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Media gateway control protocol architecture
open-in-new
<h2 id="implementations">Implementations</h2> <p>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: </p> <ul><li>The <a href="/facts/Media_Gateway_Control_Protocol/Q8Af7pRQ">Media Gateway Control Protocol</a> (MGCP) was first described in RFC 2705, and revised in RFC 3435.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></li> <li><a href="/facts/H.248/2PjUU3Lc">Megaco</a>, 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.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></li></ul> <p>Although similar in architecture, MGCP and <a href="/facts/H.248/2PjUU3Lc"> H.248/Megaco</a> are distinctly different protocols and are not interoperable. <a href="/facts/H.248/2PjUU3Lc"> H.248/Megaco</a> and <a href="/facts/Media_Gateway_Control_Protocol/Q8Af7pRQ">MGCP</a> 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.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>Other media gateway control protocols include the predecessors of MGCP, namely the <a href="/facts/Simple_Gateway_Control_Protocol/mtlKNVnx">Simple Gateway Control Protocol</a> (SGCP) and the <a href="/facts/Internet_Protocol_Device_Control/JLYdK15n">Internet Protocol Device Control</a> (IPDC). A proprietary protocol using a similar architecture is the Cisco <a href="/facts/Skinny_Client_Control_Protocol/AY8WGHlj">Skinny Client Control Protocol</a> (SCCP). </p> <h2 id="network-elements">Network elements</h2> <h3>Media gateway</h3> <p>A <a href="/facts/Media_gateway/nyXYhkPx">media gateway</a> 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 <a href="/facts/Packet_switching/olDlDP1R">packet</a>, frame, or <a href="/facts/Cellular_network/8zA0jQJ9">cell</a> network.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> For example, it may convert voice telephone calls between a traditional analog <a href="/facts/Telephone/P7uEgWQX">telephone</a> to a digital format for transmission over an <a href="/facts/Internet_Protocol/Qq6VeEal">Internet Protocol</a> (IP) network, to facilitate <a href="/facts/Voice_over_IP/5QGBbXYg">voice over IP</a> communications. </p> <h3>Media gateway controller</h3> <p>A media gateway controller (MGC), also known as a <i>call agent</i>, controls the <a href="/facts/Media_gateway/nyXYhkPx">media gateways</a>. 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 <a href="/facts/Simple_Gateway_Control_Protocol/mtlKNVnx">Simple Gateway Control Protocol</a> (SGCP) and the <a href="/facts/Internet_Protocol_Device_Control/JLYdK15n">Internet Protocol Device Control</a> (IPDC) have been replaced by the <a href="/facts/Media_Gateway_Control_Protocol/Q8Af7pRQ">Media Gateway Control Protocol</a> (MGCP) and Megaco, which is also known as <a href="/facts/H.248/2PjUU3Lc">H.248</a>. </p><p>Some MGCs interface with other signaling protocols, such as <a href="/facts/Signalling_System_No._7/YJ3T8VqE">Signalling System No. 7</a> (SS7), for interconnection with the traditional telephone system, <a href="/facts/H.323/Lfj0ykI0">H.323</a>, and the <a href="/facts/Session_Initiation_Protocol/cbjUoNqP">Session Initiation Protocol</a> (SIP). </p> <h2 id="protocols">Protocols</h2> <p>The device control protocols evolved through several versions. MGCP emerged from a group now called the International SoftSwitch Consortium. This group started early with <a href="/facts/Level_3_Communications/jT8epKBt">Level 3 Communications</a> (through its acquisition of Xcom) and <a href="/facts/Telcordia/MBQAkk4J">Telcordia</a> (BellCore). </p><p>In July 1998, Telcordia (Bellcore) and <a href="/facts/Cisco_Systems/ocDgQt6T">Cisco Systems</a> created a protocol called <a href="/facts/Simple_Gateway_Control_Protocol/mtlKNVnx">Simple Gateway Control Protocol (SGCP)</a> for controlling Telephony Gateways from external call control elements.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> 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 <a href="/facts/Internet_Protocol_Device_Control/JLYdK15n">Internet Protocol Device Control</a> (IPDC) in August 1998.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> 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, <a href="/facts/Simple_Gateway_Control_Protocol/mtlKNVnx">Simple Gateway Control Protocol</a> (SGCP) was combined with <a href="/facts/Internet_Protocol_Device_Control/JLYdK15n">Internet Protocol Device Control</a> (IPDC), resulting in MGCP.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p><p>MGCP was submitted to the <a href="/facts/IETF/tIcCsFhX">IETF</a>’s MeGaCo working group in October 1998.