draft-ietf-taps-minset-04.txt   draft-ietf-taps-minset-05.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: December 7, 2018 June 5, 2018 Expires: February 21, 2019 August 20, 2018
A Minimal Set of Transport Services for End Systems A Minimal Set of Transport Services for End Systems
draft-ietf-taps-minset-04 draft-ietf-taps-minset-05
Abstract Abstract
This draft recommends a minimal set of Transport Services offered by This draft recommends a minimal set of Transport Services offered by
end systems, and gives guidance on choosing among the available end systems, and gives guidance on choosing among the available
mechanisms and protocols. It is based on the set of transport mechanisms and protocols. It is based on the set of transport
features in RFC 8303. features in RFC 8303.
Status of This Memo Status of This Memo
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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 December 7, 2018. This Internet-Draft will expire on February 21, 2019.
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
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION . . . . . . . 5 3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION . . . . . . . 5
3.2. MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . 8
3.2.1. Connection groups . . . . . . . . . . . . . . . . . . 8 3.2.1. Connection groups . . . . . . . . . . . . . . . . . . 8
3.2.2. Individual connections . . . . . . . . . . . . . . . 10 3.2.2. Individual connections . . . . . . . . . . . . . . . 10
3.3. DATA Transfer . . . . . . . . . . . . . . . . . . . . . . 10 3.3. DATA Transfer . . . . . . . . . . . . . . . . . . . . . . 10
3.3.1. Sending Data . . . . . . . . . . . . . . . . . . . . 10 3.3.1. Sending Data . . . . . . . . . . . . . . . . . . . . 10
3.3.2. Receiving Data . . . . . . . . . . . . . . . . . . . 11 3.3.2. Receiving Data . . . . . . . . . . . . . . . . . . . 11
4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 12
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 8.1. Normative References . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Deriving the minimal set . . . . . . . . . . . . . . 15 Appendix A. Deriving the minimal set . . . . . . . . . . . . . . 15
A.1. Step 1: Categorization -- The Superset of Transport A.1. Step 1: Categorization -- The Superset of Transport
Features . . . . . . . . . . . . . . . . . . . . . . . . 15 Features . . . . . . . . . . . . . . . . . . . . . . . . 15
A.1.1. CONNECTION Related Transport Features . . . . . . . . 17 A.1.1. CONNECTION Related Transport Features . . . . . . . . 17
A.1.2. DATA Transfer Related Transport Features . . . . . . 32 A.1.2. DATA Transfer Related Transport Features . . . . . . 33
A.2. Step 2: Reduction -- The Reduced Set of Transport A.2. Step 2: Reduction -- The Reduced Set of Transport
Features . . . . . . . . . . . . . . . . . . . . . . . . 37 Features . . . . . . . . . . . . . . . . . . . . . . . . 39
A.2.1. CONNECTION Related Transport Features . . . . . . . . 38 A.2.1. CONNECTION Related Transport Features . . . . . . . . 40
A.2.2. DATA Transfer Related Transport Features . . . . . . 39 A.2.2. DATA Transfer Related Transport Features . . . . . . 41
A.3. Step 3: Discussion . . . . . . . . . . . . . . . . . . . 40 A.3. Step 3: Discussion . . . . . . . . . . . . . . . . . . . 42
A.3.1. Sending Messages, Receiving Bytes . . . . . . . . . . 40 A.3.1. Sending Messages, Receiving Bytes . . . . . . . . . . 42
A.3.2. Stream Schedulers Without Streams . . . . . . . . . . 41 A.3.2. Stream Schedulers Without Streams . . . . . . . . . . 43
A.3.3. Early Data Transmission . . . . . . . . . . . . . . . 42 A.3.3. Early Data Transmission . . . . . . . . . . . . . . . 44
A.3.4. Sender Running Dry . . . . . . . . . . . . . . . . . 43 A.3.4. Sender Running Dry . . . . . . . . . . . . . . . . . 44
A.3.5. Capacity Profile . . . . . . . . . . . . . . . . . . 43 A.3.5. Capacity Profile . . . . . . . . . . . . . . . . . . 45
A.3.6. Security . . . . . . . . . . . . . . . . . . . . . . 44 A.3.6. Security . . . . . . . . . . . . . . . . . . . . . . 46
A.3.7. Packet Size . . . . . . . . . . . . . . . . . . . . . 44 A.3.7. Packet Size . . . . . . . . . . . . . . . . . . . . . 46
Appendix B. Revision information . . . . . . . . . . . . . . . . 45 Appendix B. Revision information . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48
1. Introduction 1. Introduction
The task of a transport system is to offer transport services to its The task of a transport system is to offer transport services to its
applications, i.e. the applications running on top of the transport applications, i.e. the applications running on top of the transport
system. Ideally, it does so without statically binding applications system. Ideally, it does so without statically binding applications
to particular transport protocols. Currently, the set of transport to particular transport protocols. Currently, the set of transport
services that most applications use is based on TCP and UDP (and services that most applications use is based on TCP and UDP (and
protocols that are layered on top of them); this limits the ability protocols that are layered on top of them); this limits the ability
for the network stack to make use of features of other transport for the network stack to make use of features of other transport
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protocol. The first step towards the design of such a system was protocol. The first step towards the design of such a system was
taken by [RFC8095], which surveys a large number of transports, and taken by [RFC8095], which surveys a large number of transports, and
[RFC8303] as well as [RFC8304], which identify the specific transport [RFC8303] as well as [RFC8304], which identify the specific transport
features that are exposed to applications by the protocols TCP, features that are exposed to applications by the protocols TCP,
MPTCP, UDP(-Lite) and SCTP as well as the LEDBAT congestion control MPTCP, UDP(-Lite) and SCTP as well as the LEDBAT congestion control
mechanism. This memo is based on these documents and follows the mechanism. This memo is based on these documents and follows the
same terminology (also listed below). Because the considered same terminology (also listed below). Because the considered
transport protocols conjointly cover a wide range of transport transport protocols conjointly cover a wide range of transport
features, there is reason to hope that the resulting set (and the features, there is reason to hope that the resulting set (and the
reasoning that led to it) will also apply to many aspects of other reasoning that led to it) will also apply to many aspects of other
transport protocols. transport protocols that may be in use today, or may be designed in
the future.
