Branch Office CME design Verification

[Abayomi Smith]

Hi All,

Please refer to the attached network diagram.

I need to verify this can be implemented and would work.

We have a branch office moving to a new location and they intend to keep their existing CME (for business reasons),  provided by their local service provider with ISDN line for calls to the PSTN. This is managed by the service provider and we have no access to it. However we would like to grant them connectivity to the existing corporate voice network via an IP VPN connection, which shall be put in place soon. This will enable  the branch make site to site calls within the corporate network

With a SIP trunk between the internal and external CME, I intend to make all the phones register with the Call Manager, however on the call manager , set a route pattern for calls going out to the PSTN from this branch back to the internal CME and this will then be matched by a SIP dial peer  directing the call to the external CME out to the PSTN.

My worry is with the delay  that might be introduced when making a PSTN call as the internal CME has to first contact the call manager in order to know where to send the call.

So my questions are as follows,

1. Is this solution feasible especially in terms of delay? If not,

2. Are there any other ways to achieve the same scenario

Thanks,

Yomi

[George Thomas · Accepted solution]

Are the phones at the branch office going to register to the Internal CME? If so, all configuration for outbound dialing will be done on the Internal CME, not on UCM. ie. dial-peer on the Internal CME for outbound dialing. For phone connectivity back to UCM, you will have a SIP trunk between UCM and internal CME and that is perfectly acceptable. You "might" see some quality degradation but that is to be expected from Internet based WAN connectivity. If your RTT delay is greater than 150ms, then you might see some quality issues.

[Abayomi Smith]

Thanks George,

I was thinking the phone would register with UCM before I read your comments but its actually easier for the phones to register with the Internal CME and there will be sip trunks between the internal CME and UCM and also between the internal and external CME's.

Many thanks for your comments George, wasn't thinking in that direction before.

Cheers,

Yomi