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> In November 1998, <a href="/facts/Lucent/uzgpVmLa">Lucent</a> Technologies submitted a draft for third device protocol, called Media Device Control Protocol (MDCP) to use by media gateways and their controllers.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> IETF merged MGCP and MDCP and proposed a new and improved protocol named MeGaCo protocol (also known as H.248) in April 1999.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p><p>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 <a href="/facts/Internet_Standard/LT6VEfhg">standard-track</a> protocol, although it includes protocol specification. Even while MGCP was still an <a href="/facts/Internet_Standard/LT6VEfhg">Internet Draft</a>, 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,<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> driven by the efforts of the <a href="/facts/PacketCable/g4gzzuM9">PacketCable</a> development of <a href="/facts/Network-based_Call_Signaling/0SGqabfm">Network-based Call Signaling</a>. </p><p>Further standardization of MGCP effort was pursued in the IETF, in the MEGACO working group, and also in the <a href="/facts/ITU-T/9nJwkPYx">ITU-T</a>/SG16, under the code name H.GCP. RFC 3015 standard tracks the MEGACO protocol (also H.248) and </p><p>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. </p><p>H.248 (H.248.1 Gateway Control Protocol version 3) is published by <a href="/facts/ITU-T/9nJwkPYx">International Telecommunication Union Telecommunication (ITU-T)</a> as a protocol standard. The <a href="/facts/ITU-T/9nJwkPYx">ITU-T</a> has published three versions of <a href="http://www.itu.int/rec/T-REC-H.248.1-200509-I/en">H.248.1</a>. The IETF published it as Gateway Control Protocol Version 1 in informational RFC 3525. </p><p>Both H.248 and MGCP are protocol for controlling media gateways using a <a href="/facts/Media_gateway_controller/oaLRfehz">media gateway controller</a> 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.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> </p> <h2 id="standards-documents">Standards documents</h2> <ul><li>RFC <a href="https://www.rfc-editor.org/rfc/rfc2805">2805</a> <i>Media Gateway Control Protocol Architecture and Requirements</i>, April 2000 (Informational)</li> <li>RFC <a href="https://www.rfc-editor.org/rfc/rfc2705">2705</a> <i>Media Gateway Control Protocol (MGCP) Version 1.0</i>, October 1999 (Informational)</li> <li>RFC <a href="https://www.rfc-editor.org/rfc/rfc3435">3435</a> <i>Media Gateway Control Protocol (MGCP) Version 1.0</i>, (supersedes RFC 2705) (Informational)</li> <li>RFC <a href="https://www.rfc-editor.org/rfc/rfc3015">3015</a> <i>Megaco Protocol Version 1.0</i>, November 2000, (Standard Track)</li> <li>RFC <a href="https://www.rfc-editor.org/rfc/rfc3525">3525</a> <i>Gateway Control Protocol Version 1</i>, June 2003 (Obsoletes: RFC 3015) (Standard)</li></ul> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Softswitch/zffbQ7h5">Softswitch</a></li> <li><a href="/facts/RTP_audio_video_profile/RsPjoweL">RTP audio video profile</a></li> <li><a href="/facts/Voice_over_Internet_Protocol/5QGBbXYg">Voice over Internet Protocol</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://tools.ietf.org/html/draft-huitema-sgcp-v1-01">Simple Gateway Control Protocol 1st Draft</a>, IETF, 30 July 1998</li> <li><a href="http://tools.ietf.org/html/draft-dugan-ipdc-connection-00">Connection Control Protocol 1st Draft</a>, IETF, August 1998</li> <li><a href="http://tools.ietf.org/html/draft-huitema-MGCP-v0r1-00">Media Gateway Control Protocol (MGCP)1st Draft</a>, IETF 27 October 1998</li> <li><a href="http://tools.ietf.org/html/draft-sijben-megaco-mdcp-00">MEDIA DEVICE CONTROL PROTOCOL (MDCP) 1st Draft</a>, November 1998</li> <li><a href="http://tools.ietf.org/html/draft-ietf-megaco-protocol-01">MEGACO 1st Draft</a>, IETF, April 1999</li> <li><a href="http://www.itu.int/rec/T-REC-H/e">ITU-T H-series Recommendations</a></li> <li><a href="http://www.itu.int/rec/T-REC-H.248.1-200509-I/en">H.248.1 Base protocol specification </a>, ITU-T</li> <li><a href="http://www.packetizer.com/voip/mgcp">MGCP Information Site</a></li> <li><a href="http://www.packetizer.com/voip/h248/">H.248 Information Site</a></li> <li><a href="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> - A RADVISION White Paper</li> <li><a href="http://www.adtran.com/pub/Library/White_Papers/Public_View/MGCP_and_SIP_White_Paper__Rev_A_.pdf">A Description of MGCP and SIP</a> Michael Lamy, ADTRAN Enterprise Networks Division</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Greene, N.; Ramalho, M.; Rosen, B. (April 2000). Media Gateway Control Protocol Architecture and Requirements. doi:10.17487/RFC2805. RFC 2805. <a href="https://datatracker.ietf.org/doc/html/rfc2805" target="_blank">https://datatracker.ietf.org/doc/html/rfc2805</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Understanding VoIP Protocols". packetizer.com. Retrieved 2012-06-07. <a href="http://www.packetizer.com/ipmc/papers/understanding_voip/voip_protocols.html" target="_blank">http://www.packetizer.com/ipmc/papers/understanding_voip/voip_protocols.