Services provided by IETF transport protocols and congestion control mechanisms
draft-ietf-taps-transports-01

Network Working Group                                  G. Fairhurst, Ed.
Internet-Draft                                    University of Aberdeen
Intended status: Informational                          B. Trammell, Ed.
Expires: June 22, 2015                                M. Kuehlewind, Ed.
                                                              ETH Zurich
                                                       December 19, 2014

  Services provided by IETF transport protocols and congestion control
                               mechanisms
                     draft-ietf-taps-transports-01

Abstract

   This document describes services provided by existing IETF protocols
   and congestion control mechanisms.  It is designed to help
   application and network stack programmers and to inform the work of
   the IETF TAPS Working Group.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 22, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

1.  Introduction

   Most Internet applications make use of the Transport Services
   provided by TCP (a reliable, in-order stream protocol) or UDP (an
   unreliable datagram protocol).  We use the term "Transport Service"
   to mean the end-to-end service provided to an application by the
   transport layer.  That service can only be provided correctly if
   information about the intended usage is supplied from the
   application.  The application may determine this information at
   design time, compile time, or run time, and may include guidance on
   whether a feature is required, a preference by the application, or
   something in between.  Examples of features of Transport Services are
   reliable delivery, ordered delivery, content privacy to in-path
   devices, integrity protection, and minimal latency.

   The IETF has defined a wide variety of transport protocols beyond TCP
   and UDP, including TCP, SCTP, DCCP, MP-TCP, and UDP-Lite.  Transport
   services may be provided directly by these transport protocols, or
   layered on top of them using protocols such as WebSockets (which runs
   over TCP) or RTP (over TCP or UDP).  Services built on top of UDP or
   UDP-Lite typically also need to specify additional mechanisms,
   including a congestion control mechanism (such as a windowed
   congestion control, TFRC or LEDBAT congestion control mechanism).
   This extends the set of available Transport Services beyond those
   provided to applications by TCP and UDP.

   Transport protocols can also be differentiated by the features of the
   services they provide: for instance, SCTP offers a message-based
   service that does not suffer head-of-line blocking when used with
   multiple stream, because it can accept blocks of data out of order,
   UDP-Lite provides partial integrity protection, and LEDBAT can
   provide low-priority "scavenger" communication.

2.  Terminology

   The following terms are defined throughout this document, and in
   subsequent documents produced by TAPS describing the composition and
   decomposition of transport services.

   [Editor Note: The terminology below was presented at the TAPS WG
   meeting in Honolulu.  While the factoring of the terminology seems
   uncontroversial, there may be some entities which still require names
   (e.g. information about the interface between the transport and lower
   layers which could lead to the availablity or unavailibility of

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   certain transport protocol features).  Comments are welcome via the
   TAPS mailing list.]

   Transport Service Feature:  a specific end-to-end feature that a
      transport service provides to its clients.  Examples include
      confidentiality, reliable delivery, ordered delivery, message-
      versus-stream orientation, etc.

   Transport Service:  a set of transport service features, without an
      association to any given framing protocol, which provides a
      complete service to an application.

   Transport Protocol:  an implementation that provides one or more
      different transport services using a specific framing and header
      format on the wire.

   Transport Protocol Component:  an implementation of a transport
      service feature within a protocol.

   Transport Service Instance:  an arrangement of transport protocols
      with a selected set of features and configuration parameters that
      implements a single transport service, e.g. a protocol stack (RTP
      over UDP).

   Application:  an entity that uses the transport layer for end-to-end
      delivery data across the network (this may also be an upper layer
      protocol or tunnel encpasulation).

3.  Existing Transport Protocols

   This section provides a list of known IETF transport protocol and
   transport protocol frameworks.

   [Editor Note: Contributions to the sections in the list below are
   welcome]

3.1.  Transport Control Protocol (TCP)

   TCP is an IETF standards track transport protocol.  [RFC0793]
   introduces TCP as follows: "The Transmission Control Protocol (TCP)
   is intended for use as a highly reliable host-to-host protocol
   between hosts in packet-switched computer communication networks, and
   in interconnected systems of such networks."  Since its introduction,
   TCP has become the default connection-oriented, stream-based
   transport protocol in the Internet.  It is widely implemented by
   endpoints and widely used by common applications.

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3.1.1.  Protocol Description

   TCP is a connection-oriented protocol, providing a three way
   handshake to allow a client and server to set up a connection, and
   mechanisms for orderly completion and immediate teardown of a
   connection.  TCP is defined by a family of RFCs [RFC4614].

