We have UC Manager 7.1(3) running on a publisher and subscriber that is serving as the central voip to five (soon to be six) offices. At what point does cisco recommend an additional subscriber be added to a cluster for call processing and load balancing? I have been tearing through cisco's website and I am not finding this info. I am sure it is there, just buried!
Any feedback and links to the doc would be a huge help.
If you have access to the sizing tool you can try running your desired scenario and see what it recommends.
If you start with smalls scenarios and start increasing the endpoints don't be surprised that at some point there is a big jump in the amount of servers
This tool also follows the best practices and depending on the version you choose at some point it will tell you the same advise as Hailey and the SRND
+1000 phones we recommend a separate PUB, a separate SUB and at least 1:1 redundancy (2 SUBs)
AFAIK it follows the same numbers as the SRND so if you use 8.X, instead of 1000 phones, it would be 1250 phones.
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The answer you are looking for depends on a few things. The most basic are:
1) What hardware are you running? This will determine the maximum number of phones that can be registered to any one server.
2) The answer to the first question comes into play as you total up how many phones you need to accommodate throughout the entire cluster. In addition, you want to provide adequate redundancy as well. Right now, you have a 1:1 model (Sub should be primary call processing agent but can failover to Publisher). As your cluster expands, you may need to consider a 2:1 model (2 active Subs, 1 backup) or continue with a 1:1 model.
3) If your cluster has 1000+ phones, you need to look into going with a Pub, 2 Subs, and a dedicated TFTP server.
Without getting too far into the weeds, take a look here first: http://www.cisco.com/en/US/docs/voice_ip_comm/cust_contact/contact_center/ipcc_enterprise/srnd/7x/c7ccmsrv.pdf
Then, if you have additional questions - please ask!
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