CCM and NAT

[oj88]

Please refer to the attached drawing.

We are tasked to perform a demo of CCM on a live network. As much as possible, we don't want to change anything on the customer's existing data network just yet so it is imperative that we only "attach" the voice network over the existing one.

My question would be, what are the special tasks that's needed to be done on the voice gateway (R3) for the following to work:

1. IP phone 501 and 502 should be able to call each other

2. Both IP phones must be able to make and receive calls from the PBX.

The customer is willing to give static IP addresses in the 192.168.1.x and 192.168.2.x networks but NOT change anything on their existing routers (R1 & R2).

I have deployed a number of IP tel scenarios but they don't involve passing voice through NAT.

Also, I've read something about the command "ip nat service ...". Is it relevant in this scenario?

TIA!

[gpulos]

you shouldn't need NAT here.

if your 192.168.50.x/24 subnet steps on parts of their network, which it doesn't in the diagram you provided, then use another class such as 172.16.1.x/24 or 10.1.1.x/24. (this would be the easiest configuration for placing into their network; they would have to add routes to their network for a different class)

1) connect your ccm server and ip phone1 to switch1 (192.168.50.x/24) subnet.

2) connect your ip phone2 to switch2 (192.168.2.x./24) subnet.

3) obtain ip addresses from the respective subnets to the server and two ip phones.

4) statically configure the phones with ip, subnetMask, router and TFTP server. (tftp could be your ccm server)

5) configure call manager for the phones and gateway and dial plan. (gateway probably h323; may be able to use MGCP)

6) configure gateway with POTS dialpeers(unless pbx supports IP, then you may be able to use a VoIP dialPeer), for calls to the PBX via T1/FXO

7) configure PBX dial plan for DN 501 & 502 via the T1/FXO to voip network

8) assure ip routing is possible between the ccm server and ip phones with ping or by other means

9) test calls

NOTES:

* QoS will not be possible if they will not change any router/switch configuration.