draft-ietf-taps-minset-01.txt   draft-ietf-taps-minset-02.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: August 10, 2018 February 6, 2018 Expires: September 1, 2018 February 28, 2018
A Minimal Set of Transport Services for TAPS Systems A Minimal Set of Transport Services for TAPS Systems
draft-ietf-taps-minset-01 draft-ietf-taps-minset-02
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 in RFC 8303.
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
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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 August 10, 2018. This Internet-Draft will expire on September 1, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 12 skipping to change at page 2, line 12
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
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. ESTABLISHMENT, AVAILABILITY and TERMINATION . . . . . . . 5 3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION . . . . . . . 5
3.2. MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. DATA Transfer . . . . . . . . . . . . . . . . . . . . . . 9 3.2.1. Connection groups . . . . . . . . . . . . . . . . . . 8
3.3.1. Sending Data . . . . . . . . . . . . . . . . . . . . 9 3.2.2. Individual connections . . . . . . . . . . . . . . . 10
3.3.2. Receiving Data . . . . . . . . . . . . . . . . . . . 10 3.3. DATA Transfer . . . . . . . . . . . . . . . . . . . . . . 10
4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3.1. Sending Data . . . . . . . . . . . . . . . . . . . . 10
4.1. ESTABLISHMENT, AVAILABILITY and TERMINATION . . . . . . . 11 3.3.2. Receiving Data . . . . . . . . . . . . . . . . . . . 11
4.2. MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . 12 4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2.1. Connection groups . . . . . . . . . . . . . . . . . . 12 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
4.2.2. Individual connections . . . . . . . . . . . . . . . 13 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
4.3. DATA Transfer . . . . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 15 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 8.1. Normative References . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 8.2. Informative References . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 Appendix A. Deriving the minimal set . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
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 . . . . . . . . . . . . . . . . . . . . . . . . 19 Features . . . . . . . . . . . . . . . . . . . . . . . . 15
A.1.1. CONNECTION Related Transport Features . . . . . . . . 20 A.1.1. CONNECTION Related Transport Features . . . . . . . . 17
A.1.2. DATA Transfer Related Transport Features . . . . . . 36 A.1.2. DATA Transfer Related Transport Features . . . . . . 32
A.2. Step 2: Reduction -- The Reduced Set of Transport A.2. Step 2: Reduction -- The Reduced Set of Transport
Features . . . . . . . . . . . . . . . . . . . . . . . . 41 Features . . . . . . . . . . . . . . . . . . . . . . . . 37
A.2.1. CONNECTION Related Transport Features . . . . . . . . 42 A.2.1. CONNECTION Related Transport Features . . . . . . . . 38
A.2.2. DATA Transfer Related Transport Features . . . . . . 43 A.2.2. DATA Transfer Related Transport Features . . . . . . 39
A.3. Step 3: Discussion . . . . . . . . . . . . . . . . . . . 43 A.3. Step 3: Discussion . . . . . . . . . . . . . . . . . . . 40
A.3.1. Sending Messages, Receiving Bytes . . . . . . . . . . 44 A.3.1. Sending Messages, Receiving Bytes . . . . . . . . . . 40
A.3.2. Stream Schedulers Without Streams . . . . . . . . . . 46 A.3.2. Stream Schedulers Without Streams . . . . . . . . . . 41
A.3.3. Early Data Transmission . . . . . . . . . . . . . . . 47 A.3.3. Early Data Transmission . . . . . . . . . . . . . . . 42
A.3.4. Sender Running Dry . . . . . . . . . . . . . . . . . 48 A.3.4. Sender Running Dry . . . . . . . . . . . . . . . . . 43
A.3.5. Capacity Profile . . . . . . . . . . . . . . . . . . 48 A.3.5. Capacity Profile . . . . . . . . . . . . . . . . . . 43
A.3.6. Security . . . . . . . . . . . . . . . . . . . . . . 49 A.3.6. Security . . . . . . . . . . . . . . . . . . . . . . 44
A.3.7. Packet Size . . . . . . . . . . . . . . . . . . . . . 49 A.3.7. Packet Size . . . . . . . . . . . . . . . . . . . . . 44
Appendix B. Revision information . . . . . . . . . . . . . . . . 49 Appendix B. Revision information . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
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. the transport system, without binding them to a particular transport
protocol. Currently, the set of transport services that most
Currently, the set of transport services that most applications use applications use is based on TCP and UDP (and protocols that are
is based on TCP and UDP (and protocols running on top of them); this layered on top of them); this limits the ability for the network
limits the ability for the network stack to make use of features of stack to make use of features of other transport protocols. For
other protocols. For example, if a protocol supports out-of-order example, if a protocol supports out-of-order message delivery but
message delivery but applications always assume that the network applications always assume that the network provides an ordered
provides an ordered bytestream, then the network stack can never bytestream, then the network stack can not immediately deliver a
utilize out-of-order message delivery: doing so would break a message that arrives out-of-order: doing so would break a fundamental
fundamental assumption of the application. assumption of the application. The net result is unnecessary head-
of-line blocking delay.
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 transport system can make it possible to use these services
to statically bind an application to a specific transport protocol. without having to statically bind an application to a specific
The first step towards the design of such a system was taken by transport protocol. The first step towards the design of such a
[RFC8095], which surveys a large number of transports, and [TAPS2] as system was taken by [RFC8095], which surveys a large number of
well as [TAPS2UDP], which identify the specific transport features transports, and [RFC8303] as well as [RFC8304], which identify the
that are exposed to applications by the protocols TCP, MPTCP, UDP(- specific transport features that are exposed to applications by the
Lite) and SCTP as well as the LEDBAT congestion control mechanism. protocols TCP, MPTCP, UDP(-Lite) and SCTP as well as the LEDBAT
The present draft is based on these documents and follows the same congestion control mechanism. This memo is based on these documents
terminology (also listed below). Because the considered transport and follows the same terminology (also listed below). Because the
protocols together cover a wide range of transport features, there is considered transport protocols conjointly cover a wide range of
reason to hope that the resulting set (and the reasoning that led to transport features, there is reason to hope that the resulting set
it) will also apply to many aspects of other transport protocols such (and the reasoning that led to it) will also apply to many aspects of
as QUIC. other transport protocols.
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 transport
to automate usage of the various functions of its available set of system has to automate usage of the various functions of its
transport protocols. Some functions only exist in one particular available set of transport protocols. Some functions only exist in
protocol, and if an application would use them, this would statically one particular protocol, and if an application would use them, this
tie the application to this protocol, counteracting the purpose of a would statically tie the application to this protocol, counteracting
TAPS system. Also, if the number of exposed features is exceedingly the purpose of TAPS. Also, if the number of exposed features is
large, a TAPS system might become very hard to use for an application exceedingly large, a transport system might become very difficult to
programmer. Taking [TAPS2] as a basis, this document therefore use for an application programmer. Taking [RFC8303] as a basis, this
develops a minimal set of transport features, removing the ones that document therefore develops a minimal set of transport features,
could be harmful to the purpose of a TAPS system but keeping the ones removing the ones that could be harmful to the purpose of TAPS but
that must be retained for applications to benefit from useful keeping the ones that must be retained for applications to benefit
transport functionality. from useful 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 ways message delivery" transport feature (alternatively, there may be ways
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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 can be offered by end systems supporting TAPS. The described transport
implemented over TCP; elements of the system that may prohibit system can be implemented over TCP; elements of the system that may
implementation over UDP are marked with "!UDP". To implement a TAPS prohibit implementation over UDP are marked with "!UDP". To
system that can also work over UDP, these marked transport features implement a transport system that can also work over UDP, these
should be excluded. marked transport features should be excluded.
