Update - May 11th, 2018
Adjusting the SIP Min-SE Value and SIP Session Expiration Timer in UCM can cause other issues. I found voice-class sip session refresh under the dial peer did the trick. Calls now last more than 30 min without going into Call Preservation Mode on the phone. You may notice different behavior between SCCP and SIP phones. Our SIP 88XX phones would go into Call Preservation Mode at 30 min.
dial-peer voice 1 voip
description ITSP (Outbound Dial Peer)
translation-profile outgoing SIP-OUT
destination-pattern 91[2-9]..[2-9]......
voice-class sip session refresh
My SIP Trunk from CUCM to CUBE to the ITSP drops calls after 29 minutes 45 seconds, 15 minutes, 75 minutes. Why?
Timers. Your timers are incorrect.
I had this issue recently and found many people with the same issue but it did not resolve my issue because all of the timers were not adjusted. I needed to adjust both the SIP Min-SE Value and SIP Session Expiration Timer under the Service Parameters.
Reference Articles
https://supportforums.cisco.com/discussion/11241621/call-drops-after-75-minutes-sip-trunk http://voiceonbits.com/2011/07/21/scenario32-sip-calls-drop-after-75-minutes/