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Albany Creek, Queensland, Australia
07 3882 2933

Why won’t this trunk register?


The strange faults from last week are continuing into this week. Out of the many alarms we receive overnight from phone systems across the country indicating trunks have dropped and re-registered, one caught my eye. One trunk had been a bit unstable overnight – dropping and re-registering multiple times – but had dropped out around 7.11am and had not re-registered.

This Yeastar P550 system has been installed since June 2022 and no changes had been made to it since a software update a couple of months ago. It was due for another one so I did that because it would trigger a reboot and that may bring the trunk back – it didn’t…

Since no changes had been made to the system programming for a while there was no reason to suspect it so I lodged a call with Telstra as it’s one of their SIP services and they said that they had not seen a registration request since 7.05am. They felt that the (dreaded) SIP ALG was the problem in the router although it was already turned off. SIP Application Level Gateway is a feature that is supposed to help but in 999 out of 1000 cases it hinders implementation of SIP trunks and should generally be turned off.

Wireshark traces actually showed the system wasn’t even trying to register the trunk. Due to Telstra-specific programming the trunk is registering through the WAN port of the system where normally we would just register on the LAN port. The system could ping the router so connectivity appeared OK.

I programmed up a spare SIP trunk which registered straight away and I could make and receive calls on that OK.

Fortunately, all trunk credentials are filed away so I created a new trunk using the same credentials and it registered straight up. Why the original trunk wouldn’t even attempt to register is a mystery.

ICS Technologies is based in Brisbane, Australia. Contact us for assistance with your Yeastar or Avaya phone systems.

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