Simple LDPC-Staircase FEC Scheme for FECFRAME draft-roca-fecframe-ldpc-01
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Transcript of Simple LDPC-Staircase FEC Scheme for FECFRAME draft-roca-fecframe-ldpc-01
Simple LDPC-Staircase FEC Simple LDPC-Staircase FEC Scheme for FECFRAME Scheme for FECFRAME draft-roca-fecframe-ldpc-01draft-roca-fecframe-ldpc-01
IETF 79 – Beijing, November 2010
V. Roca – M. Cunche (INRIA)
J. Lacan (ISAE)
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GoalsGoals
specifies 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 versionModifications since -00 version
initial -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?Why yet another FEC scheme?
well suited to certain FECFRAME applicationswith 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
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/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 SetupExperimental 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 SetupExperimental Setup
SENDER: Pentium4 / 2.4 GHz
512 MB RAM / 32-bit Linux
SENDER: Pentium4 / 2.4 GHz
512 MB RAM / 32-bit Linux
RECEIVER: Core2 / 1.66GHz
512 MB RAM / 32-bit Linux
RECEIVER: Core2 / 1.66GHz
512 MB RAM / 32-bit Linux
packet loss proba.
(0% ~ 51%)7
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 capabilitiesResults: 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.Results: frame delay after FECFRAME proc.
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2D codes RS codes LDPC codes
k 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 loadResults: CPU load
sender:
receiver:
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ResultsResults
in summary:for this target environment, LDPC-staircase codes (k=170)
were the best choicesee 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 codesMore fundamentally, LDPC-staircase codes
…have excellent recovery capabilitiese.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 concludeTo conclude
LDPC-staircase codessimple, 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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