanism.
The present draft is based on these documents and follows the same The present draft is based on these documents and follows the same
terminology (also listed below). terminology (also listed below). Because the considered transport
protocols together cover a wide range of transport features, there is
reason to hope that the resulting set (and the reasoning that led to
it) will also apply to many aspects of other transport protocols such
as QUIC.
The number of transport features of current IETF transports is large, The number of transport features of current IETF transports is large,
and exposing all of them has a number of disadvantages: generally, and exposing all of them has a number of disadvantages: generally,
the more functionality is exposed, the less freedom a TAPS system has the more functionality is exposed, the less freedom a TAPS system has
to automate usage of the various functions of its available set of to automate usage of the various functions of its available set of
transport protocols. Some functions only exist in one particular transport protocols. Some functions only exist in one particular
protocol, and if an application would use them, this would statically protocol, and if an application would use them, this would statically
tie the application to this protocol, counteracting the purpose of a tie the application to this protocol, counteracting the purpose of a
TAPS system. Also, if the number of exposed features is exceedingly TAPS system. Also, if the number of exposed features is exceedingly
large, a TAPS system might become very hard to use for an application large, a TAPS system might become very hard to use for an application
skipping to change at page 3, line 44 skipping to change at page 3, line 52
transport functionality. transport functionality.
Applications use a wide variety of APIs today. The transport Applications use a wide variety of APIs today. The transport
features in the minimal set in this document must be reflected in features in the minimal set in this document must be reflected in
*all* network APIs in order for the underlying functionality to *all* network APIs in order for the underlying functionality to
become usable everywhere. For example, it does not help an become usable everywhere. For example, it does not help an
application that talks to a middleware if only the Berkeley Sockets application that talks to a middleware if only the Berkeley Sockets
API is extended to offer "unordered message delivery", but the API is extended to offer "unordered message delivery", but the
middleware only offers an ordered bytestream. Both the Berkeley middleware only offers an ordered bytestream. Both the Berkeley
Sockets API and the middleware would have to expose the "unordered Sockets API and the middleware would have to expose the "unordered
message delivery" transport feature (alternatively, there may be message delivery" transport feature (alternatively, there may be ways
interesting ways for certain types of middleware to use some for certain types of middleware to use this transport feature without
transport features without exposing them, based on knowledge about exposing it, based on knowledge about the applications -- but this is
the applications -- but this is not the general case). In most not the general case). In most situations, in the interest of being
situations, in the interest of being as flexible and efficient as as flexible and efficient as possible, the best choice will be for a
possible, the best choice will be for a middleware or library to middleware or library to expose at least all of the transport
expose at least all of the transport features that are recommended as features that are recommended as a "minimal set" here.
a "minimal set" here.
This "minimal set" can be implemented one-sided with a fall-back to This "minimal set" can be implemented one-sided over TCP (or UDP, if
TCP (or UDP, if certain limitations are put in place). This means certain limitations are put in place). This means that a sender-side
that a sender-side TAPS system can talk to a non-TAPS TCP (or UDP) TAPS system implementing it can talk to a non-TAPS TCP (or UDP)
receiver, and a receiver-side TAPS system can talk to a non-TAPS TCP receiver, and a receiver-side TAPS system implementing it can talk to
(or UDP) sender. For systems that do not have this requirement, a non-TAPS TCP (or UDP) sender.
[I-D.trammell-taps-post-sockets] describes a way to extend the
functionality of the minimal set such that some of its limitations
are removed.
2. Terminology 2. Terminology
The following terms are used throughout this document, and in The following terms are used throughout this document, and in
subsequent documents produced by TAPS that describe the composition subsequent documents produced by TAPS that describe the composition
and decomposition of transport services. and decomposition of transport services.
Transport Feature: a specific end-to-end feature that the transport Transport Feature: a specific end-to-end feature that the transport
layer provides to an application. Examples include layer provides to an application. Examples include
confidentiality, reliable delivery, ordered delivery, message- confidentiality, reliable delivery, ordered delivery, message-
skipping to change at page 5, line 9 skipping to change at page 5, line 11
Moreover, throughout the document, the protocol name "UDP(-Lite)" is Moreover, throughout the document, the protocol name "UDP(-Lite)" is
used when discussing transport features that are equivalent for UDP used when discussing transport features that are equivalent for UDP
and UDP-Lite; similarly, the protocol name "TCP" refers to both TCP and UDP-Lite; similarly, the protocol name "TCP" refers to both TCP
and MPTCP. and MPTCP.
3. The Minimal Set of Transport Features 3. The Minimal Set of Transport Features
Based on the categorization, reduction and discussion in Appendix A, Based on the categorization, reduction and discussion in Appendix A,
this section describes the minimal set of transport features that is this section describes the minimal set of transport features that is
offered by end systems supporting TAPS. This TAPS system is able to offered by end systems supporting TAPS. This TAPS system can be
fall back to TCP; elements of the system that may prohibit falling implemented over TCP; elements of the system that may prohibit
back to UDP are marked with "!UDP". To implement a TAPS system that implementation over UDP are marked with "!UDP". To implement a TAPS
is also able to fall back to UDP, these marked transport features system that can also work over UDP, these marked transport features
should be excluded. should be excluded.
3.1. Flow Creation As in Appendix A, Appendix A.2 and [TAPS2], we categorize the minimal
set of transport features as 1) CONNECTION related (ESTABLISHMENT,
AVAILABILITY, MAINTENANCE, TERMINATION) and 2) DATA Transfer related
(Sending Data, Receiving Data, Errors). Here, the focus is on "TAPS
Connections": connections that the TAPS system offers, as opposed to
connections of transport protocols that the TAPS system uses.
A TAPS flow must be "created" before it is connected, to allow for 3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION
initial configurations to be carried out. All configuration
parameters in Section 3.3 and Section 3.4 can be used initially,
although some of them may only take effect when the flow has been
connected. Configuring a flow early helps a TAPS system make the
right decisions. In particular, the "group number" can influence the
TAPS system to implement a TAPS flow as a stream of a multi-streaming
protocol's existing association or not.
For flows that use a new "group number", early configuration is A TAPS connection must first be "created" to allow for some initial
necessary because it allows the TAPS system to know which protocols configuration to be carried out before the TAPS system can actively
it should try to use (to steer a mechanism such as "Happy Eyeballs" or passively establish a transport connection. All configuration
parameters in Section 3.2 and can be used initially, although some of
them may only take effect when a transport connection has been
established. Configuring a connection early helps a TAPS system make
the right decisions. In particular, grouping information can
influence the TAPS system to implement a TAPS connection as a stream
of a multi-streaming protocol's existing association or not.
For ungrouped TAPS connections, early configuration is necessary
because it allows the TAPS system to know which protocols it should
try to use (to steer a mechanism such as "Happy Eyeballs"
[I-D.grinnemo-taps-he]). In particular, a TAPS system that only [I-D.grinnemo-taps-he]). In particular, a TAPS system that only
makes a one-time choice for a particular protocol must know early makes a one-time choice for a particular protocol must know early
about strict requirements that must be kept, or it can end up in a about strict requirements that must be kept, or it can end up in a
deadlock situation (e.g., having chosen UDP and later be asked to deadlock situation (e.g., having chosen UDP and later be asked to
support reliable transfer). As one possibility to correctly handle support reliable transfer). As a possibility to correctly handle
these cases, we provide the following decision tree (this is derived these cases, we provide the following decision tree (this is derived
from Appendix A.2.1 excluding authentication, as explained in from Appendix A.2.1 excluding authentication, as explained in
Section 8): Section 8):
- Will it ever be necessary to offer any of the following? - Will it ever be necessary to offer any of the following?
* Reliably transfer data * Reliably transfer data
* Notify the peer of closing/aborting * Notify the peer of closing/aborting
* Preserve data ordering * Preserve data ordering
Yes: SCTP or TCP can be used. Yes: SCTP or TCP can be used.
- Is any of the following useful to the application? - Is any of the following useful to the application?
* Choosing a scheduler to operate between flows in a group, * Choosing a scheduler to operate between TAPS connections
with the possibility to configure a priority or weight per flow in a group, with the possibility to configure a priority
or weight per connection
* Configurable message reliability * Configurable message reliability
* Unordered message delivery * Unordered message delivery
* Request not to delay the acknowledgement (SACK) of a message * Request not to delay the acknowledgement (SACK) of a message
Yes: SCTP is preferred. Yes: SCTP is preferred.
No: No:
- Is any of the following useful to the application? - Is any of the following useful to the application?
* Hand over a message to reliably transfer (possibly * Hand over a message to reliably transfer (possibly
multiple times) before connection establishment multiple times) before connection establishment
* Suggest timeout to the peer * Suggest timeout to the peer
skipping to change at page 6, line 44 skipping to change at page 6, line 45
* Specify minimum checksum coverage required by receiver * Specify minimum checksum coverage required by receiver
Yes: UDP-Lite is preferred. Yes: UDP-Lite is preferred.
No: UDP is preferred. No: UDP is preferred.
Note that this decision tree is not optimal for all cases. For Note that this decision tree is not optimal for all cases. For
example, if an application wants to use "Specify checksum coverage example, if an application wants to use "Specify checksum coverage
used by the sender", which is only offered by UDP-Lite, and used by the sender", which is only offered by UDP-Lite, and
"Configure priority or weight for a scheduler", which is only offered "Configure priority or weight for a scheduler", which is only offered
by SCTP, the above decision tree will always choose UDP-Lite, making by SCTP, the above decision tree will always choose UDP-Lite, making
it impossible to use SCTP's schedulers with priorities between flows it impossible to use SCTP's schedulers with priorities between
in a group. The TAPS system must know which choice is more important grouped TAPS connections. The TAPS system must know which choice is
for the application in order to make the best decision. We caution more important for the application in order to make the best
implementers to be aware of the full set of trade-offs, for which we decision. We caution implementers to be aware of the full set of
recommend consulting the list in Appendix A.2.1 when deciding how to trade-offs, for which we recommend consulting the list in
initialize a flow. Appendix A.2.1 when deciding how to initialize a TAPS connection.
Once a flow is created, it can be queried for the maximum amount of
data that an application can possibly expect to have reliably
transmitted before or during connection establishment (with zero
being a possible answer). An application can also give the flow a
message for reliable transmission before or during connection
establishment (!UDP); the TAPS system will then try to transmit it as
early as possible. An application can facilitate sending the message
particularly early by marking it as "idempotent"; in this case, the
receiving application must be prepared to potentially receive
multiple copies of the message (because idempotent messages are
reliably transferred, asking for idempotence is not necessary for
systems that support UDP-fall-back).
3.2. Flow Connection and Termination
To be compatible with multiple transports, including streams of a Once a TAPS connection is created, it can be queried for the maximum
multi-streaming protocol (used as if they were transports amount of data that an application can possibly expect to have
themselves), the semantics of opening and closing need to be the most reliably transmitted before or during transport connection
restrictive subset of all of them. For example, TCP's support of establishment (with zero being a possible answer). An application
half-closed connections can be seen as a feature on top of the more can also give the TAPS connection a message for reliable transmission
restrictive "ABORT"; this feature cannot be supported because not all before or during connection establishment (!UDP); the TAPS system
protocols used by a TAPS system (including streams of an association) will then try to transmit it as early as possible. An application
support half-closed connections. can facilitate sending the message particularly early by marking it
as "idempotent"; in this case, the receiving application must be
prepared to potentially receive multiple copies of the message
(because idempotent messages are reliably transferred, asking for
idempotence is not necessary for systems that support UDP).
After creation, a flow can be actively connected to the other side After creation, a TAPS system can actively establish communication
using "Connect", or it can passively listen for incoming connection with a peer, or it can passively listen for incoming connection
requests with "Listen". Note that "Connect" may or may not trigger a requests. Note that "Establish" may or may not trigger a
notification on the listening side. It is possible that the first notification on the listening side. It is possible that the first
notification on the listening side is the arrival of the first data notification on the listening side is the arrival of the first data
that the active side sends (a receiver-side TAPS system could handle that the active side sends (a receiver-side TAPS system could handle
this by continuing to block a "Listen" call, immediately followed by this by continuing to block a "Listen" call, immediately followed by
issuing "Receive", for example; callback-based implementations may issuing "Receive", for example; callback-based implementations could
simply skip the equivalent of "Listen"). This also means that the simply skip the equivalent of "Listen"). This also means that the
active opening side is assumed to be the first side sending data. active opening side is assumed to be the first side sending data.
A TAPS system can actively close a connection, i.e. terminate it A TAPS system can actively close a connection, i.e. terminate it
after reliably delivering all remaining data to the peer, or it can after reliably delivering all remaining data to the peer, or it can
abort it, i.e. terminate it without delivering remaining data. abort it, i.e. terminate it without delivering remaining data.
Unless all data transfers only used unreliable frame transmission Unless all data transfers only used unreliable message transmission
without congestion control (i.e., UDP-style transfer), closing a without congestion control (i.e., UDP-style transfer), closing a
connection is guaranteed to cause an event to notify the peer connection is guaranteed to cause an event to notify the peer
application that the connection has been closed (!UDP). Similarly, application that the connection has been closed (!UDP). Similarly,
for anything but (UDP-style) unreliable non-congestion-controlled for anything but (UDP-style) unreliable non-congestion-controlled
data transfer, aborting a connection will cause an event to notify data transfer, aborting a connection will cause an event to notify
the peer application that the connection has been aborted (!UDP). A the peer application that the connection has been aborted (!UDP). A
timeout can be configured to abort a flow when data could not be timeout can be configured to abort a TAPS connection when data could
delivered for too long (!UDP); however, timeout-based abortion does not be delivered for too long (!UDP); however, timeout-based abortion
not notify the peer application that the connection has been aborted. does not notify the peer application that the connection has been
aborted. Because half-closed connections are not supported, when a
Because half-closed connections are not supported, when a TAPS host TAPS host receives a notification that the peer is closing or
receives a notification that the peer is closing or aborting the flow aborting the connection (!UDP), its peer may not be able to read
(!UDP), the other side may not be able to read outstanding data. outstanding data. This means that unacknowledged data residing in
This means that unacknowledged data residing in the TAPS system's the TAPS system's send buffer may have to be dropped from that buffer
send buffer may have to be dropped from that buffer upon arrival of a upon arrival of a "close" or "abort" notification from the peer.
notification to close or abort the flow from the peer.
