Can I have Call Manager setup for Branch offices via ISDN line ?

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Apr 22nd, 2009
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I have Head Office (HO) and 50 Branch offices, at the moment Call manager is configured only in HO, but I want to integrate the branch offices and want to deploy the cisco IP phones on each site. I know to integrate them via Data network (MPLS, DSL or other internet connection), but I have no idea how to connect all the branch offices through ISDN line, as we have ISDN calls free and I want all 50 sites phone communicate and get registered to the Call Manager. I want to setup this like its been setup via Data Network!

Reply will be appreciated.


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CHRIS CHARLEBOIS Wed, 04/22/2009 - 07:11
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I don't know if I understand your network requirements here... You have 50 branch offices, with data connections back to the HO via a number of different technologies (including internet VPNs, I assume). You want to deploy IP Phones with a central CallManager and use local ISDN lines for the voice traffic. Is that correct? Are these ISDN lines point-to-point (Branch-to-HO) via frame-relay or leased line?

It is theorically possible to deploy IP Phones remotely using distributed voice gateways, but I have serious concerns about the quality of service on the data network. Sure, voice traffic would only use the local ISDN lines, but the call control traffic would need to go over those internet VPNs and that is just begging for trouble. Since you will need voice gateways at the branch offices, and would be wise to deploy SRST even if the data lines were direct, I would recommend using distributed CCME running on the local router/voice gateway. The administration will probably be more work, but it will be a much more reliable system.

wahidayat007 Wed, 04/22/2009 - 08:34
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Thanks for your reply,I know how to setup the regions and stuff for the branch offices through Data network and all SRST stuff, but now I have ISDN line in all my branch offices, we use this ISDN for visa terminal machine, but I want to use the same ISDN for voice communication. I want to know step by step solution. e.g




we do not want to use DSL (Internet line) for voice communication from the branch sites to the HO. In the above figure, I want the remote IP-Phones to be registerd through the ISDN line? All the calls to the CM should be via ISDN? For me it is a bit confusing !


CHRIS CHARLEBOIS Wed, 04/22/2009 - 09:10
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The question is what kind of ISDN network are you referring to. ISDN is just the access technology. You can have ISDN data connections (via Frame-relay, MPLS, or leased line) or ISDN voice connections (aka PSTN). If the ISDN line was brought in for Visa transactions, I'm pretty sure it's a voice ISDN connected to the PSTN. Which means you can't use it for call control or phone registration. If you try to run call control over VPN tunnels, you will probably run into issues with the phones acting sluggish, call dropped or staying up after the call is completed, and problems will transfers and calls on hold.

wahidayat007 Thu, 04/23/2009 - 07:40
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Thanks for you reply.

we use ISDN for visa terminal transaction and for voice! ISDN voice connections (aka PSTN). You are correct, but I was not comfortable setting up the remote phones through ISDN and all registration with the HO call manager. Assume we have only ISDN connection from the HO to all 50 remote branch office and I want to setup the remote IP phones to be registered with the HO call Manager. Is it possible or is there any documentations to explain this in more detail.

Really appreciated your help!


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