As in Appendix A, Appendix A.2 and [TAPS2], we categorize the minimal As in Appendix A, Appendix A.2 and [RFC8303], we categorize the
set of transport features as 1) CONNECTION related (ESTABLISHMENT, minimal set of transport features as 1) CONNECTION related
AVAILABILITY, MAINTENANCE, TERMINATION) and 2) DATA Transfer related (ESTABLISHMENT, AVAILABILITY, MAINTENANCE, TERMINATION) and 2) DATA
(Sending Data, Receiving Data, Errors). Here, the focus is on "TAPS Transfer related (Sending Data, Receiving Data, Errors). Here, the
Connections": connections that the TAPS system offers, as opposed to focus is on connections that the transport system offers, as opposed
connections of transport protocols that the TAPS system uses. to connections of transport protocols that the transport system uses.
3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION 3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION
A TAPS connection must first be "created" to allow for some initial A connection must first be "created" to allow for some initial
configuration to be carried out before the TAPS system can actively configuration to be carried out before the transport system can
or passively establish a transport connection. All configuration actively or passively establish communication with a remote endpoint.
parameters in Section 3.2 and can be used initially, although some of All configuration parameters in Section 3.2 can be used initially,
them may only take effect when a transport connection has been although some of them may only take effect when a connection has been
established. Configuring a connection early helps a TAPS system make established with a chosen transport protocol. Configuring a
the right decisions. In particular, grouping information can connection early helps a transport system make the right decisions.
influence the TAPS system to implement a TAPS connection as a stream For example, grouping information can influence the transport system
of a multi-streaming protocol's existing association or not. to implement a connection as a stream of a multi-streaming protocol's
existing association or not.
For ungrouped TAPS connections, early configuration is necessary For ungrouped connections, early configuration is necessary because
because it allows the TAPS system to know which protocols it should it allows the transport system to know which protocols it should try
try to use (to steer a mechanism such as "Happy Eyeballs" 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 transport 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 a 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 7):
- 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 TAPS connections * Choosing a scheduler to operate between connections
in a group, with the possibility to configure a priority in a group, with the possibility to configure a priority
or weight per connection 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
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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 it impossible to use SCTP's schedulers with priorities between
grouped TAPS connections. The TAPS system must know which choice is grouped connections. The transport system must know which choice is
more important for the application in order to make the best more important for the application in order to make the best
decision. We caution implementers to be aware of the full set of decision. We caution implementers to be aware of the full set of
trade-offs, for which we recommend consulting the list in trade-offs, for which we recommend consulting the list in
Appendix A.2.1 when deciding how to initialize a TAPS connection. Appendix A.2.1 when deciding how to initialize a connection.
Once a TAPS connection 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 transport connection
establishment (with zero being a possible answer). An application
can also give the TAPS connection 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).
After creation, a TAPS system can actively establish communication
with a peer, or it can passively listen for incoming connection
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 is the arrival of the first data
that the active side sends (a receiver-side TAPS system could handle
this by continuing to block a "Listen" call, immediately followed by
issuing "Receive", for example; callback-based implementations could
simply skip the equivalent of "Listen"). This also means that the
active opening side is assumed to be the first side sending data.
A TAPS system can actively close a connection, i.e. terminate it
after reliably delivering all remaining data to the peer, or it can
abort it, i.e. terminate it without delivering remaining data.
Unless all data transfers only used unreliable message transmission
without congestion control (i.e., UDP-style transfer), closing a
connection is guaranteed to cause an event to notify the peer
application that the connection has been closed (!UDP). Similarly,
for anything but (UDP-style) unreliable non-congestion-controlled
data transfer, aborting a connection will cause an event to notify
the peer application that the connection has been aborted (!UDP). A
timeout can be configured to abort a TAPS connection when data could
not be delivered for too long (!UDP); however, timeout-based abortion
does not notify the peer application that the connection has been
aborted. Because half-closed connections are not supported, when a
TAPS host receives a notification that the peer is closing or
aborting the connection (!UDP), its peer may not be able to read
outstanding data. This means that unacknowledged data residing in
the TAPS system's send buffer may have to be dropped from that buffer
upon arrival of a "close" or "abort" notification from the peer.
3.2. MAINTENANCE
A TAPS connection group can be configured with a number of transport
features, and there are some notifications to applications about a
connection group. The following transport features and notifications
from Appendix A.2 automatically apply to grouped TAPS connections
(e.g., when a TAPS connection is mapped to a stream of a multi-
streaming protocol):
Timeout, error notifications:
o Change timeout for aborting connection (using retransmit limit or
time value) (!UDP)
o Suggest timeout to the peer (!UDP)
o Notification of Excessive Retransmissions (early warning below
abortion threshold)
o Notification of ICMP error message arrival
Others:
o Choose a scheduler to operate between connections of a group
o Obtain ECN field
The following transport features are new or changed, based on the
discussion in Appendix A.3:
o Capacity profile
This describes how an application wants to use its available
capacity. Choices can be "lowest possible latency at the expense
of overhead" (which would disable any Nagle-like algorithm),
"scavenger", and values that help determine the DSCP value for a
connection (e.g. similar to table 1 in
[I-D.ietf-tsvwg-rtcweb-qos]).
The following transport features and notifications from Appendix A.2
only apply to a single TAPS connection:
Configure priority or weight for a scheduler
Checksums:
o Disable checksum when sending
o Disable checksum requirement when receiving
o Specify checksum coverage used by the sender
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).
3.3. DATA Transfer
3.3.1. Sending Data
This section discusses how to send data after connection
establishment. Section 3.1 discusses the possiblity to hand over a
message to reliably send before or during establishment.
Here we list per-message properties that a sender can optionally
configure if it hands over a delimited message for sending with
congestion control (!UDP), taken from Appendix A.2:
o Configurable Message Reliability
o Ordered message delivery (potentially slower than unordered)
o Unordered message delivery (potentially faster than ordered)
o Request not to bundle messages
o Request not to delay the acknowledgement (SACK) of a message
Additionally, an application can hand over delimited messages for
unreliable transmission without congestion control (note that such
applications should perform congestion control in accordance with
[RFC2914]). Then, none of the per-message properties listed above
have any effect, but it is possible to use the transport feature
"Specify DF field" to allow/disallow fragmentation.
Following Appendix A.3.7, there are three transport features (two
old, one new):
o Get max. transport message size that may be sent without
fragmentation from the configured interface
This is optional for a TAPS system to offer, and may return an
error ("not available"). It can aid applications implementing
Path MTU Discovery.
o Get max. transport message size that may be received from the
configured interface
This is optional for a TAPS system to offer, and may return an
error ("not available").
o Get maximum transport message size
Irrespective of fragmentation, there is a size limit for the
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
application to query this value -- the maximum size of a message
in an Application-Framed-Bytestream (see Appendix A.3.1). This
may also return an error when data is not delimited ("not
available").
There are two more sender-side notifications. These are unreliable,
i.e. a TAPS system cannot be assumed to implement them, but they may
occur:
o Notification of send failures
A TAPS system may inform a sender application of a failure to send
a specific message.
o Notification of draining below a low water mark
A TAPS system can notify a sender application when the TAPS
system's filling level of the buffer of unsent data is below a
configurable threshold in bytes. Even for TAPS systems that do
implement this notification, supporting thresholds other than 0 is
optional.
