[ale] Tunnel presistence connection issue

[Christopher Fowler]

I'm using Vtun at a remote site and am running pppd inside my tunnel. 
The remote site has Time Warner Cable as their provider.  After a few
minutes of inactivity across the tunnel, the tunnel seems to lock up. 
No data can go between the two machines.  Its as if something in between
stopped the flow of traffic.  Eventually the tunnel will time out at the
other end and close down and start a new one.  Out of 20+ sites this is
the only site that does this.  Its also the only site using cable modem.
Does anyone know what could be causing this?

Chris