The media gateway control protocol architecture is a methodology of providing telecommunication services using decomposed multimedia gateways for transmitting telephone calls between an

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. ...

network and traditional analog facilities of the public switched telephone network (PSTN). The architecture was originally defined in RFC 2805 and has been used in several prominent

voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

(VoIP) protocol implementations, such as the Media Gateway Control Protocol (MGCP) and Megaco (H.248), both successors to the obsolete Simple Gateway Control Protocol (SGCP). 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, the media gateway controller, and signaling gateways. The interaction between the media gateway and its controller is defined in the media gateway control protocol. Media gateway protocols were developed based on the Internet model of networking, the

Internet Protocol Suite The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the sui ...

, and are referred to as device control protocols. A media gateway is a device that offers an IP interface and a legacy telephone interface and that converts media, such as audio and video streams, between them. The legacy telephone interface may be complex, such as an interface to a

PSTN The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...

switch, or may be a simple interface to a traditional telephone. Depending on the size and purpose of the gateway, it may allow IP-originated calls to terminate to the PSTN or vice versa, or may simply provide a means to connect a telephone to a telecommunication system via an IP network. Originally, gateways were viewed as monolithic devices that had call control, using protocols such as H.323 and the Session Initiation Protocol, and hardware required to control the PSTN interface. In 1998, the idea of splitting the gateway into two logical parts was proposed: one part, which contains the call control logic, is called the media gateway controller (MGC) or call agent (CA), and the other part, which interfaces with the PSTN, is called the media gateway (MG). With this functional split, a new interface existed between the MGC and the MG, requiring a framework for communication between the elements, resulting in the media gateway control protocol architecture. 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

master/slave (technology) Master/slave is a model of asymmetric communication or control where one device or process (the "master") controls one or more other devices or processes (the "slaves") and serves as their communication hub. In some systems, a master is select ...

model. SIP and H.323 handle call setup, connection, management, and tear-down of calls between like interfaces, whereas media gateway control protocols define the mechanisms of setup of media paths and streams between IP and other networks.

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. * 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. 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. 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 The Skinny Client Control Protocol (SCCP) is a proprietary network terminal control protocol originally developed by Selsius Systems, which was acquired by Cisco Systems in 1998. SCCP is a lightweight IP-based protocol for session signaling with C ...

(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 Packet may refer to: * A small container or pouch ** Packet (container), a small single use container ** Cigarette packet ** Sugar packet * Network packet, a formatted unit of data carried by a packet-mode computer network * Packet radio, a fo ...

, frame, or

cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...

network. For example, it may convert voice telephone calls between a traditional analog

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

to a digital format for transmission over an

(IP) network, to facilitate

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

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(through its acquisition of Xcom) and

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(BellCore). In July 1998, Telcordia (Bellcore) and

Cisco Systems Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...

created a protocol called Simple Gateway Control Protocol (SGCP) for controlling Telephony Gateways from external call control elements. Meanwhile, in mid-1998, Level 3 created a Technical Advisory Council (TAC), composed of a dozen leading communications equipment manufacturers. The TAC proposed a device protocol called Internet Protocol Device Control (IPDC) in August 1998. IPDC was intended to be used between a media gateway and a media gateway controller. Media gateway were capable of acting as a voice over IP gateway, voice over ATM gateway, dialup modem media gateway, circuit switch, or cross- connect. In October 1998, Simple Gateway Control Protocol (SGCP) was combined with Internet Protocol Device Control (IPDC), resulting in MGCP. MGCP was submitted to the

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and a ...

’s MeGaCo working group in October 1998. In November 1998,

Lucent Lucent Technologies, Inc. was an American multinational telecommunications equipment company headquartered in Murray Hill, New Jersey. It was established on September 30, 1996, through the divestiture of the former AT&T Technologies business u ...

Technologies submitted a draft for third device protocol, called Media Device Control Protocol (MDCP) to use by media gateways and their controllers. IETF merged MGCP and MDCP and proposed a new and improved protocol named MeGaCo protocol (also known as H.248) in April 1999. 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 An Internet Draft (I-D) is a document published by the Internet Engineering Task Force (IETF) containing preliminary technical specifications, results of networking-related research, or other technical information. Often, Internet Drafts are int ...

, 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, driven by the efforts of the

PacketCable PacketCable network is a technology specification defined by the industry consortium CableLabs for using Internet Protocol (IP) networks to deliver multimedia services, such as IP telephony, conferencing, and interactive gaming on a cable televisio ...

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 The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Comm ...

/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. 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

has published three versions o
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 media gateway controller or call agent. In a VoIP system, H.248 and MGCP are used with SIP or H.323. SIP or H.323 provide intercommunication between gateway controllers and MGCP is used to manage media establishment in the media gateways.

Standards documents

* ''Media Gateway Control Protocol Architecture and Requirements'', April 2000 (Informational) * ''Media Gateway Control Protocol (MGCP) Version 1.0'', October 1999 (Informational) * ''Media Gateway Control Protocol (MGCP) Version 1.0'', (supersedes RFC 2705) (Informational) * ''Megaco Protocol Version 1.0'', November 2000, (Standard Track) * ''Gateway Control Protocol Version 1'', June 2003 (Obsoletes: RFC 3015) (Standard)

References

{{Reflist

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 RecommendationsH.248.1 Base protocol specification
ITU-T
MGCP Information SiteH.248 Information Site Implementing Media Gateway Control Protocols
- A RADVISION White Paper
A Description of MGCP and SIP
Michael Lamy, ADTRAN Enterprise Networks Division VoIP protocols Internet Standards ITU-T recommendations