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 transport the more functionality is exposed, the less freedom a transport
system has to automate usage of the various functions of its system has to automate usage of the various functions of its
available set of transport protocols. Some functions only exist in available set of transport protocols. Some functions only exist in
one particular protocol, and if an application used them, this would one particular protocol, and if an application used them, this would
statically tie the application to this protocol, limiting the statically tie the application to this protocol, limiting the
flexibility of the transport system. Also, if the number of exposed flexibility of the transport system. Also, if the number of exposed
features is exceedingly large, a transport system might become very features is exceedingly large, a transport system might become very
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a basis, this document therefore develops a minimal set of transport a basis, this document therefore develops a minimal set of transport
features, removing the ones that could get in the way of transport features, removing the ones that could get in the way of transport
flexibility but keeping the ones that must be retained for flexibility but keeping the ones that must be retained for
applications to benefit from useful transport functionality. applications to benefit 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 library which offers its own application that talks to a library which offers its own
communication interface if only the underlying Berkeley Sockets API communication interface if the underlying Berkeley Sockets API is
is extended to offer "unordered message delivery", but the library extended to offer "unordered message delivery", but the library only
only exposes an ordered bytestream. Both the Berkeley Sockets API exposes an ordered bytestream. Both the Berkeley Sockets API and the
and the library would have to expose the "unordered message delivery" library would have to expose the "unordered message delivery"
transport feature (alternatively, there may be ways for certain types transport feature (alternatively, there may be ways for certain types
of libraries to use this transport feature without exposing it, based of libraries to use this transport feature without exposing it, based
on knowledge about the applications -- but this is not the general on knowledge about the applications -- but this is not the general
case). In most situations, in the interest of being as flexible and case). In most situations, in the interest of being as flexible and
efficient as possible, the best choice will be for a library to efficient as possible, the best choice will be for a library to
expose at least all of the transport features that are recommended as expose at least all of the transport features that are recommended as
a "minimal set" here. a "minimal set" here.
This "minimal set" can be implemented one-sided over TCP (or UDP, if This "minimal set" can be implemented "one-sided" over TCP. This
certain limitations are put in place). This means that a sender-side means that a sender-side transport system can talk to a standard TCP
transport system can talk to a standard TCP (or UDP) receiver, and a receiver, and a receiver-side transport system can talk to a standard
receiver-side transport system can talk to a standard TCP (or UDP) TCP sender. If certain limitations are put in place, the "minimal
sender. set" can also be implemented "one-sided" over UDP.
2. Terminology 2. Terminology
Transport Feature: a specific end-to-end feature that the transport Transport Feature: a specific end-to-end feature that the transport
layer provides to an application. Examples include layer provides to an application. Examples include
confidentiality, reliable delivery, ordered delivery, message- confidentiality, reliable delivery, ordered delivery, message-
versus-stream orientation, etc. versus-stream orientation, etc.
Transport Service: a set of Transport Features, without an Transport Service: a set of Transport Features, without an
association to any given framing protocol, which provides a association to any given framing protocol, which provides a
complete service to an application. complete service to an application.
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over UDP). over UDP).
Application: an entity that uses the transport layer for end-to-end Application: an entity that uses the transport layer for end-to-end
delivery data across the network (this may also be an upper layer delivery data across the network (this may also be an upper layer
protocol or tunnel encapsulation). protocol or tunnel encapsulation).
Application-specific knowledge: knowledge that only applications Application-specific knowledge: knowledge that only applications
have. have.
Endpoint: an entity that communicates with one or more other Endpoint: an entity that communicates with one or more other
endpoints using a transport protocol. endpoints using a transport protocol.
Connection: shared state of two or more endpoints that persists Connection: shared state of two or more endpoints that persists
across messages that are transmitted between these endpoints. across messages that are transmitted between these endpoints.
Connection Group: a set of connections which share the same
configuration (configuring one of them causes all other
connections in the same group to be configured in the same way).
We call connections that belong to a connection group "grouped",
while "ungrouped" connections are not a part of a connection
group.
Socket: the combination of a destination IP address and a Socket: the combination of a destination IP address and a
destination port number. destination port number.
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 a minimal set of transport features that end this section describes a minimal set of transport features that end
systems should offer. The described transport system can be systems should offer. The described transport system can be
implemented over TCP. Elements of the system that are not marked implemented over TCP. Elements of the system that are not marked
with "!UDP" can also be implemented over UDP. with "!UDP" can also be implemented over UDP.
The arguments laid out in Appendix A.3 ("discussion") were used to
make the final representation of the minimal set as short, simple and
general as possible. There may be situations where these arguments
do not apply -- e.g., implementers may have specific reasons to
expose multi-streaming as a visible functionality to applications, or
the restrictive open / close semantics may be problematic under some
circumstances. In such cases, the representation in Appendix A.2
("reduction") should be considered.
As in Appendix A, Appendix A.2 and [RFC8303], we categorize the As in Appendix A, Appendix A.2 and [RFC8303], we categorize the
minimal set of transport features as 1) CONNECTION related minimal set of transport features as 1) CONNECTION related
(ESTABLISHMENT, AVAILABILITY, MAINTENANCE, TERMINATION) and 2) DATA (ESTABLISHMENT, AVAILABILITY, MAINTENANCE, TERMINATION) and 2) DATA
Transfer related (Sending Data, Receiving Data, Errors). Here, the Transfer related (Sending Data, Receiving Data, Errors). Here, the
focus is on connections that the transport system offers as an focus is on connections that the transport system offers as an
abstraction to the application, as opposed to connections of abstraction to the application, as opposed to connections of
transport protocols that the transport system uses. transport protocols that the transport system uses.
3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION 3.1. ESTABLISHMENT, AVAILABILITY and TERMINATION
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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 connections. The transport system must know which choice is grouped connections. We caution implementers to be aware of the full
more important for the application in order to make the best set of trade-offs, for which we recommend consulting the list in
decision. We caution implementers to be aware of the full set of
trade-offs, for which we recommend consulting the list in
Appendix A.2.1 when deciding how to initialize a connection. Appendix A.2.1 when deciding how to initialize a connection.
To summarize, the following parameters serve as input for the To summarize, the following parameters serve as input for the
transport system to help it choose and configure a suitable protocol: transport system to help it choose and configure a suitable protocol:
o 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.
o Checksum coverage: a boolean to specify whether it will be useful o Checksum coverage: a boolean to specify whether it will be useful
to the application to specify checksum coverage when sending or to the application to specify checksum coverage when sending or
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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 the o A buffer limit (in bytes); when the sender has less than the
provided limit of 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 it is optional notified. Notifications are not guaranteed, and it is optional
for a transport system to support buffer limit values greater than for a transport system to support buffer limit values greater than
0. Note that this limit and its notification should operate 0. Note that this limit and its notification should operate
across the buffers of the whole transport system, i.e. also any across the buffers of the whole transport system, i.e. also any
potential buffers that the transport system itself may use on top potential buffers that the transport system itself may use on top
of the transport's send buffer. of the transport's send buffer.
