Mitel VOIP dropiing calls in one directtion.

Paul Walsh
Paul Walsh used Ask the Experts™
Hi All,

We have an older Mitel 3300 using predominantly Mitel 5212 phones. We have a dedicated VLAN for voice traffic, which is tagged on our switches alongside whichever VLAN is providing the network for the computers. We are having a strange problem in which when a phone call is made, one side is unable to hear the other (in reverse it is fine). After a few seconds this will sometimes resolve itself, or they will need to hang up and try again. On the retry both sides can usually have full conversation as normal. This happens randomly throughout the day to different number / handsets that are plugged into various switches throughout the organisation. We have had a look at the switches and they don't have any obvious errors / are not reporting they have maxed out on throughput.

We have had our support engineers look at the phone system and they cannot spot anything obvious with regards to the fault.

Any clues as to where to start diagnosing this.

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Distinguished Expert 2018

Internal or external calls? Have you attempted any sort of packet capture on the voice VLAN?
Paul WalshSystem Administrator


both internal and external. Haven’t tried any packet capture as of yet. Isn’t voip mostly udp. What would be the best way to capture/ analyse the traffic and what pointers should I be looking for?

Sr Manager Cloud Networking Ops
Maybe the port range for your traffic is too small. Old Adtran voip gear by default limited the port range to about 20 ports, which is 10 concurrent calls.

Maybe post the config off your Mitel?

Good luck,
Steve J

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