[Asterisk-Users] hierarchical VoIP system

[Joao Pereira]

Hello
Im managing a WAN with a lot of Universities. Some of them already 
installed a VoIP solution based on SER (to manage SIP clients) and 
Asterisk (for services and PSTN GW). The DNS routing provided by SER is 
working perfectly, but we want to start routing all calls thru IP 
transparently.
We want our legacy PBXs (that are connected to Asterisk) to forward all 
calls to IP. The idea is to forward all calls to a central VoIP server, 
that has all the numbers that already are VoIP enabled, and then:
- if the called number is VoIP enabled, he routes the call to that Univ. 
VoIP server
- if the called number isnt in the list, the call goes back to the PBX 
and a PSTN call is dialed

This way, ppl starts using the VoIP infrastructure, without even knowing 
what VoIP means, and the telecom bill starts decreasing.

I know thats a statical and hierarchical structure and we dont want 
that, but is a good solution for this migration phase, where a lot of 
places are still using TDM systems.

Now, the top of the hierarchy should be an Asterisk or SER? I dont know 
which of the systems is the best choice for the job. Does someone has an 
idea of what should we use?

Thanks
Joao Pereira
www.fccn.pt