Following Appendix A.3.7, these properties can be queried: Following Appendix A.3.7, these properties can be queried:
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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 transport system cannot use TCP). Note that them beforehand (or the transport system cannot use TCP). Note that
an application should already be able to hand over data before the an application should already be able to hand over data before the
transport system establishes a connection with a chosen transport transport system establishes a connection with a chosen transport
protocol. Regarding the message that is being handed over, the protocol. Regarding the message that is being handed over, the
following parameters can be used: following parameters can be used:
o Reliability: this parameter is used to convey a choice of: fully o Reliability: this parameter is used to convey a choice of: fully
reliable (!UDP), unreliable without congestion control, unreliable reliable with congestion control (!UDP), unreliable without
(!UDP), partially reliable (see [RFC3758] and [RFC7496] for congestion control, unreliable with congestion control (!UDP),
details on how to specify partial reliability) (!UDP). The latter partially reliable with congestion control (see [RFC3758] and
two choices are optional for a transport system to offer and may [RFC7496] for details on how to specify partial reliability)
result in full reliability. Note that applications sending (!UDP). The latter two choices are optional for a transport
unreliable data without congestion control should themselves system to offer and may result in full reliability. Note that
perform congestion control in accordance with [RFC2914]. 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.
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minimal set presented in this document is an effort to find a middle minimal set presented in this document is an effort to find a middle
ground that can be recommended for transport systems to implement, on ground that can be recommended for transport systems to implement, on
the basis of the transport features discussed in [RFC8303]. the basis of the transport features discussed in [RFC8303].
5. Acknowledgements 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 connection connection establishment/teardown and Gorry Fairhurst with connection connection establishment/teardown and Gorry Fairhurst
for his suggestions regarding fragmentation and packet sizes. This for his suggestions regarding fragmentation and packet sizes, and
work has received funding from the European Union's Horizon 2020 Spencer Dawkins for his extremely detailed and constructive review.
This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No. 644334 research and innovation programme under grant agreement No. 644334
(NEAT). (NEAT).
6. 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.
7. 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. The minimum considerations in [RFC5925] and [RFC4895] apply. The minimum
security requirements for a transport system are discussed in a requirements for a secure transport system are discussed in a
separate document [I-D.ietf-taps-transport-security]. separate document (Section 5 of [I-D.ietf-taps-transport-security]).
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC8303] 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",
RFC 8303, DOI 10.17487/RFC8303, February 2018, RFC 8303, DOI 10.17487/RFC8303, February 2018,
<https://www.rfc-editor.org/info/rfc8303>. <https://www.rfc-editor.org/info/rfc8303>.
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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 [RFC8303] 1. Categorization (Appendix A.1): the superset of transport features
is presented, and transport features are categorized for later from [RFC8303] is presented, and transport features are
reduction. categorized for later reduction.
2. Reduction: a shorter list of transport features is derived from 2. Reduction (Appendix A.2): a shorter list of transport features is
the categorization in the first step. This removes all transport derived from the categorization in the first step. This removes
features that do not require application-specific knowledge or all transport features that do not require application-specific
cannot be implemented with TCP or UDP. knowledge or would result in semantically incorrect behavior if
3. Discussion: the resulting list shows a number of peculiarities they were implemented over TCP or UDP.
that are discussed, to provide a basis for constructing the 3. Discussion (Appendix A.3): the resulting list shows a number of
minimal set. peculiarities that are discussed, to provide a basis for
4. Construction: Based on the reduced set and the discussion of the constructing the minimal set.
transport features therein, a minimal set is constructed. 4. Construction (Section 3): Based on the reduced set and the
discussion of the transport features therein, a minimal set is
The first three steps as well as the underlying rationale for constructed.
constructing the minimal set are described in this appendix. The
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 [RFC8303], 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
skipping to change at page 16, line 29 skipping to change at page 16, line 33
features that we call "Optimizing": if a transport system features that we call "Optimizing": if a transport system
autonomously decides to enable or disable them, an application will autonomously decides to enable or disable them, an application will
not fail, but a transport system may be able to communicate more not fail, but a transport system may be able to communicate more
efficiently if the application is in control of this optimizing efficiently if the application is in control of this optimizing
transport feature. These transport features require application- transport feature. These transport features require application-
specific knowledge (e.g., about delay/bandwidth requirements or the specific knowledge (e.g., about delay/bandwidth requirements or the
length of future 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 transport system are called utilized by a transport system on its own without involving the
"Automatable". application 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 from [RFC8303] in the description below. These transport
marked as "ADDED". The corresponding transport features are features are marked as "ADDED". The corresponding transport features
automatable, and they are listed immediately below the "ADDED" are 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 [RFC8303]. We also sketch how some of the equivalent to "pass 2" in [RFC8303]. We also sketch how functional
transport features can be implemented by a transport system. For all or optimizing transport features can be implemented by a transport
transport features that are categorized as "functional" or system. The "minimal set" derived in this document is meant to be
"optimizing", and for which no matching TCP and/or UDP primitive implementable "one-sided" over TCP, and, with limitations, UDP.
exists in "pass 2" of [RFC8303], a brief discussion on how to Hence, for all transport features that are categorized as
implement them over TCP and/or UDP is included. "functional" or "optimizing", and for which no matching TCP and/or
UDP primitive exists in "pass 2" of [RFC8303], a brief discussion on
how to 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
skipping to change at page 18, line 38 skipping to change at page 18, line 42
Protocols: MPTCP Protocols: MPTCP
Automatable because the usage of multiple paths to communicate to Automatable because the usage of multiple paths to communicate to
the same end host relates to knowledge about the network, not the the same end host relates to knowledge about the network, not the
application. application.
Implementation: via a boolean parameter in CONNECT.MPTCP. Implementation: via a boolean parameter in CONNECT.MPTCP.
o Configure authentication o Configure authentication
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this has a direct influence on security. Functional because this has a direct influence on security.
Implementation: via parameters in CONNECT.TCP and CONNECT.SCTP. Implementation: via parameters in CONNECT.TCP and CONNECT.SCTP.
Implementation over TCP: With TCP, this allows to configure Master With TCP, this allows to configure Master Key Tuples (MKTs) to
Key Tuples (MKTs) to authenticate complete segments (including the authenticate complete segments (including the TCP IPv4
TCP IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this pseudoheader, TCP header, and TCP data). With SCTP, this allows
allows to specify which chunk types must always be authenticated. to specify which chunk types must always be authenticated.
Authenticating only certain chunk types creates a reduced level of Authenticating only certain chunk types creates a reduced level of
security that is not supported by TCP; to be compatible, this security that is not supported by TCP; to be compatible, this
should therefore only allow to authenticate all chunk types. Key should therefore only allow to authenticate all chunk types. Key
material must be provided in a way that is compatible with both material must be provided in a way that is compatible with both
[RFC4895] and [RFC5925]. [RFC4895] and [RFC5925].
Implementation over UDP: Not possible (UDP does not offer this
Implementation over UDP: Not possible. functionality).
o Indicate (and/or obtain upon completion) an Adaptation Layer via o Indicate (and/or obtain upon completion) an Adaptation Layer via
an adaptation code point an adaptation code point
Protocols: SCTP Protocols: SCTP
Functional because it allows to send extra data for the sake of Functional because it allows to send extra data for the sake of
identifying an adaptation layer, which by itself is application- identifying an adaptation layer, which by itself is application-
specific. specific.
