From: Dave Siegel <dave@rtd.net> Subject: Re: sell shell accounts? To: freedman@netaxs.com (Avi Freedman) Date: Fri, 19 Jul 1996 16:01:01 -0700 (MST) Cc: vansax@atmnet.net, richards@netrex.com, agislist@interstice.com, nanog@merit.edu
Acceptable arguments are: o Switches can handle more throughput
That's difficult to quantify in theory *or* practice. [...]
I may misunderstand your assertion, but it doesn't seem all that difficult to quantify, at least to some coarse level. We have been using wide-area ATM switches at OC-3c for some time. It is pretty clear that the switches can handle OC-3c. The early switches had relatively small output buffers, so they tended to loose cells before TCP could throttle back in congested circumstances. We are now using switches with much larger output buffers, and TCP appears able to throttle back fairly gracefully. After we upgraded our switches to use much larger output buffers, most of the problems we experienced were related to the hosts, (e.g., poor TCP implementations, poor ATM interfaces, etc). By the way, I believe that most people who are using ATM wide-area networks in production or as part of the Internet are using static bandwidth allocation to avoid a number of problems. We also have a number of OC-12c interfaces for our switches. They appear to work, but we haven't really had a chance to stress them yet. (Part of the problem is that it is hard to find OC-12c data sources and sinks.) The current generation of routers appears unlikely to support OC-12c, particularly since their backplanes are only about the same speed. On a more theoretical note, switches, being circuit-switched, make the complicated decisions when the connection is established, (or configured for PVCs), and need to make relatively simple decisions to switch each cell. This probably scales very well is terms of speed, although at some point might have some difficulty in scaling to a very large number of simultaneous connections. Routers, on the other hand, have to make a bit more complicated decisions per packet. This has some limitations in terms of speed and number of simultaneous "connections." -tjs