Date: Thu, 6 Nov 1997 10:05:31 -0500 (EST) From: "Paul D. Robertson" <root@gannett.com> Subject: Re: New MAE-EAST [...] I'm sure that's a part of it, I initially saw a lot of dropped packets through a couple of ATM clouds. I'm seeing some improvements in some of the providers, however, given the trumpeting of ATM (magic bullet syndrome), it seems that it's just not something which happens correctly by default.

Some ATM switches are better than others. In particular, some of the early ATM switches had very small buffers. They simply weren't designed to support bursty data like IP. There are a number of "good" ATM switches, at least in the sense that they have adequate buffering, available. Depending on whether you are using ATM as a fine-grained, relatively static multiplexing service (CBR) or as a bandwidth-on-demand service (UBR or ABR), the amount of buffering in the network may make a difference. This is probably a good question to ask your prospective service provider.

before we go off on the 'nothing happens correctly by default' tangent, it's just been my general observation that whenever my packets have been transited over ATM, my latency has been less than ideal. I would have figured that oversubscription would result more in lost packets and timed out connections (which were also seen, but more easily screamed about) than latency, but I guess that's a factor of how oversubscribed the line is. [...]

While I don't know your particular circumstances, lots of things can cause latency. Distance, or perhaps unexpected distance, is often an explanation for propagation delay. Some carriers may backhaul your ATM traffic to a switch far away. So, you don't really know what latency to expect unless you know the physical path your data traverse. By the way, the same sort of thing can happen can happen with point-to- point leased lines. We recently had a line which used a rather circuitous route to reach its destination. We asked the carrier to find a shorter path, which they did. -tjs