   TCP provides multiplexing to multiple sockets on each host using port
   numbers.  An active TCP session is identified by its four-tuple of
   local and remote IP addresses and local port and remote port numbers.

   TCP partitions a continuous stream of bytes into segments, sized to
   fit in IP packets, constrained by the maximum size of lower layer
   frame.  PathMTU discovery is supported.  Each byte in the stream is
   identified by a sequence number.  The sequence number is used to
   order segments on receipt, to identify segments in acknowledgments,
   and to detect unacknowledged segments for retransmission.  This is
   the basis of TCP's reliable, ordered delivery of data in a stream.
   TCP Selective Acknowledgment [RFC2018] extends this mechanism by
   making it possible to identify missing segments more precisely,
   reducing spurious retransmission.

   Receiver flow control is provided by a sliding window: limiting the
   amount of unacknowledged data that can be outstanding at a given
   time.  The window scale option [RFC7323] allows a receiver to use
   windows greater than 64KB.

   All TCP senders provide Congestion Control: This uses a separate
   window, where each time congestion is detected, this congestion
   window is reduced.  A receiver detects congestion using one of three
   mechanisms: A retransmission timer, loss (interpreted as a congestion
   signal), and Explicit Congestion Notification (ECN) [RFC3168] to
   provide early signaling (see [I-D.ietf-aqm-ecn-benefits])

   A TCP protocol instance can be extended [RFC4614] and tuned.  Some
   features are sender-side only, requiring no negotiation with the
   receiver; some are receiver-side only, some are explicitly negotiated
   during connection setup.

   By default, TCP segment partitioning uses Nagle's algorithm [RFC0896]
   to buffer data at the sender into large segments, potentially
   incurring sender-side buffering delay; this algorithm can be disabled
   by the sender to transmit more immediately, e.g. to enable smoother
   interactive sessions.

   A TCP service is unicast.

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3.1.2.  Interface description

   A TCP API is defined in [REF], but there is currently no API
   specified in the RFC series.

   In API implementations derived from the BSD Sockets API, TCP sockets
   are created using the "SOCK_STREAM" socket type.

   The features used by a protocol instance may be set and tuned via
   this API.

   (more on the API goes here)

3.1.3.  Transport Protocol Components

   The transport protocol components provided by TCP are:

   o  unicast

   o  connection-oriented setup with feature negotiation

   o  port multiplexing

   o  reliable delivery

   o  ordered delivery

   o  segmented, stream-oriented delivery in a single stream

   o  congestion control

   (discussion of how to map this to features and TAPS: what does the
   higher layer need to decide? what can the transport layer decide
   based on global settings? what must the transport layer decide based
   on network characteristics?)

3.2.  Multipath TCP (MP-TCP)

   [Editor Note: a few sentences describing Multipath TCP [RFC6824] go
   here.  Note that this adds transport-layer multihoming to the
   components TCP provides]

3.3.  Stream Control Transmission Protocol (SCTP)

   SCTP [RFC4960] is an IETF standards track transport protocol that
   provides a bidirectional s set of logical unicast meessage streams
   over a connection-oriented protocol.  The protocol and API use
   messages, rather than a byte-stream.  Each stream of messages is

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   independently managed, therefore retransmission does not hold back
   data sent using other logical streams.

   The SCTP Partial Reliability Extension (SCTP-PR) is defined in
   [RFC3758].

   [EDITOR'S NOTE: Michael Tuexen and Karen Nielsen signed up as
   contributors for these sections.]

3.3.1.  Protocol Description

   An SCTP service is unicast.

3.3.2.  Interface Description

   The SCTP API is described in the specifications published in the RFC
   series.

3.3.3.  Transport Protocol Components

   The transport protocol components provided by SCTP are:

   o  unicast

   o  connection-oriented setup with feature negotiation

   o  port multiplexing

   o  reliable or partially reliable delivery

   o  ordered delivery within a stream

   o  support for multiple prioritised streams

   o  message-oriented delivery

   o  congestion control

   [EDITOR'S NOTE: Please update list.]

3.4.  User Datagram Protocol (UDP)

   The User Datagram Protocol (UDP) [RFC0768] [RFC2460] is an IETF
   standards track transport protocol.  It provides a uni-directional
   minimal message-passing transport that has no inherent congestion
   control mechanisms or other transport functions.  IETF guidance on
   the use of UDP is provided in [RFC5405].  UDP is widely implemented
   by endpoints and widely used by common applications.