3.3. Flow Group Configuration 3.2. MAINTENANCE
A flow group can be configured with a number of transport features, A TAPS connection group can be configured with a number of transport
and there are some notifications to applications about a flow group. features, and there are some notifications to applications about a
Here we list transport features and notifications from Appendix A.2 connection group. The following transport features and notifications
that sometimes automatically apply to groups of flows (e.g., when a from Appendix A.2 automatically apply to grouped TAPS connections
flow is mapped to a stream of a multi-streaming protocol). (e.g., when a TAPS connection is mapped to a stream of a multi-
streaming protocol):
Timeout, error notifications: Timeout, error notifications:
o Change timeout for aborting connection (using retransmit limit or o Change timeout for aborting connection (using retransmit limit or
time value) (!UDP) time value) (!UDP)
o Suggest timeout to the peer (!UDP) o Suggest timeout to the peer (!UDP)
o Notification of Excessive Retransmissions (early warning below o Notification of Excessive Retransmissions (early warning below
abortion threshold) abortion threshold)
o Notification of ICMP error message arrival o Notification of ICMP error message arrival
Others: Others:
o Choose a scheduler to operate between flows of a group o Choose a scheduler to operate between connections of a group
o Obtain ECN field o Obtain ECN field
The following transport features are new or changed, based on the The following transport features are new or changed, based on the
discussion in Appendix A.3: discussion in Appendix A.3:
o Capacity profile o Capacity profile
This describes how an application wants to use its available This describes how an application wants to use its available
capacity. Choices can be "lowest possible latency at the expense capacity. Choices can be "lowest possible latency at the expense
of overhead" (which would disable any Nagle-like algorithm), of overhead" (which would disable any Nagle-like algorithm),
"scavenger", and some more values that help determine the DSCP "scavenger", and values that help determine the DSCP value for a
value for a flow (e.g. similar to table 1 in connection (e.g. similar to table 1 in
[I-D.ietf-tsvwg-rtcweb-qos]). [I-D.ietf-tsvwg-rtcweb-qos]).
3.4. Flow Configuration The following transport features and notifications from Appendix A.2
only apply to a single TAPS connection:
Here we list transport features and notifications from Appendix A.2
that only apply to a single flow.
Configure priority or weight for a scheduler Configure priority or weight for a scheduler
Checksums: Checksums:
o Disable checksum when sending o Disable checksum when sending
o Disable checksum requirement when receiving o Disable checksum requirement when receiving
o Specify checksum coverage used by the sender o Specify checksum coverage used by the sender
o Specify minimum checksum coverage required by receiver o Specify minimum checksum coverage required by receiver
A TAPS system must offer means to group connections; at the same
time, it cannot guarantee truly grouping them below (e.g., it cannot
be guaranteed that TAPS connections become multiplexed as streams on
a single SCTP association when SCTP may not be available). The TAPS
system must therefore ensure that group versus non-group
configurations listed above are handled correctly in some way (e.g.,
by applying the configuration to all grouped connections even when
they are not multiplexed, or informing the application about grouping
success or failure).
3.5. Data Transfer 3.3. DATA Transfer
3.5.1. The Sender 3.3.1. Sending Data
This section discusses how to send data after flow establishment. This section discusses how to send data after connection
Section 3.2 discusses the possiblity to hand over a message to establishment. Section 3.1 discusses the possiblity to hand over a
reliably send before or during establishment. message to reliably send before or during establishment.
Here we list per-frame properties that a sender can optionally Here we list per-message properties that a sender can optionally
configure if it hands over a delimited frame for sending with configure if it hands over a delimited message for sending with
congestion control (!UDP), taken from Appendix A.2: congestion control (!UDP), taken from Appendix A.2:
o Configurable Message Reliability o Configurable Message Reliability
o Ordered message delivery (potentially slower than unordered) o Ordered message delivery (potentially slower than unordered)
o Unordered message delivery (potentially faster than ordered) o Unordered message delivery (potentially faster than ordered)
o Request not to bundle messages o Request not to bundle messages
o Request not to delay the acknowledgement (SACK) of a message o Request not to delay the acknowledgement (SACK) of a message
Additionally, an application can hand over delimited frames for Additionally, an application can hand over delimited messages for
unreliable transmission without congestion control (note that such unreliable transmission without congestion control (note that such
applications should perform congestion control in accordance with applications should perform congestion control in accordance with
[RFC2914]). Then, none of the per-frame properties listed above have [RFC2914]). Then, none of the per-message properties listed above
any effect, but it is possible to use the transport feature "Specify have any effect, but it is possible to use the transport feature
DF field" to allow/disallow fragmentation. "Specify DF field" to allow/disallow fragmentation.
Following Appendix A.3.7, there are three transport features (two Following Appendix A.3.7, there are three transport features (two
old, one new) and a notification: old, one new):
o Get max. transport frame size that may be sent without o Get max. transport message size that may be sent without
fragmentation from the configured interface fragmentation from the configured interface
This is optional for a TAPS system to offer, and may return an This is optional for a TAPS system to offer, and may return an
error ("not available"). It can aid applications implementing error ("not available"). It can aid applications implementing
Path MTU Discovery. Path MTU Discovery.
o Get max. transport frame size that may be received from the o Get max. transport message size that may be received from the
configured interface configured interface
This is optional for a TAPS system to offer, and may return an This is optional for a TAPS system to offer, and may return an
error ("not available"). error ("not available").
o Get maximum transport frame size o Get maximum transport message size
Irrespective of fragmentation, there is a size limit for the Irrespective of fragmentation, there is a size limit for the
messages that can be handed over to SCTP or UDP(-Lite); because a messages that can be handed over to SCTP or UDP(-Lite); because a
TAPS system is independent of the transport, it must allow a TAPS TAPS system is independent of the transport, it must allow a TAPS
application to query this value -- the maximum size of a frame in application to query this value -- the maximum size of a message
an Application-Framed-Bytestream. This may also return an error in an Application-Framed-Bytestream (see Appendix A.3.1). This
when frames are not delimited ("not available"). may also return an error when data is not delimited ("not
available").
There are two more sender-side notifications. These are unreliable, There are two more sender-side notifications. These are unreliable,
i.e. a TAPS system cannot be assumed to implement them, but they may i.e. a TAPS system cannot be assumed to implement them, but they may
occur: occur:
o Notification of send failures o Notification of send failures
A TAPS system may inform a sender application of a failure to send A TAPS system may inform a sender application of a failure to send
a specific frame. a specific message.
o Notification of draining below a low water mark o Notification of draining below a low water mark
A TAPS system can notify a sender application when the TAPS A TAPS system can notify a sender application when the TAPS
system's filling level of the buffer of unsent data is below a system's filling level of the buffer of unsent data is below a
configurable threshold in bytes. Even for TAPS systems that do configurable threshold in bytes. Even for TAPS systems that do
implement this notification, supporting thresholds other than 0 is implement this notification, supporting thresholds other than 0 is
optional. optional.
"Notification of draining below a low water mark" is a generic "Notification of draining below a low water mark" is a generic
notification that tries to enable uniform access to notification that tries to enable uniform access to
"TCP_NOTSENT_LOWAT" as well as the "SENDER DRY" notification (as "TCP_NOTSENT_LOWAT" as well as the "SENDER DRY" notification (as
discussed in Appendix A.3.4 -- SCTP's "SENDER DRY" is a special case discussed in Appendix A.3.4 -- SCTP's "SENDER DRY" is a special case
where the threshold (for unsent data) is 0 and there is also no more where the threshold (for unsent data) is 0 and there is also no more
unacknowledged data in the send buffer). Note that this threshold unacknowledged data in the send buffer). Note that this threshold
and its notification should operate across the buffers of the whole and its notification should operate across the buffers of the whole
TAPS system, i.e. also any potential buffers that the TAPS system TAPS system, i.e. also any potential buffers that the TAPS system
itself may use on top of the transport's send buffer. itself may use on top of the transport's send buffer.
3.5.2. The Receiver 3.3.2. Receiving Data
A receiving application obtains an Application-Framed Bytestream.
Similar to TCP's receiver semantics, it is just a stream of bytes.
If frame boundaries were specified by the sender, a receiver-side
TAPS system will still not inform the receiving application about
them. Within the bytestream, frames themselves will always stay
intact (partial frames are not supported - see Appendix A.3.1).
Different from TCP's semantics, there is no guarantee that all frames
in the bytestream are transmitted from the sender to the receiver,
and that all of them are in the same sequence in which they were
handed over by the sender. If an application is aware of frame
delimiters in the bytestream, and if the sender-side application has
informed the TAPS system about these boundaries and about potentially
relaxed requirements regarding the sequence of frames or per-frame
reliability, frames within the receiver-side bytestream may be out-
of-order or missing.
4. An MinSet Abstract Interface
Here we present the minimum set in the form of an abstract interface
that a TAPS system could implement. This abstract interface is
derived from the description in the previous section. The primitives
of this abstract interface can be implemented in various ways. For
example, information that is provided to an application can either be
offered via a primitive that is polled, or via an asynchronous
notification.
We note that this is just a different form to represent the text in
the previous section, and not an abstract API that is recommended to
be implemented in this form by all TAPS systems. Specifically, TAPS
systems implementing this specific abstract interface would have the
following properties:
1. Support one-sided deployment with a fall-back to TCP (or UDP) A receiving application obtains an "Application-Framed Bytestream"
2. Offer all the transport features of (MP)TCP, UDP(-Lite), LEDBAT (AFra-Bytestream); this concept is further described in
and SCTP that require application-specific knowledge Appendix A.3.1). In line with TCP's receiver semantics, an AFra-
3. Not offer any of the transport features of these protocols and Bytestream is just a stream of bytes to the receiver. If message
the LEDBAT congestion control mechanism that do not require boundaries were specified by the sender, a receiver-side TAPS system
application-specific knowledge (to give maximum flexibility to a implementing only the minimum set of transport services defined here
TAPS system) will still not inform the receiving application about them. Within
the bytestream, messages themselves will always stay intact (partial
messages are not supported). Different from TCP's semantics, there
is no guarantee that all messages in the bytestream are transmitted
from the sender to the receiver, and that all of them are in the same
sequence in which they were handed over by the sender. If an
application is aware of message delimiters in the bytestream, and if
the sender-side application has informed the TAPS system about these
boundaries and about potentially relaxed requirements regarding the
sequence of messages or per-message reliability, messages within the
receiver-side bytestream may be out-of-order or missing.
This reciprocally means that this is probably not the ideal interface 4. Summary
to implement for systems that:
1. Assume that there is a system on both sides -- in this case, Here we summarize the minimum set of transport features in a more
richer functionality can be provided (cf. compact form.
[I-D.trammell-taps-post-sockets]) -- or assume different fall-
back protocols than TCP or UDP
2. Use other protocols than (MP)TCP, UDP(-Lite), SCTP or the LEDBAT
congestion control mechanism underneath the TAPS interface
3. Want to offer transport features that do not require application-
specific knowledge
4.1. Specification 4.1. ESTABLISHMENT, AVAILABILITY and TERMINATION
CREATE (flow-group-id, reliability, checksum_coverage, A TAPS connection is created and associated with an existing or new
config_msg_prio, earlymsg_timeout_notifications) TAPS connection group. Grouping can influence the TAPS system to
Returns: flow-id multiplex TAPS connections on a single transport connection or not,
and the other parameters serve as input to the decision tree
described in Section 3.1. The TAPS systems gives no guarantees about
honoring any of the requests at this stage, these parameters are just
meant to help it choose and configure a suitable protocol. Note that
the parameters below affect all grouped TAPS connections.
Create a flow and associate it with an existing or new flow group A TAPS connection can actively connect to a peer; this may or may not
number. The group number can influence the TAPS system to implement trigger a notification on the listening side. If the application
a TAPS flow as a stream of a multi-streaming protocol's existing sends data (see Section 4.3) before the TAPS system establishes a
association or not, and the other parameters serve as input to the transport connection, then such data may be transmitted early, upon
decision tree described in Section 3.1. The TAPS systems gives no connecting. When a TAPS system listens for incoming connections, the
guarantees about honoring any of the requests at this stage, these first arriving message may already be the first block of data.
parameters are just meant to help it to choose and configure a
suitable protocol.
PARAMETERS: Creation / connection / configuration parameters:
flow-group-id: the flow's group number; all other parameters are
only relevant when this number is not currently in use by an
ongoing flow to the same destination (in which case the flow
becomes a member of the existing flow's group and inherits the
configuration of the group).
reliability: a boolean that should be set to true when any of the reliability: a boolean that should be set to true when any of the
following will be useful to the application: reliably transfer following will be useful to the application: reliably transfer
data; notify the peer of closing/aborting; preserve data ordering. data; notify the peer of closing/aborting; preserve data ordering.
checksum_coverage: a boolean to specify whether it will be useful to checksum_coverage: a boolean to specify whether it will be useful to
the application to specify checksum coverage when sending or the application to specify checksum coverage when sending or
receiving. receiving.
config_msg_prio: a boolean that should be set to true when any of config_msg_prio: a boolean that should be set to true when any of
the following per-message configuration or prioritization the following per-message configuration or prioritization
mechanisms will be useful to the application: choosing a scheduler mechanisms will be useful to the application: choosing a scheduler
to operate between flows in a group, with the possibility to to operate between grouped connections, with the possibility to
configure a priority or weight per flow; configurable message configure a priority or weight per connection; configurable
reliability; unordered message delivery; requesting not to delay message reliability; unordered message delivery; requesting not to
the acknowledgement (SACK) of a message. delay the acknowledgement (SACK) of a message.
earlymsg_timeout_notifications: a boolean that should be set to true earlymsg_timeout_notifications: a boolean that should be set to true
when any of the following will be useful to the application: hand when any of the following will be useful to the application: hand
over a message to reliably transfer (possibly multiple times) over a message to reliably transfer (possibly multiple times)
before connection establishment; suggest timeout to the peer; before connection establishment; suggest timeout to the peer;
notification of excessive retransmissions (early warning below notification of excessive retransmissions (early warning below
abortion threshold); notification of ICMP error message arrival. abortion threshold); notification of ICMP error message arrival.
(!UDP) CONFIGURE_TIMEOUT (flow-group-id [timeout] [peer_timeout] A TAPS connection can be closed after all outstanding data is
[retrans_notify]) reliably delivered to the peer (if reliable data delivery was
requested earlier (!UDP)), in which case the peer is notified that
This configures timeouts for all flows in a group. Configuration the connection is closed. Alternatively, a TAPS connection can be
should generally be carried out as early as possible, ideally before aborted without delivering outstanding data to the peer. In case
flows are connected, to aid the TAPS system's decision taking. reliable or partially reliable data delivery was requested earlier
(!UDP), the peer is notified that the connection is aborted.
