Interesting discussions with our favorite telco this week. As I am sure people know - we are somewhat tenacious in getting issues fixed, and we have a customer (in a small village) that is having problems with congestion most evenings.
Now, we do a lot of testing and we confirmed that he gets packet loss and latency on the link from us to him when this happens. Clearly showing the problem is within the wholesale/DSL network. Testing from our router means we can be sure it is not "the Internet" being slow, which is, of course the first thing our suppliers suggested!
So we chase our suppliers and they say the VP (yes, an ATM VP for 20CN) is not congested. They claim it is below 25% of its capacity.
We got the figures from them eventually. It seems they are happy for a single 10Mb/s link to be used by 400 customers even though those customers can get 7.15M each on their links.
Now, there are contention levels - you don't just add up all the links, but this level of contention and such a small aggregate link makes no sense to us. If two of the 7.15M customers try to access the internet at the same time they get badly congestion. If one of the 400 customers torrents they would hog all of their 7.15M leaving under 3M for the remaining 399 customers.
We are, of course, trying to get them to fix this. They can simply increase the capacity on the VP. They are pretty much refusing to, saying their planning rules allow 400 customers on it. In practice we are seeing congestion with only 100 customers on the link, and are not at all surprised.