Distributed deployment migration to Clustering over the WAN

Question

Hello All,
The existing deployment is distributed with different CM versions running on each of them i.e 6.1.3(2 Clusters), 7.1.5(1 Cluster) and 8.6(1Cluster). It has been requested to get these clusters migrated to version 10.x in either centralized or CoW deployment. However, some of the clusters have around 1700 and 2600 phones in the cluster and because of SRST gateway sizing limitation, we have to approach CoW deployment. We have CUCM, UCxn(new dep) and MediaSense(new dep) applications. There are currently around 8000 users registered to the CM but considering future expansion, it must be proposed for about 20K users. My questions are :
1) With UCSS in place, how does the Migration work for different versions? I am not aware of the existing used and unused DLU's in 6.1.3 version and methinks it has to be taken into account to convert into type of Users for UCL.
2) Without UCSS in place, how tricky does the migration become?
2) There are 8 sites, with 5 sites having at least 2000 users. Considering future expansion for 20K users, how do we position the number of subscribers in each site for CoW deployment? I understand there are BHCA and bandwidth calculations involved, 1PuB, 1 SuB, 1 TFTP/MOH servr in DC, 1 SUB each in other sites and an additional TFTP server in one of the sites?
Appreciate the help!
Q

Answer 1

Q,
The first place to start is to look at the cucm 10.X SRND. Look in detail at capacity planning and call processing.
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab10/collab10/callpros.html
Each cucm 10.X node can support a total of 10,000 users/devices using the 10,000 OVA template. The cluster can support a total of 40,000 users/devices. I am sure this will meet your present and future needs.
Next you need to look at sizing. The cisco virtualization wiki details what to do in this case..
http://docwiki.cisco.com/wiki/Unified_Communications_in_a_Virtualized_Environment#How_to_Design
Download the sizing tool from here
http://tools.cisco.com/cucst/faces/landing.jsp
Then use the placement tool to determine how you should place your VMs..
You  may want to send your final output to Cisco to verify your design. Virtualization is not so straight forward as bare metal server deployments, so you need to design carefully.
From what you have said, looking at about 20,000 users I would suggest the following
1. 4 cucm subscribers--each deployed with 5,000 users/devices. This setup will allow for one to one backup
2. 2 dedicated tftp/moh servers
3. 1 publisher
That gives you a total of 7 virtual machines. This means that you will need two UCS servers-C series servers
Although the sizing tool suggested 12 VMs with six subscribers.. (this means that you will need three UCS servers-C series)
For SRST, depending on how critical the phone system is you either do the ff
1. Use the voice gateway at the site to support SRST. This obviously is limited to the capacity of the voice gateway at the site
2. Re-use the existing cucm servers and deploy them at the local site just for SRST. This will ensure you can support the whole site in SRST
It is advisable to place your UCS servers in your DC. If you have a single DC, then you place one there and then the other at another site (Hq)