Bandwidth sizing for simultaneous RDP sessions

We're doing some DR scenario planning which will require up to 150 users to RDP into their desktop machines (mainly running Windows XP) over our VPN. We have a 2mbit uncontended internet connection at the moment but there's scope to upgrade this and also to use a secondary SDSL line to give us more bandwidth.

Typical bandwidth figures I've seen suggest to plan for 64kbps per session, which works out to 9.6mbps in total. I'd like to know:

1. Does anyone have any real-world data which would support these estimates?
2. Are there any operational 'gotcha's that we need to be aware of?

Thanks!

Solution 1:

Its good your upgrading to 10M (as seen in one of your comments) but one thing I'd also consider is instituting QoS at least on the router/firewall level for your RDP traffic. RDP isn't as touch with bandwidth as it is with latency, something QoS helps with.

We have a 6Mbit connection that was close to saturation between offsite backups and, general traffic and RDP. We noticed by implementing QoS on our firewall (running IPCop for about 150+ users) that RDP issues have almost completely gone away.

Our priority setup is similar to this;

VPN - Highest
RDP - High
SFTP - High
Email - Medium
Web - Low
Everything else - Very Low

Now instead of fighting with everything, RDP only has to deal with VPN and SFTP on priority. It cut down on the random disconnects and slowness to the point where I get complaints once every few months instead of multiple times a day.