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

[Haas, Neal]

Back in the Day we had 11 Nortel PBX’s. I think that we had 11 PRI’s registered as MGCP. I don’t think we ever got the PRI’s to drop calls when a phone was transferred back to CUCM. Our next step was to look at SIP, but it just was not worth the cost to put a SIP trunk on the Nortel PBX to solve our issues (was like $30,000 or $40,000 to do so)

Best thing we do was purchase more CISCO phones :>

Thank You,

Neal Haas
NSE, Communications
Please report Troubles to the Help Desk. 559-600-5900
Telephone (559) 600-5890

From: cisco-voip [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Anthony Holloway
Sent: Tuesday, March 7, 2017 2:54 PM
To: Cisco VoIP Group <cisco-voip at puck.nether.net>
Subject: [cisco-voip] Anti-Tromboning Tie Lines to PBX

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<http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/configuration/cube-book/media-path.html#concept_674530029296875008039300537109374>

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<http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/8_5_1/ccmsys/accm-851-cm/a08procl.html#wp1156114>.

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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