Internet DRAFT - draft-roca-nwcrg-rlc-fec-scheme-for-quic
draft-roca-nwcrg-rlc-fec-scheme-for-quic
nwcrg V. Roca, Ed.
Internet-Draft INRIA
Intended status: Informational F. Michel
Expires: September 10, 2020 UCLouvain
I. Swett
Google
M-J. Montpetit
Triangle Video
March 9, 2020
Sliding Window Random Linear Code (RLC) Forward Erasure Correction (FEC)
Schemes for QUIC
draft-roca-nwcrg-rlc-fec-scheme-for-quic-03
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
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 September 10, 2020.
Copyright Notice
Copyright (c) 2020 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
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Roca, et al. Expires September 10, 2020 [Page 1]
Internet-Draft RLC for QUIC March 2020
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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. Source Symbols identification . . . . . . . . . . . . . . 4
3.3. Pseudo-Random Number Generator (PRNG) . . . . . . . . . . 4
3.4. Coding Coefficients Generation Function . . . . . . . . . 4
4. Sliding Window RLC FEC Scheme over GF(2^^8) . . . . . . . . . 5
4.1. Formats and Codes . . . . . . . . . . . . . . . . . . . . 5
4.1.1. Configuration Information . . . . . . . . . . . . . . 5
4.1.2. SRC FPI Frame Format . . . . . . . . . . . . . . . . 5
4.1.3. REPAIR Frame Format . . . . . . . . . . . . . . . . . 6
4.1.4. Additional Procedures . . . . . . . . . . . . . . . . 7
4.2. FEC Code Specification . . . . . . . . . . . . . . . . . 7
4.2.1. Encoding Side . . . . . . . . . . . . . . . . . . . . 7
4.2.2. Decoding Side . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
QUIC [QUIC-transport] is a transport protocol that aims at improving
network performance by enabling stream multiplexing, partial
reliability, and methods of recovery besides retransmission, while
also improving security. This document specifies FEC schemes for
Sliding Window Random Linear Code (RLC) [RFC8681] 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;
Roca, et al. Expires September 10, 2020 [Page 2]
Internet-Draft RLC for QUIC March 2020
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.
Roca, et al. Expires September 10, 2020 [Page 3]
Internet-Draft RLC for QUIC March 2020
QUIC packet
|<E-1-4>|< E-1 >|< E-1 >|< E-1 >|
+------|----+--|-------|-------|-------|
|Header| 0 | Packet Payload | 4 packet chunks
+------|----+--|-------|-------|-------|
/ | | \
v v v v
+-+--+----+ +-+-------+ +-+-------+ +-+-------+
|m|pn|chnk| |m| chunk| |m| chunk| |m| chunk| 4 source symbols
+-+--+----+ +-+-------+ +-+-------+ +-+-------+
| | | | | | | |
|< --E-- >| |< --E-- >| |< --E-- >| |< --E-- >|
Figure 1: Example of source symbol mapping, when the E value is
relatively small.
3.2. Source Symbols identification
Similarly to [RFC8681], the present FEC Scheme assigns a unique
identifier (ID) to each produced source symbol. The IDs are assigned
to the produced source symbols in the ascending order. The IDs start
at MUST start 0 and MUST be contiguous. For any symbol with ID x,
the source symbol with ID x+1 is :
o The source symbol containing the next packet chunk in the same
QUIC packet as the source symbol X, if it exists.
o The source symbol containing the first packet chunk of the next
generated FEC-protected QUIC packet
Do we want to authorize a wrapping of the source symbol ID ? It would
be a lot easier if wrapping is not permitted.
3.3. Pseudo-Random Number Generator (PRNG)
The RLC FEC Schemes defined in this document rely on the TinyMT32
PRNG defined in [RFC8682] along with the two mapping functions to
4-bit and 8-bit unsigned integers defined in [RFC8681].
3.4. 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
[RFC8681].
Roca, et al. Expires September 10, 2020 [Page 4]
Internet-Draft RLC for QUIC March 2020
4. Sliding Window RLC FEC Scheme over GF(2^^8)
This fully-specified FEC Scheme defines the Sliding Window Random
Linear Codes (RLC) over GF(2^^8).
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 6). 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
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. SRC FPI Frame Format
The RLC FEC Scheme requires explicit signaling of the Source Symbols
it transmits. The QUIC packets whose payload is protected by FEC
MUST contain an SRC FPI frame with the following format.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID of First Source Symbol in Packet (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SRC FPI frame format.
The SRC FPI frame contains the ID of the first source symbol
contained in this packet. Each source symbol contains a packet chunk
of E-1 bytes long. If the payload to protect is longer than E-1
bytes, this means that the packet contains several packet chunks. In
this case the source symbol ID will increase by exactly one for each
additional packet chunk contained in the payload to protect.
