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nwcrg                                                            V. Roca
Internet-Draft                                                     INRIA
Intended status: Informational                                  I. Swett
Expires: August 8, 2019                                           Google
                                                          M-J. Montpetit
                                                          Triangle Video
                                                        February 4, 2019


Sliding Window Random Linear Code (RLC) Forward Erasure Correction (FEC)
                            Schemes for QUIC
              draft-roca-nwcrg-rlc-fec-scheme-for-quic-01

Abstract

   This document specifies Sliding Window Random Linear Code (RLC)
   Forward Erasure Correction (FEC) Schemes for the QUIC transport
   protocol, in order to recover from packet losses.

Status of This Memo

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   This Internet-Draft will expire on August 8, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definitions and Abbreviations . . . . . . . . . . . . . . . .   3
   3.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Source Symbols Mapping  . . . . . . . . . . . . . . . . .   3
     3.2.  Pseudo-Random Number Generator (PRNG) . . . . . . . . . .   4
     3.3.  Coding Coefficients Generation Function . . . . . . . . .   4
   4.  Sliding Window RLC FEC Scheme over GF(2^^8) when Protecting a
       Single QUIC Stream  . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Formats and Codes . . . . . . . . . . . . . . . . . . . .   4
       4.1.1.  Configuration Information . . . . . . . . . . . . . .   4
       4.1.2.  REPAIR Frame Format . . . . . . . . . . . . . . . . .   5
       4.1.3.  Additional Procedures . . . . . . . . . . . . . . . .   6
     4.2.  FEC Code Specification  . . . . . . . . . . . . . . . . .   6
       4.2.1.  Encoding Side . . . . . . . . . . . . . . . . . . . .   6
       4.2.2.  Decoding Side . . . . . . . . . . . . . . . . . . . .   6
   5.  Sliding Window RLC FEC Scheme over GF(2^^8) when Protecting
       Several QUIC Streams  . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   QUIC [QUIC-transport] is a new transport that aims at improving
   network performance by enabling out of order delivery, partial
   reliability, and methods of recovery besides retransmission, while
   also improving security.  This document specifies FEC schemes for
   Sliding Window Random Linear Code (RLC) [RLC] to recover from lost
   packets within a single QUIC stream or across several QUIC streams,
   compliant with the FEC coding framework for QUIC [Coding4QUIC].

   The ability to add FEC coding in QUIC may be beneficial in several
   situations:

   o  for a robust transmission of latency sensitive traffic, for
      instance real-time flows, since it enables to recover packet
      losses independently of the round trip time;





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   o  for the transmission of contents to a large set of QUIC reception
      endpoints, since the same repair frame may help recovering several
      different packet losses at different receivers;

   o  for multipath communications, since repair traffic adds diversity.

2.  Definitions and Abbreviations

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Terms and definitions that apply to coding are available in
   [nc-taxonomy].  More specifically, this document uses the following
   definitions:

   Packet versus Symbol:  a Packet is the unit of data that is exchanged
      over the network while a Symbol is the unit of data that is
      manipulated during the encoding and decoding operations

   Source Symbol:  a unit of data originating from the source that is
      used as input to encoding operations

   Repair Symbol:  a unit of data that is the result of a coding
      operation

   This document uses the following abbreviations:

   E: size of an encoding symbol (i.e., source or repair symbol),
      assumed fixed (in bytes)

3.  Procedures

   This section introduces the procedures that are used by these FEC
   Schemes.

3.1.  Source Symbols Mapping

   The present FEC Scheme follows the source symbols mapping specified
   in [Coding4QUIC].  Figure 1 illustrates this mapping.











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    < -E- > < -E- > < -E- > < -E- >
   +-------+-------+-------+-------+
   |< -- Frame 1 -- >< ----- Frame |  source symbols 0, 1, 2, 3
   +-------+-------+-------+-------+
   | 2 ----- >< --- Frame 3 -- >< -|  source symbols 4, 5, 6, 7
   +-------+-------+----+--+-------+
   | Frame 4 - >< -F5- >|             source symbols 8, 9 and 10
   +-------+-------+----+             (incomplete)

      Figure 1: Example of source symbol mapping, when the E value is
                             relatively small.

3.2.  Pseudo-Random Number Generator (PRNG)

   The RLC FEC Schemes defined in this document rely on the TinyMT32
   PRNG defined in [RLC].

3.3.  Coding Coefficients Generation Function

   The coding coefficients, used during the encoding process, are
   generated at the RLC encoder by the generate_coding_coefficients()
   function each time a new repair symbol needs to be produced.  This
   specification uses the generate_coding_coefficients() defined in
   [RLC].

4.  Sliding Window RLC FEC Scheme over GF(2^^8) when Protecting a Single
    QUIC Stream

   This fully-specified FEC Scheme defines the Sliding Window Random
   Linear Codes (RLC) over GF(2^^8) when protecting a single QUIC
   stream.

4.1.  Formats and Codes

4.1.1.  Configuration Information

   This section provides the RLC configuration information that needs to
   be shared during QUIC negotiation between the QUIC sender and
   receiver endpoints in order to synchronize them.

   o  FEC Encoding ID (8 bits): the value assigned to this fully
      specified FEC Scheme MUST be XXXX, as assigned by IANA
      (Section 7).  This FEC Encoding ID is used during the QUIC
      negotiation to uniquely identify the RLC FEC Scheme for QUIC;

   o  Encoding symbol size, E (in bytes) (16 bits): a non-negative
      integer that indicates the size of each source and repair symbol,
      in bytes.  This element is required both by the QUIC sender



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      endpoint (RLC encoder) and the QUIC receiver endpoint(s) (RLC
      decoder).