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   [EDITOR'S NOTE: Kevin Fall signed up as a contributor for this
   section.]

3.4.1.  Protocol Description

   UDP is a connection-less datagram protocol, with no connection setup
   or feature negotiation.  The protocol and API use messages, rather
   than a byte-stream.  Each stream of messages is independently
   managed, therefore retransmission does not hold back data sent using
   other logical streams.

   It provides multiplexing to multiple sockets on each host using port
   numbers.  An active UDP session is identified by its four-tuple of
   local and remote IP addresses and local port and remote port numbers.

   UDP fragments packets into IP packets, constrained by the maximum
   size of lower layer frame.

   Mechanisms for receiver flow control, congestion control, PathMTU
   discovery, support for ECN, etc need to be provided by upper layer
   protocols [RFC5405].

   For IPv4 the UDP checksum is optional, but recommended for use in the
   general Internet [RFC5405].  [RFC2460] requires the use of this
   checksum for IPv6, but [RFC6935] permits this to be relaxed for
   specific types of application.  The checksum support considerations
   for omitting the checksum are defined in [RFC6936].

   A UDP service may support IPv4 broadcast, multicast, anycast and
   unicast.

3.4.2.  Interface Description

   There is no current API specified in the RFC Series, but guidance on
   use of common APIs is provided in [RFC5405].

3.4.3.  Transport Protocol Components

   The transport protocol components provided by UDP are:

   o  unicast

   o  IPv4 broadcast, multicast and anycast

   o  non-reliable, non-ordered delivery

   o  message-oriented delivery

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   o  optional checksum protection.

3.5.  Lightweight User Datagram Protocol (UDP-Lite)

   The Lightweight User Datagram Protocol (UDP-Lite) [RFC3828] is an
   IETF standards track transport protocol.  UDP-Lite provides a
   bidirectional set of logical unicast or multicast message streams
   over a datagram protocol.  IETF guidance on the use of UDP-Lite is
   provided in [RFC5405].

   [EDITOR'S NOTE: Gorry Fairhurst signed up as a contributor for this
   section.]

3.5.1.  Protocol Description

   UDP-Lite is a connection-less datagram protocol, with no connection
   setup or feature negotiation.  The protocol and API use messages,
   rather than a byte-stream.  Each stream of messages is independently
   managed, therefore retransmission does not hold back data sent using
   other logical streams.

   It provides multiplexing to multiple sockets on each host using port
   numbers.  An active UDP-Lite session is identified by its four-tuple
   of local and remote IP addresses and local port and remote port
   numbers.

   UDP-Lite fragments packets into IP packets, constrained by the
   maximum size of lower layer frame.

   UDP-Lite changes the semantics of the UDP "payload length" field to
   that of a "checksum coverage length" field.  Otherwise, UDP-Lite is
   semantically identical to UDP.  Applications using UDP-Lite therefore
   can not make assumptions regarding the correctness of the data
   received in the insensitive part of the UDP-Lite payload.

   As for UDP, mechanisms for receiver flow control, congestion control,
   PathMTU discovery, support for ECN, etc need to be provided by upper
   layer protocols [RFC5405].

   Examples of use include a class of applications that can derive
   benefit from having partially-damaged payloads delivered, rather than
   discarded.  One use is to support are tolerate payload corruption and
   over paths that include error-prone links, another application is
   when header integrity checks are required but payload integrity is
   provided by some other mechanism (e.g.  [RFC6936].

   A UDP-Lite service may support IPv4 broadcast, multicast, anycast and
   unicast.

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3.5.2.  Interface Description

   There is no current API specified in the RFC Series, but guidance on
   use of common APIs is provided in [RFC5405].

   The interface of UDP-Lite differs from that of UDP by the addition of
   a single (socket) option that communicates a checksum coverage length
   value: at the sender, this specifies the intended checksum coverage,
   with the remaining unprotected part of the payload called the "error-
   insensitive part".  The checksum coverage may also be made visible to
   the application via the UDP-Lite MIB module [RFC5097].

3.5.3.  Transport Protocol Components

   The transport protocol components provided by UDP-Lite are:

   o  unicast

   o  IPv4 broadcast, multicast and anycast

   o  non-reliable, non-ordered delivery

   o  message-oriented delivery

   o  partial integrity protection

3.6.  Datagram Congestion Control Protocol (DCCP)

   Datagram Congestion Control Protocol (DCCP) [RFC4340] is an IETF
   standards track bidirectional transport protocol that provides
   unicast connections of congestion-controlled unreliable messages.
   DCCP is suitable for applications that transfer fairly large amounts
   of data and that can benefit from control over the trade off between
   timeliness and reliability [RFC4336].

