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The business incubator our company is enrolled in is moving to a new building. There has been talk about get a three T1 lines (4.5Mbps) as opposed to business class cable internet (10-50Mbps).

How many average users will a T1 line support?


Let's say two senerios...

  1. Average: web browsing and email
  2. Heavier: audio streaming, FTP, web browsing, and email with large (4-10MB) attachments

Edit 2:

The building will host 25 client companies. Worst case of 100 users of varying network utilization dependencies.

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Doing what? the answer will be somewhere between 0 and thousands depending on what the link's being used for. – Chopper3 Sep 16 '10 at 14:43
Edited describing the "doing what". – Eddie Sep 16 '10 at 15:01

It really depends on what your average user is doing. If they're just doing basic surfing and small e-mail; probably 50+ people without any issues. I can saturate a 10Mb pipe all day by myself though downloading ISOs (our vendors new method of software delivery) and there's more than one person like me around here.

Do keep in mind that a T1 is a switched circuit. So you have 1.544 MB of bandwidth no matter what. DOCSIS Cable Modems are packet switched networks; they share transmit and receive bandwidth on the network, and use collision detection to avoid interference. Depending on your application, users might notice the difference (though this is doubtful). You should also consider the SLA; most T1s have a 4 hour response SLA. Most CMs have a best effort SLA.

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The best way to approach this is to probably get statistics on your current usage. Check at your connection point what your usage is; how much people are downloading and uploading, and how the connection "feels".

Then look at what you're moving to.

Other people already have good points about things like guaranteed bandwidth and service outage repair to consider.

The large email attachment thing kind of surprises me (although I guess it shouldn't). Anything over one or two meg should really be downloaded from a web server or some other storage media, as email wasn't really designed for such things and I've had more than one issue with people not having email work properly or get "stuck" on a large message.

It also depends on how reliable you need the network to be, are you using remote access/VPN's, etc. It's really hard to tell whether the network connection will service your needs well without knowing what you're currently using and how happy you are with the current connection.

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We currently have Time Warner Business Class (10x1.5). It has been great so far with minimal down time over the past year. – Eddie Sep 16 '10 at 17:03
True, that large attachments should be sent through some large file service (e.g., but we find that clients tend to just assume that email can handle it. Our email provider (RackSpace) supports up to 50MB attachment. – Eddie Sep 16 '10 at 17:07
My car supports going 120 mph. Not a good idea to do that though. Same with email. It might work. It often works. But it's slow, clunky, and unreliable. Plus Exchange 2010 no longer supports SIS...sending that funny 10 meg picture to 200 friends on the corporate intranet isn't so funny to the email admin anymore. – Bart Silverstrim Sep 16 '10 at 17:34
Alas, educating the end user seems to be the bane of all system admins and developers. We typically don't send large email attachments, but that doesn't mean our clients won't try. – Eddie Sep 16 '10 at 17:46
We've been known to bounce large attachments. But it depends on your environment. Sometimes the answer is "just because", as that's about as technologically in depth as the end user is willing to go. – Bart Silverstrim Sep 16 '10 at 20:32

Hard to say since it depends on your network utilization. As a point of reference my organization for the three years I've been here was running our headquarters (about 150 users peak) on a pair of bonded T1s. and we had another hundred or so peak users at the remote sites coming in on hardware VPNs (Which also take up bandwidth) We had a lot of issues with latency at the remote sites, Video conferencing had a lot of issues. We were able to get by on it though through very aggressive firewalling and our VP redirecting users around.

I had to be careful when doing windows updates like service packs to the remote sites since that many systems pulling updates bogged it down completely. What does your network utilization look like now?

Our recent upgrades involved using both systems, the bonded T1 for VPN traffic and regular internet browsing dumped over a Comcast 100Mbps cable.

Other things to think about are cost (the cable will be a lot cheaper) and service (T1s normally have service agreements that are a lot more aggressive than cable)

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The rule of thumb for ISPs is 25 to 1. This also heavily depends on your QoS setup as well as the users.

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I assume it is 25 users to 1Mbps? – Eddie Sep 16 '10 at 17:47

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