Implementation: via a parameter in CONNECT.SCTP. Implementation: via a parameter in CONNECT.SCTP.
Implementation over TCP: not possible. Implementation over TCP: not possible (TCP does not offer this
Implementation over UDP: not possible. functionality).
Implementation over UDP: not possible (UDP does not offer this
functionality).
o Request to negotiate interleaving of user messages o Request to negotiate interleaving of user messages
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
Implementation: via a parameter in CONNECT.SCTP. Implementation: via a parameter in CONNECT.SCTP.
o Hand over a message to reliably transfer (possibly multiple times) o Hand over a message to reliably transfer (possibly multiple times)
before connection establishment before connection establishment
Protocols: TCP Protocols: TCP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via a parameter in CONNECT.TCP. Implementation: via a parameter in CONNECT.TCP.
Implementation over UDP: not possible. Implementation over UDP: not possible (UDP does not provide
reliability).
o Hand over a message to reliably transfer during connection o Hand over a message to reliably transfer during connection
establishment establishment
Protocols: SCTP Protocols: SCTP
Functional because this can only work if the message is limited in Functional because this can only work if the message is limited in
size, making it closely tied to properties of the data that an size, making it closely tied to properties of the data that an
application sends or expects to receive. application sends or expects to receive.
Implementation: via a parameter in CONNECT.SCTP. Implementation: via a parameter in CONNECT.SCTP.
Implementation over UDP: not possible. Implementation over TCP: not possible (TCP does not allow
identification of message boundaries because it provides a byte
stream service)
Implementation over UDP: not possible (UDP is unreliable).
o Enable UDP encapsulation with a specified remote UDP port number o Enable UDP encapsulation with a specified remote UDP port number
Protocols: SCTP Protocols: SCTP
Automatable because UDP encapsulation relates to knowledge about Automatable because UDP encapsulation relates to knowledge about
the network, not the application. the network, not the application.
AVAILABILITY: AVAILABILITY:
o Listen o Listen
Protocols: TCP, SCTP, UDP(-Lite) Protocols: TCP, SCTP, UDP(-Lite)
skipping to change at page 21, line 24 skipping to change at page 21, line 38
Implementation: via parameters in LISTEN.TCP and LISTEN.SCTP. Implementation: via parameters in LISTEN.TCP and LISTEN.SCTP.
Implementation over TCP: With TCP, this allows to configure Master Implementation over TCP: With TCP, this allows to configure Master
Key Tuples (MKTs) to authenticate complete segments (including the Key Tuples (MKTs) to authenticate complete segments (including the
TCP IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this TCP IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this
allows to specify which chunk types must always be authenticated. allows to specify which chunk types must always be authenticated.
Authenticating only certain chunk types creates a reduced level of Authenticating only certain chunk types creates a reduced level of
security that is not supported by TCP; to be compatible, this security that is not supported by TCP; to be compatible, this
should therefore only allow to authenticate all chunk types. Key should therefore only allow to authenticate all chunk types. Key
material must be provided in a way that is compatible with both material must be provided in a way that is compatible with both
[RFC4895] and [RFC5925]. [RFC4895] and [RFC5925].
Implementation over UDP: not possible. Implementation over UDP: not possible (UDP does not offer
authentication).
o Obtain requested number of streams o Obtain requested number of streams
Protocols: SCTP Protocols: SCTP
Automatable because using multi-streaming does not require Automatable because using multi-streaming does not require
application-specific knowledge. application-specific knowledge.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Limit the number of inbound streams o Limit the number of inbound streams
Protocols: SCTP Protocols: SCTP
Automatable because using multi-streaming does not require Automatable because using multi-streaming does not require
application-specific knowledge. application-specific knowledge.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Indicate (and/or obtain upon completion) an Adaptation Layer via o Indicate (and/or obtain upon completion) an Adaptation Layer via
an adaptation code point an adaptation code point
Protocols: SCTP Protocols: SCTP
Functional because it allows to send extra data for the sake of Functional because it allows to send extra data for the sake of
identifying an adaptation layer, which by itself is application- identifying an adaptation layer, which by itself is application-
specific. specific.
Implementation: via a parameter in LISTEN.SCTP. Implementation: via a parameter in LISTEN.SCTP.
Implementation over TCP: not possible. Implementation over TCP: not possible (TCP does not offer this
Implementation over UDP: not possible. functionality).
Implementation over UDP: not possible (UDP does not offer this
functionality).
o Request to negotiate interleaving of user messages o Request to negotiate interleaving of user messages
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
Implementation: via a parameter in LISTEN.SCTP. Implementation: via a parameter in LISTEN.SCTP.
MAINTENANCE: MAINTENANCE:
skipping to change at page 25, line 15 skipping to change at page 25, line 36
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 (UDP does not offer
authentication).
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 GET_AUTH.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 (UDP does not offer
authentication).
o Reset Stream o Reset Stream
Protocols: SCTP Protocols: SCTP
Automatable because using multi-streaming does not require Automatable because using multi-streaming does not require
application-specific knowledge. application-specific knowledge.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Notification of Stream Reset o Notification of Stream Reset
Protocols: STCP Protocols: STCP
Automatable because using multi-streaming does not require Automatable because using multi-streaming does not require
skipping to change at page 26, line 30 skipping to change at page 27, line 16
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Choose a scheduler to operate between streams of an association o Choose a scheduler to operate between streams of an association
Protocols: SCTP Protocols: SCTP
Optimizing because the scheduling decision requires application- Optimizing because the scheduling decision requires application-
specific knowledge. However, if a transport system would not use specific knowledge. However, if a transport system would not use
this, or wrongly configure it on its own, this would only affect this, or wrongly configure it on its own, this would only affect
the performance of data transfers; the outcome would still be the performance of data transfers; the outcome would still be
correct within the "best effort" service model. correct within the "best effort" service model.
Implementation: using SET_STREAM_SCHEDULER.SCTP. Implementation: using SET_STREAM_SCHEDULER.SCTP.
Implementation over TCP: do nothing. Implementation over TCP: do nothing (streams are not available in
Implementation over UDP: do nothing. TCP, but no guarantee is given that this transport feature has any
effect).
Implementation over UDP: do nothing (streams are not available in
UDP, but no guarantee is given that this transport feature has any
effect).
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 transport system would not use specific knowledge. However, if a transport system would not use
this, or wrongly configure it on its own, this would only affect this, or wrongly configure it on its own, this would only affect
the performance of data transfers; the outcome would still be the performance of data transfers; the outcome would still be
correct within the "best effort" service model. correct within the "best effort" service model.
Implementation: using CONFIGURE_STREAM_SCHEDULER.SCTP. Implementation: using CONFIGURE_STREAM_SCHEDULER.SCTP.
