Don't have direct access to the DSLAM, but do have access to that information in the modem - and yes and there appears to be a large change in certain frequency buckets.
The loss rates appear to vary with the offered load - i.e the "loss" only occurs if there was real packet data in that frequency band On 10 Dec 2013, at 08:04, Mikael Abrahamsson <[email protected]> wrote: > On Tue, 10 Dec 2013, Neil Davies wrote: > >> We've seen this even when we've played with the settings through the >> customer portal (I'm' in the UK - the provisioning portal allows many such >> changes). >> >> Are you capturing any evidence of DSL modem state when this occurs? > > Well, we saw the problems mostly on medium-short spans, such as 1000-1500 > meters. The packet loss wasn't as high as 20%, but it was consistant over > time and showed up as errored seconds. I do not work there anymore, and this > was 7 years ago. > > Interleaving spans bits over longer period of time, so if you're running fast > mode and you get a 1ms "hit" on the link, the FEC (forward error correction) > gets too many bits corrupted and gets overwhelmed. If one instead has 16ms > interleaving, a lot fewer bits from one packet gets corrupted, and FEC can > correct the errors. > > So your theory about line noise on specific frequencies is probably correct, > you're not getting a big enough hit to trigger a re-train, but you're getting > enough bit errors to cause post-FEC errors and thus packet loss. A re-train > probably identifies the noise on those frequencies and uses them less. > > In our DSLAM we could see the frequency band profile via a show command, have > you done this? > > -- > Mikael Abrahamsson email: [email protected] _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
