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IPT Design Question


im trying to get the best design for my customer based on as usual a tight budget.

i have two sites that we propose to replace thier existing legacy pbx systems. both sites are interconnected by a T1 frame circut. initially, i had a Pub and Sub at the head office and a 2851 at the other location with SRST. They have currently a 2801 rtr but when we go IPT to that location they would require 65 users at least for srst.

what im looking at is the remote failover model instead and having the PUB and one SUB at the head office end, then one Sub at the other location (They register with that server) and ill leave the 2801 intact.

Now, we have one unity connection system that will be located at head office. voicemail is not critical, however the auto attendant is, which will be configured on the VM server. Now the question is if the WAN fails, then my AA will be lost correct? now how can i still route the calls to the location that does not have the VM locally?. can i simply do MGCP on the gateway and failover to h323 during WAN and for my voiceports do a plar to say the operator phone?.

say as well, i didnt want to use MGCP for some reason and wanted h323 instead, how would i be able to route to the AA when the WAN is up and still route to the local operator when the WAN is down?

sorry its late and im babbling.(its 2:45am over here)

any guidance would be greatly appreciated


Community Member

Re: IPT Design Question

Sorry, not a direct reply to your question, but I thought that I would just raise a point on what you have said.

You mentioned that these two site are connected by a t1 Frame Circuit, which will be 1.5Mbps Now you are looking at putting a sub on the remote site to the pub. Just in case you were unaware, Cisco say that intra-cluster communications (ICCS) between CCMs requires a minimum of 1.544 Mbps. That is just database transfer information and other system bits and pieces. Then, on top of that, you have to add on your phone calls and perhaps operator console traffic.

So, based upon the WAN link being only a T1, I do not think this solution will do the trick. Sorry.


Re: IPT Design Question


actually now reading in depth the srnd for 5.x and saw it. 900k + 644k. ill run into some serious issues there.

thanks again. next time ill read the manual :)

Community Member

Re: IPT Design Question

No worries

Glad to help! Just in case you are wondering, the bandwisth requirements for ICCS are the same for CUCM 6.x for whenever your client decides to upgrade!


Re: IPT Design Question

thanks again. lets hope they go with the solution first :)

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