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[[File:Converged Network Architecture.png|thumb|right|400px|Relationship of network components in a media gateway control protocol architecture]]
The '''media gateway control protocol architecture''' is a modelmethodology forof providing telecommunication services andusing controllingdecomposed devicesmultimedia andgateways for transmitting telephone calls viabetween an [[Internet Protocol]] network. Theand architecturetraditional isanalog definedfacilities inof RFCthe 2805[[public switched telephone network]] (PSTN).<ref name=rfc2805>RFC{{Cite 2805,IETF ''|title=Media Gateway Control Protocol Architecture and Requirements'', N.|rfc=2805 |last=Greene, M|first=N. |last2=Ramalho, B|first2=M. |last3=Rosen, IETF,|first3=B. |date=April 2000}}</ref> The architecture was originally defined in RFC 2805 and has been used in several prominent [[voice over IP]] (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.
A media gateway control protocol controls the function and interaction between a [[media gateway controller]] and a [[media gateway]].
 
Media gateway protocols were developed based on the Internet model of networking, the [[Internet Protocol Suite]], 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]] 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.
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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.<ref>RFC{{Cite 3435,IETF ''|title=Media Gateway Control Protocol (MGCP) Version 1.0'', F.|rfc=3435 |last=Andreasen, B|first=F. |last2=Foster, The|first2=B. Internet Society (|date=January 2003)}}</ref>
*[[H.248|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.<ref>RFC{{Cite 3525,IETF ''|title=Gateway Control Protocol Version 1'', C.|rfc=3525 |last=Groves, M|first=C. |last2=Pantaleo, T|first2=M. |last3=Anderson, |first3=T. |last4=Taylor (editors), The Internet Society|first4=T. (|date=June 2003)}}</ref><ref>RFC{{Cite 5125,IETF ''|title=Reclassification of RFC 3525 to Historic'', T.|rfc=5125 |last=Taylor, The IETF Trust|first=T. (|date=February 2008)}}</ref>
 
Although similar in architecture, MGCP and [[H.248| H.248/Megaco]] are distinctly different protocols and are not interoperable. [[H.248| H.248/Megaco]] and [[Media Gateway Control Protocol|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.<ref>[http://hive1.hive.packetizer.com/users/packetizer/papers/ipmc/MEGACOvsMGCP_v3.pdf title=Use of MEGACO vis-à-vis MGCP to build a Gateway Solution]</ref><ref name= "H2.48 history">{{cite web|url=http://www.packetizer.com/ipmc/h248/history.html |title=SIP core working group charter h2.48 history|publisher=packetizer.comg |accessdate=2012-06-07}}</ref>
 
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 CallClient 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 switching|packet]], frame, or [[cellular network|cell]] network.<ref name=rfc2805 /> 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 gateway]]s. 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]].
A '''media gateway controller''' (MGC) controls the [[media gateway]]s. The MGC receives signalling information (like dialed digits) from the Media Gateway and can instruct it to alert the called party, to send and receive voice data etc.
There are several protocols which can be used between MGC and Media Gateway: [[Simple Gateway Control Protocol|SGCP]], [[Internet Protocol Device Control |IPDC]], [[Media Gateway Control Protocol|MGCP]] and [[Megaco]] (also known as [[H.248]]).
The MGC also receives the term '''Call Agent''' when referred in the context of MGCP.
 
Some MGCs can interface with other signallingsignaling protocols, likesuch as [[Signalling System No. 7|SS7]] (SS7), for interconnection with the traditional telephone system), [[H.323]], and the [[Session Initiation Protocol|SIP]] (SIP).
 
A [[VoIP]] architecture using an MGC is sometimes called a [[softswitch]] architecture. Advantages of a softswitch architecture are that the Media Gateways are easy to maintain and that the softswitch operator retains full control. On the downside, softswitch architectures tend to be inflexible. Highly available MGCs are expensive to implement, as an MGC needs to be stateful.
 
