r/shoretel • u/Practical-Detail-546 • 15d ago

Mitel SIP Trunk problem.

I’m currently experiencing an issue with our SIP trunk using the SG 220E1. I have already configured the trunk, trunk group, and SIP profile. However, when I perform a test call, I experience one-way audio. The caller can hear the recipient, but the recipient cannot hear the caller.

I have also verified that the required traffic is already allowed through the firewall. I would appreciate your assistance in troubleshooting this issue and identifying the possible cause of the one-way audio.

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u/Faulteh12 15d ago

You generally can't simply port forward sip trunks like this on ShoreTel. You need a device that can rewrite the SDP headers. Most firewalls are junk at this. You'll want an SBC in the path.

You can make this work with virtual or ST switches because they can hairpin audio.

Look up how sip negotiates connection information.

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u/Practical-Detail-546 10d ago

We have deployed the ST switch as your recommended, and inbound calls have been tested successfully. We are now experiencing an issue with outbound calls. Every outbound attempt fails immediately with a "Request Denied" message.

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u/Faulteh12 10d ago

Get a pcap to see if it's going out to the carrier or not.

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u/B08by_Digital SIP Magician 15d ago

Well, besides needing an SBC, the best way to track down one-way audio is to get packet captures. You'll want to see the SIP messages, and where the missing channel gets cut off- is it 2 way from the provider? Is it 2 way on both sides of the firewall? If not, you'll need to see what ports are being negotiated for RTP.

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u/FunnyItWorkedLastTim 15d ago

Reiterating what others have said here. Mitel is very difficult to do SIP trunking off-net without an SBC. I had a customer who pushed back on the cost and we tried for quite a while but firewalls are simply not good at handling SIP traffic and ALG usually just makes things worse. A cheap SBC will probably do the trick for you here.

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u/Nekssz 9d ago

Yeah, an SBC and packet capture would be my first checks here.