PARAMETERS:
timeout: a timeout value for aborting connections, in seconds
peer_timeout: a timeout value to be suggested to the peer (if
possible), in seconds
retrans_notify: the number of retransmissions after which the
application should be notifed of "Excessive Retransmissions"
CONFIGURE_CHECKSUM (flow-id [send [send_length]] [receive 4.2. MAINTENANCE
[receive_length]])
This configures the usage of checksums for a flow in a group. As a general rule, any configuration described below should be
Configuration should generally be carried out as early as possible, carried out as early as possible to aid the TAPS system's decision
ideally before the flow is connected, to aid the TAPS system's taking.
decision taking. "send" parameters concern using a checksum when
sending, "receive" parameters concern requiring a checksum when
receiving. There is no guarantee that any checksum limitations will
indeed be enforced; all defaults are: "full coverage, checksum
enabled".
PARAMETERS: 4.2.1. Connection groups
send: boolean, enable / disable usage of a checksum The transport features below apply to all TAPS connections in the
send_length: if send is true, this optional parameter can provide same group:
the desired coverage of the checksum in bytes
receive: boolean, enable / disable requiring a checksum
receive_length: if receive is true, this optional parameter can
provide the required minimum coverage of the checksum in bytes
CONFIGURE_URGENCY (flow-group-id [scheduler] [capacity_profile] (!UDP) Configure a timeout: this can be done with the following
[low_watermark]) parameters:
This carries out configuration related to the urgency of sending data o A timeout value for aborting connections, in seconds
on flows of a group. Configuration should generally be carried out o A timeout value to be suggested to the peer (if possible), in
as early as possible, ideally before flows are connected, to aid the seconds
TAPS system's decision taking. o The number of retransmissions after which the application should
be notifed of "Excessive Retransmissions"
PARAMETERS: Configure urgency: this can be done with the following parameters:
scheduler: a number to identify the type of scheduler that should be o A number to identify the type of scheduler that should be used to
used to operate between flows in the group (no guarantees given). operate between connections in the group (no guarantees given).
Future versions of this document will be self contained, but for Schedulers are defined in [RFC8260].
now we suggest the schedulers defined in o A "capacity profile" number to identify how an application wants
[I-D.ietf-tsvwg-sctp-ndata]. to use its available capacity. Choices can be "lowest possible
capacity_profile: a number to identify how an application wants to
use its available capacity. Future versions of this document will
be self contained, but for now choices can be "lowest possible
latency at the expense of overhead" (which would disable any latency at the expense of overhead" (which would disable any
Nagle-like algorithm), "scavenger", and some more values that help Nagle-like algorithm), "scavenger", or values that help determine
determine the DSCP value for a flow (e.g. similar to table 1 in the DSCP value for a connection (e.g. similar to table 1 in
[I-D.ietf-tsvwg-rtcweb-qos]). [I-D.ietf-tsvwg-rtcweb-qos]).
low_watermark: a buffer limit (in bytes); when the sender has less o A buffer limit (in bytes); when the sender has less then
then low_watermark bytes in the buffer, the application may be low_watermark bytes in the buffer, the application may be
notified. Notifications are not guaranteed, and supporting notified. Notifications are not guaranteed, and supporting
watermark numbers greater than 0 is not guaranteed. watermark values greater than 0 is not guaranteed.
CONFIGURE_PRIORITY (flow-id priority)
This configures a flow's priority or weight for a scheduler.
Configuration should generally be carried out as early as possible,
ideally before flows are connected, to aid the TAPS system's decision
taking.
PARAMETERS:
priority: future versions of this document will be self contained, The following properties can be queried:
but for now we suggest the priority as described in
[I-D.ietf-tsvwg-sctp-ndata].
NOTIFICATIONS o The maximum message size that may be sent without fragmentation,
Returns: flow-group-id notification_type in bytes (or "not available")
o The maximum transport message size that can be sent, in bytes (or
"not available")
o The maximum transport message size that can be received, in bytes
(or "not available")
o The maximum amount of data that can possibly be sent before or
during connection establishment, in bytes (or "not available")
This is fired when an event occurs, notifying the application about In addition to the already mentioned closing / aborting notifications
something happening in relation to a flow group. Notification types and possible send errors, the following notifications can occur:
are:
Excessive Retransmissions: the configured (or a default) number of o Excessive Retransmissions: the configured (or a default) number of
retransmissions has been reached, yielding this early warning retransmissions has been reached, yielding this early warning
below an abortion threshold. below an abortion threshold.
ICMP Arrival (parameter: ICMP message): an ICMP packet carrying the o ICMP Arrival (parameter: ICMP message): an ICMP packet carrying
conveyed ICMP message has arrived. the conveyed ICMP message has arrived.
ECN Arrival (parameter: ECN value): a packet carrying the conveyed o ECN Arrival (parameter: ECN value): a packet carrying the conveyed
ECN value has arrived. This can be useful for applications ECN value has arrived. This can be useful for applications
implementing congestion control. implementing congestion control.
Timeout (parameter: s seconds): data could not be delivered for s o Timeout (parameter: s seconds): data could not be delivered for s
seconds. seconds.
Close: the peer has closed the connection. The peer has no more o Drain: the send buffer has either drained below the configured low
data to send, and will not read more data. Data that is in
transit or resides in the local send buffer will be discarded.
Abort: the peer has aborted the connection. The peer has no more
data to send, and will not read more data. Data that is in
transit or resides in the local send buffer will be discarded.
Note that there is no guarantee that this notification will be
invoked when the peer aborts.
Drain: the send buffer has either drained below the configured low
water mark or it has become completely empty. water mark or it has become completely empty.
Path Change (parameter: path identifier): the path has changed; the
path identifier is a number that can be used to determine a
previously used path is used again (e.g., the TAPS system has
switched from one interface to the other and back).
Send Failure (parameter: frame identifier): this informs the
application of a failure to send a specific frame. There can be a
send failure without this notification happening.
QUERY_PROPERTIES (flow-group-id property_identifier)
Returns: requested property (see below)
This allows to query some properties of a flow group. Return values
per property identifier are:
o The maximum frame size that may be sent without fragmentation, in 4.2.2. Individual connections
bytes (or "not available")
o The maximum transport frame size that can be sent, in bytes (or
"not available")
o The maximum transport frame size that can be received, in bytes
(or "not available")
o The maximum amount of data that can possibly be sent before or
during connection establishment, in bytes (or "not available")
CONNECT (flow-id dst_addr)
Connects a flow. This primitive may or may not trigger a
notification (continuing LISTEN) on the listening side. If a send
precedes this call, then data may be transmitted with this connect.
PARAMETERS:
dst_addr: the destination transport address to connect to The transport features below apply to individual TAPS connections:
LISTEN (flow-id) Configure priority or weight for a scheduler, as described in
[RFC8260].
Blocking passive connect, listening on all interfaces. This may not Configure checksum usage: this can be done with the following
be the direct result of the peer calling CONNECT - it may also be parameters, but there is no guarantee that any checksum limitations
invoked upon reception of the first block of data. In this case, will indeed be enforced (the default behavior is "full coverage,
RECEIVE_FRAME is invoked immediately after. checksum enabled"):
SEND_FRAME (flow-id frame [reliability] [ordered] [bundle] [delack] o A boolean to enable / disable usage of a checksum when sending
[fragment] [idempotent]) o The desired coverage (in bytes) of the checksum used when sending
o A boolean to enable / disable requiring a checksum when receiving
o The required minimum coverage (in bytes) of the checksum when
receiving
Sends an application frame. No guarantees are given about the 4.3. DATA Transfer
preservation of frame boundaries to the peer; if frame boundaries are
needed, the receiving application at the peer must know about them
beforehand (or the TAPS system cannot fall back to TCP). Note that
this call can already be used before a flow is connected. All
parameters refer to the frame that is being handed over.
PARAMETERS: When sending a message, no guarantees are given about the
preservation of message boundaries to the peer; if message boundaries
are needed, the receiving application at the peer must know about
them beforehand (or the TAPS system cannot use TCP). Note that an
application should already be able to hand over data before the TAPS
system establishes a transport connection. Regarding the message
that is being handed over, the following parameters can be used:
(!UDP) reliability: this parameter is used to convey a choice of: o (!UDP) Reliability: this parameter is used to convey a choice of:
fully reliable, unreliable without congestion control (which is fully reliable, unreliable without congestion control (which is
guaranteed), unreliable, partially reliable (how to configure: guaranteed), unreliable, partially reliable (see [RFC3758] and
TBD, probably using a time value). The latter two choices are not [RFC7496] for details on how to specify partial reliability). The
guaranteed and may result in full reliability. latter two choices are not guaranteed and may result in full
(!UDP) ordered: this boolean parameter lets an application choose reliability.
o (!UDP) Ordered: this boolean parameter lets an application choose
between ordered message delivery (true) and possibly unordered, between ordered message delivery (true) and possibly unordered,
potentially faster message delivery (false). potentially faster message delivery (false).
bundle: a boolean that expresses a preference for allowing to bundle o Bundle: a boolean that expresses a preference for allowing to
frames (true) or not (false). No guarantees are given. bundle messages (true) or not (false). No guarantees are given.
delack: a boolean that, if false, lets an application request that o DelAck: a boolean that, if false, lets an application request that
the peer would not delay the acknowledgement for this frame. the peer would not delay the acknowledgement for this message.
fragment: a boolean that expresses a preference for allowing to o Fragment: a boolean that expresses a preference for allowing to
fragment frames (true) or not (false), at the IP level. No fragment messages (true) or not (false), at the IP level. No
guarantees are given. guarantees are given.
(!UDP) idempotent: a boolean that expresses whether a frame is o (!UDP) Idempotent: a boolean that expresses whether a message is
idempotent (true) or not (false). Idempotent frames may arrive idempotent (true) or not (false). Idempotent messages may arrive
multiple times at the receiver (but they will arrive at least multiple times at the receiver (but they will arrive at least
once). When data is idempotent it can be used by the receiver once). When data is idempotent it can be used by the receiver
immediately on a connection establishment attempt. Thus, if immediately on a connection establishment attempt. Thus, if data
SEND_FRAME is used before connecting, stating that a frame is is handed over before the TAPS system establishes a transport
idempotent facilitates transmitting it to the peer application connection, stating that a message is idempotent facilitates
particularly early. transmitting it to the peer application particularly early.
(!UDP) CLOSE (flow-id)
Closes the flow after all outstanding data is reliably delivered to
the peer (if reliable data delivery was requested). In case reliable
or partially reliable data delivery was requested earlier, the peer
is notified of the CLOSE.
ABORT (flow-id)
Aborts the flow without delivering outstanding data to the peer. In
case reliable or partially reliable data delivery was requested
earlier (!UDP), the peer is notified of the ABORT.
RECEIVE_FRAME (flow-id buffer) An application can be notified of a failure to send a specific
message. There is no guarantee of such notifications, i.e. send
failures can also silently occur.
This receives a block of data. This block may or may not correspond When receiving data blocks, these blocks may or may not correspond to
to a sender-side frame, i.e. the receiving application is not a sender-side message, i.e. the receiving application is not informed
informed about frame boundaries (this limitation is only needed for about message boundaries (this limitation is only needed for TAPS
TAPS systems that want to be able to fall back to TCP). However, if systems that are implemented to directly use TCP). However, if the
the sending application has allowed that frames are not fully sending application has allowed that messages are not fully reliably
reliably transferred, or delivered out of order, then such re- transferred, or delivered out of order, then such re-ordering or
ordering or unreliability may be reflected per frame in the arriving unreliability may be reflected per message in the arriving data.
data. Frames will always stay intact - i.e. if an incomplete frame Messages will always stay intact - i.e. if an incomplete message is
is contained at the end of the arriving data block, this frame is contained at the end of the arriving data block, this message is
guaranteed to continue in the next arriving data block. guaranteed to continue in the next arriving data block.
PARAMETERS:
buffer: the buffer where the received data will be stored.
5. Conclusion 5. Conclusion
By decoupling applications from transport protocols, a TAPS system By decoupling applications from transport protocols, a TAPS system
provides a different abstraction level than the Berkeley sockets provides a different abstraction level than the Berkeley sockets
interface. As with high- vs. low-level programming languages, a interface. As with high- vs. low-level programming languages, a
higher abstraction level allows more freedom for automation below the higher abstraction level allows more freedom for automation below the
interface, yet it takes some control away from the application interface, yet it takes some control away from the application
programmer. This is the design trade-off that a TAPS system programmer. This is the design trade-off that a TAPS system
developer is facing, and this document provides guidance on the developer is facing, and this document provides guidance on the
design of this abstraction level. Some transport features are design of this abstraction level. Some transport features are
currently rarely offered by APIs, yet they must be offered or they currently rarely offered by APIs, yet they must be offered or they
can never be used ("functional" transport features). Other transport can never be used ("functional" transport features). Other transport
features are offered by the APIs of the protocols covered here, but features are offered by the APIs of the protocols covered here, but
not exposing them in a TAPS API would allow for more freedom to not exposing them in a TAPS API would allow for more freedom to
automate protocol usage in a TAPS system. automate protocol usage in a TAPS system. The minimal set presented
in this document is an effort to find a middle ground that can be
The minimal set presented in this document is an effort to find a recommended for TAPS systems to implement, on the basis of the
middle ground that can be recommended for TAPS systems to implement, transport features discussed in [TAPS2].
on the basis of the transport features discussed in [TAPS2]. This
middle ground eliminates a large number of transport features because
they do not require application-specific knowledge, but instead rely
on knowledge about the network or the Operating System. This leaves
us with an unanswered question about how exactly a TAPS system should
automate using all of these "automatable" transport features.
In some cases, it may be best to not entirely automate the decision
making, but leave it up to a system-wide policy. For example, when
multiple paths are available, a system policy could guide the
decision on whether to connect via a WiFi or a cellular interface.
Such high-level guidance could also be provided by application
developers, e.g. via a primitive that lets applications specify such
preferences. As long as this kind of information from applications
is treated as advisory, it will not lead to a permanent protocol
binding and does therefore not limit the flexibility of a TAPS
system. Decisions to add such primitives are therefore left open to
TAPS system designers.
