CUCM 6.1 - how do CMG's balance IP phone requests?

[andy_vvc2]

Hi all,

We have three CUCM servers, 1x Pub and 2x Subs.  Both subs are identified in the 'CMG' (CallManager Group).  The DP for this site is linked to the CMG. All the site phones are in the DP.

Within the CMG, how exactly does CUCM loadbalance the IP phones ?

We will be powering one server off via the OS Admin > version > shutdown GUI.  We need to replace a failed hard drive in the server (RAID1+) i think - two logical drives, each with 2 disks where the second mirrors the first.

I'm curious to understand how CUCM will react when we power one of the two subscribers off.  In theory any IP phones that try to make a call after this will automatically use the second subscriber in the CMG.  But how does CUCM loadbalance/regulate which member of a CMG an IP phone contacts?  Is there a Service setting such as round robin ??   Also, am i correct in assuming that because the IP phones are registered currently, they wont de-register or blip when we power a subscriber off?  (I expect any active calls might drop though)

Rgds

[Rob Huffman · Accepted solution]

Hi Andy,

The phones will always try to register with the first member of the CCM Group

and if it is unavailable they try the second member and finally the third.

So if your CCM Group looks like

Sub 1

Sub 2

Pub

The phones that reference this CCM Group (via their Device Pool settings)

will try Sub 1 first and if it is unavailable they try Sub 2 and if it is unavailable they try

Pub. So if in our example, it is Sub 1 that needs to be shut down the phones will all

fail over to Sub 2 when you shut down Sub 1. You can also re-order the CCM Group

ahead of time to look like;

Sub 2

Sub 1

Pub

And bounce the phones so that they are all registered to Sub 2 ahead of time.This way

they won't take a hit. Active calls will remain up until call completion in either scenario

Cheers!

Rob

[andy_vvc2]

Thanks Rob.  Concise and quick response as always!  Much appreciated!

We have the disk-swop instructions from Cisco TAC so hopefully (if that goes smoothly out of hours) the re-register of the phones wont matter. Infact, it will be a good test of the failover capabilities of the CM Group