   [EDITOR'S NOTE: Gorry Fairhurst signed up as a contributor for this
   section.]

3.6.1.  Protocol Description

   DCCP is a connection-oriented datagram protocol, providing a three
   way handshake to allow a client and server to set up a connection,
   and mechanisms for orderly completion and immediate teardown of a
   connection.  The protocol is defined by a family of RFCs.

   It provides multiplexing to multiple sockets on each host using port
   numbers.  An active DCCP session is identified by its four-tuple of
   local and remote IP addresses and local port and remote port numbers.

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   At connection setup, DCCP also exchanges the the service code
   [RFC5595] mechanism to allow transport instantiations to indicate the
   service treatment that is expected from the network.

   The protocol segments data into messages, sized to fit in IP packets,
   constrained by the maximum size of lower layer frame.  Each message
   is identified by a sequence number.  The sequence number is used to
   identify segments in acknowledgments, to detect unacknowledged
   segments, to measure RTT, etc.  The protocol may support ordered or
   unordered delivery of data, and does not itself provide
   retransmission.

   Receiver flow control is supported: limiting the amount of
   unacknowledged data that can be outstanding at a given time.

   A DCCP protocol instance can be extended [RFC4340] and tuned.  Some
   features are sender-side only, requiring no negotiation with the
   receiver; some are receiver-side only, some are explicitly negotiated
   during connection setup.

   DCCP supports negotiation of the congestion control profile, examples
   of specified profiles include [RFC4341] [RFC4342] [RFC5662].  All
   IETF-defined methods provide Congestion Control.

   Examples of suitable applications include interactive applications,
   streaming media or on-line games [RFC4336].

   A DCCP service is unicast.

3.6.2.  Interface Description

   There is no current API specified in the RFC Series.

3.6.3.  Transport Protocol Components

   The transport protocol components provided by DCCP are:

   o  unicast

   o  connection-oriented setup

   o  feature negotiation

   o  non-reliable, ordered delivery

   o  message-oriented delivery

   o  partial integrity protection

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3.7.  Realtime Transport Protocol (RTP)

   RTP provides an end-to-end network transport service, suitable for
   applications transmitting real-time data, such as audio, video or
   data, over multicast or unicast network services, including TCP, UDP,
   UDP-Lite, DCCP.

   [EDITOR'S NOTE: Varun Singh signed up as contributor for this
   section.]

3.8.  Transport Layer Security (TLS) and Datagram TLS (DTLS) as a

   pseudotransport

   (A few words on TLS [RFC5246] and DTLS [RFC6347] here, and how they
   get used by other protocols to meet security goals as an add-on
   interlayer above transport.)

3.8.1.  Protocol Description

3.8.2.  Interface Description

3.8.3.  Transport Protocol Components

3.9.  Hypertext Transport Protocol (HTTP) as a pseudotransport

   [RFC3205]

3.9.1.  Protocol Description

3.9.2.  Interface Description

3.9.3.  Transport Protocol Components

3.10.  WebSockets

   [RFC6455]

3.10.1.  Protocol Description

3.10.2.  Interface Description

3.10.3.  Transport Protocol Components

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4.  Transport Service Features

   (drawn from the candidate features provided by protocol components in
   the previous section - please discussion on list)

4.1.  Complete Protocol Feature Matrix

   (a comprehensive matrix table goes here; Volunteer: Dave Thaler)

5.  IANA Considerations

   This document has no considerations for IANA.

6.  Security Considerations

   This document surveys existing transport protocols and protocols
   providing transport-like services.  Confidentiality, integrity, and
   authenticity are among the features provided by those services.  This
   document does not specify any new components or mechanisms for
   providing these features.  Each RFC listed in this document discusses
   the security considerations of the specification it contains.

7.  Contributors

   Non-editor contributors of text will be listed here, as in the
   authors section.

8.  Acknowledgments

   This work is partially supported by the European Commission under
   grant agreement FP7-ICT-318627 mPlane; support does not imply
   endorsement.

9.  References

9.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791, September
              1981.

9.2.  Informative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, September 1981.

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   [RFC0896]  Nagle, J., "Congestion control in IP/TCP internetworks",
              RFC 896, January 1984.