Roca, et al. Expires September 10, 2020 [Page 5]
Internet-Draft RLC for QUIC March 2020
Note: This frame is not idempotent. In the current version of QUIC,
all the frames are idempotent (but this is not especially
required). It would be great to preserve this property (a quick
fix would be to add the packet number in the frame, but it takes
a lot of space and I don't think it is very useful). Another bad
property is that the frames are not independant anymore (several
SRC FPI frames contained in the same packet have a confusing
meaning). I really think that the correct solution would be a
(encrypted) header field but I guess it is more complicated to
propose (maybe in v2 we'll have a mechanism to define dynamic
encrypted header fields during negotiation).
4.1.3. REPAIR Frame Format
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. Note that the notion of REPAIR frame format
is equivalent to the notion of Repair FEC Payload ID in [RFC8681].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID of First Source Symbol in EW (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Repair_Key | NSS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DT | NRS | Repair Symbols ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: REPAIR frame format when protecting a single QUIC stream.
More precisely, the REPAIR frame format is composed of the following
fields (Figure 3):
ID of the first Source Symbol in the Encoding Window (variable-size
field):
a variable-length integer specifying the ID of the first source
symbol in the encoding window. When a FEC REPAIR frame contains
several repair symbols, this value applies to all of them;
Repair_Key (16-bit field): this unsigned integer is used as a seed
by the coefficient generation function (Section 3.4) 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.
Roca, et al. Expires September 10, 2020 [Page 6]
Internet-Draft RLC for QUIC March 2020
Number of Source Symbols in the encoding window, NSS (16-bit field):
this unsigned integer indicates the number of source symbols in
the encoding window when this repair symbol was generated. When a
REPAIR frame contains several repair symbols, the NSS value
applies to all of them;
Density Threshold for the coding coefficients, DT (4-bit field): thi
s unsigned integer carries the Density Threshold (DT) used by the
coding coefficient generation function Section 3.4. More
precisely, it controls the probability of having a non zero coding
coefficient, which equals (DT+1) / 16. When a REPAIR frame
contains several repair symbols, the DT value applies to all of
them;
Number of Repair Symbols contained in the frame, NRS (12-bit field):
this unsigned integer specifies the number of Repair Symbols
contained in this REPAIR frame;
Repair Symbols: data for this repair symbol(s). This field is NRS*E
bytes long.
4.1.4. Additional Procedures
4.2. FEC Code Specification
This RLC FEC Scheme relies on the FEC code specification defined in
[RFC8681].
4.2.1. Encoding Side
[RFC8681] high level description of a Sliding Window RLC encoder also
applies here to this FEC Scheme.
4.2.2. Decoding Side
[RFC8681] high level description of a Sliding Window RLC decoder also
applies here to this FEC Scheme.
5. Security Considerations
TBD
Roca, et al. Expires September 10, 2020 [Page 7]
Internet-Draft RLC for QUIC March 2020
6. 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.
7. Acknowledgments
TBD
8. References
8.1. Normative References
[Coding4QUIC]
Swett, I., Montpetit, M-J., Roca, V., and F. Michel,
"Coding for QUIC", Work in Progress, NWCRG draft-swett-
nwcrg-coding-for-quic (Work in Progress), March 2020,
<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), November
2019, <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>.
[RFC8681] Roca, V. and B. Teibi, "Sliding Window Random Linear Code
(RLC) Forward Erasure Correction (FEC) Schemes for
FECFRAME", RFC 8681, DOI 10.17487/RFC8681, January 2020,
<https://www.rfc-editor.org/info/rfc8681>.
[RFC8682] Saito, M., Matsumoto, M., Roca, V., Ed., and E. Baccelli,
"TinyMT32 Pseudorandom Number Generator (PRNG)", RFC 8682,
DOI 10.17487/RFC8682, January 2020,
<https://www.rfc-editor.org/info/rfc8682>.
Roca, et al. Expires September 10, 2020 [Page 8]
Internet-Draft RLC for QUIC March 2020
8.2. 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 (editor)
INRIA
Univ. Grenoble Alpes
France
Email: vincent.roca@inria.fr
Francois Michel
UCLouvain
Louvain-la-Neuve
Belgium
Email: francois.michel@uclouvain.be
Ian Swett
Google
Cambridge, MA
US
Email: ianswett@google.com
Marie-Jose Montpetit
Triangle Video
Boston, MA
US
Email: marie@mjmontpetit.com
Roca, et al. Expires September 10, 2020 [Page 9]
