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Reed-Solomon FEC Schemes for FECFRAME draft-roca-fecframe-rs-02

Reed-Solomon FEC Schemes for FECFRAME draft-roca-fecframe-rs-02. IETF 77 – Anaheim, March 2010 V. Roca – M. Cunche (INRIA) J. Lacan – A. Bouabdallah (ISAE) K. Matsuzono (Keio Univ.). General. goals (reminder) specifies the use of Reed-Solomon codes in FECFRAME

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Reed-Solomon FEC Schemes for FECFRAME draft-roca-fecframe-rs-02

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  1. Reed-Solomon FEC Schemes for FECFRAME draft-roca-fecframe-rs-02 IETF 77– Anaheim, March 2010 V. Roca – M. Cunche (INRIA) J. Lacan – A. Bouabdallah (ISAE) K. Matsuzono (Keio Univ.)

  2. General • goals (reminder) • specifies the use of Reed-Solomon codes in FECFRAME • complements our RFC 5510 (RMT WG) • DOES NOT consider RTP framing of FEC repair packets • see draft-galanos-fecframe-rtp-reedsolomon-01.txt • changes w.r.t. -01 are motivated by Qualcomm IPR disclosure 1183 • https://datatracker.ietf.org/ipr/1183/ • see US Patent 7,660,245: • granted on Feb. 2010, previously "undisclosed pending patent" • our I-D is modified so as to avoid infringing this patent…

  3. Changes W.R.T. -01 version • new way of building source symbols from ADU • before: potentially different # of symbols per ADU • now: all ADUs of a given block contribute to the samenumber of source symbols, thanks to padding • particular case: E = max ADU size +3 ⇒ one symbol per ADU • NB: symbol size is set for the whole session (it's signaled in the FSSI), but it's probably wiser now to set it per source block… Enc Symbol Len (E) Enc Symbol Len (E) Enc Symbol Len (E) < ------------------ >< ------------------ >< ------------------ > +----+----+-----------------------+------------------------------+ |F[0]|L[0]| R[0] | Pad[0] | +----+----+----------+------------+------------------------------+ |F[1]|L[1]| R[1] | Pad[1] | +----+----+----------+--------------------------------------+----+ |F[2]|L[2]| R[2] |P[2]| +----+----+----------+--------------------------------------+----+ 1st ADU 2nd ADU 3rd ADU

  4. Changes W.R.T. -01 version… (cont') • four schemes were specified until version -01, now only 2 schemes remain: • scheme 1: RS over GF(2m) (with m in {2..16}), for arbitrary packet flows • scheme 2: special case of a single sequenced flow • reason: • the new source block creation scheme makes the other two schemes suboptimal… remove them! • if large blocks are needed, then use LDPC FEC codes (draft-roca-fecframe-ldpc-00) ;-)

  5. Changes W.R.T. -01 version… (cont') • updated source/repair FEC Payload ID • new 4-bit field: Number of Source Symbols per ADU (NumSPA) for this source block • motivated by the new source block creation scheme 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NumSPA| Source Block Number (28-8=20 bits) | Enc. Symb. ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Block Length (k) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  6. Next steps • finish scheme 2 and clarify a few details • accept it as a WG Item?

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