Implementation over TCP: do nothing. Implementation over TCP: do nothing (streams are not available in
Implementation over UDP: do nothing. TCP, but no guarantee is given that this transport feature has any
effect).
Implementation over UDP: do nothing (streams are not available in
UDP, but no guarantee is given that this transport feature has any
effect).
o Configure send buffer size o Configure send buffer size
Protocols: SCTP Protocols: SCTP
Automatable because this decision relates to knowledge about the Automatable because this decision relates to knowledge about the
network and the Operating System, not the application (see also network and the Operating System, not the application (see also
the discussion in Appendix A.3.4). the discussion in Appendix A.3.4).
o Configure receive buffer (and rwnd) size o Configure receive buffer (and rwnd) size
Protocols: SCTP Protocols: SCTP
Automatable because this decision relates to knowledge about the Automatable because this decision relates to knowledge about the
skipping to change at page 28, line 4 skipping to change at page 28, line 35
(it can be relevant for a sending application to request not to (it can be relevant for a sending application to request not to
delay the SACK of a message, but this is a different transport delay the SACK of a message, but this is a different transport
feature). feature).
o Set Cookie life value o Set Cookie life value
Protocols: SCTP Protocols: SCTP
Functional because it relates to security (possibly weakened by Functional because it relates to security (possibly weakened by
keeping a cookie very long) versus the time between connection keeping a cookie very long) versus the time between connection
establishment attempts. Knowledge about both issues can be establishment attempts. Knowledge about both issues can be
application-specific. application-specific.
Implementation over TCP: the closest specified TCP functionality Implementation over TCP: the closest specified TCP functionality
is the cookie in TCP Fast Open; for this, [RFC7413] states that is the cookie in TCP Fast Open; for this, [RFC7413] states that
the server "can expire the cookie at any time to enhance security" the server "can expire the cookie at any time to enhance security"
and section 4.1.2 describes an example implementation where and section 4.1.2 describes an example implementation where
updating the key on the server side causes the cookie to expire. updating the key on the server side causes the cookie to expire.
Alternatively, for implementations that do not support TCP Fast Alternatively, for implementations that do not support TCP Fast
Open, this transport feature could also affect the validity of SYN Open, this transport feature could also affect the validity of SYN
cookies (see Section 3.6 of [RFC4987]). cookies (see Section 3.6 of [RFC4987]).
Implementation over UDP: do nothing.
Implementation over UDP: not possible (UDP does not offer this
functionality).
o Set maximum burst o Set maximum burst
Protocols: SCTP Protocols: SCTP
Automatable because it relates to knowledge about the network, not Automatable because it relates to knowledge about the network, not
the application. the application.
o Configure size where messages are broken up for partial delivery o Configure size where messages are broken up for partial delivery
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation over TCP: not possible. Implementation over TCP: not possible (TCP does not offer
Implementation over UDP: not possible. identification of message boundaries).
Implementation over UDP: not possible (UDP does not fragment
messages).
o Disable checksum when sending o Disable checksum when sending
Protocols: UDP Protocols: UDP
Functional because application-specific knowledge is necessary to Functional because application-specific knowledge is necessary to
decide whether it can be acceptable to lose data integrity. decide whether it can be acceptable to lose data integrity.
Implementation: via SET_CHECKSUM_ENABLED.UDP. Implementation: via SET_CHECKSUM_ENABLED.UDP.
Implementation over TCP: do nothing. Implementation over TCP: do nothing (TCP does not offer to disable
the checksum, but transmitting data with an intact checksum will
not yield a semantically wrong result).
o Disable checksum requirement when receiving o Disable checksum requirement when receiving
Protocols: UDP Protocols: UDP
Functional because application-specific knowledge is necessary to Functional because application-specific knowledge is necessary to
decide whether it can be acceptable to lose data integrity. decide whether it can be acceptable to lose data integrity.
Implementation: via SET_CHECKSUM_REQUIRED.UDP. Implementation: via SET_CHECKSUM_REQUIRED.UDP.
Implementation over TCP: do nothing. Implementation over TCP: do nothing (TCP does not offer to disable
the checksum, but transmitting data with an intact checksum will
not yield a semantically wrong result).
o Specify checksum coverage used by the sender o Specify checksum coverage used by the sender
Protocols: UDP-Lite Protocols: UDP-Lite
Functional because application-specific knowledge is necessary to Functional because application-specific knowledge is necessary to
decide for which parts of the data it can be acceptable to lose decide for which parts of the data it can be acceptable to lose
data integrity. data integrity.
Implementation: via SET_CHECKSUM_COVERAGE.UDP-Lite. Implementation: via SET_CHECKSUM_COVERAGE.UDP-Lite.
Implementation over TCP: do nothing. Implementation over TCP: do nothing (TCP does not offer to limit
the checksum length, but transmitting data with an intact checksum
will not yield a semantically wrong result). Implementation over
UDP: if checksum coverage is set to cover payload data, do
nothing. Else, either do nothing (transmitting data with an
intact checksum will not yield a semantically wrong result), or
use the transport feature "Disable checksum when sending".
o Specify minimum checksum coverage required by receiver o Specify minimum checksum coverage required by receiver
Protocols: UDP-Lite Protocols: UDP-Lite
Functional because application-specific knowledge is necessary to Functional because application-specific knowledge is necessary to
decide for which parts of the data it can be acceptable to lose decide for which parts of the data it can be acceptable to lose
data integrity. data integrity.
Implementation: via SET_MIN_CHECKSUM_COVERAGE.UDP-Lite. Implementation: via SET_MIN_CHECKSUM_COVERAGE.UDP-Lite.
Implementation over TCP: do nothing. Implementation over TCP: do nothing (TCP does not offer to limit
the checksum length, but transmitting data with an intact checksum
will not yield a semantically wrong result). Implementation over
UDP: if checksum coverage is set to cover payload data, do
nothing. Else, either do nothing (transmitting data with an
intact checksum will not yield a semantically wrong result), or
use the transport feature "Disable checksum requirement when
receiving".
o Specify DF field o Specify DF field
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Optimizing because the DF field can be used to carry out Path MTU Optimizing because the DF field can be used to carry out Path MTU
Discovery, which can lead an application to choose message sizes Discovery, which can lead an application to choose message sizes
that can be transmitted more efficiently. that can be transmitted more efficiently.
Implementation: via MAINTENANCE.SET_DF.UDP(-Lite) and Implementation: via MAINTENANCE.SET_DF.UDP(-Lite) and
SEND_FAILURE.UDP(-Lite). SEND_FAILURE.UDP(-Lite).
