[asterisk-users] compatibility of PRI Two B channel transfers TBTC/2BTC

[Matthew Fredrickson]

Matt Florell wrote:
> Hello,
> 
> A client has asked for Two B channel Transfer capability (known as
> TBCT or 2BCT, similar to other features such as ECT, RTL and Q,SIG
> Path Replacement) in a new Asterisk system and so I researched the
> capability and came up with quite a few gaps in documentation.
> 
> From what I've gathered, the official Digium statement is that is
> works with DMS100 only, and only in Asterisk 1.4.X :
> http://kb.digium.com/entry/26/140/

This definitely works.  I wrote it and tested it myself.

> 
> Although in a bugtracker posting with a patch from over two years ago,
> Matt Fredrickson from Digium says that it works with 5ESS under
> Asterisk 1.2.X:
> http://bugs.digium.com/view.php?id=3554

There's an implementation I scrubbed out a couple of years ago, but I 
think there was a bug in it that I was not able to fix.  When push came 
to shove, and I needed a switch to debug it on (and when I had more time 
to work on it), nobody offered switch access so that I could debug it. 
So I don't think it is working right now.

> There are also bounties and claims of this feature working on NI2
> protocol(although no patches posted) on the voip-info.org Wiki:
> http://www.voip-info.org/wiki/view/Asterisk+bounty+PRI+2B+channel+transfer+for+NI2+PRI+line
> http://www.voip-info.org/wiki/index.php?page=Asterisk%20bounty%20PRI%202B%20channel%20transfer

Yeah, well, they're really old :-)  Try getting a hold of the authors.

> 
> As for actually using this feature, you apparently need to add the
> following lines to the zapata.conf section that you want to be able to
> use 2BCT:
> facilityenable = yes
> transfer=yes

Yes, that is correct.

> 
> To execute the transfer, you need to use the "Transfer" cmd within Asterisk:
> http://voipinfo.org/wiki/view/Asterisk+cmd+Transfer

This is incorrect.  If you have transfer=yes and facility=yes in 
zapata.conf for both channels, and both channels meet all the other 
criteria for TBCT (on the same PRI, and a few other switch dependent 
rules), when a native bridge is attempted, it automatically attempts to 
pass the calls up to the upstream switch.  If it is successful, your 
calls will remain up, but you will get a hangup in asterisk on both calls.

> 
> And according to this post, you can only do 2BCT transfers if the
> first call is inbound:
> http://www.mail-archive.com/asterisk-dev@lists.digium.com/msg25131.html

That's a rule only for DMS100.

> 
> 
> Does 2BCT work with DMS100 and 5ESS right now?

Last I heard (a couple of years ago) it doesn't.

> Are there people using this in production right now that can shed some
> more light on exactly how they are using it, and executing the
> transfers?

I hope I answered your questions :-)

-- 
Matthew Fredrickson
Software/Firmware Engineer
Digium, Inc.