I have an ip406 version 2 at one end ip403 at other with a 100mb laser link with a vcm20 module a both ends

The problem i get is sometimes you can call an extension the phone ring but there is no speech path but i can call external via the link test ok .If you call the same extension from another extension on the same switch all ok so i moved the extension  that could not hear to a diffrent port the made a call back across the link to the same extension again worked ok

I have replaced the laser just in case i dont think its a vcm module problem cos i can call out external via the link no probs

Any Ideas

I suspect one of your DSP chips on your VCM modules is playing up have you tried changing the VCMs yet

With the SysMon and Advanced monitoring enabled you can see if VCMs are ok.

Start SysMon, goto Trace Options -> System and select Development tracing.
Then goto Status and select Voice Compression.
A new window opens were you can monitor the VCM chanels.
No call no data of course.
Both columns Sends and Recvs should have data during a call, if not then there is no UDP data received or the VCM is faulty.
The UDP data can also be checked with SysMon.

nice info thanks