Mitel 3300 VPN No Audio

We have a Mitel ICP 3300 at Head Office. All handsets are 5330.

Branch Office #1 has a Site-to-Site VPN to Head Office
Branch Office #2 has a Site-to-Site VPN to Head Office.

The issue I am having, is if a user from Branch #1 calls a user at Branch #2 the phone will ring, when they pickup it is dead air. This is the same in both directions.

Here is what I'm wondering. Does the Handset in Branch #1 talk directly to the handset in Branch #2 or does everything pass through the ICP? Both Branches DO NOT have a route to each other, just to the subnet at Head Office.

I thought I read somewhere that when you make a call the ICP initiates then hands off the communication directly between the handsets. Which would explain the problem.

Anyone able to confirm my thoughts or offer some insight?
cvadminAsked:
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JRSCGIConnect With a Mentor Commented:
You are exactly correct - and this is true of most all IP phone systems.  Once the call is established, the ICP is not part of the communications link until a call control function is selected (such as transfer, conference, etc.)  The actual voice packets travel directly across the IP network between the two endpoints.  Many folks set up a single VLAN for all voice traffice to ensure that it will route instead of creating static routes.
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davdjevansCommented:
I agree, IP phones communicate directly with each other once the call is established.
The call setup tells each phone what the other's IP address is and which port they are listening on.


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JRSCGICommented:
One other thing - with VPNs you also need to check firewall settings.  I believe the Mitel uses a specific UDP port range for voice packets - a VPN firewall must not block the necessary range.
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