Media gateway control protocol architecture
The media gateway control protocol architecture is a methodology of providing telecommunication services using decomposed multimedia gateways for transmitting telephone calls between an
The architecture divides the functions required for the integration of traditional telecommunication networks and modern packet networks into several physical and logical components, notably the
Media gateway protocols were developed based on the Internet model of networking, the
Originally, gateways were viewed as monolithic devices that had call control, using protocols such as
SIP and H.323 are signaling protocols, while media gateway control protocols are device control protocols. The architectural difference between SIP and H.323, and the media gateway control protocols is that the relationships between entities in SIP and H.323 are peer-to-peer, while the relationships between entities in media gateway control protocols use the
Implementations
Several implementations of the media gateway control protocol are in common use. The names of the best-known protocols are abbreviations of the protocol group:
- The Media Gateway Control Protocol (MGCP) was first described in RFC 2705, and revised in RFC 3435.[3]
- Megaco, or H.248, or Megaco/H.248, was first described in RFC 3525, which was revised and extended in various specifications, leading to its obsolescence as explained in RFC 5125.[4][5]
Although similar in architecture, MGCP and H.248/Megaco are distinctly different protocols and are not interoperable. H.248/Megaco and MGCP protocols are complementary to H.323 and SIP, which both may be referred to as intelligent endpoint protocols. H.248/Megaco and MGCP may be referred to as device control protocols.[6][7]
Other media gateway control protocols include the predecessors of MGCP, namely the Simple Gateway Control Protocol (SGCP) and the Internet Protocol Device Control (IPDC). A proprietary protocol using a similar architecture is the Cisco Skinny Client Control Protocol (SCCP).
Network elements
Media gateway
A media gateway is a device that converts media streams in the form of digital data or analog signals in telecommunication for services such as voice, video, and fax applications between two, usually dissimilar, interfaces using different technologies. One of the technologies usually is a packet, frame, or cell network.[1] For example, it may convert voice telephone calls between a traditional analog telephone to a digital format for transmission over an Internet Protocol (IP) network, to facilitate voice over IP communications.
Media gateway controller
A media gateway controller (MGC), also known as a call agent, controls the media gateways. It monitors the gateways for events, such as an off-hook state when a user intends to initiate a telephone call, and issues requests to the gateway to initiate or complete sessions, to alert the called party, or to terminate a call. The protocols used for this interaction between the gateway and its controller have evolved through various types and versions. The Simple Gateway Control Protocol (SGCP) and the Internet Protocol Device Control (IPDC) have been replaced by the Media Gateway Control Protocol (MGCP) and Megaco, which is also known as H.248.
Some MGCs interface with other signaling protocols, such as Signalling System No. 7 (SS7), for interconnection with the traditional telephone system, H.323, and the Session Initiation Protocol (SIP).
Protocols
The device control protocols evolved through several versions. MGCP emerged from a group now called the International SoftSwitch Consortium. This group started early with
In July 1998, Telcordia (Bellcore) and
MGCP was submitted to the
The first "official" version of MGCP is defined in RFC 2705 as informational. RFC 3435 obsoleted RFC 2705. MGCP currently is purely informational rather than a standard-track protocol, although it includes protocol specification. Even while MGCP was still an Internet Draft, many companies developed included MGCP with their own development rather than wait for a standardized protocol. Therefore, the decision was made to release MGCP as an informational RFC in October 1999. IETF development of MGCP has stopped, although companies continue to implement MGCP,[14] driven by the efforts of the PacketCable development of Network-based Call Signaling.
Further standardization of MGCP effort was pursued in the IETF, in the MEGACO working group, and also in the ITU-T/SG16, under the code name H.GCP. RFC 3015 standard tracks the MEGACO protocol (also H.248) and
The motivation of Megaco was the need to satisfy various requirements that were not addressed properly by MGCP.[citation needed] Megaco is an evolution of MGCP. It is a combination of MGCP and MDCP, and was published as Standard in RFC 3015 in November 2000. Megaco and MGCP are different and not interoperable.
H.248 (H.248.1 Gateway Control Protocol version 3) is published by International Telecommunication Union Telecommunication (ITU-T) as a protocol standard. The ITU-T has published three versions of H.248.1. The IETF published it as Gateway Control Protocol Version 1 in informational RFC 3525.
Both H.248 and MGCP are protocol for controlling media gateways using a
Standards documents
- RFC 2805 Media Gateway Control Protocol Architecture and Requirements, April 2000 (Informational)
- RFC 2705 Media Gateway Control Protocol (MGCP) Version 1.0, October 1999 (Informational)
- RFC 3435 Media Gateway Control Protocol (MGCP) Version 1.0, (supersedes RFC 2705) (Informational)
- RFC 3015 Megaco Protocol Version 1.0, November 2000, (Standard Track)
- RFC 3525 Gateway Control Protocol Version 1, June 2003 (Obsoletes: RFC 3015) (Standard)
See also
- Softswitch
- RTP audio video profile
- Voice over Internet Protocol
References
- ^ .
- ^ "Understanding VoIP Protocols". packetizer.com. Retrieved 2012-06-07.
- .
- .
- .
- ^ title=Use of MEGACO vis-à-vis MGCP to build a Gateway Solution
- ^ "SIP core working group charter h2.48 history". packetizer.comg. Retrieved 2012-06-07.
- ^ "Simple Gateway Control Protocol (SGCP". IETF. 30 July 1998. Retrieved 8 June 2012.
- ^ "IPDC - Connection Control Protocol". IETF. August 1998. Retrieved 8 June 2012.
- ^ "Level 3 Communications, Bellcore Announce Merger of Protocol Specifications for Voice Over IPe". Level 3 Communications. Retrieved 8 June 2012.
- ^ "Media Gateway Control Protocol (MGCP)". IETF. 27 October 1998. Retrieved 8 June 2012.
- ^ "Toward the PSTN/Internet Inter-Networking - MEDIA DEVICE CONTROL PROTOCOL". IETF. November 1998. Retrieved 8 June 2012.
- ^ "MEGACO Protocol". IETF. 16 April 1999. Retrieved 8 June 2012.
- ISBN 0071363262.
- ^ "Media Gateway Control Protocol". telecomspace.com. Retrieved 2012-06-07.
External links
- Simple Gateway Control Protocol 1st Draft, IETF, 30 July 1998
- Connection Control Protocol 1st Draft, IETF, August 1998
- Media Gateway Control Protocol (MGCP)1st Draft, IETF 27 October 1998
- MEDIA DEVICE CONTROL PROTOCOL (MDCP) 1st Draft, November 1998
- MEGACO 1st Draft, IETF, April 1999
- ITU-T H-series Recommendations
- H.248.1 Base protocol specification , ITU-T
- MGCP Information Site
- H.248 Information Site
- Implementing Media Gateway Control Protocols - A RADVISION White Paper
- A Description of MGCP and SIP Michael Lamy, ADTRAN Enterprise Networks Division