nwcrg V. Roca
Internet-Draft INRIA
Intended status: Informational I. Swett
Expires: December 23, 2018 Google
M-J. Montpetit
Triangle Video
June 21, 2018
Sliding Window Random Linear Code (RLC) Forward Erasure Correction (FEC)
Schemes for QUIC
draft-roca-nwcrg-rlc-fec-scheme-for-quic-00
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.
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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 . . . . . . . . . . . . . . . . . . . . 6
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: 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): a non-negative integer that
indicates the size of each source and repair symbol, in bytes.
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This element is required both by the QUIC sender endpoint (RLC
encoder) and the QUIC receiver endpoint(s) (RLC decoder).
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
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;
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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.
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.
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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), June 2018,
<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-12 (work in progress), May 2018,
<https://datatracker.ietf.org/doc/
draft-ietf-quic-transport/>.
[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>.
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[RLC] Roca, V., "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), May 2018,
<https://tools.ietf.org/html/
draft-ietf-tsvwg-rlc-fec-scheme>.
9.2. Informative References
[nc-taxonomy]
Roca et al., V., "Taxonomy of Coding Techniques for
Efficient Network Communications", draft-irtf-nwcrg-
network-coding-taxonomy (Work in Progress) (work in
progress), 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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