Mobile Twinning and SIP Trunk Usage

[Lectronics Inc]

When using Mobile Twinning, and the call comes in on a SIP trunk, and when the destination is a user twinned to their cell phone, how many SIP channels are used ?

A) One, as the call remains on the initial channel
B) Two, similar to trunk-to-trunk transfer, one inbound and one outbound
C) None, as the call is switched like a Centrex Transfer

 

[derfloh]

B - one for incoming and one for outgoing call

C would only work for call forwarding, if the trunk supports forwarding by using SIP302.

 

[Lectronics Inc]

derfloh, thank you for the info. However, I am not sure what you mean by "SIP302". Can you please elaborate?

 

[derfloh]

Usually in case of call forwarding you need one channel for the inbound call and a second call for the outbound call. Only for call forwarding, this is not possible for mobile twinning.

For call forwarding you can tell the carrier that you want to reach someone else. You will then respond towards the carrier with a SIP 302 message containing the call forwarding destination number. The carrier will then release the call to your PBX and send the original call directly to the destination. You will lose control over the call but you also don’t consume SIP trunk channels anymore.

 

[finest]

This feature is sometime called SIP REFER (and sometimes confused with SIP RE INVITE). You’ll need to program these features on the line tab in IP office and if you’re using a session border controller, you’ll need to do it there as well. It should work in the following conditions: Forwarding (all types) and call transfer (after youve completed the transfer). It will not be involved with twinning or any type of conferencing. If you are able to get this working with your carrier and your system, please let us know. I know are people have a lot of difficulty with this feature.

 

[Lectronics Inc]

Thank you, finest..... So, is it only the "LINE>SIP LINE>Outgoing Blind REFER" box that needs to be checked? Or do I need to do something with the "Incoming (and/or) Outgoing SUPERVISED REFER options?

My plan is to use this from a selection on the AA. It is currently set up in this way on analog lines with a Centrex Transfer feature:

1. Call comes to main AA
2. Caller chooses * for the person on call
3. Call is routed to the "On Call" hunt group
   1. Each tech is set up with a virtual user extension.
   2. Only one virtual user is logged in on the HG at a time (when they are on-call)
   3. Each virtual user is unconditionally forwarded to their own AA
4. The user's AA instructs the caller to press 1
5. Action 1 is set to Centrex Transfer to the user's cell phone, then transfer's the call off switch, leaving the lines free for other calls.

This has worked great for a few years. Until the customer changed DT providers (to save money), where the new provider does not have this feature. So, I am proposing SIP trunks. Then I plan to eliminate the individual AA's and just transfer the call directly to the cell phone (from the virtual user). The other thing that this setup allows is for the manager to control who is on-call, by hotdesking into the virtual users' extensions and logging them in or out of the HG.

Do you foresee any issue doing it this way with SIP trunks? Thank you for your input.