[UKFSN Status] Changes to network (fwd)

[Jason Clifford]

I have just received the following notice from Enta regarding a change to 
their ADSL network.

Note that the change is an adaptive one so please read the details below 
carefully. This should make for a far better connection when the central 
capacity is very busy and will only affect offpeak periods. It will not 
prevent users being able to use their full bandwidth allowance.

Also notice the last paragraph. The 4th pipe is on order and the 2nd 
segment of the 3rd pipe will light up on 1st Feb.

Jason
---------- Forwarded message ----------

After noticing severe packetloss on Friday night we have introduced an anti-loss tool. The tool works by reducing the maximum rate limit when capacity hits a certain point and then allows it back up slowly if the capacity returns. 
At the minute non-L2TP customers have an 8Mbps rate-limit applied to their accounts as a default so that additional traffic is not sent to the end user unnecessarily (BT would just throw this away anyway so it makes sense to do it at the furthest sensible point from the end user). 

The variation in limits are applied on a per central basis so that if only one has a problem then only it has its limits adjusted. Users will be able to switch centrals and the limit will be reset to that of the central they reconnect to. 

The rate limit changes only happen once the 5 minute average usage for that central hits 96%, once this occurs then the maximum rate limit is reduced by 500kbps. 
One minute later the next 5 minute average is calculated, if usage remains above 96% then a further 500kbps will taken from the maximum limit and this will continue to a minimum of 2Mbps. 

Once usage fall below 91% then the rate limit is raised by 200kbps. If the capacity hovers between 91% and 96% then the limit will continue at its current setting. 

The intent here is to deal with the short period at the start of off-peak where everybodies automated systems tries to download the world. We are looking at a number of different solutions for distributing the start time of off-peak so that the rate limit should only change in extreme conditions. 

2Mbps is the equivalent to a 4:1 contention ratio for someone at 8Mbps and capacity planning is currently scheduling for the limiting to only occur for short periods of time during off-peak. If users could move the majority of their downloads to after 12pm during weekdays then the issue would be reduced, as we would rather see a few users going slower and there be minimal packet loss and latency. 

We have ordered a 4th central (due to be installed in 3-4 months - updates when we have dates from BT) and the next segment of the 622Mbps will be scheduled to be live on the 1st February 2007.