I have an issue with outgoing calls from Lync Server user to mobile network.
Lync Server is connected through Direct SIP connection to a DMG2000 (2060). The Media Gateway connects to PSTN Mobile Network through an E1 interface card with ISDN protocol.
Lync user makes an outgoing call to a PSTN mobile user. The SETUP message is sent successfully to the PSTN Mobile Operator, and it responds with a CALL PROCEEDING message. If the PSTN Mobile Operator takes more than 2000 milliseconds to respond with an ALERTING message, the call fails. The DMG2000 starts a timer of 2000 milliseconds when it receives the CALL PROCEEDING message. When ALERTING message takes longer than 2 seconds, the DMG2000 disconnects the call, and sends a SIP CANCEL to Lync Server
Mobile Telephony Operators typically take longer to send the ALERTING message, since they have to locate the user. So this is a typical situation.
TRACE OF AN UNSUCCESSFUL CALL:
In this case, the ALERT message does not arrive before timer expires. The DMG2000 disconnects the call, and sends a SIP CANCEL to Lync Server (337:59.616 - 337:57.456 = 2160 milliseconds)
TRACE OF A SUCCESSFUL CALL
In this case, the ALERT message arrives before 2000 milliseconds after receiving CALL PROCEEDING message. (337:24.096 - 337:22.720 = 1376 milliseconds)
I am sure that if I could set this timer to a value greater than 2000 milliseconds, the calls would not drop. Is there any possibility to increase this timer to a value greater than 2000 milliseconds?
This timer is equivalent to T310 timer.
I will appreciate any help
That Cancel is actually sent by Lync to the DMG, ie its Lync who is clearing the call, the DMG is not going to clear the call :
337:59.616 [Tel-2 ] Code (3c14fb0) remaining in eSTATE_OUTBOUND_PROCEEDING
Then approx 400ms later Lync sends a cancel:
338:00.080 [VoIP ] Prot ---->CANCEL sip:firstname.lastname@example.org;user=phone SIP/2.0
Have a look and see if Lync has a timer for receiving Alerting messages and see if you can increase it.
The other option is to force early media on in the DMG, then the DMG will send a 183 progress message to Lync as soon as it gets the Call Proceeding from ISDN so I wouldn't think that Lync will drop the call then.
To enable early media on the DMG go to VoIP/Media and set "RFC3960 Early Media support" to Always".
Early media means that the voice channel between the DMG and Lync is connected as soon as the DMG receives a call proceeding.
Note that this will change the user experience as now the Lync users will hear the real network tones and messages and not Lync's artificial ring tone. In most cases this is better as Lync users will be able to hear network announcements such as 'that number does not exist' etc but in this case with the delayed ringback they will hear silence until the actual ringback is sent from the mobile operator. This is the same as they would hear when making the same call from a pstn phone of course.
Thanks for the answer.
You are right. DMG sends a disconnect after receiving SIP CANCEL.
We think that the source of the problem could be in the firewall port configuration between Front End Servers and Edge Servers (ICE protocol and MRAS)