H.323, used for Local Area Networks (LANs), isn’t capable of scaling to larger public networks. Enter Megaco, the result of a joint effort between the Internet Engineering Task Force (IETF) and the ITU-T Study Group 16. The IETF defines Megaco as RFC 3015 and as recommendation H.248.MGCP. Megaco/H.248, or the Media Gateway Control Protocol (MGCP), is also known as H.248 and Megaco.

This is a general-purpose standard protocol for handling signaling and session management required during a multimedia conference. It’s also used for control of elements in a physically decomposed multimedia gateway, which enables separation of call control from media conversion.

How it Works

MGCP and Megaco/H.248 are complementary to H.323 and SIP, and are referred to as “device control protocols” because they remove the signaling control from the gateway and send it to a media gateway controller (MGC - sometimes is called a “call agent” or softswitch), which dictates the service logic of communications traffic. Megaco/H.248 contains terminations and contexts, two basic components. Terminations represent streams entering or leaving the MG, such as analog telephone lines or RTP or MP3 streams. Terminations have properties such as the maximum size of a jitter buffer, which can be inspected and modified by the MGC.

Terminations can be placed into contexts, which are defined as when two or more termination streams are mixed and connected together. Contexts are created and released by the MG under command of the MGC when the first termination is added and released by removing the last termination. A termination may contain more than one stream, which is why a context may carry multistream context. Audio, video, and data streams may exist in context within several terminations.

All Megaco/H.248 messages are in the format of ASN.1 text messages that display demands. These demands are the messages sent from the MGC to the MG, although the command, “ServiceChange” can also be sent by the MG. The MG sends the “Notify” command to the MGC to inform the MGC that one of the events the MGC was interested in has occurred.

Basic Usage

Megaco/H.248 is similar to MGCP from an architectural and controller-to-gateway relationship, but Megaco/H.248 supports a broader range of networks. This protocol is central to VoP (Voice over Packet) solutions, and it can be integrated easily into products such as Central Office Switches, Gateways (Trunking, Residential and Access), Network Access Servers, Cable Modems, PBXs, IP Phones, Soft Phones, IADs, Middleboxes etc. to develop a convergent voice and data solution.

Are you looking for a VoIP service provider? Try browsing our list of featured VoIP providers below...

Featured VoIP Providers