Emulating ADSL bandwidth shaping

Tue May 4 19:58:29 UTC 2010

On Tue, 4 May 2010, Scott Weeks wrote:

> "Interleaved" turned on to correct errors.  This adds ~25msec between 
> the CPE and the nearest router.  Sometimes folks ask for it to be 
> changed to "Fast".  We explain that errors may cause resyncs to happen 
> and then make the change if the customer still wants it.  That takes the

Basically "interleaved" is a way "smearing" bits over time, so FEC can do 
its job when there is a 1ms line hit that causes a lot of errors during 
that 1ms.

Turning off interleaving (changing to "fast") usually means your "errored 
seconds" counter will increase over time because of lack of error 
correction, and your customer experiences packet loss intermittently. 
Never seen it cause resyncs, but that might happen, dunno.

It is usually settable to 1,4,16 ms in each direction, so 25ms is not a 
"law of nature", it's just the default 16/4 ms downstream/upstream 
interleaving and then the added coding delay.

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