is it possible to do an ISDN hangup when TCP session closes ?

[rmachenbaum]

We have deployed Cisco 1601-R routers configured for dial-on-demand over ISDN satellite links to connect our remote messaging servers to our hub. The idle timeout has been set to 45 seconds, a lower value causes disconnection problems.

The remote sites call about 15 times per days and this means that about 11 min of very expensive satellite airtime is wasted by the idle-timeout interval.

The solution would be to have the router monitor the active TCP sessions across the ISDN link and hangup the line as soon as all TCP session closes. I am wondering if the router has this capability ?

[tepatel]

YES..It is possible to configure the router to consider only TCP traffic as interesting, which will be allowed to bringup the isdn line and reset the idle-timeout.

So when the TCP traffic needs to send across, the isdn line will be brought up and stay connected as long as the TCP traffic is going across. After that the isdn line will be dropped once the idle-timeout expires.

Is that what you want?

[rmachenbaum]

Not exactly as this behaviour is still based on an idle-timeout which in our case cannot be reduced to less than 45 seconds because of some delays in the application. What I was wondering is if the router can "understand" what is happening, see that a TCP SYN and ACK has been sent/received over the ISDN interface so that a TCP session is active across the link. When the router sees the TCP FIN followed by the ACK he can assume that the TCP session is over and can hangup without any delay.

[zahmed]

To me, looks like you will have to work on the application to reduce its delays so that you can use

a smaller idle timeout.

~Zulfi