How many on a T1 2903

It greatly depends on what your clients will be doing with the t1. If you're talking about general web surfing, you can get a *lot* from a t1. One of the offices for which I manage the connectivity uses a t1 for ~40 desktops, where the general workflow of most of them involves HTTP transactions all day, and the 5-minute average on the router rarely rises above 300 kilobits - or at least it doesn't when P2P-bit torrents aren't being used.

P2P-bit torrents are the largest persons of bandwidth. The biggest problem isn't that they're using lots of bandwidth (one or two people can saturate the t1 with single FTP downloads, and nobody in the office even notices) - it's that they open up such a large number of concurrent connections. If Joe Schmoe with a P2P client has 300 concurrent connections vying for bandwidth, and you've got two, you're going to get the short end of it. If your clients will be using P2P *without* traffic shaping, a t1 is good for about one, maybe two clients.

Luckily, you have a lot of powerful options for traffic-shaping. The most rudimentary, simple bandwidth-limitting, can be the most simple, and most effective - at the cost of lower peak for each user. My quick-and-dirty solution in said office was to limit each user to 256k sustained, with something like a 1- or 2-megabyte burst to full speed. With that in place, it would take at least six users at full usage to flood the t1, but in that population, that doesn't happen - 5 minute averages stay around 500-600 kilobits-second.

There are plenty of more advanced ways of doing the shaping, but the options available will depend on the router you choose. A caching proxy is a very good thing on such a network - even if for nothing else, when Micro$haft releases a 100+ megabyte service pack, your t1 will only have to choke along for ten minutes downloading the file for each and every user.

In implementing such a network, you really do want to route between individual user connections, don't just connect them all to the same switch. That will greatly help contain viral spread-outbreaks, as well as a very good deal of other potential problems. Low-cost, low-power machines with quad-port Ethernet cards from ebay will fill the bill on a budget, and let you use very advanced firewalling-traffic shaping features of Linux (or the BSDs) without having to sell organs to pay for Ciscos.

(It's sort of a shame that you're only getting a t1 - at $900, that's $600 per megabit. I've had commercial carriers offer me full t3s at less than $140 per megabit, including line and termination charges. Your costs go down GREATLY as the size of the pipe increases.)

steve