Implementation over TCP: do nothing. With TCP the sender is not Implementation over TCP: do nothing (with TCP, the sending
in control of transport message sizes, making this functionality application is not in control of transport message sizes, making
irrelevant. this functionality irrelevant).
o Get max. transport-message size that may be sent using a non- o Get max. transport-message size that may be sent using a non-
fragmented IP packet from the configured interface fragmented IP packet from the configured interface
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Optimizing because this can lead an application to choose message Optimizing because this can lead an application to choose message
sizes that can be transmitted more efficiently. sizes that can be transmitted more efficiently.
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 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 transport system can use a large enough Automatable because a transport system can use a large enough
system default to avoid communication failures. Allowing an system default to avoid communication failures. Allowing an
application to configure it differently can produce notifications application to configure it differently can produce notifications
of ICMP error message arrivals that yield information which only of ICMP error message arrivals that yield information which only
relates 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
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Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because the ECN field relates to knowledge about the Automatable because the ECN field relates to knowledge about the
network, not the application. network, not the application.
o Obtain ECN field o Obtain ECN field
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Optimizing because this information can be used by an application Optimizing because this information can be used by an application
to better carry out congestion control (this is relevant when to better carry out congestion control (this is relevant when
choosing a data transmission transport service that does not choosing a data transmission transport service that does not
already do congestion control). already do congestion control).
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 IP Options o Specify IP Options
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because IP Options relate to knowledge about the Automatable because IP Options relate to knowledge about the
network, not the application. network, not the application.
o Obtain IP Options o Obtain IP Options
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because IP Options relate to knowledge about the Automatable because IP Options relate to knowledge about the
network, not the application. network, not the application.
skipping to change at page 31, line 16 skipping to change at page 32, line 23
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 transport including other transfers that may compete with the transport
system's transfer in the network), so it is still correct within system's transfer in the network), so it is still correct within
the "best effort" 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 (TCP does not support LEDBAT
Implementation over UDP: do nothing. congestion control, but not implementing this functionality will
not yield a semantically wrong behavior).
Implementation over UDP: do nothing (UDP does not offer congestion
control).
TERMINATION: TERMINATION:
o Close after reliably delivering all remaining data, causing an o Close after reliably delivering all remaining data, causing an
event informing the application on the other side event informing the application on the other side
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because the notion of a connection is often reflected Functional because the notion of a connection is often reflected
in applications as an expectation to have all outstanding data in applications as an expectation to have all outstanding data
delivered and no longer be able to communicate after a "Close" delivered and no longer be able to communicate after a "Close"
succeeded, with a communication sequence relating to this succeeded, with a communication sequence relating to this
transport feature that is defined by the application protocol. transport feature that is defined by the application protocol.
Implementation: via CLOSE.TCP and CLOSE.SCTP. Implementation: via CLOSE.TCP and CLOSE.SCTP.
Implementation over UDP: not possible. Implementation over UDP: not possible (UDP is unreliable and hence
does not know when all remaining data is delivered; it does also
not offer to cause an event related to closing at the peer).
o Abort without delivering remaining data, causing an event o Abort without delivering remaining data, causing an event
informing the application on the other side informing the application on the other side
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because the notion of a connection is often reflected Functional because the notion of a connection is often reflected
in applications as an expectation to potentially not have all in applications as an expectation to potentially not have all
outstanding data delivered and no longer be able to communicate outstanding data delivered and no longer be able to communicate
after an "Abort" succeeded. On both sides of a connection, an after an "Abort" succeeded. On both sides of a connection, an
application protocol may define a communication sequence relating application protocol may define a communication sequence relating
to this transport feature. to this transport feature.
Implementation: via ABORT.TCP and ABORT.SCTP. Implementation: via ABORT.TCP and ABORT.SCTP.
Implementation over UDP: not possible. Implementation over UDP: not possible (UDP does not offer to cause
an event related to aborting at the peer).
o Abort without delivering remaining data, not causing an event o Abort without delivering remaining data, not causing an event
informing the application on the other side informing the application on the other side
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Functional because the notion of a connection is often reflected Functional because the notion of a connection is often reflected
in applications as an expectation to potentially not have all in applications as an expectation to potentially not have all
outstanding data delivered and no longer be able to communicate outstanding data delivered and no longer be able to communicate
after an "Abort" succeeded. On both sides of a connection, an after an "Abort" succeeded. On both sides of a connection, an
application protocol may define a communication sequence relating application protocol may define a communication sequence relating
to this transport feature. to this transport feature.
Implementation: via ABORT.UDP(-Lite). Implementation: via ABORT.UDP(-Lite).
Implementation over TCP: stop using the connection, wait for a Implementation over TCP: stop using the connection, wait for a
timeout. timeout.
o Timeout event when data could not be delivered for too long o Timeout event when data could not be delivered for too long
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this notifies that potentially assumed reliable Functional because this notifies that potentially assumed reliable
data delivery is no longer provided. data delivery is no longer provided.
Implementation: via TIMEOUT.TCP and TIMEOUT.SCTP. Implementation: via TIMEOUT.TCP and TIMEOUT.SCTP.
Implementation over UDP: do nothing: this event will not occur Implementation over UDP: do nothing (this event will not occur
with UDP. with UDP).
A.1.2. DATA Transfer Related Transport Features A.1.2. DATA Transfer Related Transport Features
A.1.2.1. Sending Data A.1.2.1. Sending Data
o Reliably transfer data, with congestion control o Reliably transfer data, with congestion control
Protocols: TCP, SCTP Protocols: TCP, SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via SEND.TCP and SEND.SCTP. Implementation: via SEND.TCP and SEND.SCTP.
Implementation over UDP: not possible. Implementation over UDP: not possible (UDP is unreliable).
o Reliably transfer a message, with congestion control o Reliably transfer a message, with congestion control
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Implementation over TCP: via SEND.TCP. With SEND.TCP, messages Implementation over TCP: via SEND.TCP. With SEND.TCP, message
will not be identifiable by the receiver. boundaries will not be identifiable by the receiver, because TCP
Implementation over UDP: not possible. provides a byte stream service.
Implementation over UDP: not possible (UDP is unreliable).
o Unreliably transfer a message o Unreliably transfer a message
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Optimizing because only applications know about the time Optimizing because only applications know about the time
criticality of their communication, and reliably transfering a criticality of their communication, and reliably transfering a
message is never incorrect for the receiver of a potentially message is never incorrect for the receiver of a potentially
unreliable data transfer, it is just slower. unreliable data transfer, it is just slower.
ADDED. This differs from the 2 automatable transport features ADDED. This differs from the 2 automatable transport features
below in that it leaves the choice of congestion control open. below in that it leaves the choice of congestion control open.
Implementation: via SEND.SCTP or SEND.UDP(-Lite). Implementation: via SEND.SCTP or SEND.UDP(-Lite).
