Emulating ADSL bandwidth shaping

Mark Smith nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
Tue May 4 16:27:00 CDT 2010


On Tue, 4 May 2010 16:44:06 +0200 (CEST)
Mikael Abrahamsson <swmike at swm.pp.se> wrote:

> On Tue, 4 May 2010, Chris Boyd wrote:
> 
> > Most of the ADSL installations I've seen in SBC 13 state area had 
> > interleaving turned on, which significantly increases latency.  I 
> > suspect that's why many cable MSOs in the same territory have "cable is 
> > better for gaming" marketing campaigns running all the time.
> >
> > So the latency you see on an ADSL line is dependent on how the carrier 
> > set up the DSLAM.
> 
> Interleaving is good because it reduces bit error rate on the line. Would 
> be good though if the carrier let the customer change the properties of 
> the line to optimize for different things, high snr target/no interleaving 
> for low bw/low BER/low latency applications, low snr target/interleaving 
> for file transfers.
> 

It's common for ISPs in Australia who own their own DSLAMs to do this
via 'line profiles'. I'm on the most aggressive one, and have line
latency of around 9.5 to 10ms.

Also what is interesting is that ADSL firmware in the modem can
contribute significantly. I used to need to be on ADSL1 with
interleaving to get any sort of reliable line sync. After a
modem firmware upgrade, which I knew also involved an ADSL chipset
firmware upgrade, I didn't get any more bandwidth, but was able to get
stability (i.e. no loss of sync for weeks on end) without interleaving.

Regards,
Mark.




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