Any problems with demoting a CallManager from Publisher to Subscriber?

[8dgoswick]

I have two Callmanagers, both are publishers. One is our main one and one is at another location which was our initial test site. We want to move those 20 users from the test site to the main Callmanager (centralized call-processing) and make their Callmanager a subscriber for redundancy. Their Callmanager currently has a DT-24+ card for local PSTN access. Can we still use the DT-24+ card if we rebuild the Callmanager as a subscriber, and do you have any recomendations as to the best way to do accomplish everything I have said here?

[dgoodwin]

Couple comments here:

1) You can't demote or promote. End of story. So the best advice is to wipe the machine you want to make a subscriber by starting with Disc 1 of the CallManager CDs and start from scratch. When you get to the CallManager installation, make it a subscriber to the other CallManager

2) You can't cluster over the WAN. To be more specific, clustering is not supported over a WAN network. Chances are that if you have a large amount of bandwidth (e.g. 10Mbps or better, maybe even less) that you will probably be able to get it to work, and you may not even have problems in this regard, but know that this setup is not being blessed by Cisco at this point due to lack of full regression testing and specific requirements being put in place on exact bandwidth, delay requirements, outage times, etc. all for a full mesh scenario.

3) Yes, you can still use the DT-24+ card just the same. You can force local calls at the remote site to go through their DT-24+ gateway by using Calling Search Spaces and Partitions. See this URL for an exaplantion of those topics:

http://www.cisco.com/warp/public/788/AVVID/part_css_tn.html

[8dgoswick]

Ok, so clustering over a WAN is not supported. What kind of information is being sent between each server? To give you an idea, we will have only about 100 phones and 6 PSTN gateways spread over the WAN. Each of the 6 locations can communicate to any other location at about T1 speed. Thoughts?

[dgoodwin]

There's no guidance on how big of an installation, how many devices, how much call volume, etc. in order to support clustering over the WAN. It's simply not officially supported by Cisco currently.

As far as what kind of information is being sent between the CallManagers, there is a variety of information. Most of it is what is called ICCS (Intra Cluster Communications Signaling) which actually performs a variety of tasks. For example, the Cisco Database Layer Monitor service on each subscriber monitors and facilitates access to the publisher SQL database, also all the CDR records of calls handled on the subscriber CMs are written to the publisher database. The CMs within the cluster are contstantly exchanging information about things such as gateway status, shared line information, and the list goes on and on. And don't forget about the Microsoft SQL Server publication/subscription data.