Implementation over TCP: use SEND.TCP. With SEND.TCP, messages Implementation over TCP: use SEND.TCP. With SEND.TCP, messages
will be sent reliably, and they will not be identifiable by the will be sent reliably, and message boundaries will not be
receiver. identifiable by the receiver.
o Unreliably transfer a message, with congestion control o Unreliably transfer a message, with congestion control
Protocols: SCTP Protocols: SCTP
Automatable because congestion control relates to knowledge about Automatable because congestion control relates to knowledge about
the network, not the application. the network, not the application.
o Unreliably transfer a message, without congestion control o Unreliably transfer a message, without congestion control
Protocols: UDP(-Lite) Protocols: UDP(-Lite)
Automatable because congestion control relates to knowledge about Automatable because congestion control relates to knowledge about
the network, not the application. the network, not the application.
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Optimizing because only applications know about the time Optimizing because only applications know about the time
criticality of their communication, and reliably transfering a criticality of their communication, and reliably transfering a
message is never incorrect for the receiver of a potentially message is never incorrect for the receiver of a potentially
unreliable data transfer, it is just slower. unreliable data transfer, it is just slower.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Implementation over TCP: By using SEND.TCP and ignoring this Implementation over TCP: By using SEND.TCP and ignoring this
configuration: based on the assumption of the best-effort service configuration: based on the assumption of the best-effort service
model, unnecessarily delivering data does not violate application model, unnecessarily delivering data does not violate application
expectations. Moreover, it is not possible to associate the expectations. Moreover, it is not possible to associate the
requested reliability to a "message" in TCP anyway. requested reliability to a "message" in TCP anyway.
Implementation over UDP: not possible. Implementation over UDP: not possible (UDP is unreliable).
o Choice of stream o Choice of stream
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. Implementation: see Appendix A.3.2. category is automatable. Implementation: see Appendix A.3.2.
o Choice of path (destination address) o Choice of path (destination address)
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple sockets, but Automatable because it requires using multiple sockets, but
obtaining multiple sockets in the CONNECTION.ESTABLISHMENT obtaining multiple sockets in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
o Ordered message delivery (potentially slower than unordered) o Ordered message delivery (potentially slower than unordered)
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Implementation over TCP: By using SEND.TCP. With SEND.TCP, Implementation over TCP: By using SEND.TCP. With SEND.TCP,
messages will not be identifiable by the receiver. messages will not be identifiable by the receiver.
Implementation over UDP: not possible. Implementation over UDP: not possible (UDP does not offer any
guarantees regarding ordering).
o Unordered message delivery (potentially faster than ordered) o Unordered message delivery (potentially faster than ordered)
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via SEND.SCTP. Implementation: via SEND.SCTP.
Implementation over TCP: By using SEND.TCP and always sending data Implementation over TCP: By using SEND.TCP and always sending data
ordered: based on the assumption of the best-effort service model, ordered: based on the assumption of the best-effort service model,
ordered delivery may just be slower and does not violate ordered delivery may just be slower and does not violate
application expectations. Moreover, it is not possible to application expectations. Moreover, it is not possible to
associate the requested delivery order to a "message" in TCP associate the requested delivery order to a "message" in TCP
anyway. anyway.
o Request not to bundle messages o Request not to bundle messages
Protocols: SCTP Protocols: SCTP
Optimizing because this decision depends on knowledge about the Optimizing because this decision depends on knowledge about the
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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 (this functionality is not
Implementation over UDP: not possible. available in TCP).
Implementation over UDP: not possible (this functionality is not
available in UDP).
o Specifying a key id to be used to authenticate a message o Specifying a key id to be used to authenticate a message
Protocols: SCTP Protocols: SCTP
Functional because this has a direct influence on security. Functional because this has a direct influence on security.
Implementation: via a parameter in SEND.SCTP. Implementation: via a parameter in SEND.SCTP.
Implementation over TCP: This could be emulated by using Implementation over TCP: This could be emulated by using
SET_AUTH.TCP before and after the message is sent. Note that this SET_AUTH.TCP before and after the message is sent. Note that this
is not fully equivalent because it relates to the time of issuing is not fully equivalent because it relates to the time of issuing
the request rather than a specific message. the request rather than a specific message.
Implementation over UDP: not possible. Implementation over UDP: not possible (UDP does not offer
authentication).
o Request not to delay the acknowledgement (SACK) of a message o Request not to delay the acknowledgement (SACK) of a message
Protocols: SCTP Protocols: SCTP
Optimizing because only an application knows for which message it Optimizing because only an application knows for which message it
wants to quickly be informed about success / failure of its wants to quickly be informed about success / failure of its
delivery. delivery.
Implementation over TCP: do nothing. Implementation over TCP: do nothing (TCP does not offer this
Implementation over UDP: do nothing. functionality, but ignoring this request from the application will
not yield a semantically wrong behavior).
Implementation over UDP: do nothing (UDP does not offer this
functionality, but ignoring this request from the application will
not yield a semantically wrong behavior).
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 transport system must be able to send and Functional because a transport system must be able to send and
receive 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 (UDP only works on messages;
application ignore message boundaries). these can be handed over, the application can still ignore the
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 (TCP does not support
identification of message boundaries).
o Choice of stream to receive from o Choice of stream to receive from
Protocols: SCTP Protocols: SCTP
Automatable because it requires using multiple streams, but Automatable because it requires using multiple streams, but
requesting multiple streams in the CONNECTION.ESTABLISHMENT requesting multiple streams in the CONNECTION.ESTABLISHMENT
category is automatable. category is automatable.
Implementation: see Appendix A.3.2. Implementation: see Appendix A.3.2.
o Information about partial message arrival o Information about partial message arrival
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
Implementation: via RECEIVE.SCTP. Implementation: via RECEIVE.SCTP.
Implementation over TCP: do nothing: this information is not Implementation over TCP: do nothing (this information is not
available with TCP. available with TCP).
Implementation over UDP: do nothing: this information is not Implementation over UDP: do nothing (this information is not
available with UDP. available with UDP).
A.1.2.3. Errors A.1.2.3. Errors
This section describes sending failures that are associated with a This section describes sending failures that are associated with a
specific call to in the "Sending Data" category (Appendix A.1.2.1). specific call to in the "Sending Data" category (Appendix A.1.2.1).
o Notification of send failures o Notification of send failures
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Functional because this notifies that potentially assumed reliable Functional because this notifies that potentially assumed reliable
data delivery is no longer provided. data delivery is no longer provided.
ADDED. This differs from the 2 automatable transport features ADDED. This differs from the 2 automatable transport features
below in that it does not distinugish between unsent and below in that it does not distinugish between unsent and
unacknowledged messages. unacknowledged messages.
Implementation: via SENDFAILURE-EVENT.SCTP and SEND_FAILURE.UDP(- Implementation: via SENDFAILURE-EVENT.SCTP and SEND_FAILURE.UDP(-
Lite). Lite).