"Notification of draining below a low water mark" is a generic
notification that tries to enable uniform access to
"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
where the threshold (for unsent data) is 0 and there is also no more
unacknowledged data in the send buffer). Note that this threshold
and its notification should operate across the buffers of the whole
TAPS system, i.e. also any potential buffers that the TAPS system
itself may use on top of the transport's send buffer.
3.3.2. Receiving Data
A receiving application obtains an "Application-Framed Bytestream"
(AFra-Bytestream); this concept is further described in
Appendix A.3.1). In line with TCP's receiver semantics, an AFra-
Bytestream is just a stream of bytes to the receiver. If message
boundaries were specified by the sender, a receiver-side TAPS system
implementing only the minimum set of transport services defined here
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.
4. Summary
Here we summarize the minimum set of transport features in a more
compact form.
4.1. ESTABLISHMENT, AVAILABILITY and TERMINATION
A TAPS connection is created and associated with an existing or new
TAPS connection group. Grouping can influence the TAPS system to
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.
A TAPS connection can actively connect to a peer; this may or may not
trigger a notification on the listening side. If the application
sends data (see Section 4.3) before the TAPS system establishes a
transport connection, then such data may be transmitted early, upon
connecting. When a TAPS system listens for incoming connections, the
first arriving message may already be the first block of data.
Creation / connection / configuration parameters: To summarize, the following parameters serve as input for the
transport system to help it choose and configure a suitable protocol:
reliability: a boolean that should be set to true when any of the o 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 o Checksum_coverage: a boolean to specify whether it will be useful
the application to specify checksum coverage when sending or to 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 o 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 grouped connections, with the possibility to to operate between grouped connections, with the possibility to
configure a priority or weight per connection; configurable configure a priority or weight per connection; configurable
message reliability; unordered message delivery; requesting not to message reliability; unordered message delivery; requesting not to
delay the acknowledgement (SACK) of a message. delay the acknowledgement (SACK) of a message.
earlymsg_timeout_notifications: a boolean that should be set to true o Earlymsg_timeout_notifications: a boolean that should be set to
when any of the following will be useful to the application: hand true when any of the following will be useful to the application:
over a message to reliably transfer (possibly multiple times) hand 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.
A TAPS connection can be closed after all outstanding data is Once a connection is created, it can be queried for the maximum
reliably delivered to the peer (if reliable data delivery was amount of data that an application can possibly expect to have
requested earlier (!UDP)), in which case the peer is notified that reliably transmitted before or during transport connection
the connection is closed. Alternatively, a TAPS connection can be establishment (with zero being a possible answer) (see
aborted without delivering outstanding data to the peer. In case Section 3.2.1). An application can also give the connection a
reliable or partially reliable data delivery was requested earlier message for reliable transmission before or during connection
(!UDP), the peer is notified that the connection is aborted. establishment (!UDP); the transport system will then try to transmit
it as early as possible. An application can facilitate sending a
message particularly early by marking it as "idempotent" (see
Section 3.3.1); 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).
4.2. MAINTENANCE After creation, a transport system can actively establish
communication with a peer, or it can passively listen for incoming
connection requests. Note that active establishment may or may not
trigger a notification on the listening side. It is possible that
the first notification on the listening side is the arrival of the
first data that the active side sends (a receiver-side transport
system could handle this by continuing to block a "Listen" call,
immediately followed by issuing "Receive", for example; callback-
based implementations could simply skip the equivalent of "Listen").
This also means that the active opening side is assumed to be the
first side sending data.
A transport system can actively close a connection, i.e. terminate it
after reliably delivering all remaining data to the peer (if reliable
data delivery was requested earlier (!UDP)), in which case the peer
is notified that the connection is closed. Alternatively, a
connection can be aborted without delivering outstanding data to the
peer. In case reliable or partially reliable data delivery was
requested earlier (!UDP), the peer is notified that the connection is
aborted. A timeout can be configured to abort a connection when data
could not be delivered for too long (!UDP); however, timeout-based
abortion does not notify the peer application that the connection has
been aborted. Because half-closed connections are not supported,
when a host implementing TAPS receives a notification that the peer
is closing or aborting the connection (!UDP), its peer may not be
able to read outstanding data. This means that unacknowledged data
residing a transport system's send buffer may have to be dropped from
that buffer upon arrival of a "close" or "abort" notification from
the peer.
3.2. MAINTENANCE
A transport system must offer means to group connections, but it
cannot guarantee truly grouping them using the transport protocols
that it uses (e.g., it cannot be guaranteed that connections become
multiplexed as streams on a single SCTP association when SCTP may not
be available). The transport system must therefore ensure that
group- versus non-group-configurations 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).
As a general rule, any configuration described below should be As a general rule, any configuration described below should be
carried out as early as possible to aid the TAPS system's decision carried out as early as possible to aid the transport system's
taking. decision making.
4.2.1. Connection groups 3.2.1. Connection groups
The transport features below apply to all TAPS connections in the The following transport features and notifications (some directly
same group: from Appendix A.2, some new or changed, based on the discussion in
Appendix A.3) automatically apply to all grouped connections:
(!UDP) Configure a timeout: this can be done with the following (!UDP) Configure a timeout: this can be done with the following
parameters: parameters:
o A timeout value for aborting connections, in seconds o A timeout value for aborting connections, in seconds
o A timeout value to be suggested to the peer (if possible), in o A timeout value to be suggested to the peer (if possible), in
seconds seconds
o The number of retransmissions after which the application should o The number of retransmissions after which the application should
be notifed of "Excessive Retransmissions" be notifed of "Excessive Retransmissions"
skipping to change at page 13, line 7 skipping to change at page 9, line 16
o A number to identify the type of scheduler that should be used to o A number to identify the type of scheduler that should be used to
operate between connections in the group (no guarantees given). operate between connections in the group (no guarantees given).
Schedulers are defined in [RFC8260]. Schedulers are defined in [RFC8260].
o A "capacity profile" number to identify how an application wants o A "capacity profile" number to identify how an application wants
to use its available capacity. Choices can be "lowest possible to use its available capacity. 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", or values that help determine Nagle-like algorithm), "scavenger", or values that help determine
the DSCP value for a connection (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]).
o A buffer limit (in bytes); when the sender has less then o A buffer limit (in bytes); when the sender has less then the
low_watermark bytes in the buffer, the application may be provided limit of bytes in the buffer, the application may be
notified. Notifications are not guaranteed, and supporting notified. Notifications are not guaranteed, and it is optional
watermark values greater than 0 is not guaranteed. for a transport system to support buffer limit values greater than
0. Note that this limit and its notification should operate
across the buffers of the whole transport system, i.e. also any
potential buffers that the transport system itself may use on top
of the transport's send buffer.
The following properties can be queried: Following Appendix A.3.7, these properties can be queried:
o The maximum message size that may be sent without fragmentation, o The maximum message size that may be sent without fragmentation
in bytes (or "not available") via the configured interface. This is optional for a transport
o The maximum transport message size that can be sent, in bytes (or system to offer, and may return an error ("not available"). It
"not available") can aid applications implementing Path MTU Discovery.
o The maximum transport message size that can be received, in bytes o The maximum transport message size that can be sent, in bytes.
