Forward Erasure Correction (FEC) and network performance

Fri Apr 10 17:43:26 UTC 2009

Marshall Eubanks wrote:
> If there is some consensus around this, it would effectively set an 
> upper bound for the need for FEC in network transit.

The bit error rate of copper is better than 1 error in 10^9 bits. The 
bit error rate of fiber is better than 1 error in 10^12 bits. So the 
packet loss rate of the transport media is approximately zero.*

Thus any packet loss you see is congestion. If you see packet loss, you 
should SLOW DOWN, not just keep sending and using more and more FEC to 
get recoverable video out the far end. (And by "SLOW DOWN" I mean in a 
way that is TCP-friendly, as anything less will starve out TCP flows 
unfairly and anything more will itself find that it is starved out by TCP)

Matthew Kaufman

* The bit error rate of RF-based connections like Wi-Fi is higher *but* 
because they need to transport TCP, and TCP interprets loss as 
congestion, they implement link-level ARQ in order to emulate the 
bit-error-rate performance of wire as best they can.