MGCP Megaco H.248 by Bob Young

MGCP - Megaco - H.248 "It's all one."

MGCP is a generic term, not an IETF standard. RFC 2705 RFC 2805 and the documents that superseded them.

RFC 2805 (MGCP) IETF Status: "Informational" "This memo provides information for the Internet community. It does not specify an Internet standard of any kind."

By the way, in the slides that follow, everything in quotes is copied straight from an IETF RFC. IETF = Internet Engineering Task Force RFC = Request for Comment

RFC 2805 (MGCP) Abstract: "This document describes protocol requirements for the Media Gateway Control Protocol between a Media Gateway Controller and a Media Gateway."

Megaco is currently an IETF proposed standard.

Megaco IETF designation: Gateway Control Protocol Version 1

Megaco is RFC 3525 (as of Dec. 6, 2004)

RFC 3525 "The protocol presented in this document meets the requirements for a media gateway control protocol as presented in RFC 2805."

RFC 3525 "It is the result of continued cooperation between the IETF Megaco Working Group and ITU-T Study Group 16."

RFC 3525 "The present version of this document... was published by the ITU-T as Recommendation H.248.1, Gateway Control Protocol Version 1."

RFC 3525 "This document replaces RFC 3015." Remember to always make sure you're using the most up-to-date version of an RFC.

Some IETF Definitions

Access gateway "A type of gateway that provides a User-Network Interface (UNI) such as ISDN."

Media Gateway (MG) #1 "The media gateway converts media provided in one type of network to the format required in another type of network."

Media Gateway (MG) #2 "For example, a MG could terminate bearer channels from a switched circuit network (e.g., DS0s) and media streams from a packet network (e.g., RTP streams in an IP network)."

Media Gateway (MG) #3 "This gateway may be capable of processing audio, video and T.120 alone or in any combination, and will be capable of full duplex media translations."

Media Gateway (MG) #4 "The MG may also play audio/video messages and perform other IVR functions, or may perform media conferencing."

Media Gateway Controller (MGC): "Controls the parts of the call state that pertain to connection control for media channels in a MG."

Multipoint Control Unit (MCU): "An entity that controls the setup and coordination of a multi-user conference that typically includes processing of audio, video and data."

Residential gateway: "A gateway that interworks an analogue line to a packet network. A residential gateway typically contains one or two analogue lines and is located at the customer premises."

Signaling gateway: "This function contains the switched circuit network (SCN) Signaling Interface that terminates SS7 or other signaling links."

Trunking gateway: "A gateway between switched circuit network (SCN) and packet network that typically terminates a large number of digital circuits."

Contexts and Terminations

Termination "A Termination sources and/or sinks one or more streams." (In other words, it's where the media stream comes from, or where it goes).

Context "A Context is an association between a collection of Terminations."

The NULL CONTEXT is special. "The null Context contains all Terminations that are not associated to any other Termination."

Placing a call with MGCP/Megaco

MGCP/Megaco's Place In The World

(1) The Media Gateway is controlled by the Media Gateway Controller using MGCP/Megaco

(2) If more than one MGC is involved in the call, inter-MGC traffic is carried via SIP or H.323 (or similar protocols)

(3) The conversation (session) is carried directly from MG to MG using Real-Time Transport Protocol (RTP) (or a similar protocol).

Note that the conversation does not need to be routed through the controller.

Note also that the Media Gateway may be an end device, i.e., an IP phone, OR many "dumb" IP phones may be connected to an Enterprise Gateway.

Terminations & Contexts

MGCP/Megaco's Place In The Network

MGCP/Megaco and GSM Cellular

MGCP/Megaco In The OSI Model

"The End"