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External calls to MCU

Hi all

This is my infra

- Endpoints (Tandberg / Cisco) external to my network not registered in any VCS

- VCS-Expressway (8.1.1) with public IP address

- VCS-Control (8.1.1)

- MCU Codian MSE 8510 (4.4)

- Registered Internal Endpoints in the VCS control.

- Domains published in internal and external DNS.

My problem is that when I mark IDROOMMCU@domain from an external endpoint (not registered in VCS Expressway) (H323 call) the call is established but no audio or video endpoint is received in the endpoint. However the MCU receives audio and video from de endpoint.

If instead of calling a room of the MCU, i call to an endpoint registered with VCS Control, the call is stable and smooth media streaming (audio and video) is correct.

Now, if the external endpoint is registered in the VCS Expressway and call to the same MCU room as before, the call is set perfectly with audio and video in both directions.

More Details:

The rooms of the MCU are registered in the VCS Control

The MCU does not have public IP address.


Unregistered external EndPoint -> MCU room. not Ok

Unregistered external EndPoint -> Registered Endpoint in VCS-C. Ok

EndPoint registered in VCS-E -> MCU room. Ok.

Any idea where can be the problem?

Thank you very much.



It would be interesting to

It would be interesting to know what kind of call protocols are used.


If media does not flow its most likely a firewall issue, either that simply some ports or udp are blocked in one direction.

Or what also often happens, that there is some ALG, NAT Helper, inspection,. ... running on the firewall which causes issues.



If you register a Tandberg/Cisco MXP or TC endpoint with the VCS in a default setup it would use assent,

which uses different ports and also some NAT and firewall traversal mechanisms.


Is it ALL external not registered calls, or only of this specific endpoint.

It might also be the firewall / nat router of the remote site.

Please remember to rate helpful responses and identify

Good morning. First, thanks

Good morning. First, thanks for your answer.

The protocol which is used is H.323 (for SIP,  i need a register server).

I've tested the calls with Tandberg endpoints (software updated to 9.3.1) and some softphones (Polycom Real Presence, Ekiga) in differents networks without firewall (the endpoint is directly connected to the router without NAT or filtered ports)

My internal architecture is this:


Internet - VCS Expressway - VCS Control - MCU/Endpoint. (No firewalls between all elements)

And, if the problem is a firewall. Why does the call work from internet to and endpoint and not to the MCU?