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Our company is growing, and growing fast. And everything we do is online -- e.g. our internal business applications are web-apps, hosted in a datacentre (we have multiple office locations), and we scan all our mail into a DMS hosted in the same datacentre.

Up until now, we've had an ADSL line (or two, at sites that have inter-site VOIP set up -- we have a dedicated ADSL line for this to avoid contention issues) per site, and this has been fine, but we're starting to run into speed issues -- not helped by the fact at our primary site we're so far from a telephone exchange, our ADSL syncs at ~2M down, ~0.5M up, on a good day, with a following wind.

Clearly, I need more bandwidth, and I've been asked to present proposals to management, with costs. No problem -- I need to go away and research pricing for EFM, leased lines, and all the usual jazz.

When we looked at phone lines, we were advised by a Telco to allow 1 line per 3 typical office users, as an industry norm, and this has largely been borne out -- I guess in our telephony usage, we're quite typical. But I've seen no such recommendation for Internet bandwidth, and searching for "bandwidth per user" and similar just finds discussion of quota or throughput management, not how much capacity to allow.

Is this information out there? What do those of you in larger organisations allow, when you're setting up sites and connections? Is there some typical number of Mbps per user that you'd be comfortable above and unhappy below?

I appreciate my piece of string might not be the same length as anyone else's, but I think as we scale up, we'll approach a "typical" figure that other organisations have also reached...

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2 Answers 2

up vote 2 down vote accepted

This is my opinion (just an opinion):

Your bandwidth needs are going to depend on the actual usage patterns for each user so giving you some hard fast rule is not something we'll be able to give you, but here are two approaches you can take to get an idea of how much bandwidth you'll need:

  1. The simple approach is to conceptually allocate a particular slice of the available bandwidth to each user and scale by the number of users you have. I like to allocate 100Kbps per user, so for 10 - 15 users I like to have a T1. If you go with ADSL you should make sure your upload speed accomodates this 100Kbps per user allocation. The 100Kbps per user allocation is based on a user who is busy all day and who spends a considerable amount of time on the internet; browsing, uploading files, sending emails, etc.

  2. The more scientific approach would be to insert a network tap (a hub works well here) between your firewall/router and your DSL modem. Then install a traffic monitoring program on a laptop (PRTG comes to mind), plug the laptop in to the hub, and set up a packet sniffing sensor. The sensor will see all traffic traversing the hub, and since the hub will be placed between your firewall/router and your DSL modem it will see all internet traffic, both inbound and outbound. Capture the data for a full work day and then base your calculations on the captured traffic. PRTG's packet sniffer sensor can show you the top talkers, top connections, and top protocols for the traffic it's captured. This should give you a very good idea of how much bandwidth you need.

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+1 for evidence based approach, a full day's data capture would certainly be informative. I think the switch my ADSL router hangs off can mirror a port, which should give me the same sort of effect -- if not I'll try find a hub kicking around, but I fear I've only seen switches in the last 5 years ;) –  James Green Mar 8 '11 at 22:46
    
Yep, port mirroring the switch uplink to the modem should accomplish the same thing. –  joeqwerty Mar 9 '11 at 1:17

If possible as well it's useful to prioritise your traffic and use smart routers (such as pfSense) to make sure that a single user cannot saturate the link. Email (in the grand scheme of things) is fairly low traffic and for the most part can tolerate slowdown at peak periods.

Web browsing however is going to affect productivity if users have to wait.

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