6. Acknowledgements 6. Acknowledgements
The authors would like to thank the participants of the TAPS Working The authors would like to thank all the participants of the TAPS
Group and the NEAT research project for valuable input to this Working Group and the NEAT and MAMI research projects for valuable
document. We especially thank Michael Tuexen for help with TAPS flow input to this document. We especially thank Michael Tuexen for help
connection establishment/teardown and Gorry Fairhurst for his with TAPS connection connection establishment/teardown and Gorry
suggestions regarding fragmentation and packet sizes. This work has Fairhurst for his suggestions regarding fragmentation and packet
received funding from the European Union's Horizon 2020 research and sizes. This work has received funding from the European Union's
innovation programme under grant agreement No. 644334 (NEAT). Horizon 2020 research and innovation programme under grant agreement
No. 644334 (NEAT).
7. IANA Considerations 7. IANA Considerations
XX RFC ED - PLEASE REMOVE THIS SECTION XXX XX RFC ED - PLEASE REMOVE THIS SECTION XXX
This memo includes no request to IANA. This memo includes no request to IANA.
8. Security Considerations 8. Security Considerations
Authentication, confidentiality protection, and integrity protection Authentication, confidentiality protection, and integrity protection
skipping to change at page 19, line 38 skipping to change at page 17, line 5
[I-D.grinnemo-taps-he] [I-D.grinnemo-taps-he]
Grinnemo, K., Brunstrom, A., Hurtig, P., Khademi, N., and Grinnemo, K., Brunstrom, A., Hurtig, P., Khademi, N., and
Z. Bozakov, "Happy Eyeballs for Transport Selection", Z. Bozakov, "Happy Eyeballs for Transport Selection",
draft-grinnemo-taps-he-03 (work in progress), July 2017. draft-grinnemo-taps-he-03 (work in progress), July 2017.
[I-D.ietf-tsvwg-rtcweb-qos] [I-D.ietf-tsvwg-rtcweb-qos]
Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP
Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb- Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb-
qos-18 (work in progress), August 2016. qos-18 (work in progress), August 2016.
[I-D.ietf-tsvwg-sctp-ndata]
Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann,
"Stream Schedulers and User Message Interleaving for the
Stream Control Transmission Protocol", draft-ietf-tsvwg-
sctp-ndata-13 (work in progress), September 2017.
[I-D.pauly-taps-transport-security] [I-D.pauly-taps-transport-security]
Pauly, T. and C. Wood, "A Survey of Transport Security Pauly, T., Rose, K., and C. Wood, "A Survey of Transport
Protocols", draft-pauly-taps-transport-security-00 (work Security Protocols", draft-pauly-taps-transport-
in progress), July 2017. security-01 (work in progress), January 2018.
[I-D.trammell-taps-post-sockets]
Trammell, B., Perkins, C., Pauly, T., Kuehlewind, M., and
C. Wood, "Post Sockets, An Abstract Programming Interface
for the Transport Layer", draft-trammell-taps-post-
sockets-01 (work in progress), September 2017.
[LBE-draft] [LBE-draft]
Bless, R., "A Lower Effort Per-Hop Behavior (LE PHB)", Bless, R., "A Lower Effort Per-Hop Behavior (LE PHB)",
Internet-draft draft-tsvwg-le-phb-02, June 2017. Internet-draft draft-tsvwg-le-phb-03, February 2018.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000, RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/info/rfc2914>. <https://www.rfc-editor.org/info/rfc2914>.
[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758,
DOI 10.17487/RFC3758, May 2004,
<https://www.rfc-editor.org/info/rfc3758>.
[RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla, [RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
"Authenticated Chunks for the Stream Control Transmission "Authenticated Chunks for the Stream Control Transmission
Protocol (SCTP)", RFC 4895, DOI 10.17487/RFC4895, August Protocol (SCTP)", RFC 4895, DOI 10.17487/RFC4895, August
2007, <https://www.rfc-editor.org/info/rfc4895>. 2007, <https://www.rfc-editor.org/info/rfc4895>.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common [RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common
Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007, Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007,
<https://www.rfc-editor.org/info/rfc4987>. <https://www.rfc-editor.org/info/rfc4987>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
skipping to change at page 20, line 43 skipping to change at page 17, line 48
Yasevich, "Sockets API Extensions for the Stream Control Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, Transmission Protocol (SCTP)", RFC 6458,
DOI 10.17487/RFC6458, December 2011, DOI 10.17487/RFC6458, December 2011,
<https://www.rfc-editor.org/info/rfc6458>. <https://www.rfc-editor.org/info/rfc6458>.
[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration", Transmission Protocol (SCTP) Stream Reconfiguration",
RFC 6525, DOI 10.17487/RFC6525, February 2012, RFC 6525, DOI 10.17487/RFC6525, February 2012,
<https://www.rfc-editor.org/info/rfc6525>. <https://www.rfc-editor.org/info/rfc6525>.
[RFC7305] Lear, E., Ed., "Report from the IAB Workshop on Internet
Technology Adoption and Transition (ITAT)", RFC 7305,
DOI 10.17487/RFC7305, July 2014,
<https://www.rfc-editor.org/info/rfc7305>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>. <https://www.rfc-editor.org/info/rfc7413>.
[RFC7496] Tuexen, M., Seggelmann, R., Stewart, R., and S. Loreto,
"Additional Policies for the Partially Reliable Stream
Control Transmission Protocol Extension", RFC 7496,
DOI 10.17487/RFC7496, April 2015,
<https://www.rfc-editor.org/info/rfc7496>.
[RFC8260] Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann,
"Stream Schedulers and User Message Interleaving for the
Stream Control Transmission Protocol", RFC 8260,
DOI 10.17487/RFC8260, November 2017,
<https://www.rfc-editor.org/info/rfc8260>.
[WWDC2015] [WWDC2015]
Lakhera, P. and S. Cheshire, "Your App and Next Generation Lakhera, P. and S. Cheshire, "Your App and Next Generation
Networks", Apple Worldwide Developers Conference 2015, San Networks", Apple Worldwide Developers Conference 2015, San
Francisco, USA, June 2015, Francisco, USA, June 2015,
<https://developer.apple.com/videos/wwdc/2015/?id=719>. <https://developer.apple.com/videos/wwdc/2015/?id=719>.
Appendix A. Deriving the minimal set Appendix A. Deriving the minimal set
We approach the construction of a minimal set of transport features We approach the construction of a minimal set of transport features
in the following way: in the following way:
skipping to change at page 21, line 38 skipping to change at page 19, line 16
Following [TAPS2], we divide the transport features into two main Following [TAPS2], we divide the transport features into two main
groups as follows: groups as follows:
1. CONNECTION related transport features 1. CONNECTION related transport features
- ESTABLISHMENT - ESTABLISHMENT
- AVAILABILITY - AVAILABILITY
- MAINTENANCE - MAINTENANCE
- TERMINATION - TERMINATION
2. DATA Transfer Related transport features 2. DATA Transfer related transport features
- Sending Data - Sending Data
- Receiving Data - Receiving Data
- Errors - Errors
We assume that TAPS applications have no specific requirements that We assume that TAPS applications have no specific requirements that
need knowledge about the network, e.g. regarding the choice of need knowledge about the network, e.g. regarding the choice of
network interface or the end-to-end path. Even with these network interface or the end-to-end path. Even with these
assumptions, there are certain requirements that are strictly kept by assumptions, there are certain requirements that are strictly kept by
transport protocols today, and these must also be kept by a TAPS transport protocols today, and these must also be kept by a TAPS
system. Some of these requirements relate to transport features that system. Some of these requirements relate to transport features that
skipping to change at page 22, line 39 skipping to change at page 20, line 17
marked as "ADDED". The corresponding transport features are marked as "ADDED". The corresponding transport features are
automatable, and they are listed immediately below the "ADDED" automatable, and they are listed immediately below the "ADDED"
transport feature. transport feature.
In this description, transport services are presented following the In this description, transport services are presented following the
nomenclature "CATEGORY.[SUBCATEGORY].SERVICENAME.PROTOCOL", nomenclature "CATEGORY.[SUBCATEGORY].SERVICENAME.PROTOCOL",
equivalent to "pass 2" in [TAPS2]. We also sketch how some of the equivalent to "pass 2" in [TAPS2]. We also sketch how some of the
TAPS transport features can be implemented by a TAPS system. For all TAPS transport features can be implemented by a TAPS system. For all
transport features that are categorized as "functional" or transport features that are categorized as "functional" or
"optimizing", and for which no matching TCP and/or UDP primitive "optimizing", and for which no matching TCP and/or UDP primitive
exists in "pass 2" of [TAPS2], a brief discussion on how to fall back exists in "pass 2" of [TAPS2], a brief discussion on how to implement
to TCP and/or UDP is included. them over TCP and/or UDP is included.
We designate some transport features as "automatable" on the basis of We designate some transport features as "automatable" on the basis of
a broader decision that affects multiple transport features: a broader decision that affects multiple transport features:
o Most transport features that are related to multi-streaming were o Most transport features that are related to multi-streaming were
designated as "automatable". This was done because the decision designated as "automatable". This was done because the decision
on whether to use multi-streaming or not does not depend on on whether to use multi-streaming or not does not depend on
application-specific knowledge. This means that a connection that application-specific knowledge. This means that a connection that
is exhibited to an application could be implemented by using a is exhibited to an application could be implemented by using a
single stream of an SCTP association instead of mapping it to a single stream of an SCTP association instead of mapping it to a
skipping to change at page 24, line 12 skipping to change at page 21, line 33
application-specific knowledge. application-specific knowledge.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Specify number of attempts and/or timeout for the first o Specify number of attempts and/or timeout for the first
establishment message establishment message
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this is closely related to potentially assumed Functional because this is closely related to potentially assumed
reliable data delivery for data that is sent before or during reliable data delivery for data that is sent before or during
connection establishment. connection establishment.
Implementation: Using a parameter of CONNECT.TCP and CONNECT.SCTP. Implementation: Using a parameter of CONNECT.TCP and CONNECT.SCTP.
Fall-back to UDP: Do nothing (this is irrelevant in case of UDP Implementation over UDP: Do nothing (this is irrelevant in case of
because there, reliable data delivery is not assumed). UDP because there, reliable data delivery is not assumed).
o Obtain multiple sockets o Obtain multiple sockets
Protocols: SCTP Protocols: SCTP
Automatable because the usage of multiple paths to communicate to Automatable because the usage of multiple paths to communicate to
the same end host relates to knowledge about the network, not the the same end host relates to knowledge about the network, not the
application. application.
o Disable MPTCP o Disable MPTCP
Protocols: MPTCP Protocols: MPTCP
Automatable because the usage of multiple paths to communicate to Automatable because the usage of multiple paths to communicate to
the same end host relates to knowledge about the network, not the the same end host relates to knowledge about the network, not the
application. application.
Implementation: via a boolean parameter in CONNECT.MPTCP. Implementation: via a boolean parameter in CONNECT.MPTCP.
o Configure authentication o Configure authentication
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this has a direct influence on security. Functional because this has a direct influence on security.
Implementation: via parameters in CONNECT.TCP and CONNECT.SCTP. Implementation: via parameters in CONNECT.TCP and CONNECT.SCTP.
Fall-back to TCP: With TCP, this allows to configure Master Key Implementation over TCP: With TCP, this allows to configure Master
Tuples (MKTs) to authenticate complete segments (including the TCP Key Tuples (MKTs) to authenticate complete segments (including the
IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this TCP IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this
allows to specify which chunk types must always be authenticated. allows to specify which chunk types must always be authenticated.
Authenticating only certain chunk types creates a reduced level of Authenticating only certain chunk types creates a reduced level of
security that is not supported by TCP; to be compatible, this security that is not supported by TCP; to be compatible, this
should therefore only allow to authenticate all chunk types. Key should therefore only allow to authenticate all chunk types. Key
material must be provided in a way that is compatible with both material must be provided in a way that is compatible with both
[RFC4895] and [RFC5925]. [RFC4895] and [RFC5925].
Fall-back to UDP: Not possible. Implementation over UDP: Not possible.
o Indicate (and/or obtain upon completion) an Adaptation Layer via o Indicate (and/or obtain upon completion) an Adaptation Layer via
an adaptation code point an adaptation code point
Protocols: SCTP Protocols: SCTP
Functional because it allows to send extra data for the sake of Functional because it allows to send extra data for the sake of
identifying an adaptation layer, which by itself is application- identifying an adaptation layer, which by itself is application-
specific. specific.
Implementation: via a parameter in CONNECT.SCTP. Implementation: via a parameter in CONNECT.SCTP.
Fall-back to TCP: not possible. Implementation over TCP: not possible.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Request to negotiate interleaving of user messages o Request to negotiate interleaving of user messages
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
Implementation: via a parameter in CONNECT.SCTP. Implementation: via a parameter in CONNECT.SCTP.
o Hand over a message to reliably transfer (possibly multiple times) o Hand over a message to reliably transfer (possibly multiple times)
before connection establishment before connection establishment
Protocols: TCP Protocols: TCP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via a parameter in CONNECT.TCP. Implementation: via a parameter in CONNECT.TCP.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Hand over a message to reliably transfer during connection o Hand over a message to reliably transfer during connection
establishment establishment
Protocols: SCTP Protocols: SCTP
Functional because this can only work if the message is limited in Functional because this can only work if the message is limited in
size, making it closely tied to properties of the data that an size, making it closely tied to properties of the data that an
application sends or expects to receive. application sends or expects to receive.
Implementation: via a parameter in CONNECT.SCTP. Implementation: via a parameter in CONNECT.SCTP.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Enable UDP encapsulation with a specified remote UDP port number o Enable UDP encapsulation with a specified remote UDP port number
Protocols: SCTP Protocols: SCTP
Automatable because UDP encapsulation relates to knowledge about Automatable because UDP encapsulation relates to knowledge about
the network, not the application. the network, not the application.
AVAILABILITY: AVAILABILITY:
o Listen o Listen
Protocols: TCP, SCTP, UDP(-Lite) Protocols: TCP, SCTP, UDP(-Lite)
skipping to change at page 27, line 12 skipping to change at page 24, line 32
o Disable MPTCP o Disable MPTCP
Protocols: MPTCP Protocols: MPTCP
Automatable because the usage of multiple paths to communicate to Automatable because the usage of multiple paths to communicate to
the same end host relates to knowledge about the network, not the the same end host relates to knowledge about the network, not the
application. application.
o Configure authentication o Configure authentication
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this has a direct influence on security. Functional because this has a direct influence on security.