(or "not available") Irrespective of fragmentation, there is a size limit for the
messages that can be handed over to SCTP or UDP(-Lite); because
the service provided by a transport system is independent of the
transport protocol, it must allow an application to query this
value -- the maximum size of a message in an Application-Framed-
Bytestream (see Appendix A.3.1). This may also return an error
when data is not delimited ("not available").
o The maximum transport message size that can be received from the
configured interface, in bytes (or "not available").
o The maximum amount of data that can possibly be sent before or o The maximum amount of data that can possibly be sent before or
during connection establishment, in bytes (or "not available") during connection establishment, in bytes.
In addition to the already mentioned closing / aborting notifications In addition to the already mentioned closing / aborting notifications
and possible send errors, the following notifications can occur: and possible send errors, the following notifications can occur:
o 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.
o ICMP Arrival (parameter: ICMP message): an ICMP packet carrying o ICMP Arrival (parameter: ICMP message): an ICMP packet carrying
the conveyed ICMP message has arrived. the conveyed ICMP message has arrived.
o 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.
o 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.
o Drain: the send buffer has either drained below the configured low o Drain: the send buffer has either drained below the configured
water mark or it has become completely empty. buffer limit or it has become completely empty. This is a generic
notification that tries to enable uniform access to
4.2.2. Individual connections "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 where the threshold (for unsent data) is 0 and there is also
no more unacknowledged data in the send buffer).
The transport features below apply to individual TAPS connections: 3.2.2. Individual connections
Configure priority or weight for a scheduler, as described in Configure priority or weight for a scheduler, as described in
[RFC8260]. [RFC8260].
Configure checksum usage: this can be done with the following Configure checksum usage: this can be done with the following
parameters, but there is no guarantee that any checksum limitations parameters, but there is no guarantee that any checksum limitations
will indeed be enforced (the default behavior is "full coverage, will indeed be enforced (the default behavior is "full coverage,
checksum enabled"): checksum enabled"):
o A boolean to enable / disable usage of a checksum when sending o A boolean to enable / disable usage of a checksum when sending
o The desired coverage (in bytes) of the checksum used when sending o The desired coverage (in bytes) of the checksum used when sending
o A boolean to enable / disable requiring a checksum when receiving o A boolean to enable / disable requiring a checksum when receiving
o The required minimum coverage (in bytes) of the checksum when o The required minimum coverage (in bytes) of the checksum when
receiving receiving
4.3. DATA Transfer 3.3. DATA Transfer
3.3.1. Sending Data
When sending a message, no guarantees are given about the When sending a message, no guarantees are given about the
preservation of message boundaries to the peer; if message boundaries preservation of message boundaries to the peer; if message boundaries
are needed, the receiving application at the peer must know about are needed, the receiving application at the peer must know about
them beforehand (or the TAPS system cannot use TCP). Note that an them beforehand (or the transport system cannot use TCP). Note that
application should already be able to hand over data before the TAPS an application should already be able to hand over data before the
system establishes a transport connection. Regarding the message transport system establishes a connection with a chosen transport
that is being handed over, the following parameters can be used: protocol. Regarding the message that is being handed over, the
following parameters can be used:
o (!UDP) Reliability: this parameter is used to convey a choice of: o Reliability: this parameter is used to convey a choice of: fully
fully reliable, unreliable without congestion control (which is reliable (!UDP), unreliable without congestion control, unreliable
guaranteed), unreliable, partially reliable (see [RFC3758] and (!UDP), partially reliable (see [RFC3758] and [RFC7496] for
[RFC7496] for details on how to specify partial reliability). The details on how to specify partial reliability) (!UDP). The latter
latter two choices are not guaranteed and may result in full two choices are optional for a transport system to offer and may
reliability. result in full reliability. Note that applications sending
unreliable data without congestion control should themselves
perform congestion control in accordance with [RFC2914].
o (!UDP) Ordered: this boolean parameter lets an application choose 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).
o Bundle: a boolean that expresses a preference for allowing to o Bundle: a boolean that expresses a preference for allowing to
bundle messages (true) or not (false). No guarantees are given. bundle messages (true) or not (false). No guarantees are given.
o 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 message. the peer would not delay the acknowledgement for this message.
o Fragment: a boolean that expresses a preference for allowing to o Fragment: a boolean that expresses a preference for allowing to
fragment messages (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.
o (!UDP) Idempotent: a boolean that expresses whether a message is o (!UDP) Idempotent: a boolean that expresses whether a message is
idempotent (true) or not (false). Idempotent messages 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 data immediately on a connection establishment attempt. Thus, if data
is handed over before the TAPS system establishes a transport is handed over before the transport system establishes a
connection, stating that a message is idempotent facilitates connection with a chosen transport protocol, stating that a
transmitting it to the peer application particularly early. message is idempotent facilitates transmitting it to the peer
application particularly early.
An application can be notified of a failure to send a specific An application can be notified of a failure to send a specific
message. There is no guarantee of such notifications, i.e. send message. There is no guarantee of such notifications, i.e. send
failures can also silently occur. failures can also silently occur.
When receiving data blocks, these blocks may or may not correspond to 3.3.2. Receiving Data
a sender-side message, i.e. the receiving application is not informed
about message boundaries (this limitation is only needed for TAPS
systems that are implemented to directly use TCP). However, if the
sending application has allowed that messages are not fully reliably
transferred, or delivered out of order, then such re-ordering or
unreliability may be reflected per message in the arriving data.
Messages will always stay intact - i.e. if an incomplete message is
contained at the end of the arriving data block, this message is
guaranteed to continue in the next arriving data block.
5. Conclusion A receiving application obtains an "Application-Framed Bytestream"
(AFra-Bytestream); this concept is further described in
Appendix A.3.1). In line with TCP's receiver semantics, an AFra-
Bytestream is just a stream of bytes to the receiver. If message
boundaries were specified by the sender, a receiver-side transport
system implementing only the minimum set of transport services
defined here will still not inform the receiving application about
them (this limitation is only needed for transport systems that are
implemented to directly use TCP).
By decoupling applications from transport protocols, a TAPS system Different from TCP's semantics, if the sending application has
provides a different abstraction level than the Berkeley sockets allowed that messages are not fully reliably transferred, or
interface. As with high- vs. low-level programming languages, a delivered out of order, then such re-ordering or unreliability may be
higher abstraction level allows more freedom for automation below the reflected per message in the arriving data. Messages will always
interface, yet it takes some control away from the application stay intact - i.e. if an incomplete message is contained at the end
programmer. This is the design trade-off that a TAPS system of the arriving data block, this message is guaranteed to continue in
developer is facing, and this document provides guidance on the the next arriving data block.
design of this abstraction level. Some transport features are
currently rarely offered by APIs, yet they must be offered or they
can never be used ("functional" transport features). Other transport
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
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
recommended for TAPS systems to implement, on the basis of the
transport features discussed in [TAPS2].
6. Acknowledgements 4. Conclusion
By decoupling applications from transport protocols, a TAPS transport
system provides a different abstraction level than the Berkeley
sockets interface. As with high- vs. low-level programming
languages, a higher abstraction level allows more freedom for
automation below the interface, yet it takes some control away from
the application programmer. This is the design trade-off that a
transport system developer is facing, and this document provides
guidance on the design of this abstraction level. Some transport
features are currently rarely offered by APIs, yet they must be
offered or they can never be used ("functional" transport features).
Other transport 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 automate protocol usage in a transport system. The
minimal set presented in this document is an effort to find a middle
ground that can be recommended for transport systems to implement, on
the basis of the transport features discussed in [RFC8303].