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).
o Notification of an unsent (part of a) message o Notification of an unsent (part of a) message
Protocols: SCTP, UDP(-Lite) Protocols: SCTP, UDP(-Lite)
Automatable because the distinction between unsent and Automatable because the distinction between unsent and
unacknowledged is network-specific. unacknowledged is network-specific.
o Notification of an unacknowledged (part of a) message o Notification of an unacknowledged (part of a) message
Protocols: SCTP Protocols: SCTP
Automatable because the distinction between unsent and Automatable because the distinction between unsent and
unacknowledged is network-specific. unacknowledged is network-specific.
o Notification that the stack has no more user data to send o Notification that the stack has no more user data to send
Protocols: SCTP Protocols: SCTP
Optimizing because reacting to this notification requires the Optimizing because reacting to this notification requires the
application to be involved, and ensuring that the stack does not application to be involved, and ensuring that the stack does not
run dry of data (for too long) can improve performance. run dry of data (for too long) can improve performance.
Implementation over TCP: do nothing. See also the discussion in Implementation over TCP: do nothing (see the discussion in
Appendix A.3.4. Appendix A.3.4).
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).
o Notification to a receiver that a partial message delivery has o Notification to a receiver that a partial message delivery has
been aborted been aborted
Protocols: SCTP Protocols: SCTP
Functional because this is closely tied to properties of the data Functional because this is closely tied to properties of the data
that an application sends or expects to receive. that an application sends or expects to receive.
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 By hiding automatable transport features from the application, a
transport system can gain opportunities to automate the usage of transport system can gain opportunities to automate the usage of
network-related functionality. This can facilitate using the network-related functionality. This can facilitate using the
transport system for the application programmer and it allows for transport system for the application programmer and it allows for
optimizations that may not be possible for an application. For optimizations that may not be possible for an application. For
instance, system-wide configurations regarding the usage of multiple instance, system-wide configurations regarding the usage of multiple
interfaces can better be exploited if the choice of the interface is interfaces can better be exploited if the choice of the interface is
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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.
In the following list, we precede a transport feature with "T:" if an The "minimal set" derived in this document is meant to be
implementation over TCP is possible, "U:" if an implementation over implementable "one-sided" over TCP, and, with limitations, UDP. In
UDP is possible, and "TU:" if an implementation over either TCP or the following list, we therefore precede a transport feature with
UDP is possible. "T:" if an implementation over TCP is possible, "U:" if an
implementation over UDP is possible, and "TU:" if an implementation
over either TCP or UDP is possible.
A.2.1. CONNECTION Related Transport Features A.2.1. CONNECTION Related Transport Features
ESTABLISHMENT: ESTABLISHMENT:
o T,U: Connect o T,U: Connect
o T,U: Specify number of attempts and/or timeout for the first o T,U: Specify number of attempts and/or timeout for the first
establishment message establishment message
o T: Configure authentication o T: Configure authentication
o T: Hand over a message to reliably transfer (possibly multiple o T: Hand over a message to reliably transfer (possibly multiple
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considered out of scope of this document. considered out of scope of this document.
For example, if an application requests to transfer fixed-size For example, if an application requests to transfer fixed-size
messages of 100 bytes with partial reliability, this needs the messages of 100 bytes with partial reliability, this needs the
receiving application to be prepared to accept data in chunks of 100 receiving application to be prepared to accept data in chunks of 100
bytes. If, then, some of these 100-byte messages are missing (e.g., bytes. If, then, some of these 100-byte messages are missing (e.g.,
if SCTP with Configurable Reliability is used), this is the expected if SCTP with Configurable Reliability is used), this is the expected
application behavior. With TCP, no messages would be missing, but application behavior. With TCP, no messages would be missing, but
this is also correct for the application, and the possible this is also correct for the application, and the possible
retransmission delay is acceptable within the best effort service retransmission delay is acceptable within the best effort service
model [RFC7305]. Still, the receiving application would separate the model (see [RFC7305], Section 3.5). Still, the receiving application
byte stream into 100-byte chunks. would separate the byte stream into 100-byte chunks.
Note that this usage of messages does not require all messages to be Note that this usage of messages does not require all messages to be
equal in size. Many application protocols use some form of Type- equal in size. Many application protocols use some form of Type-
Length-Value (TLV) encoding, e.g. by defining a header including Length-Value (TLV) encoding, e.g. by defining a header including
length fields; another alternative is the use of byte stuffing length fields; another alternative is the use of byte stuffing
methods such as COBS [COBS]. If an application needs message methods such as COBS [COBS]. If an application needs message
numbers, e.g. to restore the correct sequence of messages, these must numbers, e.g. to restore the correct sequence of messages, these must
also be encoded by the application itself, as the sequence number also be encoded by the application itself, as the sequence number
related transport features of SCTP are 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).
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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 transport 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 document Security is discussed in a separate document
[I-D.ietf-taps-transport-security]. The minimal set presented in the [I-D.ietf-taps-transport-security]. The minimal set presented in the
present document therefore excludes all security related transport present document excludes all security related transport features:
features: "Configure authentication", "Change authentication "Configure authentication", "Change authentication parameters",
parameters", "Obtain authentication information" and and "Set Cookie "Obtain authentication information" and and "Set Cookie life value"
life value" as well as "Specifying a key id to be used to as well as "Specifying a key id to be used to authenticate a
authenticate a message". message".
A.3.7. Packet Size A.3.7. Packet Size
UDP(-Lite) has a transport feature called "Specify DF field". This UDP(-Lite) has a transport feature called "Specify DF field". This
yields an error message in case of sending a message that exceeds the yields an error message in case of sending a message that exceeds the
Path MTU, which is necessary for a UDP-based application to be able Path MTU, which is necessary for a UDP-based application to be able
to implement Path MTU Discovery (a function that UDP-based to implement Path MTU Discovery (a function that UDP-based
applications must do by themselves). The "Get max. transport-message applications must do by themselves). The "Get max. transport-message
size that may be sent using a non-fragmented IP packet from the size that may be sent using a non-fragmented IP packet from the
configured interface" transport feature yields an upper limit for the configured interface" transport feature yields an upper limit for the
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[I-D.ietf-taps-transport-security] to say that "the minimum security [I-D.ietf-taps-transport-security] to say that "the minimum security
requirements for a taps system are discussed in a separate security requirements for a taps system are discussed in a separate security
document", wrote "example" in the paragraph introducing the decision document", wrote "example" in the paragraph introducing the decision
tree. Removed reference draft-grinnemo-taps-he-03 and the sentence tree. Removed reference draft-grinnemo-taps-he-03 and the sentence
that referred to it. that referred to it.
WG -04: addressed comments from Theresa Enghardt and Tommy Pauly. As WG -04: addressed comments from Theresa Enghardt and Tommy Pauly. As
part of that, removed "TAPS" as a term everywhere (abstract, intro, part of that, removed "TAPS" as a term everywhere (abstract, intro,
..). ..).
WG -05: addressed comments from Spencer Dawkins.
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
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