Implementation: via parameters in LISTEN.TCP and LISTEN.SCTP. Implementation: via parameters in LISTEN.TCP and LISTEN.SCTP.
Fall-back to TCP: With TCP, this allows to configure Master Key Implementation over TCP: With TCP, this allows to configure Master
Tuples (MKTs) to authenticate complete segments (including the TCP Key Tuples (MKTs) to authenticate complete segments (including the
IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this TCP IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this
allows to specify which chunk types must always be authenticated. allows to specify which chunk types must always be authenticated.
Authenticating only certain chunk types creates a reduced level of Authenticating only certain chunk types creates a reduced level of
security that is not supported by TCP; to be compatible, this security that is not supported by TCP; to be compatible, this
should therefore only allow to authenticate all chunk types. Key should therefore only allow to authenticate all chunk types. Key
material must be provided in a way that is compatible with both material must be provided in a way that is compatible with both
[RFC4895] and [RFC5925]. [RFC4895] and [RFC5925].
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Obtain requested number of streams o Obtain requested number of streams
Protocols: SCTP Protocols: SCTP
Automatable because using multi-streaming does not require Automatable because using multi-streaming does not require
application-specific knowledge. application-specific knowledge.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Limit the number of inbound streams o Limit the number of inbound streams
Protocols: SCTP Protocols: SCTP
Automatable because using multi-streaming does not require Automatable because using multi-streaming does not require
application-specific knowledge. application-specific knowledge.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Indicate (and/or obtain upon completion) an Adaptation Layer via o Indicate (and/or obtain upon completion) an Adaptation Layer via
an adaptation code point an adaptation code point
Protocols: SCTP Protocols: SCTP
Functional because it allows to send extra data for the sake of Functional because it allows to send extra data for the sake of
identifying an adaptation layer, which by itself is application- identifying an adaptation layer, which by itself is application-
specific. specific.
Implementation: via a parameter in LISTEN.SCTP. Implementation: via a parameter in LISTEN.SCTP.
Fall-back to TCP: not possible. Implementation over TCP: not possible.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Request to negotiate interleaving of user messages o Request to negotiate interleaving of user messages
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
Implementation: via a parameter in LISTEN.SCTP. Implementation: via a parameter in LISTEN.SCTP.
MAINTENANCE: MAINTENANCE:
o Change timeout for aborting connection (using retransmit limit or o Change timeout for aborting connection (using retransmit limit or
time value) time value)
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this is closely related to potentially assumed Functional because this is closely related to potentially assumed
reliable data delivery. reliable data delivery.
Implementation: via CHANGE-TIMEOUT.TCP or CHANGE-TIMEOUT.SCTP. Implementation: via CHANGE-TIMEOUT.TCP or CHANGE-TIMEOUT.SCTP.
Fall-back to UDP: not possible (UDP is unreliable and there is no Implementation over UDP: not possible (UDP is unreliable and there
connection timeout). is no connection timeout).
o Suggest timeout to the peer o Suggest timeout to the peer
Protocols: TCP Protocols: TCP
Functional because this is closely related to potentially assumed Functional because this is closely related to potentially assumed
reliable data delivery. reliable data delivery.
Implementation: via CHANGE-TIMEOUT.TCP. Implementation: via CHANGE-TIMEOUT.TCP.
Fall-back to UDP: not possible (UDP is unreliable and there is no Implementation over UDP: not possible (UDP is unreliable and there
connection timeout). is no connection timeout).
o Disable Nagle algorithm o Disable Nagle algorithm
Protocols: TCP, SCTP Protocols: TCP, SCTP
Optimizing because this decision depends on knowledge about the Optimizing because this decision depends on knowledge about the
size of future data blocks and the delay between them. size of future data blocks and the delay between them.
Implementation: via DISABLE-NAGLE.TCP and DISABLE-NAGLE.SCTP. Implementation: via DISABLE-NAGLE.TCP and DISABLE-NAGLE.SCTP.
Fall-back to UDP: do nothing (UDP does not implement the Nagle Implementation over UDP: do nothing (UDP does not implement the
algorithm). Nagle algorithm).
o Request an immediate heartbeat, returning success/failure o Request an immediate heartbeat, returning success/failure
Protocols: SCTP Protocols: SCTP
Automatable because this informs about network-specific knowledge. Automatable because this informs about network-specific knowledge.
o Notification of Excessive Retransmissions (early warning below o Notification of Excessive Retransmissions (early warning below
abortion threshold) abortion threshold)
Protocols: TCP Protocols: TCP
Optimizing because it is an early warning to the application, Optimizing because it is an early warning to the application,
informing it of an impending functional event. informing it of an impending functional event.
Implementation: via ERROR.TCP. Implementation: via ERROR.TCP.
Fall-back to UDP: do nothing (there is no abortion threshold). Implementation over UDP: do nothing (there is no abortion
threshold).
o Add path o Add path
Protocols: MPTCP, SCTP Protocols: MPTCP, SCTP
MPTCP Parameters: source-IP; source-Port; destination-IP; MPTCP Parameters: source-IP; source-Port; destination-IP;
destination-Port destination-Port
SCTP Parameters: local IP address SCTP Parameters: local IP address
Automatable because the usage of multiple paths to communicate to Automatable because the usage of multiple paths to communicate to
the same end host relates to knowledge about the network, not the the same end host relates to knowledge about the network, not the
application. application.
skipping to change at page 31, line 9 skipping to change at page 28, line 30
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
Implementation: via a parameter in GETINTERL.SCTP. Implementation: via a parameter in GETINTERL.SCTP.
o Change authentication parameters o Change authentication parameters
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this has a direct influence on security. Functional because this has a direct influence on security.
Implementation: via SET_AUTH.TCP and SET_AUTH.SCTP. Implementation: via SET_AUTH.TCP and SET_AUTH.SCTP.
Fall-back to TCP: With SCTP, this allows to adjust key_id, key, Implementation over TCP: With SCTP, this allows to adjust key_id,
and hmac_id. With TCP, this allows to change the preferred key, and hmac_id. With TCP, this allows to change the preferred
outgoing MKT (current_key) and the preferred incoming MKT outgoing MKT (current_key) and the preferred incoming MKT
(rnext_key), respectively, for a segment that is sent on the (rnext_key), respectively, for a segment that is sent on the
connection. Key material must be provided in a way that is connection. Key material must be provided in a way that is
compatible with both [RFC4895] and [RFC5925]. compatible with both [RFC4895] and [RFC5925].
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Obtain authentication information o Obtain authentication information
Protocols: SCTP Protocols: SCTP
Functional because authentication decisions may have been made by Functional because authentication decisions may have been made by
the peer, and this has an influence on the necessary application- the peer, and this has an influence on the necessary application-
level measures to provide a certain level of security. level measures to provide a certain level of security.
Implementation: via GETAUTH.SCTP. Implementation: via GETAUTH.SCTP.
Fall-back to TCP: With SCTP, this allows to obtain key_id and a
chunk list. With TCP, this allows to obtain current_key and Implementation over TCP: With SCTP, this allows to obtain key_id
and a chunk list. With TCP, this allows to obtain current_key and
rnext_key from a previously received segment. Key material must rnext_key from a previously received segment. Key material must
be provided in a way that is compatible with both [RFC4895] and be provided in a way that is compatible with both [RFC4895] and
[RFC5925]. [RFC5925].
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Reset Stream o Reset Stream
Protocols: SCTP Protocols: SCTP
Automatable because using multi-streaming does not require Automatable because using multi-streaming does not require
application-specific knowledge. application-specific knowledge.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Notification of Stream Reset o Notification of Stream Reset
Protocols: STCP Protocols: STCP
Automatable because using multi-streaming does not require Automatable because using multi-streaming does not require
skipping to change at page 32, line 30 skipping to change at page 30, line 16
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Choose a scheduler to operate between streams of an association o Choose a scheduler to operate between streams of an association
Protocols: SCTP Protocols: SCTP
Optimizing because the scheduling decision requires application- Optimizing because the scheduling decision requires application-
specific knowledge. However, if a TAPS system would not use this, specific knowledge. However, if a TAPS system would not use this,
or wrongly configure it on its own, this would only affect the or wrongly configure it on its own, this would only affect the
performance of data transfers; the outcome would still be correct performance of data transfers; the outcome would still be correct
within the "best effort" service model. within the "best effort" service model.
Implementation: using SETSTREAMSCHEDULER.SCTP. Implementation: using SETSTREAMSCHEDULER.SCTP.
Fall-back to TCP: do nothing. Implementation over TCP: do nothing.
Fall-back to UDP: do nothing. Implementation over UDP: do nothing.
o Configure priority or weight for a scheduler o Configure priority or weight for a scheduler
Protocols: SCTP Protocols: SCTP
Optimizing because the priority or weight requires application- Optimizing because the priority or weight requires application-
specific knowledge. However, if a TAPS system would not use this, specific knowledge. However, if a TAPS system would not use this,
or wrongly configure it on its own, this would only affect the or wrongly configure it on its own, this would only affect the
performance of data transfers; the outcome would still be correct performance of data transfers; the outcome would still be correct
within the "best effort" service model. within the "best effort" service model.
Implementation: using CONFIGURESTREAMSCHEDULER.SCTP. Implementation: using CONFIGURESTREAMSCHEDULER.SCTP.
Fall-back to TCP: do nothing. Implementation over TCP: do nothing.
Fall-back to UDP: do nothing. Implementation over UDP: do nothing.
o Configure send buffer size o Configure send buffer size
Protocols: SCTP Protocols: SCTP
Automatable because this decision relates to knowledge about the Automatable because this decision relates to knowledge about the
network and the Operating System, not the application (see also network and the Operating System, not the application (see also
the discussion in Appendix A.3.4). the discussion in Appendix A.3.4).
o Configure receive buffer (and rwnd) size o Configure receive buffer (and rwnd) size
Protocols: SCTP Protocols: SCTP
Automatable because this decision relates to knowledge about the Automatable because this decision relates to knowledge about the
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(it can be relevant for a sending application to request not to (it can be relevant for a sending application to request not to
delay the SACK of a message, but this is a different transport delay the SACK of a message, but this is a different transport
feature). feature).
o Set Cookie life value o Set Cookie life value
Protocols: SCTP Protocols: SCTP
Functional because it relates to security (possibly weakened by Functional because it relates to security (possibly weakened by
keeping a cookie very long) versus the time between connection keeping a cookie very long) versus the time between connection
establishment attempts. Knowledge about both issues can be establishment attempts. Knowledge about both issues can be
application-specific. application-specific.
Implementation over TCP: the closest specified TCP functionality
Fall-back to TCP: the closest specified TCP functionality is the is the cookie in TCP Fast Open; for this, [RFC7413] states that
cookie in TCP Fast Open; for this, [RFC7413] states that the the server "can expire the cookie at any time to enhance security"
server "can expire the cookie at any time to enhance security" and and section 4.1.2 describes an example implementation where
section 4.1.2 describes an example implementation where updating updating the key on the server side causes the cookie to expire.
the key on the server side causes the cookie to expire.
Alternatively, for implementations that do not support TCP Fast Alternatively, for implementations that do not support TCP Fast
Open, this transport feature could also affect the validity of SYN Open, this transport feature could also affect the validity of SYN
cookies (see Section 3.6 of [RFC4987]). cookies (see Section 3.6 of [RFC4987]).
Fall-back to UDP: do nothing. Implementation over UDP: do nothing.
o Set maximum burst o Set maximum burst
Protocols: SCTP Protocols: SCTP
Automatable because it relates to knowledge about the network, not Automatable because it relates to knowledge about the network, not
the application. the application.
o Configure size where messages are broken up for partial delivery o Configure size where messages are broken up for partial delivery
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Fall-back to TCP: not possible. Implementation over TCP: not possible.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Disable checksum when sending o Disable checksum when sending
Protocols: UDP Protocols: UDP
Functional because application-specific knowledge is necessary to Functional because application-specific knowledge is necessary to
decide whether it can be acceptable to lose data integrity. decide whether it can be acceptable to lose data integrity.
Implementation: via SET_CHECKSUM_ENABLED.UDP. Implementation: via SET_CHECKSUM_ENABLED.UDP.
Fall-back to TCP: do nothing. Implementation over TCP: do nothing.
o Disable checksum requirement when receiving o Disable checksum requirement when receiving
Protocols: UDP Protocols: UDP
Functional because application-specific knowledge is necessary to Functional because application-specific knowledge is necessary to
decide whether it can be acceptable to lose data integrity. decide whether it can be acceptable to lose data integrity.
Implementation: via SET_CHECKSUM_REQUIRED.UDP. Implementation: via SET_CHECKSUM_REQUIRED.UDP.
Fall-back to TCP: do nothing. Implementation over TCP: do nothing.
o Specify checksum coverage used by the sender o Specify checksum coverage used by the sender
Protocols: UDP-Lite Protocols: UDP-Lite
Functional because application-specific knowledge is necessary to Functional because application-specific knowledge is necessary to
decide for which parts of the data it can be acceptable to lose decide for which parts of the data it can be acceptable to lose
data integrity. data integrity.
Implementation: via SET_CHECKSUM_COVERAGE.UDP-Lite. Implementation: via SET_CHECKSUM_COVERAGE.UDP-Lite.
Fall-back to TCP: do nothing. Implementation over TCP: do nothing.
o Specify minimum checksum coverage required by receiver o Specify minimum checksum coverage required by receiver
Protocols: UDP-Lite Protocols: UDP-Lite
Functional because application-specific knowledge is necessary to Functional because application-specific knowledge is necessary to
decide for which parts of the data it can be acceptable to lose decide for which parts of the data it can be acceptable to lose
data integrity. data integrity.
Implementation: via SET_MIN_CHECKSUM_COVERAGE.UDP-Lite. Implementation: via SET_MIN_CHECKSUM_COVERAGE.UDP-Lite.
Fall-back to TCP: do nothing. Implementation over TCP: do nothing.
o Specify DF field o Specify DF field
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Optimizing because the DF field can be used to carry out Path MTU Optimizing because the DF field can be used to carry out Path MTU
Discovery, which can lead an application to choose message sizes Discovery, which can lead an application to choose message sizes
that can be transmitted more efficiently. that can be transmitted more efficiently.
Implementation: via MAINTENANCE.SET_DF.UDP(-Lite) and Implementation: via MAINTENANCE.SET_DF.UDP(-Lite) and
SEND_FAILURE.UDP(-Lite). SEND_FAILURE.UDP(-Lite).
