[VoiceOps] Hairpin Call from certain PBXs - No Audio issue

Ujjval Karihaloo ujjval at simplesignal.com
Fri May 10 00:29:30 EDT 2013

Hi Team:

       Have you all seen issues with hairpin calls from PSTNà ITSP
(Broadsoft/ACME)à SIP Trunk – which in turn forwards the call back out the
SIP trunk to the PSTN and there is no Audio in either direction (Transfer
via Auto-attendant OR Blind – Attended Xfer works as Media is
anchored/reinitiated on PBX)

Having worked on a few PBXs (Allworx, Zultys) that cause this issue on
ACME/Broadsoft Sip trunk setup – we see RTP in both direction on our
traces, but due to the pass through RTP nature of this call flow, the TTL
get way down to 5-6 in some cases, and that is what I believe is the issue,
and our upstream vendors like Level3, Bandwidth etc suggest the same.

Other than implementing a RTP repeater of sorts, I don’t see an
alternative. Ideas appreciated


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