Conference Calls Drop on VVX 410/411

Occasional Visitor

Conference Calls Drop on VVX 410/411

I've ran into a strange issue that I can only replicate on the VVX 410 and VVX 411.  Running Version 5.6.0, and now 5.6.1.  Conference calls fail to establish when using the conference softkey to convert an in-progress call to a Skype Conference Call.  This does not seem to affect the VVX310 or VVX600 phones I've tried it on.  We run an on prem S4B environment, and all devices are connected via edge.


Steps to reproduce:

Call a PSTN number

Press Conference Softkey

Dial another number (can be PSTN, or Internal Skype Ext)

"connecting to conference" is displayed for about 30 seconds, then the call drops.


Oddly, this also only happens when the original call is to a PSTN user.  Looking at packet captures for said failures, on the VVX410/411's the captures are full of repeated STUN attempts, on the other models, the STUN looks like any other call, and the conference service bridges the two calls together like a normal skype for business conference.  All testing has been done with configs from the same provisioning server, with phones on the same switch, behind the same firewall, connecting to the same edge server, etc..


Unfortunately, at this time, I have no in-warranty devices to open a ticket.  I've opened a ticket with microsoft - since the issue appeared to be with the conferencing service initially.  They validated the configuration and said everything looks fine with our on-prem topology in thier point of view.  I'm hoping someone in the community might be able to provide suggestions.

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Polycom Employee & Community Manager

Re: Conference Calls Drop on VVX 410/411

Hello @Andy_OSI,

welcome to the Polycom Community.

First of all the warranty status should not hinder you to open a ticket as you simply would pay per incident / PPI.


I assume Microsoft support does also charge you for their support?


Usually all our phones should behave the same as they are using the same software but as you did not post any kind of logs or backups or traces there is not a lot we can try and guess.

Best Regards

Steffen Baier

Polycom Global Services

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