[cisco-voip] Anti-Tromboning Tie Lines to PBX

[Carlo Calabrese]

QSIG with MGCP. I use this to connect to a few Nortel PBX's. The main reason was to get rid of Meridian Mail and put it on Unity.  Started this bad in the 4.2 days. When the call transfers out it will release the channels and the PRI is no longer in the call.Easy to set up. just a couple of configs on the gateway and a few options changes on the PBX. Cisco has a document on it somewhere. I am trying to find it on my PC, but that was 10 years ago. 

    On Tuesday, March 7, 2017 3:25 PM, Brian Meade <bmeade90 at vt.edu> wrote:
 

 Also known as 2 B-channel Transfer or TBCT (should help your searching).
On Tue, Mar 7, 2017 at 5:54 PM, Anthony Holloway <avholloway+cisco-voip at gmail.com> wrote:

I'm not sure how often this gets configured out in the wild, but I do know that there are few different flavors of this feature, depending on your scenario.  E.g., CUBE Media Anti-Tromboning
The one I'm interested in would involve a tie line to a legacy PBX, and I'm not married to the IP technology: SIP, H323, MGCP, whichever will get the job done.
CUCM ---IP---> VGW ---T1/PRI---> PBX
The call scenario I'd like to see if we can avoid is when a call is established from CUCM to the other PBX, and then a phone on the far side transfers the call to an IP Phone on the CUCM side, I'd like the PRI usage to drop to 0 trunks in use, instead of nailing up 2 trunks for the duration of that call.
I'm looking for your experience and feedback in configuring anti-tromboning in this scenario.  One of the hardest parts in researching this, is knowing what terms to search for.  I think I've narrowed down the terminology to QSIG Path Replacement, as described in the CUCM SRND.
Though, without real-world working experience, it's hard to know if I'm right or not.
So, I know there's some good legacy telco knowledge out on this list.  What do you know?  Thanks!
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