5. Acknowledgements
The authors would like to thank all the participants of the TAPS The authors would like to thank all the participants of the TAPS
Working Group and the NEAT and MAMI research projects for valuable Working Group and the NEAT and MAMI research projects for valuable
input to this document. We especially thank Michael Tuexen for help input to this document. We especially thank Michael Tuexen for help
with TAPS connection connection establishment/teardown and Gorry with connection connection establishment/teardown and Gorry Fairhurst
Fairhurst for his suggestions regarding fragmentation and packet for his suggestions regarding fragmentation and packet sizes. This
sizes. This work has received funding from the European Union's work has received funding from the European Union's Horizon 2020
Horizon 2020 research and innovation programme under grant agreement research and innovation programme under grant agreement No. 644334
No. 644334 (NEAT). (NEAT).
7. IANA Considerations 6. 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 7. Security Considerations
Authentication, confidentiality protection, and integrity protection Authentication, confidentiality protection, and integrity protection
are identified as transport features by [RFC8095]. As currently are identified as transport features by [RFC8095]. As currently
deployed in the Internet, these features are generally provided by a deployed in the Internet, these features are generally provided by a
protocol or layer on top of the transport protocol; no current full- protocol or layer on top of the transport protocol; no current full-
featured standards-track transport protocol provides all of these featured standards-track transport protocol provides all of these
transport features on its own. Therefore, these transport features transport features on its own. Therefore, these transport features
are not considered in this document, with the exception of native are not considered in this document, with the exception of native
authentication capabilities of TCP and SCTP for which the security authentication capabilities of TCP and SCTP for which the security
considerations in [RFC5925] and [RFC4895] apply. considerations in [RFC5925] and [RFC4895] apply. Security is
discussed further in a separate TAPS document
9. References [I-D.pauly-taps-transport-security].
9.1. Normative References 8. References
[RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind, 8.1. Normative References
Ed., "Services Provided by IETF Transport Protocols and
Congestion Control Mechanisms", RFC 8095,
DOI 10.17487/RFC8095, March 2017,
<https://www.rfc-editor.org/info/rfc8095>.
[TAPS2] Welzl, M., Tuexen, M., and N. Khademi, "On the Usage of [RFC8303] Welzl, M., Tuexen, M., and N. Khademi, "On the Usage of
Transport Features Provided by IETF Transport Protocols", Transport Features Provided by IETF Transport Protocols",
Internet-draft draft-ietf-taps-transports-usage-08, August RFC 8303, DOI 10.17487/RFC8303, February 2018,
2017. <https://www.rfc-editor.org/info/rfc8303>.
[TAPS2UDP]
Fairhurst, G. and T. Jones, "Features of the User Datagram
Protocol (UDP) and Lightweight UDP (UDP-Lite) Transport
Protocols", Internet-draft draft-ietf-taps-transports-
usage-udp-07, September 2017.
9.2. Informative References 8.2. Informative References
[COBS] Cheshire, S. and M. Baker, "Consistent Overhead Byte [COBS] Cheshire, S. and M. Baker, "Consistent Overhead Byte
Stuffing", September 1997, Stuffing", September 1997,
<http://stuartcheshire.org/papers/COBSforToN.pdf>. <http://stuartcheshire.org/papers/COBSforToN.pdf>.
[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.
skipping to change at page 17, line 37 skipping to change at page 14, line 18
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
Authentication Option", RFC 5925, DOI 10.17487/RFC5925, Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>. June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458,
DOI 10.17487/RFC6458, December 2011,
<https://www.rfc-editor.org/info/rfc6458>.
[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration",
RFC 6525, DOI 10.17487/RFC6525, February 2012,
<https://www.rfc-editor.org/info/rfc6525>.
[RFC7305] Lear, E., Ed., "Report from the IAB Workshop on Internet [RFC7305] Lear, E., Ed., "Report from the IAB Workshop on Internet
Technology Adoption and Transition (ITAT)", RFC 7305, Technology Adoption and Transition (ITAT)", RFC 7305,
DOI 10.17487/RFC7305, July 2014, DOI 10.17487/RFC7305, July 2014,
<https://www.rfc-editor.org/info/rfc7305>. <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, [RFC7496] Tuexen, M., Seggelmann, R., Stewart, R., and S. Loreto,
"Additional Policies for the Partially Reliable Stream "Additional Policies for the Partially Reliable Stream
Control Transmission Protocol Extension", RFC 7496, Control Transmission Protocol Extension", RFC 7496,
DOI 10.17487/RFC7496, April 2015, DOI 10.17487/RFC7496, April 2015,
<https://www.rfc-editor.org/info/rfc7496>. <https://www.rfc-editor.org/info/rfc7496>.
[RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
Ed., "Services Provided by IETF Transport Protocols and
Congestion Control Mechanisms", RFC 8095,
DOI 10.17487/RFC8095, March 2017,
<https://www.rfc-editor.org/info/rfc8095>.
[RFC8260] Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann, [RFC8260] Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann,
"Stream Schedulers and User Message Interleaving for the "Stream Schedulers and User Message Interleaving for the
Stream Control Transmission Protocol", RFC 8260, Stream Control Transmission Protocol", RFC 8260,
DOI 10.17487/RFC8260, November 2017, DOI 10.17487/RFC8260, November 2017,
<https://www.rfc-editor.org/info/rfc8260>. <https://www.rfc-editor.org/info/rfc8260>.
[RFC8304] Fairhurst, G. and T. Jones, "Transport Features of the
User Datagram Protocol (UDP) and Lightweight UDP (UDP-
Lite)", RFC 8304, DOI 10.17487/RFC8304, February 2018,
<https://www.rfc-editor.org/info/rfc8304>.
[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:
1. Categorization: the superset of transport features from [TAPS2] 1. Categorization: the superset of transport features from [RFC8303]
is presented, and transport features are categorized for later is presented, and transport features are categorized for later
reduction. reduction.
2. Reduction: a shorter list of transport features is derived from 2. Reduction: a shorter list of transport features is derived from
the categorization in the first step. This removes all transport the categorization in the first step. This removes all transport
features that do not require application-specific knowledge or features that do not require application-specific knowledge or
cannot be implemented with TCP. !!!TODO discuss UDP cannot be implemented with TCP or UDP.
3. Discussion: the resulting list shows a number of peculiarities 3. Discussion: the resulting list shows a number of peculiarities
that are discussed, to provide a basis for constructing the that are discussed, to provide a basis for constructing the
minimal set. minimal set.
4. Construction: Based on the reduced set and the discussion of the 4. Construction: Based on the reduced set and the discussion of the
transport features therein, a minimal set is constructed. transport features therein, a minimal set is constructed.
The first three steps as well as the underlying rationale for The first three steps as well as the underlying rationale for
constructing the minimal set are described in this appendix. The constructing the minimal set are described in this appendix. The
minimal set itself is described in Section 3. minimal set itself is described in Section 3.
A.1. Step 1: Categorization -- The Superset of Transport Features A.1. Step 1: Categorization -- The Superset of Transport Features
Following [TAPS2], we divide the transport features into two main Following [RFC8303], 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 applications have no specific requirements that need
need knowledge about the network, e.g. regarding the choice of knowledge about the network, e.g. regarding the choice of network
network interface or the end-to-end path. Even with these interface or the end-to-end path. Even with these assumptions, there
assumptions, there are certain requirements that are strictly kept by are certain requirements that are strictly kept by transport
transport protocols today, and these must also be kept by a TAPS protocols today, and these must also be kept by a transport system.
system. Some of these requirements relate to transport features that Some of these requirements relate to transport features that we call
we call "Functional". "Functional".