Fall-back to TCP: do nothing. With TCP the sender is not in Implementation over TCP: do nothing. With TCP the sender is not
control of transport message sizes, making this functionality in control of transport message sizes, making this functionality
irrelevant. irrelevant.
o Get max. transport-message size that may be sent using a non- o Get max. transport-message size that may be sent using a non-
fragmented IP packet from the configured interface fragmented IP packet from the configured interface
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Optimizing because this can lead an application to choose message Optimizing because this can lead an application to choose message
sizes that can be transmitted more efficiently. sizes that can be transmitted more efficiently.
Fall-back to TCP: do nothing: this information is not available Implementation over TCP: do nothing: this information is not
with TCP. available with TCP.
o Get max. transport-message size that may be received from the o Get max. transport-message size that may be received from the
configured interface configured interface
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Optimizing because this can, for example, influence an Optimizing because this can, for example, influence an
application's memory management. application's memory management.
Fall-back to TCP: do nothing: this information is not available Implementation over TCP: do nothing: this information is not
with TCP. available with TCP.
o Specify TTL/Hop count field o Specify TTL/Hop count field
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because a TAPS system can use a large enough system Automatable because a TAPS system can use a large enough system
default to avoid communication failures. Allowing an application default to avoid communication failures. Allowing an application
to configure it differently can produce notifications of ICMP to configure it differently can produce notifications of ICMP
error message arrivals that yield information which only relates error message arrivals that yield information which only relates
to knowledge about the network, not the application. to knowledge about the network, not the application.
o Obtain TTL/Hop count field o Obtain TTL/Hop count field
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Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because the ECN field relates to knowledge about the Automatable because the ECN field relates to knowledge about the
network, not the application. network, not the application.
o Obtain ECN field o Obtain ECN field
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Optimizing because this information can be used by an application Optimizing because this information can be used by an application
to better carry out congestion control (this is relevant when to better carry out congestion control (this is relevant when
choosing a data transmission transport service that does not choosing a data transmission transport service that does not
already do congestion control). already do congestion control).
Fall-back to TCP: do nothing: this information is not available Implementation over TCP: do nothing: this information is not
with TCP. available with TCP.
o Specify IP Options o Specify IP Options
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because IP Options relate to knowledge about the Automatable because IP Options relate to knowledge about the
network, not the application. network, not the application.
o Obtain IP Options o Obtain IP Options
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because IP Options relate to knowledge about the Automatable because IP Options relate to knowledge about the
network, not the application. network, not the application.
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Protocols: A protocol implementing the LEDBAT congestion control Protocols: A protocol implementing the LEDBAT congestion control
mechanism mechanism
Optimizing because whether this service is appropriate or not Optimizing because whether this service is appropriate or not
depends on application-specific knowledge. However, wrongly using depends on application-specific knowledge. However, wrongly using
this will only affect the speed of data transfers (albeit this will only affect the speed of data transfers (albeit
including other transfers that may compete with the TAPS transfer including other transfers that may compete with the TAPS transfer
in the network), so it is still correct within the "best effort" in the network), so it is still correct within the "best effort"
service model. service model.
Implementation: via CONFIGURE.LEDBAT and/or SET_DSCP.TCP / Implementation: via CONFIGURE.LEDBAT and/or SET_DSCP.TCP /
SET_DSCP.SCTP / SET_DSCP.UDP(-Lite) [LBE-draft]. SET_DSCP.SCTP / SET_DSCP.UDP(-Lite) [LBE-draft].
Fall-back to TCP: do nothing. Implementation over TCP: do nothing.
Fall-back to UDP: do nothing. Implementation over UDP: do nothing.
TERMINATION: TERMINATION:
o Close after reliably delivering all remaining data, causing an o Close after reliably delivering all remaining data, causing an
event informing the application on the other side event informing the application on the other side
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because the notion of a connection is often reflected Functional because the notion of a connection is often reflected
in applications as an expectation to have all outstanding data in applications as an expectation to have all outstanding data
delivered and no longer be able to communicate after a "Close" delivered and no longer be able to communicate after a "Close"
succeeded, with a communication sequence relating to this succeeded, with a communication sequence relating to this
transport feature that is defined by the application protocol. transport feature that is defined by the application protocol.
Implementation: via CLOSE.TCP and CLOSE.SCTP. Implementation: via CLOSE.TCP and CLOSE.SCTP.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Abort without delivering remaining data, causing an event o Abort without delivering remaining data, causing an event
informing the application on the other side informing the application on the other side
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because the notion of a connection is often reflected Functional because the notion of a connection is often reflected
in applications as an expectation to potentially not have all in applications as an expectation to potentially not have all
outstanding data delivered and no longer be able to communicate outstanding data delivered and no longer be able to communicate
after an "Abort" succeeded. On both sides of a connection, an after an "Abort" succeeded. On both sides of a connection, an
application protocol may define a communication sequence relating application protocol may define a communication sequence relating
to this transport feature. to this transport feature.
Implementation: via ABORT.TCP and ABORT.SCTP. Implementation: via ABORT.TCP and ABORT.SCTP.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Abort without delivering remaining data, not causing an event o Abort without delivering remaining data, not causing an event
informing the application on the other side informing the application on the other side
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Functional because the notion of a connection is often reflected Functional because the notion of a connection is often reflected
in applications as an expectation to potentially not have all in applications as an expectation to potentially not have all
outstanding data delivered and no longer be able to communicate outstanding data delivered and no longer be able to communicate
after an "Abort" succeeded. On both sides of a connection, an after an "Abort" succeeded. On both sides of a connection, an
application protocol may define a communication sequence relating application protocol may define a communication sequence relating
to this transport feature. to this transport feature.
Implementation: via ABORT.UDP(-Lite). Implementation: via ABORT.UDP(-Lite).
Fall-back to TCP: stop using the connection, wait for a timeout. Implementation over TCP: stop using the connection, wait for a
timeout.
o Timeout event when data could not be delivered for too long o Timeout event when data could not be delivered for too long
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this notifies that potentially assumed reliable Functional because this notifies that potentially assumed reliable
data delivery is no longer provided. data delivery is no longer provided.
Implementation: via TIMEOUT.TCP and TIMEOUT.SCTP. Implementation: via TIMEOUT.TCP and TIMEOUT.SCTP.
Fall-back to UDP: do nothing: this event will not occur with UDP. Implementation over UDP: do nothing: this event will not occur
with UDP.
A.1.2. DATA Transfer Related Transport Features A.1.2. DATA Transfer Related Transport Features
A.1.2.1. Sending Data A.1.2.1. Sending Data
o Reliably transfer data, with congestion control o Reliably transfer data, with congestion control
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via SEND.TCP and SEND.SCTP. Implementation: via SEND.TCP and SEND.SCTP.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Reliably transfer a message, with congestion control o Reliably transfer a message, with congestion control
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Fall-back to TCP: via SEND.TCP. With SEND.TCP, messages will not Implementation over TCP: via SEND.TCP. With SEND.TCP, messages
be identifiable by the receiver. will not be identifiable by the receiver.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Unreliably transfer a message o Unreliably transfer a message
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Optimizing because only applications know about the time Optimizing because only applications know about the time
criticality of their communication, and reliably transfering a criticality of their communication, and reliably transfering a
message is never incorrect for the receiver of a potentially message is never incorrect for the receiver of a potentially
unreliable data transfer, it is just slower. unreliable data transfer, it is just slower.
ADDED. This differs from the 2 automatable transport features ADDED. This differs from the 2 automatable transport features
below in that it leaves the choice of congestion control open. below in that it leaves the choice of congestion control open.
Implementation: via SEND.SCTP or SEND.UDP(-Lite). Implementation: via SEND.SCTP or SEND.UDP(-Lite).
Fall-back to TCP: use SEND.TCP. With SEND.TCP, messages will be Implementation over TCP: use SEND.TCP. With SEND.TCP, messages
sent reliably, and they will not be identifiable by the receiver. will be sent reliably, and they will not be identifiable by the
receiver.
o Unreliably transfer a message, with congestion control o Unreliably transfer a message, with congestion control
Protocols: SCTP Protocols: SCTP
Automatable because congestion control relates to knowledge about Automatable because congestion control relates to knowledge about
the network, not the application. the network, not the application.
o Unreliably transfer a message, without congestion control o Unreliably transfer a message, without congestion control
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because congestion control relates to knowledge about Automatable because congestion control relates to knowledge about
the network, not the application. the network, not the application.
o Configurable Message Reliability o Configurable Message Reliability
Protocols: SCTP Protocols: SCTP
Optimizing because only applications know about the time Optimizing because only applications know about the time
criticality of their communication, and reliably transfering a criticality of their communication, and reliably transfering a
message is never incorrect for the receiver of a potentially message is never incorrect for the receiver of a potentially
unreliable data transfer, it is just slower. unreliable data transfer, it is just slower.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Fall-back to TCP: By using SEND.TCP and ignoring this Implementation over TCP: By using SEND.TCP and ignoring this
configuration: based on the assumption of the best-effort service configuration: based on the assumption of the best-effort service
model, unnecessarily delivering data does not violate application model, unnecessarily delivering data does not violate application
expectations. Moreover, it is not possible to associate the expectations. Moreover, it is not possible to associate the
requested reliability to a "message" in TCP anyway. requested reliability to a "message" in TCP anyway.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Choice of stream o Choice of stream
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. Implementation: see Appendix A.3.2. category is automatable. Implementation: see Appendix A.3.2.
o Choice of path (destination address) o Choice of path (destination address)
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple sockets, but Automatable because it requires using multiple sockets, but
obtaining multiple sockets in the CONNECTION.ESTABLISHMENT obtaining multiple sockets in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
o Ordered message delivery (potentially slower than unordered) o Ordered message delivery (potentially slower than unordered)
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Fall-back to TCP: By using SEND.TCP. With SEND.TCP, messages will Implementation over TCP: By using SEND.TCP. With SEND.TCP,
not be identifiable by the receiver. messages will not be identifiable by the receiver.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Unordered message delivery (potentially faster than ordered) o Unordered message delivery (potentially faster than ordered)
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Fall-back to TCP: By using SEND.TCP and always sending data Implementation over TCP: By using SEND.TCP and always sending data
ordered: based on the assumption of the best-effort service model, ordered: based on the assumption of the best-effort service model,
ordered delivery may just be slower and does not violate ordered delivery may just be slower and does not violate
application expectations. Moreover, it is not possible to application expectations. Moreover, it is not possible to
associate the requested delivery order to a "message" in TCP associate the requested delivery order to a "message" in TCP
anyway. anyway.
o Request not to bundle messages o Request not to bundle messages
Protocols: SCTP Protocols: SCTP
Optimizing because this decision depends on knowledge about the Optimizing because this decision depends on knowledge about the
size of future data blocks and the delay between them. size of future data blocks and the delay between them.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Fall-back to TCP: By using SEND.TCP and DISABLE-NAGLE.TCP to Implementation over TCP: By using SEND.TCP and DISABLE-NAGLE.TCP
disable the Nagle algorithm when the request is made and enable it to disable the Nagle algorithm when the request is made and enable
again when the request is no longer made. Note that this is not it again when the request is no longer made. Note that this is
fully equivalent because it relates to the time of issuing the not fully equivalent because it relates to the time of issuing the
request rather than a specific message. request rather than a specific message.
Fall-back to UDP: do nothing (UDP never bundles messages). Implementation over UDP: do nothing (UDP never bundles messages).
o Specifying a "payload protocol-id" (handed over as such by the o Specifying a "payload protocol-id" (handed over as such by the
receiver) receiver)
Protocols: SCTP Protocols: SCTP
Functional because it allows to send extra application data with Functional because it allows to send extra application data with
every message, for the sake of identification of data, which by every message, for the sake of identification of data, which by
itself is application-specific. itself is application-specific.
Implementation: SEND.SCTP. Implementation: SEND.SCTP.
Fall-back to TCP: not possible. Implementation over TCP: not possible.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Specifying a key id to be used to authenticate a message o Specifying a key id to be used to authenticate a message
Protocols: SCTP Protocols: SCTP
Functional because this has a direct influence on security. Functional because this has a direct influence on security.
Implementation: via a parameter in SEND.SCTP. Implementation: via a parameter in SEND.SCTP.
Fall-back to TCP: This could be emulated by using SET_AUTH.TCP Implementation over TCP: This could be emulated by using
before and after the message is sent. Note that this is not fully SET_AUTH.TCP before and after the message is sent. Note that this
equivalent because it relates to the time of issuing the request is not fully equivalent because it relates to the time of issuing
rather than a specific message. the request rather than a specific message.
Fall-back to UDP: not possible. Implementation over UDP: not possible.
o Request not to delay the acknowledgement (SACK) of a message o Request not to delay the acknowledgement (SACK) of a message
Protocols: SCTP Protocols: SCTP
Optimizing because only an application knows for which message it Optimizing because only an application knows for which message it
wants to quickly be informed about success / failure of its wants to quickly be informed about success / failure of its
delivery. delivery.
Fall-back to TCP: do nothing. Implementation over TCP: do nothing.
Fall-back to UDP: do nothing. Implementation over UDP: do nothing.
A.1.2.2. Receiving Data A.1.2.2. Receiving Data
o Receive data (with no message delimiting) o Receive data (with no message delimiting)
Protocols: TCP Protocols: TCP
Functional because a TAPS system must be able to send and receive Functional because a TAPS system must be able to send and receive
data. data.
Implementation: via RECEIVE.TCP. Implementation: via RECEIVE.TCP.
Fall-back to UDP: do nothing (hand over a message, let the Implementation over UDP: do nothing (hand over a message, let the
application ignore frame boundaries). application ignore message boundaries).
o Receive a message o Receive a message
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via RECEIVE.SCTP and RECEIVE.UDP(-Lite). Implementation: via RECEIVE.SCTP and RECEIVE.UDP(-Lite).
Fall-back to TCP: not possible. Implementation over TCP: not possible.
o Choice of stream to receive from o Choice of stream to receive from
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Information about partial message arrival o Information about partial message arrival
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via RECEIVE.SCTP. Implementation: via RECEIVE.SCTP.
Fall-back to TCP: do nothing: this information is not available Implementation over TCP: do nothing: this information is not
with TCP. available with TCP.
Fall-back to UDP: do nothing: this information is not available
with UDP. Implementation over UDP: do nothing: this information is not
available with UDP.
