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Community Member

Call manager implementation

Hi experts,

I have two locations.At each side we are having 3640 wan edge routers with wan link speed of 2mb.We need to implement 700 ip phones at one side and 400 ip phones at other side.Need of max 20 simultaneaous call should travel across wan.Question is could i put two call managers server in the same cluster in these two different location.Or do i need more than 2 call managers,can we use 2950 switches for ip phone connectivity.Can a single voice vlan can handle all these phones.

Thanks in advance



Re: Call manager implementation

Hi Tom,

We are using aproximatly the same Design:

2MB WAN Connection. 300IP-Phone on each loc.

1CCM PUB + 1CCM SUB at each location. Using G.729 Codec (with overhead...etc approx 18 to 25 Calls). I think you?d better use 2CCM for each location, in case you encounter a WAN or CCM failure. Use a CCM-trunk to forward Calls over the WAN.

Hope this helps,


Community Member

Re: Call manager implementation

Thanks so much Zin.

I am very new to voip.So could i ask some more detail for this scenario??


Re: Call manager implementation

Like what exactly? Products versions?

Community Member

Re: Call manager implementation

Is it one voice vlan is sufficient for all the phones?

which is better FXO or Bri for 6 pstn calls while the wan outage

Do i need to enable Srst in both side or one side??

Community Member

Re: Call manager implementation

Hi Tom ! Your set up is quit simple 700 phones at one location and 400 phones at the other. With this amount of phones a two-server cluster would work for you, the amount of phones a server can support is depend on the server hardware if you have MCS-7845 model with dual CPUs, a single MCS-7845 can support up to 7500 phones. In your case you can put a Publisher at one location and a Subscriber at the other location and have the phones at each location register to their local CCM server and one server can be the back for the other, if you do that then you wouldn't have to worry about SRST.

In regard to your vlan question. With the amount of phones that you have I recommend that you configure multiple vlans to support both voice and data. Cisco does not recommend voice and data in the same vlan.

I have a 6509 at the core and 3560 switches at the access layer. If you plan to 2950 at the access layer that would work as well and make sure you have QoS enable throughout your network.

You can use FXO or BRI either one would work but with the amount of phones that you have I think you'll need at least a PRI.

Hope that helps !!


Re: Call manager implementation

Hie Tom,

You can palce servers in a cluster across WAN but just check the delay in your network. The delay should not exceed 40 ms. Practcally it should be much less than this. I am concerned just because you are using one 2 MB link for data and voice.

Design suggested by Zin is a lso a good option. Where you will have two separate clusters at each site which will be connected by a CCM trunk. Of course I will not believe in having only one server at each location. It will be good to have at leats two in each cluster (1P + 1S). This will in turn increase the cost.

I will seconf Danny's suggestion of having multiple voice VLANs. Its not good idea to have 1100 plus phones in one single VLAN especially when they will be spread across WAN.

Regarding switches, are 2950 PoE capable. I guess not. It will be a better idea to go for PoE switches. Or are you going to use power cubes for all the phones


Re: Call manager implementation

Hi again,

forgot to say that i calculated the 18 to 25 Calls for 600KB. As we are using the rest of our 2MB (1400kb) for Data(see Configuring location on CCM). You also need to configure QoS.

Using power cube for all Phones would be a nightmare for you as Administrator. You d better look for PoE.


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