There are a number of reasons why this could be happening, the first thing to check would be the IP network itself. If the link indicator is dissapearing completely it would appear that the network connection has gone down. A simple test would be to run a simple ping from the Quintum, try this from the root CLI prompt:
> ping -n 50 126.96.36.199
This will ping the address 188.8.131.52 50 times in succession. If you see a number of time-outs here you know you may have a network problem.
I should point out here that there is a little publicised problem with the Quintum Digital Series Ethernet port. Basically it experiences extensive packet loss if run at 100Mbs. When setting up the unit make sure you force the port to 10Mbs – this is far faster than the combined voice channels require so you won’t experience any quality problems.
If this doesn’t solve the problem then check the network cable, hub, router etc.
If all else fails please feel free to contact me at: email@example.com
Hope this helps