[Bloat] CFP: Workshop on Reducing Internet Latency

Mikael Abrahamsson swmike at swm.pp.se
Tue Dec 10 01:48:03 EST 2013

On Mon, 9 Dec 2013, Matthew Ford wrote:

> The report of the Reducing Internet Latency workshop is now available:
> http://www.internetsociety.org/blog/2013/12/speeding-internet-reducing-latency

Reading through this I generally like it. It's a good summary and 

However, this part:
"Hiding packet losses in broadband lines using interleaving can add about 
20ms of delay, even though modern transports and applications are robust 
to such low packet loss levels;"

Having been part of a decently sized ADSL2+ deployment ISP, I have some 
experience with this and the above doesn't match them. We actually did get 
customer complaints when we were running ADSL2+ in fast-mode (no 
interleaving), that the customers were getting packet losses that affected 
their applications.

So I would have liked the above to not say "broadband lines" but instead 
said ADSL(2+) broadband lines (because the above statement only relates to 
ADSL(2+) afaik), and also that the packet losses can be non-trivial for 
some and that ISPs don't turn on interleaving out of ignorance. It's hard 
to measure customer impact of "errored seconds" which is the only way the 
ISP can see packet losses. Also, these errored seconds can be quite 
severer when it comes to number of packets dropped.

We actually did talk about having a self-service portal where the customer 
could choose their preferred profile, either fast (no interleaving), 4ms 
or 16 ms interleaving, and also their safety margin to 6, 9 or 12 dB. Fast 
or 4ms interleaving worked well with 12 dB SNR margin (which means lower 
latency but also lower access speeds), whereas 6dB margin often required 
16ms interleaving to work well.

Mikael Abrahamsson    email: swmike at swm.pp.se

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