Ulpfecreading rfc5109

========================================================

traditional FEC schemes

such as Reed-Solomon, and Hamming codes.

• rfc2733
• rfc3009

bandwidth utilization issue

unequal error protection

• protection levels
  • lower levels – greater protection, smaller group sizes
  • higher levels – inverse
• different protection level for different data importance.
  the more important parts of the data are always at the beginning of the data packet.
• media payload – raw user data
• media header – rtp header
• media packet – rtp header + raw user data
• fec packet – take media packets as input
  • output: media packets
  • output: fec packets for error correction
• fec header – header info in fec packet
• fec level header – header info in fec packet for each level

• fec payload – payload of fec packet. may be divided into multiple levels

• relationship between fec packet and media packet

basic operation

• XOR
• offset mask m(k)
• the amount of data is protected at level k – L(k)

parity codes

for example, protection on every two data blocks

a        b        c        d               <-- media stream
           f(a,b)            f(c,d)        <-- FEC stream

why XOR?

• effectiveness
• simplicity

in protocol design and implementation.

important! for implementation in embedded devices.

Uneven Level Protection (ULP)

• trade-off between the bandwidth and the protection strength.
  • different importance with different level of protection.

transfer via separated stream

• origin meida stream is not affected. clients without fec can work well.
• tracking the amount of fec.

issues

• separated stream?
• redundant coding?