While detailed troubleshooting is required, yet from my past practical experience of similar problem of ISDN call getting cleared after some time , i can say that it may be an IOS problem. It is expected that with newer versions of IOS software basic things like ISDN would work flawlessly , but that is not so with some of newer releases of Cisco IOS. That means you have to check all the features you intend to use and cann't take them granted for in newer releases.
I suggest that you may try, as i did, to use some earlier version of s/w on the same platform.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...