This article relates to Cisco TelePresence Advanced Media Gateway 3610.
Q. All my calls through an AM gateway drop after about 30 seconds or sooner
A. On the OCS Gateway VCS, go to System configuration > DNS. Are there values for the settings Local host name and Domain name?
If both of these are set, the VCS will use these as a fully-qualified domain name (FQDN) in SIP signalling to the OCS server. In order for OCS to be able to use this information, it must be able to perform a DNS lookup on the FQDN.
To rectify this, ensure that the DNS server used by the OCS server contains an entry for the VCS's FQDN.