I am having CM5.1 and configured SIP trunk (unauthenticated) directly to my services provider.
Also i have 2851 router in which NAT is configured with the services provider IPs for call manager and phones.
I can able to make calls using this SIP trunk but call is getting disconnects after every 15 min.
Services provider says he is sending SIP UPDATE message to call manager every 15 min which is not unauthorised by call manager and call gets disconects.
Can anyone help with this. Attaching the output of debug ip nat sip on router.