Module 5 VoIP Signaling Protocols. VoIP Call Signaling. H.323. The first call control standard for VoIP was H.323, which was adopted by the ITU-T in 1996 An umbrella standard that covers specification for transmitting audio, video and data across an IP network including the Internet
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Optional component of H.323 Perform Call processing, address translation, and distributed application manager functions
Note: Gatekeepers, Gateways and MCU’s are logically different components of a H.323 network but can be implemented on one device.
- H.225 Registration, Admission, and Status (RAS) messages
- Admission Request (ARQ)
- Admission Confirm (ACF)
- Admission Reject (ARJ)
- Bandwidth Request (BRQ)
- Bandwidth Confirm (BCF)
- Bandwidth Reject (BRJ)
There are two types of gatekeeper call signaling methods:
Three main areas of control:
Signaling can occur between:
- Endpoints and Gatekeepers
- Endpoints directly, without gatekeepers (In this case, no RAS messages exchanged).
Occurs after the discovery process but before you can place any calls
Admissions messages between endpoints and gatekeepers provide the basis for call admissions and bandwidth control
The GK can use the RAS channel to obtain status info. Typical polling period for status messages is 10 seconds
Bandwidth is initially managed through the ARQ/ACF/ARJ but bandwidth can change during the call
Alternative to H.323:
SIP is a peer-to-peer protocol as each node can be a client and server. Two main components: User agents and network servers
Six kinds of message requests: