Incoming calls are being disconnected when put on hold or transferred

[asoto]

We are experiencing an issue where calls are disconnecting when we try to put the call on hold or transfer to another phone. I've narrowed it down to incoming calls only as when we place a call it allows both functions normally. The moment we hit the hold or transfer button it ends the call. Not sure where to start to look for a solution. Any help will be greatly appreciated.

[wshrader]

basics: model/version of the server?
network topology: what's changed? Did this start suddenly?
My first thought is SIP ALG. This is going to be network related unless you have are using an obsolete Allworx firmware.

[allwrxprtnr]

This could also be an ISP issue, assuming you are using SIP for your voice.
It could be a misconfigured SIP account on the Allworx, or the wrong CODEC (such as G.711A, G.711U)

It may be best to gather some call details (time/date of issue, description, incoming call number, number they dialed to reach you) before calling your ISP, so that you can hand them the information they will inevitably ask for.

[wshrader]

Good point, allwrxprtnr. Call examples! Don't confuse ISP (Internet Service Provider) with ITSP (Internet Telephony Service Provider). Call examples would be given to the ITSP. I have seen though, this exact behavior when using a SonicWall with an Ubee DDW32 and DDW36 series cable MODEM. I cannot count how many times this combination of devices has problems.