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Andreasen, F.; Foster, B. (January 2003). Media Gateway Control Protocol (MGCP) Version 1.0. doi:10.17487/RFC3435. RFC 3435. <a href="https://datatracker.ietf.org/doc/html/rfc3435" target="_blank">https://datatracker.ietf.org/doc/html/rfc3435</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Groves, C.; Pantaleo, M.; Anderson, T.; Taylor, T. (June 2003). Gateway Control Protocol Version 1. doi:10.17487/RFC3525. RFC 3525. <a href="https://datatracker.ietf.org/doc/html/rfc3525" target="_blank">https://datatracker.ietf.org/doc/html/rfc3525</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Taylor, T. (February 2008). Reclassification of RFC 3525 to Historic. doi:10.17487/RFC5125. RFC 5125. <a href="https://datatracker.ietf.org/doc/html/rfc5125" target="_blank">https://datatracker.ietf.org/doc/html/rfc5125</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>title=Use of MEGACO vis-à-vis MGCP to build a Gateway Solution <a href="http://hive1.hive.packetizer.com/users/packetizer/papers/ipmc/MEGACOvsMGCP_v3.pdf" target="_blank">http://hive1.hive.packetizer.com/users/packetizer/papers/ipmc/MEGACOvsMGCP_v3.pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"SIP core working group charter h2.48 history". packetizer.comg. Retrieved 2012-06-07. <a href="http://www.packetizer.com/ipmc/h248/history.html" target="_blank">http://www.packetizer.com/ipmc/h248/history.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Greene, N.; Ramalho, M.; Rosen, B. (April 2000). Media Gateway Control Protocol Architecture and Requirements. doi:10.17487/RFC2805. RFC 2805. <a href="https://datatracker.ietf.org/doc/html/rfc2805" target="_blank">https://datatracker.ietf.org/doc/html/rfc2805</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"Simple Gateway Control Protocol (SGCP". IETF. 30 July 1998. Retrieved 8 June 2012. <a href="http://tools.ietf.org/html/draft-huitema-sgcp-v1-01" target="_blank">http://tools.ietf.org/html/draft-huitema-sgcp-v1-01</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"IPDC - Connection Control Protocol". IETF. August 1998. Retrieved 8 June 2012. <a href="http://tools.ietf.org/html/draft-dugan-ipdc-connection-00" target="_blank">http://tools.ietf.org/html/draft-dugan-ipdc-connection-00</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>"Level 3 Communications, Bellcore Announce Merger of Protocol Specifications for Voice Over IPe". Level 3 Communications. Retrieved 8 June 2012. <a href="http://level3.mediaroom.com/index.php?s=23600&item=65733" target="_blank">http://level3.mediaroom.com/index.php?s=23600&item=65733</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"Media Gateway Control Protocol (MGCP)". IETF. 27 October 1998. Retrieved 8 June 2012. <a href="http://tools.ietf.org/html/draft-huitema-MGCP-v0r1-00" target="_blank">http://tools.ietf.org/html/draft-huitema-MGCP-v0r1-00</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>"Toward the PSTN/Internet Inter-Networking - MEDIA DEVICE CONTROL PROTOCOL". IETF. November 1998. Retrieved 8 June 2012. <a href="http://tools.ietf.org/html/draft-sijben-megaco-mdcp-00" target="_blank">http://tools.ietf.org/html/draft-sijben-megaco-mdcp-00</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"MEGACO Protocol". IETF. 16 April 1999. Retrieved 8 June 2012. <a href="http://tools.ietf.org/html/draft-ietf-megaco-protocol-01" target="_blank">http://tools.ietf.org/html/draft-ietf-megaco-protocol-01</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Collins, Daniel (September 22, 2000). "Chapter 6: Media Gateway Control and the Softswitch Architecture". Big Compilation Book With Many Chapters and distinct chapter authors. Book Publishers. pp. 239–240. ISBN 0071363262. <a href="0071363262" target="_blank">0071363262</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>"Media Gateway Control Protocol". telecomspace.com. Retrieved 2012-06-07. <a href="http://www.telecomspace.com/vop-mgcp.html" target="_blank">http://www.telecomspace.com/vop-mgcp.html</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> </ol>