From the user's perspective, there's really no difference. They make a call and it goes out to the PSTN. The administrator sees a difference, though. The most significant difference is that with SIP or H.323, one can use a single gateway that interco...

Think of MGCP as a "device control" protocol. You can interface that gateway to what is referred to in the standard as a "call agent".  CUCM is that call agent in Cisco enterprise voice/video networks.  You can obviously log into the gateway and do s...

H.323 can use a variety of address forms, including phone numbers (e.g., E.164), URIs, and email addresses.  SIP uses URIs.  Of course, a URI can be a phone number, a "SIP" URI, email address, etc.  So, technically either protocol can address any ent...

Presently, I'm not working on gateways and so I might not be the best person to ask.  However, I'm unaware of any development happening on MGCP at the moment.  Any discussion on progressing MGCP would take place on the IETF's "megaco" mailing list (h...

H.323 and SIP are both referred to as "call control" protocols.  They allow a device, such as a desk phone, softphone, or videoconferencing system to place a call to another person over IP.  H.323 was created by the ITU-T and was primarily focused on...