Are you running an old Citrix client on Win7? try running a ping -t>>Somelogfile.log to a local service to see what the issue is.
Is this for a local or WAN connection?
And less barking at trees.
There is probably something else using high B/W running on the same segment, try enabling Session Reliability and changing the ICA timeout. Also speak to the local networking team to monitor traffic, do your switches support QoS?
Session Reliability is enabled and we set the ICA to not timeout. And yes we are running QoS. I have downloaded this: http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx to help find the culprit.
I wondered whether its worth disabling Sesson Reliability, and setting the ICA Keep Alives (that are bypassed if using S/R).
I've seen something similar before, where a session was being disconnected because the server genuinely thought the client had gone - it had lost visibility of it (caused by wan acceleration caching).
I think I read a similar post not long ago about this. Your server, does it have unused NIC cards? The easy thing to do is to try disabling the unused NIC cards and see if your sessions are still disconnected.
The other thing you can try is going to Network and Sharing Center assuming you're using 2008 or 2008 R2 for your citrix server and look in Change Adapter Settings. Once in there type hit Alt-N and in the drop down menu click on Advanced Settings. Make sure your active network adapter is on top and TCP/IPv4 is above TCP/IPv6 not the other way around unless you're using TCP/IPv6.