[Bloat] Does VDSL interleaving+FEC help bufferbloat?

[Mikael Abrahamsson]

On Fri, 4 Jan 2019, Dave Taht wrote:

> dsl interleave was added primarily to make multicast udp tv streams work 
> better (as they are very intolerant of packet loss). Often (as in free's 
> implementation) these streams are "invisible" to the overlying IP 
> applications. It typically adds at least 6ms of delay to an already slow 
> technology.

ADSL2+ is very prone to short bursts of interference, so setting no 
interleaving means quite high packet loss. Setting interleaving to 16ms 
means FEC has a much better chance of correcting errors and thus reduce 
packet loss.

At several jobs ago we actually had several different profiles for 
customers, they could choose 1, 4 or 16ms interlaving depending on their 
needs for gaming etc. The 1 and 4 ms interleaving targets had different 
SNR margin targets so they were sacrificing speed for lower latency, 
because that's the tradeoff you basically have to do with normal L4 
protocols that end customers typically use.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se