Functional transport features provide functionality that cannot be Functional transport features provide functionality that cannot be
used without the application knowing about them, or else they violate used without the application knowing about them, or else they violate
assumptions that might cause the application to fail. For example, assumptions that might cause the application to fail. For example,
ordered message delivery is a functional transport feature: it cannot ordered message delivery is a functional transport feature: it cannot
be configured without the application knowing about it because the be configured without the application knowing about it because the
application's assumption could be that messages always arrive in application's assumption could be that messages always arrive in
order. Failure includes any change of the application behavior that order. Failure includes any change of the application behavior that
is not performance oriented, e.g. security. is not performance oriented, e.g. security.
"Change DSCP" and "Disable Nagle algorithm" are examples of transport "Change DSCP" and "Disable Nagle algorithm" are examples of transport
features that we call "Optimizing": if a TAPS system autonomously features that we call "Optimizing": if a transport system
decides to enable or disable them, an application will not fail, but autonomously decides to enable or disable them, an application will
a TAPS system may be able to communicate more efficiently if the not fail, but a transport system may be able to communicate more
application is in control of this optimizing transport feature. efficiently if the application is in control of this optimizing
These transport features require application-specific knowledge transport feature. These transport features require application-
(e.g., about delay/bandwidth requirements or the length of future specific knowledge (e.g., about delay/bandwidth requirements or the
data blocks that are to be transmitted). length of future data blocks that are to be transmitted).
The transport features of IETF transport protocols that do not The transport features of IETF transport protocols that do not
require application-specific knowledge and could therefore be require application-specific knowledge and could therefore be
transparently utilized by a TAPS system are called "Automatable". transparently utilized by a transport system are called
"Automatable".
Finally, some transport features are aggregated and/or slightly Finally, some transport features are aggregated and/or slightly
changed in the description below. These transport features are changed in the description below. These transport features are
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 [RFC8303]. 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 transport system.
transport features that are categorized as "functional" or For all 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 implement exists in "pass 2" of [RFC8303], a brief discussion on how to
them over TCP and/or UDP is included. implement 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
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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.
Implementation over UDP: not possible (UDP is unreliable and there Implementation over UDP: not possible (UDP is unreliable and there
is no 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.
Implementation over UDP: not possible (UDP is unreliable and there Implementation over UDP: not possible (UDP is unreliable and there
is no 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.
Implementation over UDP: do nothing (UDP does not implement the Implementation over UDP: do nothing (UDP does not implement the
Nagle 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
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Optimizing because these messages can inform about success or Optimizing because these messages can inform about success or
failure of functional transport features (e.g., host unreachable failure of functional transport features (e.g., host unreachable
relates to "Connect") relates to "Connect")
Implementation: via ERROR.TCP or ERROR.UDP(-Lite). Implementation: via ERROR.TCP or ERROR.UDP(-Lite).
o Obtain information about interleaving support o Obtain information about interleaving support
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 STATUS.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.
Implementation over TCP: With SCTP, this allows to adjust key_id, Implementation over TCP: With SCTP, this allows to adjust key_id,
key, 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].
Implementation over 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 GET_AUTH.SCTP.
Implementation over TCP: With SCTP, this allows to obtain key_id Implementation over TCP: With SCTP, this allows to obtain key_id
and a chunk list. With TCP, this allows to obtain current_key and 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].
Implementation over 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
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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
application-specific knowledge. application-specific knowledge.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Reset Association o Reset Association
Protocols: SCTP Protocols: SCTP
Automatable because deciding to reset an association does not Automatable because deciding to reset an association does not
require application-specific knowledge. require application-specific knowledge.
Implementation: via RESETASSOC.SCTP. Implementation: via RESET_ASSOC.SCTP.
o Notification of Association Reset o Notification of Association Reset
Protocols: STCP Protocols: STCP
Automatable because this notification does not relate to Automatable because this notification does not relate to
application-specific knowledge. application-specific knowledge.
o Add Streams o Add 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.
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o Notification of Added Stream o Notification of Added Stream
Protocols: STCP Protocols: STCP
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 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 transport system would not use
or wrongly configure it on its own, this would only affect the this, or wrongly configure it on its own, this would only affect
performance of data transfers; the outcome would still be correct the performance of data transfers; the outcome would still be
within the "best effort" service model. correct within the "best effort" service model.
Implementation: using SETSTREAMSCHEDULER.SCTP. Implementation: using SET_STREAM_SCHEDULER.SCTP.
Implementation over TCP: do nothing. Implementation over TCP: do nothing.
Implementation over 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 transport system would not use
or wrongly configure it on its own, this would only affect the this, or wrongly configure it on its own, this would only affect
performance of data transfers; the outcome would still be correct the performance of data transfers; the outcome would still be
within the "best effort" service model. correct within the "best effort" service model.
Implementation: using CONFIGURESTREAMSCHEDULER.SCTP. Implementation: using CONFIGURE_STREAM_SCHEDULER.SCTP.
Implementation over TCP: do nothing. Implementation over TCP: do nothing.
Implementation over 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
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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.
Implementation over TCP: do nothing: this information is not Implementation over TCP: do nothing: this information is not
available 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 transport system can use a large enough
default to avoid communication failures. Allowing an application system default to avoid communication failures. Allowing an
to configure it differently can produce notifications of ICMP application to configure it differently can produce notifications
error message arrivals that yield information which only relates of ICMP error message arrivals that yield information which only
to knowledge about the network, not the application. relates to knowledge about the network, not the application.
o Obtain TTL/Hop count field o Obtain TTL/Hop count field
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because the TTL/Hop count field relates to knowledge Automatable because the TTL/Hop count field relates to knowledge
about the network, not the application. about the network, not the application.
o Specify ECN field o Specify ECN field
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.
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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 Enable and configure a "Low Extra Delay Background Transfer" o Enable and configure a "Low Extra Delay Background Transfer"
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 transport
in the network), so it is still correct within the "best effort" system's transfer in the network), so it is still correct within
service model. the "best effort" 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].
Implementation over TCP: do nothing. Implementation over TCP: do nothing.
Implementation over 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
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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.
Implementation over TCP: By using SEND.TCP and DISABLE-NAGLE.TCP Implementation over TCP: By using SEND.TCP and DISABLE_NAGLE.TCP
to disable the Nagle algorithm when the request is made and enable to disable the Nagle algorithm when the request is made and enable
it again when the request is no longer made. Note that this is it again when the request is no longer made. Note that this is
not 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.
Implementation over 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.
Implementation over TCP: not possible. Implementation over TCP: not possible.
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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.
Implementation over TCP: do nothing. Implementation over TCP: do nothing.
Implementation over 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 transport system must be able to send and
data. receive data.
Implementation: via RECEIVE.TCP. Implementation: via RECEIVE.TCP.
Implementation over UDP: do nothing (hand over a message, let the Implementation over UDP: do nothing (hand over a message, let the
application ignore message 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).
Implementation over TCP: not possible. Implementation over TCP: not possible.
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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 over TCP: do nothing. This notification is not Implementation over TCP: do nothing. This notification is not
available and will therefore not occur with TCP. available and will therefore not occur with TCP.
