1 RaptorG Forward Error Correction Scheme for Object Delivery draft-luby-rmt-bb-fec-raptorg-object-00 (update to this to be officially submitted soon) Michael Luby IETF#76 – Hiroshima 8-13 November 2009

2 RaptorG code properties

3  Systematic code  Supports 1 to 56,404 source symbols per source block Memory available at decoder generally limits # source symbols –Even with sub-blocking  Supports 0 to 16+ million repair symbols Application/network generally determines # repair symbols Fountain code property –Protection from 0 up to 300+ times the source block size –Repair symbols independently generated –No need to set code rate in advance  Supports symbol size from 1 to 65,536 bytes Packet size generally limits source symbol size One symbol per packet recommended Can choose symbol size to adjust to desired packet size  Limits are not fundamental to the code design Practical specification choices based on foreseeable use cases

4 RaptorG code properties  If the number of source symbols is K then… Receive K symbols  Pr[decode fails] ≤ Receive K+1 symbols  Pr[decode fails] ≤ Receive K+2 symbols  Pr[decode fails] ≤  True for the entire range of K values From K = 1 to K = 56,404  True for very low to very high loss From loss = 0% to loss = 97%  Strongly systematic Recovery properties are independent of mix of received source and repair symbols

5 RaptorG code properties

6  Linear time encoding and decoding Comparable to Raptor specified in RFC 5053

7 RaptorG Forward Error Correction Scheme for Object Delivery

8  Same organization and parameters as RFC 5053 Same FEC Payload ID parameters –4 bytes total – same as for RFC 5053 –SBN is 8 bits –ESI is 24 bits Same FEC OTI parameters –F, Al, T, Z, N  Parameters have same meaning as in RFC 5053

9 RaptorG Forward Error Correction Scheme for Object Delivery  Similar suggested derivation of FEC OTI parameters as RFC 5053 Improved and simpler –Recommends one symbol per packet Improved support for sub-blocking provided –Large source blocks decodable using small receiver memory –Derivation of parameters improved compared to RFC 5053 –Allows larger source blocks due to more source symbols Example of sub-blocking –Maximum sub-block size is 1 MB –Minimum sub-symbol size is 32 bytes –Packet size is 1500 bytes –Can use a source block of size up to 43 MB

10 Raptor RFC 5053 vs. RaptorG PropertyRaptor RFC 5053RaptorG # source symbols8,19256,404 # encoded symbols65,53616,777,216 Max. sym. size65,536 # source blocks65, Recovery propertiesGoodExceptional # symbols/packetOften multiple1 Sub-block supportGoodImproved

11 Next steps  Adopt as a RMT working group draft