==Protocols==
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In July 1998, Telcordia (Bellcore) and [[Cisco Systems]] created a protocol called [[Simple Gateway Control Protocol|Simple Gateway Control Protocol (SGCP)]] for controlling Telephony Gateways from external call control elements.<ref name=SGCP>{{cite web|title=Simple Gateway Control Protocol (SGCP|url=http://tools.ietf.org/html/draft-huitema-sgcp-v1-01|publisher=IETF|date=30 July 1998|accessdate=8 June 2012}}</ref>
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.<ref name=IPDC>{{cite web|title=IPDC - Connection Control Protocol|url=http://tools.ietf.org/html/draft-dugan-ipdc-connection-00|publisher=IETF|date=August 1998|accessdate=8 June 2012}}</ref> 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.<ref name=merger>{{cite web|title=Level 3 Communications, Bellcore Announce Merger of Protocol Specifications for Voice Over IPe|url=http://level3.mediaroom.com/index.php?s=23600&item=65733|publisher=Level 3 Communications|accessdate=8 June 2012}}</ref>
 
MGCP was submitted to the [[IETF]]’s MeGaCo working group in October 1998.<ref name=MGCp-01>{{cite web|title=Media Gateway Control Protocol (MGCP)|url=http://tools.ietf.org/html/draft-huitema-MGCP-v0r1-00|publisher=IETF|date=27 October 1998|accessdate=8 June 2012}}</ref> In November 1998, [[Lucent]] Technologies submitted a draft for third device protocol, called [[Media Device Control Protocol]] (MDCP) to used by media gateways and their controllers.<ref name=MDCP>{{cite web|title=Toward the PSTN/Internet Inter-Networking - MEDIA DEVICE CONTROL PROTOCOL|url=http://tools.ietf.org/html/draft-sijben-megaco-mdcp-00|publisher=IETF|date=November 1998|accessdate=8 June 2012}}</ref> IETF merged MGCP and MDCP and proposed a new and improved protocol named MeGaCo protocol (also known as H.248) in April 1999.<ref name=MEGACO>{{cite web|title=MEGACO Protocol|url=http://tools.ietf.org/html/draft-ietf-megaco-protocol-01|publisher=IETF|date=16 April 1999|accessdate=8 June 2012}}</ref>▼
 
▲MGCP was submitted to the [[IETF]]’s MeGaCo working group in October 1998.<ref name=MGCp-01>{{cite web|title=Media Gateway Control Protocol (MGCP)|url=http://tools.ietf.org/html/draft-huitema-MGCP-v0r1-00|publisher=IETF|date=27 October 1998|accessdate=8 June 2012}}</ref> In November 1998, [[Lucent]] Technologies submitted a draft for third device protocol, called [[Media Device Control Protocol]] (MDCP) to useduse by media gateways and their controllers.<ref name=MDCP>{{cite web|title=Toward the PSTN/Internet Inter-Networking - MEDIA DEVICE CONTROL PROTOCOL|url=http://tools.ietf.org/html/draft-sijben-megaco-mdcp-00|publisher=IETF|date=November 1998|accessdate=8 June 2012}}</ref> IETF merged MGCP and MDCP and proposed a new and improved protocol named MeGaCo protocol (also known as H.248) in April 1999.<ref name=MEGACO>{{cite web|title=MEGACO Protocol|url=http://tools.ietf.org/html/draft-ietf-megaco-protocol-01|publisher=IETF|date=16 April 1999|accessdate=8 June 2012}}</ref>
[[File:Gateway Control Protocol Evolution-Migration.png|thumb|centre|900px| Gateway Control Evolution. Current version of MGCP is informational as per RFC 3435. H.248/Megaco is standard as defined in RFC 3525.<br> Current version of H.248 - Gateway control protocol: Version 3 is standard and in force<ref name=h.248>{{cite web|url=http://www.itu.int/rec/T-REC-H.248.1/en|title=H.248.1 : Gateway control protocol: Version 3|publisher=ITU Telecommunication}}</ref>]]
 