   TODO: specify exact format, with binary encoding, to be carried
   within the opaque 32-bit field during negotiation.

4.1.2.  REPAIR Frame Format

   The RLC FEC Scheme does not use any explicit Source FEC Payload ID,
   meaning that QUIC STREAM frame format is not modified.

   On the opposite, the RLC FEC Scheme requires QUIC REPAIR frames to
   convey enough information.  This section specifies the REPAIR frame
   format specific to the RLC FEC Scheme and a single QUIC stream.  Note
   that the notion of REPAIR frame format is equivalent to the notion of
   Repair FEC Payload ID in [RLC].

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Stream ID (i)                       ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               [Offset of First Source Symbol in EW (i)]     ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         [Length (i)]                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Repair_Key              |  DT   |NSS (# src symb in ew) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Stream Data                          ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 2: REPAIR frame format when protecting a single QUIC stream.

   More precisely, the REPAIR frame format is composed of the following
   fields (Figure 2):

   Stream ID (variable-size field):  a variable-length integer
      indicating the stream ID of the stream.  See [QUIC-transport].
      The Stream ID for an RLC REPAIR frame MUST be equal to the Stream
      ID used for the data stream it protects;

   Offset of First Source Symbol in the Encoding Window (variable-size
   field):
      a variable-length integer specifying the byte offset in the stream
      for the first source symbol of the encoding window.

   Length (variable-size field):  a variable-length integer specifying
      the length of the Stream Data field in this REPAIR frame.  This



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      length MUST be a non zero multiple of the source symbol size, E,
      since a REPAIR frame contains one or more repair symbols for this
      stream;

   Repair_Key (16-bit field):  this unsigned integer is used as a seed
      by the coefficient generation function (Section 3.3) in order to
      generate the desired number of coding coefficients.  When a FEC
      Repair Packet contains several repair symbols, this repair key
      value is that of the first repair symbol.  The remaining repair
      keys can be deduced by incrementing by 1 this value, up to a
      maximum value of 65535 after which it loops back to 0.

   Density Threshold for the coding coefficients, DT (4-bit field):
      this unsigned integer carries the Density Threshold (DT) used by
      the coding coefficient generation function Section 3.3.  More
      precisely, it controls the probability of having a non zero coding
      coefficient, which equals (DT+1) / 16.  When a FEC Repair Packet
      contains several repair symbols, the DT value applies to all of
      them;

   Number of Source Symbols in the encoding window, NSS (12-bit field):

      this unsigned integer indicates the number of source symbols in
      the encoding window when this repair symbol was generated.  When a
      FEC Repair Packet contains several repair symbols, this NSS value
      applies to all of them;

   Stream Data:  data for this repair symbol(s).

4.1.3.  Additional Procedures

4.2.  FEC Code Specification

   This RLC FEC Scheme relies on the FEC code specification defined in
   [RLC].

4.2.1.  Encoding Side

   [RLC] high level description of a Sliding Window RLC encoder also
   applies here to this FEC Scheme.

4.2.2.  Decoding Side

   [RLC] high level description of a Sliding Window RLC decoder also
   applies here to this FEC Scheme.






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5.  Sliding Window RLC FEC Scheme over GF(2^^8) when Protecting Several
    QUIC Streams

   This section focusses on the general case where FEC protection is
   globally applied across two or more QUIC streams.

   TODO

6.  Security Considerations

   TBD

7.  IANA Considerations

   This document registers two values in the "QUIC FEC Encoding IDs"
   registry as follows:

   o  XXXX refers to the Sliding Window Random Linear Codes (RLC) over
      GF(2^^8) FEC Scheme for a Single QUIC Stream, as defined in
      Section 4 of this document.

   o  YYYY refers to the Sliding Window Random Linear Codes (RLC) over
      GF(2^^8) FEC Scheme for a Several QUIC Stream, as defined in
      Section 5 of this document.

8.  Acknowledgments

   TBD

9.  References

9.1.  Normative References

   [Coding4QUIC]
              Swett, I., Montpetit, M-J., and V. Roca, "Coding for
              QUIC", Work in Progress, NWCRG draft-swett-nwcrg-coding-
              for-quic (Work in Progress), February 2019,
              <https://tools.ietf.org/html/
              draft-swett-nwcrg-coding-for-quic>.

   [QUIC-transport]
              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", draft-ietf-quic-
              transport (Work in Progress) (work in progress), January
              2019, <https://datatracker.ietf.org/doc/
              draft-ietf-quic-transport/>.





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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RLC]      Roca, V. and B. Teibi, "Sliding Window Random Linear Code
              (RLC) Forward Erasure Correction (FEC) Scheme for
              FECFRAME", Work in Progress, Transport Area Working Group
              (TSVWG) draft-ietf-tsvwg-rlc-fec-scheme (Work in
              Progress), February 2019, <https://tools.ietf.org/html/
              draft-ietf-tsvwg-rlc-fec-scheme>.

9.2.  Informative References

   [nc-taxonomy]
              Roca (Ed.) et al., V., "Taxonomy of Coding Techniques for
              Efficient Network Communications", Request For
              Comments RFC 8406, June 2018,
              <https://datatracker.ietf.org/doc/
              draft-irtf-nwcrg-network-coding-taxonomy/>.

Authors' Addresses

   Vincent Roca
   INRIA
   Univ. Grenoble Alpes
   France

   Email: vincent.roca@inria.fr


   Ian Swett
   Google
   Cambridge, MA
   US

   Email: ianswett@google.com


   Marie-Jose Montpetit
   Triangle Video
   Boston, MA
   US

   Email: marie@mjmontpetit.com






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