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On Tue, 2007-09-11 at 16:21 -0400, Brian Bartholomew wrote:

> If you have a building full of the UF-recommended brand of VOIP phones
> on the same LAN, can they talk to each other without involving any
> additional central points of failure?  I'm not asking for conference
> calls, voicemail, recordings with beeps, queues, forwarding, or
> whatever.  Just using the last quad of the IP as an extension number.

The server piece in a Cisco IP phone solution is a 'Call Manager' which
would be the central point of failure you refer to. After the Call
Manager sets up a call (looks up the number you dialed, cross refs with
it's IP, rings the phone, then passes it off), the actual voice
connection is directly between the two phones (if within the same phone
system) or between your phone and the gateway if one end crosses the
telco. If the Call Manager takes a dive during a call, the call should
not be interrupted. 

The bad news (since this is the Linux list :) is that the Call Manager
runs on Windows (in the current version, next version is Linux). The
good news is that Cisco recommends (and I understand CNS has
implemented) multiple redundant Call Managers, so that the system can
tolerate failures of individual pieces. 

I'm also fairly certain that the CNS VoIP implementation is using SCCP
('Cisco Skinny'), so the SIP dial-by-IP functionality isn't present. 

All the same goes for the Health Science Center VoIP system, of which
I'm much more familiar. I will say that in the 6 or so years we've been
running the Cisco phone system in the HSC, it has been extremely
reliable, give or take a few times Bellsouth has screwed up a PRI (which
actually isn't much of a problem as long as there is capacity on
non-screwed-up PRIs). Yes, parts have died, but service outages have
been prevented by the built in redundancy. 

-avi