problem with RH ES 4.0 network sockets

[Edmunds Priede]

good day!

i have following system :  RH 4.0 ES  kernel 2.6.9-11   Intel SE7520JR2 board
with latest network drivers.
i am running application on SUN Java Application Server 8.1 .

some specific workstations after some time working with www application (1/2 -
1 hrs)  freeze network connection to the port which they use to connect.
netstat shows ESTABLISHED socket to that workstation and server never releases
this socket, even if the workstation is rebooted. in this situation noone can
connect to that port. browser shows 'Connected to server.com' and hangs on this
message for ever and does not release it. other ports on SUN server continue to
work, only the affected port is frozen. after i reboot SUN AS server, sockets
are released and  normal operation resumes.

this happens from specific computers only so far. what can cause network socket
to freeze?  has anybody seen something similar on other systems? any
suggestions? is it SUN AS problem or OS or network?

thanks

edmunds