A.1.2.3. Errors A.1.2.3. Errors
This section describes sending failures that are associated with a This section describes sending failures that are associated with a
specific call to in the "Sending Data" category (Appendix A.1.2.1). specific call to in the "Sending Data" category (Appendix A.1.2.1).
o Notification of send failures o Notification of send failures
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Functional because this notifies that potentially assumed reliable Functional because this notifies that potentially assumed reliable
data delivery is no longer provided. data delivery is no longer provided.
ADDED. This differs from the 2 automatable transport features ADDED. This differs from the 2 automatable transport features
below in that it does not distinugish between unsent and below in that it does not distinugish between unsent and
unacknowledged messages. unacknowledged messages.
Implementation: via SENDFAILURE-EVENT.SCTP and SEND_FAILURE.UDP(- Implementation: via SENDFAILURE-EVENT.SCTP and SEND_FAILURE.UDP(-
Lite). Lite).
Fall-back to TCP: do nothing: this notification is not available Implementation over TCP: do nothing: this notification is not
and will therefore not occur with TCP. available and will therefore not occur with TCP.
o Notification of an unsent (part of a) message o Notification of an unsent (part of a) message
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Automatable because the distinction between unsent and Automatable because the distinction between unsent and
unacknowledged is network-specific. unacknowledged is network-specific.
o Notification of an unacknowledged (part of a) message o Notification of an unacknowledged (part of a) message
Protocols: SCTP Protocols: SCTP
Automatable because the distinction between unsent and Automatable because the distinction between unsent and
unacknowledged is network-specific. unacknowledged is network-specific.
o Notification that the stack has no more user data to send o Notification that the stack has no more user data to send
Protocols: SCTP Protocols: SCTP
Optimizing because reacting to this notification requires the Optimizing because reacting to this notification requires the
application to be involved, and ensuring that the stack does not application to be involved, and ensuring that the stack does not
run dry of data (for too long) can improve performance. run dry of data (for too long) can improve performance.
Fall-back to TCP: do nothing. See also the discussion in Implementation over TCP: do nothing. See also the discussion in
Appendix A.3.4. Appendix A.3.4.
Fall-back to UDP: do nothing. This notification is not available Implementation over UDP: do nothing. This notification is not
and will therefore not occur with UDP. available and will therefore not occur with UDP.
o Notification to a receiver that a partial message delivery has o Notification to a receiver that a partial message delivery has
been aborted been aborted
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Fall-back to TCP: do nothing. This notification is not available Implementation over TCP: do nothing. This notification is not
and will therefore not occur with TCP. available and will therefore not occur with TCP.
Fall-back to UDP: do nothing. This notification is not available Implementation over UDP: do nothing. This notification is not
and will therefore not occur with UDP. available and will therefore not occur with UDP.
A.2. Step 2: Reduction -- The Reduced Set of Transport Features A.2. Step 2: Reduction -- The Reduced Set of Transport Features
By hiding automatable transport features from the application, a TAPS By hiding automatable transport features from the application, a TAPS
system can gain opportunities to automate the usage of network- system can gain opportunities to automate the usage of network-
related functionality. This can facilitate using the TAPS system for related functionality. This can facilitate using the TAPS system for
the application programmer and it allows for optimizations that may the application programmer and it allows for optimizations that may
not be possible for an application. For instance, system-wide not be possible for an application. For instance, system-wide
configurations regarding the usage of multiple interfaces can better configurations regarding the usage of multiple interfaces can better
be exploited if the choice of the interface is not entirely up to the be exploited if the choice of the interface is not entirely up to the
application. Therefore, since they are not strictly necessary to application. Therefore, since they are not strictly necessary to
expose in a TAPS system, we do not include automatable transport expose in a TAPS system, we do not include automatable transport
features in the reduced set of transport features. This leaves us features in the reduced set of transport features. This leaves us
with only the transport features that are either optimizing or with only the transport features that are either optimizing or
functional. functional.
A TAPS system should be able to fall back to TCP or UDP if A TAPS system should be able to communicate via TCP or UDP if
alternative transport protocols are found not to work. For many alternative transport protocols are found not to work. For many
transport features, this is possible -- often by simply not doing transport features, this is possible -- often by simply not doing
anything. For some transport features, however, it was identified anything when a specific request is made. For some transport
that neither a fall-back to TCP nor a fall-back to UDP is possible: features, however, it was identified that direct usage of neither TCP
in these cases, even not doing anything would incur semantically nor UDP is possible: in these cases, even not doing anything would
incorrect behavior. Whenever an application would make use of one of incur semantically incorrect behavior. Whenever an application would
these transport features, this would eliminate the possibility to use make use of one of these transport features, this would eliminate the
TCP or UDP. Thus, we only keep the functional and optimizing possibility to use TCP or UDP. Thus, we only keep the functional and
transport features for which a fall-back to either TCP or UDP is optimizing transport features for which an implementation over either
possible in our reduced set. TCP or UDP is possible in our reduced set.
In the following list, we precede a transport feature with "T:" if a In the following list, we precede a transport feature with "T:" if an
fall-back to TCP is possible, "U:" if a fall-back to UDP is possible, implementation over TCP is possible, "U:" if an implementation over
and "TU:" if a fall-back to either TCP or UDP is possible. UDP is possible, and "TU:" if an implementation over either TCP or
UDP is possible.
A.2.1. CONNECTION Related Transport Features A.2.1. CONNECTION Related Transport Features
ESTABLISHMENT: ESTABLISHMENT:
o T,U: Connect o T,U: Connect
o T,U: Specify number of attempts and/or timeout for the first o T,U: Specify number of attempts and/or timeout for the first
establishment message establishment message
o T: Configure authentication o T: Configure authentication
o T: Hand over a message to reliably transfer (possibly multiple o T: Hand over a message to reliably transfer (possibly multiple
skipping to change at page 46, line 28 skipping to change at page 43, line 50
o T,U: Notification to a receiver that a partial message delivery o T,U: Notification to a receiver that a partial message delivery
has been aborted has been aborted
A.3. Step 3: Discussion A.3. Step 3: Discussion
The reduced set in the previous section exhibits a number of The reduced set in the previous section exhibits a number of
peculiarities, which we will discuss in the following. This section peculiarities, which we will discuss in the following. This section
focuses on TCP because, with the exception of one particular focuses on TCP because, with the exception of one particular
transport feature ("Receive a message" -- we will discuss this in transport feature ("Receive a message" -- we will discuss this in
Appendix A.3.1), the list shows that UDP is strictly a subset of TCP. Appendix A.3.1), the list shows that UDP is strictly a subset of TCP.
We can first try to understand how to build a TAPS system that is We can first try to understand how to build a TAPS system that can
able to fall back to TCP, and then narrow down the result further to run over TCP, and then narrow down the result further to allow that
allow that the system can always fall back to either TCP or UDP the system can always run over either TCP or UDP (which effectively
(which effectively means removing everything related to reliability, means removing everything related to reliability, ordering,
ordering, authentication and closing/aborting with a notification to authentication and closing/aborting with a notification to the peer).
the peer).
Note that, because the functional transport features of UDP are -- Note that, because the functional transport features of UDP are --
with the exception of "Receive a message" -- a subset of TCP, TCP can with the exception of "Receive a message" -- a subset of TCP, TCP can
be used as a fall-back for UDP whenever an application does not need be used as a replacement for UDP whenever an application does not
message delimiting (e.g., because the application-layer protocol need message delimiting (e.g., because the application-layer protocol
already does it). This has been recognized by many applications that already does it). This has been recognized by many applications that
already do this in practice, by trying to communicate with UDP at already do this in practice, by trying to communicate with UDP at
first, and falling back to TCP in case of a connection failure. first, and falling back to TCP in case of a connection failure.
A.3.1. Sending Messages, Receiving Bytes A.3.1. Sending Messages, Receiving Bytes
When considering to fall back to TCP, there are several transport For implementing a TAPS system over TCP, there are several transport
features related to sending, but only a single transport feature features related to sending, but only a single transport feature
related to receiving: "Receive data (with no message delimiting)" related to receiving: "Receive data (with no message delimiting)"
(and, strangely, "information about partial message arrival"). (and, strangely, "information about partial message arrival").
Notably, the transport feature "Receive a message" is also the only Notably, the transport feature "Receive a message" is also the only
non-automatable transport feature of UDP(-Lite) for which no fall- non-automatable transport feature of UDP(-Lite) for which no
back to TCP is possible. implementation over TCP is possible.
To support these TCP receiver semantics, we define an "Application- To support these TCP receiver semantics, we define an "Application-
Framed Bytestream" (AFra-Bytestream). AFra-Bytestreams allow senders Framed Bytestream" (AFra-Bytestream). AFra-Bytestreams allow senders
to operate on messages while minimizing changes to the TCP socket to operate on messages while minimizing changes to the TCP socket
API. In particular, nothing changes on the receiver side - data can API. In particular, nothing changes on the receiver side - data can
be accepted via a normal TCP socket. be accepted via a normal TCP socket.
In an AFra-Bytestream, the sending application can optionally inform In an AFra-Bytestream, the sending application can optionally inform
the transport about frame boundaries and required properties per the transport about message boundaries and required properties per
frame (configurable order and reliability, or embedding a request not message (configurable order and reliability, or embedding a request
to delay the acknowledgement of a frame). Whenever the sending not to delay the acknowledgement of a message). Whenever the sending
application specifies per-frame properties that relax the notion of application specifies per-message properties that relax the notion of
reliable in-order delivery of bytes, it must assume that the reliable in-order delivery of bytes, it must assume that the
receiving application is 1) able to determine frame boundaries, receiving application is 1) able to determine message boundaries,
provided that frames are always kept intact, and 2) able to accept provided that messages are always kept intact, and 2) able to accept
these relaxed per-frame properties. Any signaling of such these relaxed per-message properties. Any signaling of such
information to the peer is up to an application-layer protocol and information to the peer is up to an application-layer protocol and
considered out of scope of this document. considered out of scope of this document.
For example, if an application requests to transfer fixed-size For example, if an application requests to transfer fixed-size
messages of 100 bytes with partial reliability, this needs the messages of 100 bytes with partial reliability, this needs the
receiving application to be prepared to accept data in chunks of 100 receiving application to be prepared to accept data in chunks of 100
bytes. If, then, some of these 100-byte messages are missing (e.g., bytes. If, then, some of these 100-byte messages are missing (e.g.,
if SCTP with Configurable Reliability is used), this is the expected if SCTP with Configurable Reliability is used), this is the expected
application behavior. With TCP, no messages would be missing, but application behavior. With TCP, no messages would be missing, but
this is also correct for the application, and the possible this is also correct for the application, and the possible
retransmission delay is acceptable within the best effort service retransmission delay is acceptable within the best effort service
model. Still, the receiving application would separate the byte model [RFC7305]. Still, the receiving application would separate the
stream into 100-byte chunks. byte stream into 100-byte chunks.
Note that this usage of messages does not require all messages to be Note that this usage of messages does not require all messages to be
equal in size. Many application protocols use some form of Type- equal in size. Many application protocols use some form of Type-
Length-Value (TLV) encoding, e.g. by defining a header including Length-Value (TLV) encoding, e.g. by defining a header including
length fields; another alternative is the use of byte stuffing length fields; another alternative is the use of byte stuffing
methods such as COBS [COBS]. If an application needs message methods such as COBS [COBS]. If an application needs message
numbers, e.g. to restore the correct sequence of messages, these must numbers, e.g. to restore the correct sequence of messages, these must
also be encoded by the application itself, as the sequence number also be encoded by the application itself, as the sequence number
related transport features of SCTP are no longer provided (in the related transport features of SCTP are not provided by the "minimum
interest of enabling a fall-back to TCP). set" (in the interest of enabling usage of TCP).
!!!NOTE: IMPLEMENTATION DETAILS BELOW WILL BE MOVED TO A SEPARATE
DRAFT IN A FUTURE VERSION.!!!
For the implementation of a TAPS system, this has the following For the implementation of a TAPS system, this has the following
consequences: consequences:
o Because the receiver-side transport leaves it up to the o Because the receiver-side transport leaves it up to the
application to delimit messages, messages must always remain application to delimit messages, messages must always remain
intact as they are handed over by the transport receiver. Data intact as they are handed over by the transport receiver. Data
can be handed over at any time as they arrive, but the byte stream can be handed over at any time as they arrive, but the byte stream
must never "skip ahead" to the beginning of the next message. must never "skip ahead" to the beginning of the next message.
o With SCTP, a "partial flag" informs a receiving application that a o With SCTP, a "partial flag" informs a receiving application that a
message is incomplete. Then, the next receive calls will only message is incomplete. Then, the next receive calls will only
deliver remaining parts of the same message (i.e., no messages or deliver remaining parts of the same message (i.e., no messages or
partial messages will arrive on other streams until the message is partial messages will arrive on other streams until the message is
complete) (see Section 8.1.20 in [RFC6458]). This can facilitate complete) (see Section 8.1.20 in [RFC6458]). This can facilitate
the implementation of the receiver buffer in the receiving the implementation of the receiver buffer in the receiving
application, but then such an application does not support message application, but then such an application does not support message
interleaving (which is required by stream schedulers). However, interleaving (which is required by stream schedulers). However,
receiving a byte stream from multiple SCTP streams requires a per- receiving a byte stream from multiple SCTP streams requires a per-
stream receiver buffer anyway, so this potential benefit is lost stream receiver buffer anyway, so this potential benefit is lost
skipping to change at page 48, line 32 skipping to change at page 46, line 9
comes at no additional implementation cost on the receiver side. comes at no additional implementation cost on the receiver side.
Stream schedulers operate on the sender side. Hence, because a Stream schedulers operate on the sender side. Hence, because a
TAPS sender-side application may talk to an SCTP receiver that TAPS sender-side application may talk to an SCTP receiver that
does not support interleaving, it cannot assume that stream does not support interleaving, it cannot assume that stream
schedulers will always work as expected. schedulers will always work as expected.
A.3.2. Stream Schedulers Without Streams A.3.2. Stream Schedulers Without Streams
We have already stated that multi-streaming does not require We have already stated that multi-streaming does not require
application-specific knowledge. Potential benefits or disadvantages application-specific knowledge. Potential benefits or disadvantages
of, e.g., using two streams over an SCTP association versus using two of, e.g., using two streams of an SCTP association versus using two
separate SCTP associations or TCP connections are related to separate SCTP associations or TCP connections are related to
knowledge about the network and the particular transport protocol in knowledge about the network and the particular transport protocol in
use, not the application. However, the transport features "Choose a use, not the application. However, the transport features "Choose a
scheduler to operate between streams of an association" and scheduler to operate between streams of an association" and
"Configure priority or weight for a scheduler" operate on streams. "Configure priority or weight for a scheduler" operate on streams.
