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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: ATM Wide-Area Networks (was: sell shell accounts?)
> > > 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. It's difficult to quantify wrt to how ATM plays a role in end-to-end performance on the Internet. There is very little research to support how ATM affects the overall performance. Even Ameritech and PacBell restricted the majority of their performance evaluation on performance in the switch, and only extended their scope if they leased an ADSU to a customer. Even with the improved buffering, if you fill your pipe into the ATM switch, your ATM switch still becomes a packet shredder, compared to the more graceful packet drops seen on a clear channel line. The performance of the switched technology is integral with the equipment attached to it. You cannot evaluate the performance of the system by analyzing small chunks of it, and coming to conclusions on the whole system. This is what I'm talking about. It's easy to qualify that ATM switches can switch cells much faster than routers can switch packets (with current commercially available routers), but it's much more difficult to qualify the scope of how ATM improves performance in the big picture. Dave -- Dave Siegel Sr. Network Engineer, RTD Systems & Networking (520)623-9663 x130 Network Consultant -- Regional/National NSPs [email protected] User Tracking & Acctg -- "Written by an ISP, http://www.rtd.com/~dsiegel/ for an ISP." - - - - - - - - - - - - - - - - -
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