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 [[Internet Standard#Standardization process|standard-track]] protocol, although it includes protocol specification. Even while MGCP was still an [[Internet Standard|Internet Draft]], many companies developed included MGCP with their own development rather than wait for astandardizeda standardized protocol. Therefore, the decision was made to release MGCP as an informational RFC in October 1999. SpecificationIETF ondevelopment of MGCP has stopped, although companies continue to implement MGCP within their systems ,<ref>{{cite book |last1= Collins |first1=Daniel |title=Big Compilation Book With Many Chapters and distinct chapter authors |publisher=Book Publishers |date=September 22, 2000 |pages=[https://archive.org/details/carriergradevoic0000coll_t3t4/page/239 239–240] |chapter=Chapter 6: Media Gateway Control and the Softswitch Architecture |isbn=0071363262 |url=https://archive.org/details/carriergradevoic0000coll_t3t4/page/239 }}</ref> 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 drive behind the developmentmotivation of Megaco/H.248 was the need to providesatisfy various requirements that were not addressed properly by MGCP.{{cn|date=June 2016}} Megaco/H.248 is an evolution of MGCP. Megaco/H.248It is a combination of MGCP and MDCP, and was published as Standard in RFC 3015 in November 2000. The implementation of H.248/Megaco and MGCP isare different and they are not directly compatibleinteroperable.
 
Currently H.248 (H.248.1 Gateway Control Protocol version 3) is published by [[ITU-T|International Telecommunication Union Telecommunication (ITU-T)]] as standarda protocol standard. The [[ITU-T]] has published three versions of [http://www.itu.int/rec/T-REC-H.248.1-200509-I/en H.248.1]. MediaThe GatewayIETF Controlpublished Protocolit (MGCP)as isGateway definedControl [[InternetProtocol EngineeringVersion Task1 Force]] asin informational by RFC 3525.
 
Both H.248 and MGCP are protocol for controlling media gateways using a [[media gateway controller]] or called [[call agent]]s. In a VoIP system, H.248 and MGCP are used with SIP or H.323. SIP or H.323 will provide theintercommunication callbetween controlgateway functionalitycontrollers and MGCP can beis used to manage media establishment in the media gateways.<ref name= "MGCP">{{cite web|url=http://www.telecomspace.com/vop-mgcp.html |title=Media Gateway Control Protocol| publisher=telecomspace.com |accessdate=2012-06-07}}</ref>
 
==Standards documents==
==RFCs==
* {{IETF RFC |2805|link=no}} - ''Media Gateway Control Protocol Architecture and Requirements'', April 2000 (Informational)
* {{IETF RFC |2705|link=no}} ''Media Gateway Control Protocol (MGCP) Version 1.0'', October 1999 (Informational)
* RFC{{IETF RFC|3435|link=no}} - ''Media Gateway Control Protocol (MGCP) Version 1.0'', (this supersedes RFC 2705) (Informational)
* {{IETF RFC |3015|link=no}} - ''Megaco Protocol Version 1.0'', November 2000, (Standard Track)
* {{IETF RFC |3525|link=no}} - ''Gateway Control Protocol Version 1'', June 2003 (Obsoletes: RFC 3015) (Standard)
 
==See also==
*[[Softswitch]]
*[[RTP audio video profile]]
*[[Voice over Internet Protocol]]
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*[http://tools.ietf.org/html/draft-sijben-megaco-mdcp-00 MEDIA DEVICE CONTROL PROTOCOL (MDCP) 1st Draft], November 1998
*[http://tools.ietf.org/html/draft-ietf-megaco-protocol-01 MEGACO 1st Draft], IETF, April 1999
*[http://www.itu.int/rec/T-REC-H/e ITU-T H-series Recommendations] ITU-T Publication site where the H-series, including the H.248 Sub-series, Recommendations can be downloaded in PDF format free of charge
*[http://www.itu.int/rec/T-REC-H.248.1-200509-I/en H.248.1 Base protocol specification ], ITU-T
*[http://www.packetizer.com/voip/mgcp MGCP Information Site] Information related to MGCP.
*[http://www.packetizer.com/voip/h248/ H.248 Information Site] Information related to H.248/Megaco, including pointers to standards and draft specifications.
*[https://web.archive.org/web/20120511050504/http://www.radvision.com/NR/rdonlyres/1C34D0AA-C455-428B-A839-306926516053/0/RADVISIONMediaGatewayControlProtocol.pdf Implementing Media Gateway Control Protocols] - A RADVISION White Paper
*[http://www.adtran.com/pub/Library/White_Papers/Public_View/MGCP_and_SIP_White_Paper__Rev_A_.pdf A Description of MGCP and SIP] Michael Lamy, ADTRAN Enterprise Networks Division
 
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