Implementation over UDP: do nothing. This notification is not Implementation over UDP: do nothing. This notification is not
available 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
system can gain opportunities to automate the usage of network- transport system can gain opportunities to automate the usage of
related functionality. This can facilitate using the TAPS system for network-related functionality. This can facilitate using the
the application programmer and it allows for optimizations that may transport system for the application programmer and it allows for
not be possible for an application. For instance, system-wide optimizations that may not be possible for an application. For
configurations regarding the usage of multiple interfaces can better instance, system-wide configurations regarding the usage of multiple
be exploited if the choice of the interface is not entirely up to the interfaces can better be exploited if the choice of the interface is
application. Therefore, since they are not strictly necessary to not entirely up to the application. Therefore, since they are not
expose in a TAPS system, we do not include automatable transport strictly necessary to expose in a transport system, we do not include
features in the reduced set of transport features. This leaves us automatable transport features in the reduced set of transport
with only the transport features that are either optimizing or features. This leaves us with only the transport features that are
functional. either optimizing or functional.
A TAPS system should be able to communicate via TCP or UDP if A transport 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 when a specific request is made. For some transport anything when a specific request is made. For some transport
features, however, it was identified that direct usage of neither TCP features, however, it was identified that direct usage of neither TCP
nor UDP is possible: in these cases, even not doing anything would nor UDP is possible: in these cases, even not doing anything would
incur semantically incorrect behavior. Whenever an application would incur semantically incorrect behavior. Whenever an application would
make use of one of these transport features, this would eliminate the make use of one of these transport features, this would eliminate the
possibility to use TCP or UDP. Thus, we only keep the functional and possibility to use TCP or UDP. Thus, we only keep the functional and
optimizing transport features for which an implementation over either optimizing transport features for which an implementation over either
TCP or UDP is possible in our reduced set. TCP or UDP is possible in our reduced set.
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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 can We can first try to understand how to build a transport system that
run over TCP, and then narrow down the result further to allow that can run over TCP, and then narrow down the result further to allow
the system can always run over either TCP or UDP (which effectively that the system can always run over either TCP or UDP (which
means removing everything related to reliability, ordering, effectively means removing everything related to reliability,
authentication and closing/aborting with a notification to the peer). ordering, authentication and closing/aborting with a notification to
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 replacement for UDP whenever an application does not be used as a replacement for UDP whenever an application does not
need 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
For implementing a TAPS system over TCP, there are several transport For implementing a transport system over TCP, there are several
features related to sending, but only a single transport feature transport features related to sending, but only a single transport
related to receiving: "Receive data (with no message delimiting)" feature related to receiving: "Receive data (with no message
(and, strangely, "information about partial message arrival"). delimiting)" (and, strangely, "information about partial message
Notably, the transport feature "Receive a message" is also the only arrival"). Notably, the transport feature "Receive a message" is
non-automatable transport feature of UDP(-Lite) for which no also the only non-automatable transport feature of UDP(-Lite) for
implementation over TCP is possible. which no 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 message boundaries and required properties per the transport about message boundaries and required properties per
message (configurable order and reliability, or embedding a request message (configurable order and reliability, or embedding a request
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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 not provided by the "minimum related transport features of SCTP are not provided by the "minimum
set" (in the interest of enabling usage of 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
consequences:
o Because the receiver-side transport leaves it up to the
application to delimit messages, messages must always remain
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
must never "skip ahead" to the beginning of the next message.
o With SCTP, a "partial flag" informs a receiving application that a
message is incomplete. Then, the next receive calls will only
deliver remaining parts of the same message (i.e., no messages or
partial messages will arrive on other streams until the message is
complete) (see Section 8.1.20 in [RFC6458]). This can facilitate
the implementation of the receiver buffer in the receiving
application, but then such an application does not support message
interleaving (which is required by stream schedulers). However,
receiving a byte stream from multiple SCTP streams requires a per-
stream receiver buffer anyway, so this potential benefit is lost
and the "partial flag" (the transport feature "Information about
partial message arrival") becomes unnecessary for a TAPS system.
With it, the transport feature "Notification to a receiver that a
partial message delivery has been aborted" becomes unnecessary
too.
o From the above, a TAPS system should always support message
interleaving because it enables the use of stream schedulers and
comes at no additional implementation cost on the receiver side.
Stream schedulers operate on the sender side. Hence, because a
TAPS sender-side application may talk to an SCTP receiver that
does not support interleaving, it cannot assume that stream
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 of 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 assume that TAPS connections may be transport system becomes easier if we assume that connections may be
a transport connection or association, but could also be a stream of a transport protocol's connection or association, but could also be a
an existing SCTP association, for example. We only need to allow for stream of an existing SCTP association, for example. We only need to
a way to define a possible grouping of TAPS connections. Then, all allow for a way to define a possible grouping of connections. Then,
MAINTENANCE transport features can be said to operate on TAPS all MAINTENANCE transport features can be said to operate on
connection groups, not TAPS connections, and a scheduler operates on connection groups, not connections, and a scheduler operates on the
the connections within a group. 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
consequences:
o Streams may be identified in different ways across different
protocols. The only multi-streaming protocol considered in this
document, SCTP, uses a stream id. The transport association below
still uses a Transport Address (which includes one port number)
for each communicating endpoint. To implement a TAPS system
without exposed streams, an application must be given an
identifier for each TAPS connection (akin to a socket), and
depending on whether streams are used or not, there will be a 1:1
mapping between this identifier and local ports or not.
o In SCTP, a fixed number of streams exists from the beginning of an
association; streams are not "established", there is no handshake
or any other form of signaling to create them: they can just be
used. They are also not "gracefully shut down" -- at best, an
"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
equivalent of an "Abort". This has an impact on the semantics
connection establishment and teardown (see Section 3.1).
o To support stream schedulers, a receiver-side TAPS system should
always support message interleaving because it comes at no
additional implementation cost (because of the receiver-side
stream reception discussed in Appendix A.3.1). Note, however,
that Stream schedulers operate on the sender side. Hence, because
a TAPS sender-side application may talk to a native TCP-based
receiver-side application, it cannot assume that stream schedulers
will always work as expected.
To be compatible with multiple transport protocols and uniformly To be compatible with multiple transport protocols and uniformly
allow access to both transport connections and streams of a multi- allow access to both transport connections and streams of a multi-
streaming protocol, the semantics of opening and closing need to be streaming protocol, the semantics of opening and closing need to be
the most restrictive subset of all of the underlying options. For the most restrictive subset of all of the underlying options. For
example, TCP's support of half-closed connections can be seen as a example, TCP's support of half-closed connections can be seen as a
feature on top of the more restrictive "ABORT"; this feature cannot feature on top of the more restrictive "ABORT"; this feature cannot
be supported because not all protocols used by a TAPS system be supported because not all protocols used by a transport system
(including streams of an association) support half-closed (including streams of an association) support half-closed
connections. 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 transport system could differentiate between the cases of
data "before" (possibly multiple times) or "during" the handshake. transmitting data "before" (possibly multiple times) or "during" the
Alternatively, it could also assume that data that are handed over handshake. Alternatively, it could also assume that data that are
early will be transmitted as early as possible, and "before" the handed over early will be transmitted as early as possible, and
handshake would only be used for messages that are explicitly marked "before" the handshake would only be used for messages that are
as "idempotent" (i.e., it would be acceptable to transfer them explicitly marked as "idempotent" (i.e., it would be acceptable to
multiple times). transfer them 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 transport 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
The transport feature "Notification that the stack has no more user The transport feature "Notification that the stack has no more user
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.
