Simple LDPC-Staircase FEC Scheme for FECFRAME draft-roca-fecframe-ldpc-01

IETF 79 – Beijing, November 2010

V. Roca – M. Cunche (INRIA)J. Lacan (ISAE)

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Goalsspecifies how to use LDPC-staircase codes in

FECFRAMEcomplements our RFC 5170 (RMT WG)provides a single scheme: LDPC-Staircase for arbitrary

packet flows

DOES NOT consider RTP framing of FEC repair packets

left to future works if the need arises…

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Modifications since -00 versioninitial -00 version in July 2009get stuck by Qualcomm's patent on FECFRAME

same situation as that of Reed-Solomonforced to wait until the situation is clarified

00 versus 01 modifications:take draft-roca-fecframe-simple-rs-01 and replace

reference to "Reed-Solomon" by "LDPC-Staircase"• RS and LDPC I-D are now almost the same• only minor modifications to address LDPC specificities (e.g.

FSSI)same philosophy : K.I.S.S.restrict to the case where G==1 in RFC 5170

• see: http://www.ietf.org/mail-archive/web/rmt/current/msg01384.html

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Why yet another FEC scheme?well suited to certain FECFRAME applications

with high bitrate flowswhen a large number of flows must be globally protectedwhen low complexity software decoding is a MUST

complements (but does not replace) Reed-Solomon and 2D parity schemes

An example of use:

K. Matsuzono, J. Detchart, M. Cunche, V. Roca, H. Asaeda

"Performance Analysis of a High-Performance Real-Time Application with Several AL-FEC Schemes"IEEE Local Computer Networks (LCN'10), October 2010

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DVTS/FECFRAME results (from LCN'10)DVTS: a high-performance/high-throughput real-

time/interactive video application over IPDigital Video Transport System (DVTS)support DV/HDV formats

CBR flows: 30 Mbps (DV format)widespread use (symposium, e-learning, telemedicine)

• see: http://www.sfc.wide.ad.jp/DVTS/ • http://www.internet2.edu/communities/dvts/

sender

DVTS

fecframe lib.

DVTS

fecframe lib.IP networks

(congestion, fading, etc) 5

Experimental Setup

3 performance metrics:recovery capabilitiesframe delay above FECFRAMECPU load

FEC Codes Symbol Length (Bytes)

Code Rate Source Block Length (k)

N1

2D Codes 1375 2/3 16 none

RSE Codes 1375 2/3 170 none

LDPC Codes 1375 2/3 (1) 170(2) 500(3) 1000

755

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Experimental Setup

SENDER: Pentium4 / 2.4 GHz512 MB RAM / 32-bit Linux

RECEIVER: Core2 / 1.66GHz512 MB RAM / 32-bit Linux

packet loss proba. (0% ~ 51%)

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2D codes

2D codes ☹unrecovered data loss continuously happens

RS, LDPC codes ☺no data loss until 30% packet loss probability

RS codes

LDPC codes(k=170)

LDPC codes(k=500, 1000)

Results: recovery capabilities

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2D codes: usually lower than 50msec ☺ RS: ☹

over 100msec around 12% loss rate over 500msec around 30% loss rate

LDPC codes ☺ When k=170, 50msec until 24% loss rate, 89msec above ☺ When k= 500,1000, greater especially in high loss rates ☹

RS codes LDPC codes(k=500, 1000)

Results: frame delay after FECFRAME proc.

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2D codes RS codes LDPC codesk 16 170 170 500 1000

Ave. CPU load (%) 14.1 74.3 12.0 11.0 12.6

RS codes

2D codes

LDPC codes(k=170)

LDPC codes

(k=500, 1000)

Results: CPU loadsender:

receiver:

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Resultsin summary:

for this target environment, LDPC-staircase codes (k=170) were the best choice

see paper for additional details…

additionally…if several DVTS flows were to be carried between the

same locations, globally FECFRAME protected, LDPC-staircase codes (with higher k) would be even more beneficial

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More fundamentally, LDPC-staircase codes…have excellent recovery capabilities

e.g. k=256 symbols, N1=7: average overhead=0.68%(i.e. 1.74 symbols in addition to k)

…while keeping very high decoding speedse.g. k=256, N1=7: 1.39-2.46 Gbps (Xeon 5120/1.86GHz, 64-bit

Linux)12.6 to 28.2 times faster than RS over GF(28)

RS over GF(28)

RS over GF(24)

LDPC (N1=5 & 7)

RS over GF(24)

RS over GF(28)

LDPC (N1=7)

Erasure recovery tests Decoding speed tests 12

To concludeLDPC-staircase codes

simple, easy to understand and implementclose to ideal recovery performanceshigh performance codec developed in an open source

projectan interesting alternative to proprietary codesconsidered in standards

current I-D is considered as finishedready for WGLC if accepted as WG Item

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