[cisco-voip] Design suggestions

[Curt Shaffer]

All,

I am in the planning phase of a multi site system for voice. The two choices
I was looking at are 1. Asterisk and 2. Cisco. I am comfortable with
Asterisk and like a lot of the features but there are some things that I
like better about the Cisco solution. Each office (only three planned with
some home users as well) will have no more than 20 users. The goal is to cut
costs on dedicated lines. Here is the plan, please let me know if this is
feasible.

2801router at each office interconnected to the main office via VPN.
SIP trunk from remote offices back to main office
2 PRI lines at the main office
2 POTs lines at each remote office for backup and 911 access.

We would like for all calls to route over the SIP trunk from the remote
office to the main office and out to the PSTN there and from a number on the
PRI in the main office routed to the remote offices. In the event of an
Internet outage anywhere in the mix, we would like the failover to go out of
the POTS lines and we can call forward to the POTS for inbound. We are aware
that our concurrent calls at the remote office at this time would be limited
to 2 but at least things could still function. We also had the idea of
adding a SIP provider for each location in case the lost connection is with
the main office only. This way they could route via POTS or to the SIP
provider.

My questions are the following:

Is this feasible with Cisco routers and if so can I use Call Manger Express
on the routers to do this or will I need to do a full Call Manger install.

In either case. Can I use an external system such as Asterisk for Voicemail,
Conferences, etc with both CME and Call Manager?

Thanks for the suggestions.

Curt
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