Can't leave voicemail - Early Dialog Terminated SIP message

Environment

• PSTN (T1 PRI) — CUCM 7 – Dialogic 2030 IP-to-IP GW – OCS 2007 R2

Problem

• Some calls to cell phones from OCS would terminate unexpectedly either while leaving a voicemail or before the greeting finished playing.
• Calls to cell phones in the West and East exhibited this behaviour, but calls to cell phones in Montreal didn’t seem to.
• One user said he had this problem calling the US and the Niagara area, too.
• The same call made from a Cisco phone would be fine.
• The OCS error logs show the SIP message 199 Early Dialog Terminated.

Resolution

• Changed the TCP Inactivity Timer on the Dialogic GW from default 30 s to 90 s.
• Test to cell in the East was successful.
• Also verified that cell vs. home phone is not relevant, and call connect time is in play
  • Changed the number of rings on a home phone, before voicemail pickup, to 6 (cell phone had a lot of rings before pickup, too) and the same behaviour was seen

Below is text from trace on MOC log file:

04/20/201015:02:36.547 1784:8D0 INFO :: Data Received - 172.20.1.120:5061 (To Local Address: 172.20.2.46:49856) 726 bytes:
04/20/201015:02:36.547 1784:8D0 INFO :: SIP/2.0 199 Early Dialog Terminated
Proxy-Authentication-Info: Kerberos rspauth="602306092A864886F71201020201011100FFFFFFFF4147CAB224E8230B8A11DD2DC5ADE3B1", srand="F7B56919", snum="1584", opaque="35F8D7D2", qop="auth", targetname="sip/ulocs02.domain.com", realm="SIP Communications Service"
Content-Length: 0
Via: SIP/2.0/TLS 172.20.2.46:49856;ms-received-port=49856;ms-received-cid=47E600
From: "First Last";tag=61e9453d78;epid=d2b3504585
Call-ID: 06cd7690782c4d27ad5c3d92646b08b3
CSeq: 1 INVITE
To: ;tag=fed66b776
Server: http%3A%2F%2Fwww.microsoft.com%2FLCS%2FOutboundRouting(Microsoft Office Communications Server 2007 R2 3.5.6907.0)
04/20/201015:02:36.547 1784:8D0 INFO :: End of Data Received - 172.20.1.120:5061 (To Local Address: 172.20.2.46:49856) 726 bytes