Here, streams identify communication channels between which a Here, streams identify communication channels between which a
scheduler operates, and they can be assigned a priority. Moreover, scheduler operates, and they can be assigned a priority. Moreover,
the transport features in the MAINTENANCE category all operate on the transport features in the MAINTENANCE category all operate on
assocations in case of SCTP, i.e. they apply to all streams in that assocations in case of SCTP, i.e. they apply to all streams in that
assocation. assocation.
With only these semantics necessary to represent, the interface to a With only these semantics necessary to represent, the interface to a
TAPS system becomes easier if we rename connections into "TAPS flows" TAPS system becomes easier if we assume that TAPS connections may be
(the TAPS equivalent of a connection which may be a transport a transport connection or association, but could also be a stream of
connection or association, but could also become a stream of an an existing SCTP association, for example. We only need to allow for
existing SCTP association, for example) and allow assigning a "Group a way to define a possible grouping of TAPS connections. Then, all
Number" to a TAPS flow. Then, all MAINTENANCE transport features can MAINTENANCE transport features can be said to operate on TAPS
be said to operate on flow groups, not connections, and a scheduler connection groups, not TAPS connections, and a scheduler operates on
also operates on the flows within a group. the connections within a group.
!!!NOTE: IMPLEMENTATION DETAILS BELOW WILL BE MOVED TO A SEPARATE
DRAFT IN A FUTURE VERSION.!!!
For the implementation of a TAPS system, this has the following For the implementation of a TAPS system, this has the following
consequences: consequences:
o Streams may be identified in different ways across different o Streams may be identified in different ways across different
protocols. The only multi-streaming protocol considered in this protocols. The only multi-streaming protocol considered in this
document, SCTP, uses a stream id. The transport association below document, SCTP, uses a stream id. The transport association below
still uses a Transport Address (which includes one port number) still uses a Transport Address (which includes one port number)
for each communicating endpoint. To implement a TAPS system for each communicating endpoint. To implement a TAPS system
without exposed streams, an application must be given an without exposed streams, an application must be given an
identifier for each TAPS flow (akin to a socket), and depending on identifier for each TAPS connection (akin to a socket), and
whether streams are used or not, there will be a 1:1 mapping depending on whether streams are used or not, there will be a 1:1
between this identifier and local ports or not. mapping between this identifier and local ports or not.
o In SCTP, a fixed number of streams exists from the beginning of an o In SCTP, a fixed number of streams exists from the beginning of an
association; streams are not "established", there is no handshake association; streams are not "established", there is no handshake
or any other form of signaling to create them: they can just be or any other form of signaling to create them: they can just be
used. They are also not "gracefully shut down" -- at best, an used. They are also not "gracefully shut down" -- at best, an
"SSN Reset Request Parameter" in a "RE-CONFIG" chunk [RFC6525] can "SSN Reset Request Parameter" in a "RE-CONFIG" chunk [RFC6525] can
be used to inform the peer that of a "Stream Reset", as a rough be used to inform the peer that of a "Stream Reset", as a rough
equivalent of an "Abort". This has an impact on the semantics equivalent of an "Abort". This has an impact on the semantics
connection establishment and teardown (see Section 3.2). connection establishment and teardown (see Section 3.1).
o To support stream schedulers, a receiver-side TAPS system should o To support stream schedulers, a receiver-side TAPS system should
always support message interleaving because it comes at no always support message interleaving because it comes at no
additional implementation cost (because of the receiver-side additional implementation cost (because of the receiver-side
stream reception discussed in Appendix A.3.1). Note, however, stream reception discussed in Appendix A.3.1). Note, however,
that Stream schedulers operate on the sender side. Hence, because that Stream schedulers operate on the sender side. Hence, because
a TAPS sender-side application may talk to a native TCP-based a TAPS sender-side application may talk to a native TCP-based
receiver-side application, it cannot assume that stream schedulers receiver-side application, it cannot assume that stream schedulers
will always work as expected. will always work as expected.
To be compatible with multiple transport protocols and uniformly
allow access to both transport connections and streams of a multi-
streaming protocol, the semantics of opening and closing need to be
the most restrictive subset of all of the underlying options. For
example, TCP's support of half-closed connections can be seen as a
feature on top of the more restrictive "ABORT"; this feature cannot
be supported because not all protocols used by a TAPS system
(including streams of an association) support half-closed
connections.
A.3.3. Early Data Transmission A.3.3. Early Data Transmission
There are two transport features related to transferring a message There are two transport features related to transferring a message
early: "Hand over a message to reliably transfer (possibly multiple early: "Hand over a message to reliably transfer (possibly multiple
times) before connection establishment", which relates to TCP Fast times) before connection establishment", which relates to TCP Fast
Open [RFC7413], and "Hand over a message to reliably transfer during Open [RFC7413], and "Hand over a message to reliably transfer during
connection establishment", which relates to SCTP's ability to connection establishment", which relates to SCTP's ability to
transfer data together with the COOKIE-Echo chunk. Also without TCP transfer data together with the COOKIE-Echo chunk. Also without TCP
Fast Open, TCP can transfer data during the handshake, together with Fast Open, TCP can transfer data during the handshake, together with
the SYN packet -- however, the receiver of this data may not hand it the SYN packet -- however, the receiver of this data may not hand it
over to the application until the handshake has completed. Also, over to the application until the handshake has completed. Also,
different from TCP Fast Open, this data is not delimited as a message different from TCP Fast Open, this data is not delimited as a message
by TCP (thus, not visible as a ``message''). This functionality is by TCP (thus, not visible as a ``message''). This functionality is
commonly available in TCP and supported in several implementations, commonly available in TCP and supported in several implementations,
even though the TCP specification does not explain how to provide it even though the TCP specification does not explain how to provide it
to applications. to applications.
A TAPS system could differentiate between the cases of transmitting A TAPS system could differentiate between the cases of transmitting
data "before" (possibly multiple times) or during the handshake. data "before" (possibly multiple times) or "during" the handshake.
Alternatively, it could also assume that data that are handed over Alternatively, it could also assume that data that are handed over
early will be transmitted as early as possible, and "before" the early will be transmitted as early as possible, and "before" the
handshake would only be used for data that are explicitly marked as handshake would only be used for messages that are explicitly marked
"idempotent" (i.e., it would be acceptable to transfer it multiple as "idempotent" (i.e., it would be acceptable to transfer them
times). multiple times).
The amount of data that can successfully be transmitted before or The amount of data that can successfully be transmitted before or
during the handshake depends on various factors: the transport during the handshake depends on various factors: the transport
protocol, the use of header options, the choice of IPv4 and IPv6 and protocol, the use of header options, the choice of IPv4 and IPv6 and
the Path MTU. A TAPS system should therefore allow a sending the Path MTU. A TAPS system should therefore allow a sending
application to query the maximum amount of data it can possibly application to query the maximum amount of data it can possibly
transmit before (or, if exposed, during) connection establishment. transmit before (or, if exposed, during) connection establishment.
A.3.4. Sender Running Dry A.3.4. Sender Running Dry
skipping to change at page 50, line 31 skipping to change at page 48, line 20
data to send" relates to SCTP's "SENDER DRY" notification. Such data to send" relates to SCTP's "SENDER DRY" notification. Such
notifications can, in principle, be used to avoid having an notifications can, in principle, be used to avoid having an
unnecessarily large send buffer, yet ensure that the transport sender unnecessarily large send buffer, yet ensure that the transport sender
always has data available when it has an opportunity to transmit it. always has data available when it has an opportunity to transmit it.
This has been found to be very beneficial for some applications This has been found to be very beneficial for some applications
[WWDC2015]. However, "SENDER DRY" truly means that the entire send [WWDC2015]. However, "SENDER DRY" truly means that the entire send
buffer (including both unsent and unacknowledged data) has emptied -- buffer (including both unsent and unacknowledged data) has emptied --
i.e., when it notifies the sender, it is already too late, the i.e., when it notifies the sender, it is already too late, the
transport protocol already missed an opportunity to send data. Some transport protocol already missed an opportunity to send data. Some
modern TCP implementations now include the unspecified modern TCP implementations now include the unspecified
"TCP_NOTSENT_LOWAT" socket option proposed in [WWDC2015], which "TCP_NOTSENT_LOWAT" socket option that was proposed in [WWDC2015],
limits the amount of unsent data that TCP can keep in the socket which limits the amount of unsent data that TCP can keep in the
buffer; this allows to specify at which buffer filling level the socket buffer; this allows to specify at which buffer filling level
socket becomes writable, rather than waiting for the buffer to run the socket becomes writable, rather than waiting for the buffer to
empty. run empty.
SCTP allows to configure the sender-side buffer too: the automatable SCTP allows to configure the sender-side buffer too: the automatable
Transport Feature "Configure send buffer size" provides this Transport Feature "Configure send buffer size" provides this
functionality, but only for the complete buffer, which includes both functionality, but only for the complete buffer, which includes both
unsent and unacknowledged data. SCTP does not allow to control these unsent and unacknowledged data. SCTP does not allow to control these
two sizes separately. A TAPS system should allow for uniform access two sizes separately. It therefore makes sense for a TAPS system to
to "TCP_NOTSENT_LOWAT" as well as the "SENDER DRY" notification. allow for uniform access to "TCP_NOTSENT_LOWAT" as well as the
"SENDER DRY" notification.
A.3.5. Capacity Profile A.3.5. Capacity Profile
The transport features: The transport features:
o Disable Nagle algorithm o Disable Nagle algorithm
o Enable and configure a "Low Extra Delay Background Transfer" o Enable and configure a "Low Extra Delay Background Transfer"
o Specify DSCP field o Specify DSCP field
all relate to a QoS-like application need such as "low latency" or all relate to a QoS-like application need such as "low latency" or
"scavenger". In the interest of flexibility of a TAPS system, they "scavenger". In the interest of flexibility of a TAPS system, they
could therefore be offered in a uniform, more abstract way, where a could therefore be offered in a uniform, more abstract way, where a
TAPS system could e.g. decide by itself how to use combinations of TAPS system could e.g. decide by itself how to use combinations of
LEDBAT-like congestion control and certain DSCP values, and an LEDBAT-like congestion control and certain DSCP values, and an
application would only specify a general "capacity profile" (a application would only specify a general "capacity profile" (a
description of how it wants to use the available capacity). A need description of how it wants to use the available capacity). A need
for "lowest possible latency at the expense of overhead" could then for "lowest possible latency at the expense of overhead" could then
translate into automatically disabling the Nagle algorithm. translate into automatically disabling the Nagle algorithm.
skipping to change at page 51, line 50 skipping to change at page 49, line 41
UDP(-Lite) has a transport feature called "Specify DF field". This UDP(-Lite) has a transport feature called "Specify DF field". This
yields an error message in case of sending a message that exceeds the yields an error message in case of sending a message that exceeds the
Path MTU, which is necessary for a UDP-based application to be able Path MTU, which is necessary for a UDP-based application to be able
to implement Path MTU Discovery (a function that UDP-based to implement Path MTU Discovery (a function that UDP-based
applications must do by themselves). The "Get max. transport-message applications must do by themselves). The "Get max. transport-message
size that may be sent using a non-fragmented IP packet from the size that may be sent using a non-fragmented IP packet from the
configured interface" transport feature yields an upper limit for the configured interface" transport feature yields an upper limit for the
Path MTU (minus headers) and can therefore help to implement Path MTU Path MTU (minus headers) and can therefore help to implement Path MTU
Discovery more efficiently. Discovery more efficiently.
This also relates to the fact that the choice of path is automatable:
if a TAPS system can switch a path at any time, unknown to an
application, yet the application intends to do Path MTU Discovery,
this could yield a very inefficient behavior. Thus, a TAPS system
should probably avoid automatically switching paths, and inform the
application about any unavoidable path changes, when applications
request to disallow fragmentation with the "Specify DF field"
feature.
Appendix B. Revision information Appendix B. Revision information
XXX RFC-Ed please remove this section prior to publication. XXX RFC-Ed please remove this section prior to publication.
-02: implementation suggestions added, discussion section added, -02: implementation suggestions added, discussion section added,
terminology extended, DELETED category removed, various other fixes; terminology extended, DELETED category removed, various other fixes;
list of Transport Features adjusted to -01 version of [TAPS2] except list of Transport Features adjusted to -01 version of [TAPS2] except
that MPTCP is not included. that MPTCP is not included.
-03: updated to be consistent with -02 version of [TAPS2]. -03: updated to be consistent with -02 version of [TAPS2].
skipping to change at page 53, line 5 skipping to change at page 50, line 36
divided into two features, one for ordered, one for unordered divided into two features, one for ordered, one for unordered
delivery. The word "reliably" was added to the transport features delivery. The word "reliably" was added to the transport features
"Hand over a message to reliably transfer (possibly multiple times) "Hand over a message to reliably transfer (possibly multiple times)
before connection establishment" and "Hand over a message to reliably before connection establishment" and "Hand over a message to reliably
transfer during connection establishment" to make it clearer why this transfer during connection establishment" to make it clearer why this
is not supported by UDP. Clarified that the "minset abstract is not supported by UDP. Clarified that the "minset abstract
interface" is not proposing a specific API for all TAPS systems to interface" is not proposing a specific API for all TAPS systems to
implement, but it is just a way to describe the minimum set. Author implement, but it is just a way to describe the minimum set. Author
order changed. order changed.
Authors' Addresses draft-ietf-taps-minset-01: "fall-back to" (TCP or UDP) replaced
(mostly with "implementation over"). References to post-sockets
removed (these were statments that assumed that post-sockets requires
two-sided implementation). Replaced "flow" with "TAPS Connection"
and "frame" with "message" to avoid introducing new terminology.
Made sections 3 and 4 in line with the categorization that is already
used in the appendix and [TAPS2], and changed style of section 4 to
be even shorter and less interface-like. Updated reference draft-
ietf-tsvwg-sctp-ndata to RFC8260.
Authors' Addresses
Michael Welzl Michael Welzl
University of Oslo University of Oslo
PO Box 1080 Blindern PO Box 1080 Blindern
Oslo N-0316 Oslo N-0316
Norway Norway
Phone: +47 22 85 24 20 Phone: +47 22 85 24 20
Email: michawe@ifi.uio.no Email: michawe@ifi.uio.no
Stein Gjessing Stein Gjessing
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