IP dialling to a MCU (codian) registered to a gatekeeper (VCS)

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Jan 31st, 2012
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So I have been racking my brain trying to figure out an issue that I am having.

I am trying to figure out why I cannot dial to the IP address of my codian bridge when it is registered via H.323 to my VCS controller.

I can dial to any endpoint registered via H.323, but not the bridge.

Currently, the codian bridge is registered as a MCU (standard). When I disable the h.323 registeration, I can dial into the codian without issue (dials into an autoattendant).

Anyone happen to have any ideas why this is so?

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Jonathan Schulenberg Tue, 01/31/2012 - 08:43
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I'm pretty sure this is by design. If the bridge is registered to a gatekeeper (VCS) it will send an admission request (ARQ) for any H225 call setup request. If the call did not cross VCS then this will probably be rejected.

Out of curiosity, why wouldn't you wan the call to cross VCS?

Darren Lapierre Tue, 01/31/2012 - 08:51
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Yeah, that has been my assumption as well. But why would an MXP endpoint (1700mxp) allow the call to come in when the bridge would not?

It is more around having users dial into the bridge from legacy endpoints that do not support URL dialing (old polycom 512's, as an example), that are not registered to one of the gatekeepers.

my preference is to never let any call to not pass the VCSC (or VCSE) before coming to the bridge. I was merely curious as to why this is, and to see if anyone has possibly found a work around.

The only possible work around I can perceive via licensing (video firewall option on the bridge). Thus it would lead me to believe even moreso that this is done by design.

Jonathan Schulenberg Tue, 01/31/2012 - 09:20
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Well the MCU has an entirely different software code base than the endpoint since it was acquired from Codian. I cannot find an xconfiguration command for the MXPs that would allow/deny non-routed calls; however, someone else may know of a way to control that behavior on the endpoint.

As for the Polycom and URL dialing: The MCU should also register E164 IDs to VCS for each conference based on the Prefix for MCU Registration + conference ID values. This should be dialable by the legacy endpoints without the need for a domain suffex.

Jens Didriksen Tue, 01/31/2012 - 14:16
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Just to give you another option for the old Polycom end-point; you could implement a pre-search transform on the

VCS-E (assuming PLCM is external) which will allow these to use their proprietary dialing method of





\[email protected]

will transform this to [email protected].

As an additional option, you could also set the "Fallback Alias" to point to an Auto Attendant etc, which will allow users to dial the IP address of the VCS-E and be sent to an address of your choice.

We don't allow IP address dialling at all as a large number of our end-points are on DHCP, and as we'll eventually have to implement IPv6, dialling one of those addresses becomes a bit more complex, to put it mildly.

If these older end-points are internal, then registering the Alias with prefix, as Jonathan pointed out, should work nicely.

cheers jens

gustavogomez Tue, 01/31/2012 - 15:37
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I could suggest to register the MCU in SIP only, so any endpoint registered to the VCSs could reach the MCU, it doen't matter if the call comes in H.323 or SIP (Transcoding must to be ON in VCS). That way a legacy, or not in VCS endpoint, could dial directly to the MCU via its IP. 

Hope this workaroud work.

Cheers.  Gustavo

Garvan Long Tue, 01/31/2012 - 17:15
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Your MCU should respond to the calling systems setup message indicating it should route the call via your GK and you should see a call attempt in the logs on the VCS. As the VCS is in routed mode you need to ensure the s IP of the VCS is permitted in any firewall rules

Calls in the other direction to the IP of  the Polycoms will be impacted by your call to unknow IP address and your search rules for AnyIPaddress on your VSC


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