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC2018]  Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
              Selective Acknowledgment Options", RFC 2018, October 1996.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP", RFC
              3168, September 2001.

   [RFC3205]  Moore, K., "On the use of HTTP as a Substrate", BCP 56,
              RFC 3205, February 2002.

   [RFC3390]  Allman, M., Floyd, S., and C. Partridge, "Increasing TCP's
              Initial Window", RFC 3390, October 2002.

   [RFC3758]  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
              Conrad, "Stream Control Transmission Protocol (SCTP)
              Partial Reliability Extension", RFC 3758, May 2004.

   [RFC3828]  Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and
              G. Fairhurst, "The Lightweight User Datagram Protocol
              (UDP-Lite)", RFC 3828, July 2004.

   [RFC4336]  Floyd, S., Handley, M., and E. Kohler, "Problem Statement
              for the Datagram Congestion Control Protocol (DCCP)", RFC
              4336, March 2006.

   [RFC4340]  Kohler, E., Handley, M., and S. Floyd, "Datagram
              Congestion Control Protocol (DCCP)", RFC 4340, March 2006.

   [RFC4341]  Floyd, S. and E. Kohler, "Profile for Datagram Congestion
              Control Protocol (DCCP) Congestion Control ID 2: TCP-like
              Congestion Control", RFC 4341, March 2006.

   [RFC4342]  Floyd, S., Kohler, E., and J. Padhye, "Profile for
              Datagram Congestion Control Protocol (DCCP) Congestion
              Control ID 3: TCP-Friendly Rate Control (TFRC)", RFC 4342,
              March 2006.

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   [RFC4614]  Duke, M., Braden, R., Eddy, W., and E. Blanton, "A Roadmap
              for Transmission Control Protocol (TCP) Specification
              Documents", RFC 4614, September 2006.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol", RFC
              4960, September 2007.

   [RFC5097]  Renker, G. and G. Fairhurst, "MIB for the UDP-Lite
              protocol", RFC 5097, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5348]  Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
              Friendly Rate Control (TFRC): Protocol Specification", RFC
              5348, September 2008.

   [RFC5405]  Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
              for Application Designers", BCP 145, RFC 5405, November
              2008.

   [RFC5595]  Fairhurst, G., "The Datagram Congestion Control Protocol
              (DCCP) Service Codes", RFC 5595, September 2009.

   [RFC5662]  Shepler, S., Eisler, M., and D. Noveck, "Network File
              System (NFS) Version 4 Minor Version 1 External Data
              Representation Standard (XDR) Description", RFC 5662,
              January 2010.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, June 2010.

   [RFC5681]  Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
              Control", RFC 5681, September 2009.

   [RFC6093]  Gont, F. and A. Yourtchenko, "On the Implementation of the
              TCP Urgent Mechanism", RFC 6093, January 2011.

   [RFC6298]  Paxson, V., Allman, M., Chu, J., and M. Sargent,
              "Computing TCP's Retransmission Timer", RFC 6298, June
              2011.

   [RFC6935]  Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
              UDP Checksums for Tunneled Packets", RFC 6935, April 2013.

   [RFC6936]  Fairhurst, G. and M. Westerlund, "Applicability Statement
              for the Use of IPv6 UDP Datagrams with Zero Checksums",
              RFC 6936, April 2013.

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   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
              6455, December 2011.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC6691]  Borman, D., "TCP Options and Maximum Segment Size (MSS)",
              RFC 6691, July 2012.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, January 2013.

   [RFC7323]  Borman, D., Braden, B., Jacobson, V., and R.
              Scheffenegger, "TCP Extensions for High Performance", RFC
              7323, September 2014.

   [I-D.ietf-aqm-ecn-benefits]
              Welzl, M. and G. Fairhurst, "The Benefits and Pitfalls of
              using Explicit Congestion Notification (ECN)", draft-ietf-
              aqm-ecn-benefits-00 (work in progress), October 2014.

Authors' Addresses

   Godred Fairhurst (editor)
   University of Aberdeen
   School of Engineering, Fraser Noble Building
   Aberdeen AB24 3UE

   Email: gorry@erg.abdn.ac.uk

   Brian Trammell (editor)
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich
   Switzerland

   Email: ietf@trammell.ch

   Mirja Kuehlewind (editor)
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich
   Switzerland

   Email: mirja.kuehlewind@tik.ee.ethz.ch

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