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Community Member


I currently have two sites on a LAN that are running VoIP off a cluster of CCM, which includes Pub, Sub, Unity, and CER. A total of about 180 phones exist. I have an additional 3 individual remote sites and another 3 sites that are cluster together at another campus. Considering deploying Voice, I am guessing that an SRST Router would be good at each remote site for fialover of the wan link. What is the best solution for the other campus where the 3 sites are clustered? Could I add another CCM cluster? Can the additional cluster interact with the existing cluster? Can they be confured to be primary at their sites and secondary for the other sites.

Thanks in advance.



1) YES, an SRST router at each remote site is an excellent idea in case the WAN link to the phones CCM cluster fails.

2) YES, the clusters can interact with each other. since you would have three clusters now, it would be beneficial to look into creating a gatekeeper to handle the CAC, along with many other features, between the clusters.

(a gatekeeper could greatly increase efficiency in administration of the dial plan)

3) how many phones at the other campus with 3 sites that you want to go voip? using another cluster will be fine. you will not be able to have phones between sites depend on the other clusters as secondary. a secondary CCM server for a phone must belong to the same cluster as the primary for that phone.

Community Member


Thanks for the response, this is very helpful with sketching the design.

I would probably have around 500 phones at the campus that has 3 sites clustered together. Basically 5 DID ranges of 100 extensions per.

With that many DID ranges, what is the ideal solution for PRIs and Voice Gateways. How many PRI would be necessary to handle all the DIDs? I know that it would depend on usage and peak times, but generally speaking. I would need a voice card for every PRI, what router/gatewway supports the amount of cards that I would need.

Thanks again.

VIP Purple


Yes, you would definitely want a SRST capable gateway at each location for local PSTN access and call processing failover. My preference for the remote campus would be to make it part of the same cluster for ease of administration. If it's the same size as the current campus, a single cluster will easily handle the number of phones with plenty of room for growth. This is assuming that your connectivity to this site allows for acceptable latency, jitter, and delay. You could add another cluster at the remote site and use an Intercluster Trunk (ICT) for communication between the 2. This configuration is not used for primary/secondary coverage as you describe. For this type of failover, you could deploy additional subscribers at each location which would all be part of the same cluster. Take a look at the Callmanager SRND for recommendations and limitations for clustering over the WAN as well as other deployment models.


Hope this helps. If so, please rate the post.


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