Our office network is currently 100mbit, switched. There are two main 24-port switches, and a couple of 8-port switches for specific subnets, such as my desk. The exact topology doesn't matter, although a GbE uplink between the two main switches would be nice.

Anyway, the advantage of ATM over fast ethernet (as has been explained to us) is that it can guarantee the delivery of our critical voice traffic at the same time as it maintains a best-effort attempt at delivering data. Which is nice... But I have 100mbits available, unshared, to every desktop. If you are on two phone calls at once, at ISDN quality, that's a little more than one tenth of one percent of your bandwidth. You have to chew through most of the remaining 99.9% before you will start to affect the sound quality of those calls. And your PC (thanks to Microsoft's IP stack) isn't nearly powerful enough to do that. A full-size fast ethernet frame takes, what, 0.12ms to transmit, so the jitter will barely be measurable, much less noticeable.

Essentially, if you have the bandwidth, ATM isn't necessary, and if you don't have the bandwidth, you're going to lose something anyway. So where do we need it at all?

In modems.

If you're a typical home user, you want to do stuff like downloading the latest episode of 24 over BitTorrent while making a VoIP call on your videophone. You've got what, a megabit upstream? Problem.

Enter ATM.

It guarantees the bandwidth for your videophone. Good.

To do so, it has to throw out some BitTorrent packets. Who cares? BitTorrent is completely self-healing at three different protocol levels. Anyway, it's your data it's throwing out, not anyone else's.

And the kicker: High-speed ATM is expensive, because you need high-speed processors to do all the fancy quality-of-service stuff. But we're talking about a megabit or so in an ADSL modem. We don't even need end-to-end QoS, since downstream bandwidth isn't in short supply, only upstream. So, finally, a win for ATM.

Unless you live in Japan, Korea, or Canberra, where ADSL has already been supplanted by something better.

Posted by: Pixy Misa at 11:04 AM | No Comments | Add Comment | Trackbacks (Suck)
Post contains 371 words, total size 2 kb.