skipping to change at page 48, line 30 skipping to change at page 43, line 37
"TCP_NOTSENT_LOWAT" socket option that was proposed in [WWDC2015], "TCP_NOTSENT_LOWAT" socket option that was proposed in [WWDC2015],
which limits the amount of unsent data that TCP can keep in the which limits the amount of unsent data that TCP can keep in the
socket buffer; this allows to specify at which buffer filling level socket buffer; this allows to specify at which buffer filling level
the socket becomes writable, rather than waiting for the buffer to the socket becomes writable, rather than waiting for the buffer to
run 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. It therefore makes sense for a TAPS system to two sizes separately. It therefore makes sense for a transport
allow for uniform access to "TCP_NOTSENT_LOWAT" as well as the system to allow for uniform access to "TCP_NOTSENT_LOWAT" as well as
"SENDER DRY" notification. 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 transport system,
could therefore be offered in a uniform, more abstract way, where a they could therefore be offered in a uniform, more abstract way,
TAPS system could e.g. decide by itself how to use combinations of where a transport system could e.g. decide by itself how to use
LEDBAT-like congestion control and certain DSCP values, and an combinations of LEDBAT-like congestion control and certain DSCP
application would only specify a general "capacity profile" (a values, and an application would only specify a general "capacity
description of how it wants to use the available capacity). A need profile" (a description of how it wants to use the available
for "lowest possible latency at the expense of overhead" could then capacity). A need for "lowest possible latency at the expense of
translate into automatically disabling the Nagle algorithm. overhead" could then translate into automatically disabling the Nagle
algorithm.
In some cases, the Nagle algorithm is best controlled directly by the In some cases, the Nagle algorithm is best controlled directly by the
application because it is not only related to a general profile but application because it is not only related to a general profile but
also to knowledge about the size of future messages. For fine-grain also to knowledge about the size of future messages. For fine-grain
control over Nagle-like functionality, the "Request not to bundle control over Nagle-like functionality, the "Request not to bundle
messages" is available. messages" is available.
A.3.6. Security A.3.6. Security
Both TCP and SCTP offer authentication. TCP authenticates complete Both TCP and SCTP offer authentication. TCP authenticates complete
segments. SCTP allows to configure which of SCTP's chunk types must segments. SCTP allows to configure which of SCTP's chunk types must
always be authenticated -- if this is exposed as such, it creates an always be authenticated -- if this is exposed as such, it creates an
undesirable dependency on the transport protocol. For compatibility undesirable dependency on the transport protocol. For compatibility
with TCP, a TAPS system should only allow to configure complete with TCP, a transport system should only allow to configure complete
transport layer packets, including headers, IP pseudo-header (if any) transport layer packets, including headers, IP pseudo-header (if any)
and payload. and payload.
Security is discussed in a separate TAPS document Security is discussed in a separate TAPS document
[I-D.pauly-taps-transport-security]. The minimal set presented in [I-D.pauly-taps-transport-security]. The minimal set presented in
the present document therefore excludes all security related the present document therefore excludes all security related
transport features: "Configure authentication", "Change transport features: "Configure authentication", "Change
authentication parameters", "Obtain authentication information" and authentication parameters", "Obtain authentication information" and
and "Set Cookie life value" as well as "Specifying a key id to be and "Set Cookie life value" as well as "Specifying a key id to be
used to authenticate a message". used to authenticate a message".
skipping to change at page 49, line 47 skipping to change at page 45, line 11
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.
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 [RFC8303]
that MPTCP is not included. except that MPTCP is not included.
-03: updated to be consistent with -02 version of [TAPS2]. -03: updated to be consistent with -02 version of [RFC8303].
-04: updated to be consistent with -03 version of [TAPS2]. -04: updated to be consistent with -03 version of [RFC8303].
Reorganized document, rewrote intro and conclusion, and made a first Reorganized document, rewrote intro and conclusion, and made a first
stab at creating a real "minimal set". stab at creating a real "minimal set".
-05: updated to be consistent with -05 version of [TAPS2] (minor -05: updated to be consistent with -05 version of [RFC8303] (minor
changes). Fixed a mistake regarding Cookie Life value. Exclusion of changes). Fixed a mistake regarding Cookie Life value. Exclusion of
security related transport features (to be covered in a separate security related transport features (to be covered in a separate
document). Reorganized the document (now begins with the minset, document). Reorganized the document (now begins with the minset,
derivation is in the appendix). First stab at an abstract API for derivation is in the appendix). First stab at an abstract API for
the minset. the minset.
draft-ietf-taps-minset-00: updated to be consistent with -08 version draft-ietf-taps-minset-00: updated to be consistent with -08 version
of [TAPS2] ("obtain message delivery number" was removed, as this has of [RFC8303] ("obtain message delivery number" was removed, as this
also been removed in [TAPS2] because it was a mistake in RFC4960. has also been removed in [RFC8303] because it was a mistake in
This led to the removal of two more transport features that were only RFC4960. This led to the removal of two more transport features that
designated as functional because they affected "obtain message were only designated as functional because they affected "obtain
delivery number"). Fall-back to UDP incorporated (this was requested message delivery number"). Fall-back to UDP incorporated (this was
at IETF-99); this also affected the transport feature "Choice between requested at IETF-99); this also affected the transport feature
unordered (potentially faster) or ordered delivery of messages" "Choice between unordered (potentially faster) or ordered delivery of
because this is a boolean which is always true for one fall-back messages" because this is a boolean which is always true for one
protocol, and always false for the other one. This was therefore now fall-back protocol, and always false for the other one. This was
divided into two features, one for ordered, one for unordered therefore now divided into two features, one for ordered, one for
delivery. The word "reliably" was added to the transport features unordered delivery. The word "reliably" was added to the transport
"Hand over a message to reliably transfer (possibly multiple times) features "Hand over a message to reliably transfer (possibly multiple
before connection establishment" and "Hand over a message to reliably times) before connection establishment" and "Hand over a message to
transfer during connection establishment" to make it clearer why this reliably transfer during connection establishment" to make it clearer
is not supported by UDP. Clarified that the "minset abstract why this is not supported by UDP. Clarified that the "minset
interface" is not proposing a specific API for all TAPS systems to abstract interface" is not proposing a specific API for all TAPS
implement, but it is just a way to describe the minimum set. Author systems to implement, but it is just a way to describe the minimum
order changed. set. Author order changed.
draft-ietf-taps-minset-01: "fall-back to" (TCP or UDP) replaced WG -01: "fall-back to" (TCP or UDP) replaced (mostly with
(mostly with "implementation over"). References to post-sockets "implementation over"). References to post-sockets removed (these
removed (these were statments that assumed that post-sockets requires were statments that assumed that post-sockets requires two-sided
two-sided implementation). Replaced "flow" with "TAPS Connection" implementation). Replaced "flow" with "TAPS Connection" and "frame"
and "frame" with "message" to avoid introducing new terminology. with "message" to avoid introducing new terminology. Made sections 3
Made sections 3 and 4 in line with the categorization that is already and 4 in line with the categorization that is already used in the
used in the appendix and [TAPS2], and changed style of section 4 to appendix and [RFC8303], and changed style of section 4 to be even
be even shorter and less interface-like. Updated reference draft- shorter and less interface-like. Updated reference draft-ietf-tsvwg-
ietf-tsvwg-sctp-ndata to RFC8260. sctp-ndata to RFC8260.
WG -02: rephrased "the TAPS system" and "TAPS connection" etc. to
more generally talk about transport after the intro (mostly replacing
"TAPS system" with "transport system" and "TAPS connection" with
"connection". Merged sections 3 and 4 to form a new section 3.
Authors' Addresses 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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