the connections will be, so i am wondering which protocol works better to configure it in the Gw to work with:
1.PRI E1 (to psnt)
2.E1 Qsig (to pbx)
3.sip trunk (service provider)
the gateway should provide redundancy for the UCM.
what do you think?
H323 is the most reliable and vetted protocol, and you will have greater interoperability
H323 also requires for you to enable your entire dial plan on every device. If you have a simple dial plan, this is a good choice.
MGCP is good for a configure-and-forget configuration. It's not quite as stable, but you won't need to change it (or understand it) nearly as well.
SIP is the next H323. A lot of new 3rd party devices are SIP only, as well as SIP trunks. When it eventually comes around, switching your trunks around will be more harmless.
In more words, I more or less agree.
For PSTN connectivity:
PRI is the best. You will have the least amount of troubles. QSIG is a close secondary, and you get some more features, but it becomes a little harder to troubleshoot.
T1/E1 CAS should be avoided unless it's the only choice.
SIP Trunking is nice because you don't have to worry about analog problems, but SIP has it's own world of interoperability problems and requires more understanding of the protocol.