VCS architecture, components, call control and integration with CUCM

• VCS control  – Providing call control
• VCS Expressway – VCS Expressway is an appliance that works in conjunction with the VCS Control to provide firewall traversal using H.460.18, Assent, or SIP protocols. It supports Traversal Using Relay NAT (TURN) servers. VCS Expressway also provides endpoint registration and signal and media interworking for SIP and H.323 video devices across the public Internet.

Enough said, back to VCS and its splendor. The VCS is, in essence, a gatekeeper in terms of call control. It allows endpoint registration, call routing,monitoring and maintaining connections. It registers MCU for video conferencing and SIP trunks to CUCM for calls to CUCM endpoints.  Lets have a look at endpoint registration for a moment. The table below shows the support for the various video capable endpoints on either CUCM or VCS.

Either way, VCS was designed and will support both SIP and H323.  

So the only thing that you will need to do is create the SIP trunk in such a way that it points to your VCS server, or servers if you have your VCS’s clustered. Then create a route pattern with a Route List and Groups all very stock standard stuff. Remember it is considered best practice to use a dedicated SIP profile for this SIP trunk, so when tweaking it, this will not interfere with existing trunks. The other thing you will need to take into consideration is how you will point to your VCS servers. If you are going to use IP addresses as the destination address in your CUCM trunk configuration, you will need to apply, what VCS calls “transforms” to bring these IP addresses back to domain names. For example if you use 192.168.12.1 as the destination of your SIP trunk, and all your endpoints are registered as XXX@acme.com.au  your INVITES will reach VCS as XXX@192.168.12.1 and the call will fail.

<Normalization scripts, addition needed> 


So what about making calls from a VCS registered endpoint back to CUCM? Remember I mentioned the VCS is mostly an enhance Gatekeeper? Well guess what, you need zones (Zones are VCS speak for what CUCM calls trunks, I guess if you consider VCS to be a Gatekeeper, the term “zone” is still pretty accurate). So the first thing to configure on the VCS is a neighbor zone (think of it like a gateway, very much the same way as CUCM uses a GW in a route pattern).

The screen shot below shows a default zone, a CUCM zone and a zone to a VCS Express Way.

  For example:

Figure 3a – VCS Neighbor zone configuration

In the zone configuration, figure 3, put in the IP addresses of the CUCM servers that you will use for call routing. In my example I have used just two CUCMs. Please note that there is no authentication used in this zone.

So now lets add a pattern that uses the zone, as added in figure 3, to route calls. I am not worry about the priority of the patterns as there is no overlap in the dial plan anyway. As you can see these patterns are handed over to a zone called “CUCM”, which is the zone that was configured as per figure 3.