The sites are connected by a gigabit link (extended LAN), with rtd less than 2 ms. There will not be any QoS markings.

Thanks

For the same query, how can we achieve ip phone service redundancy?

You need to create multiple Device Pools and Media Resource Group lists. The Device Pools use the corresponding MRGL. The first MRGL has the first subscriber services listed first and the other subscriber's services listed second. For the other MRGL, you define it vice versa.

You could, for example, differentiate between the HQ and the branch offices. Hence, you could point the branch office Device Pools to the 2nd MRGL (assuming that the total of your branch office phones is somewhat equal to the number of phones in the HQ.

--bas

Let me clearify myself a bit, I was talking about two subscribers, but essentially any two CUCM machines performing call processing will do.

In terms of failover, the planned and unplanned failover behaviour is described here (for CUCM 5): http://www.cisco.com/en/US/docs/voice_ip_comm/uc_system/UC5.0.1/ipt_system_arch/COL_FFR.html#wp1100434

--bas

Cisco recommend using a server load balancing appliance (or IOS license for Server Load Balancing on Catalyst 6500) to make IP phone services resilient.

This is not really realistic for smaller customers so I tend to configure the DNS servers used by the phones to use round robin to give out the addresses of all CCM servers in the cluster and set the phone service URL to use a name rather than IP address. Hopefully an example will make this clear.

ip dns server

ip domain round-robin

ip domain name example.net

ip host cucm.example.net 10.180.44.11 10.180.44.139 10.180.52.11

This enables DNS on a router and responds to queries for cucm.example.net (the name used in the services URL) with the following addresses in turn 10.180.44.11 10.180.44.139 10.180.52.11

Obviously if you have a server based DNS system available you can configure round robin on that instead of using IOS.

With DNS, what is the DNS timeout, in case the one of the CUCM server goes down?

Can we control the DNS timeout on IOS / DNS Server?

Thanks