Media Gateway Control Protocol architecture

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Gateway Control Protocol Relationship

The Media Gateway Control Protocol architecture is a model for providing telecommunication services and controlling devices and transmitting calls via an Internet Protocol network. The architecture is defined in RFC 2805.[1]

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 on one side and some sort of legacy telephone interface on the other side. The legacy telephone interface may be complex, such as an interface to a legacy PSTN switch, or may be a simple interface that allows one to connect one or a few traditional telephones. Depending on the size and purpose of the gateway, it may allow IP-originated calls to terminate to the PSTN (and vice-versa) or may simply provide a means for a person to connect a telephone to the Internet.

Originally, gateways were viewed as monolithic devices that had call control (H.323/SIP) 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 MG, driving the necessity to define the Media Gateway Control Protocol architecture.

The Session Initiation Protocol (SIP) and H.323 are signaling protocols, while Media Gateway Control protocols are device control protocol. An important difference between SIP and H.323, and the Media Gateway Control protocols is that the relationship between entities in SIP and H.323 is peer-to-peer, while the relationship between entities in Media Gateway Control protocols is master/slave. SIP and H.323 fundamentally have a peer-to-peer protocol character that handle call setup, connect, manage calls and tear-down, whereas Media Gateway Control protocols define how media streams are set up and establish media paths between IP and other networks.[2]

Implementations[edit]

Several implementations of the Media Gateway Control Protocol are in common use. The names of the best-known are abbreviations of the protocol group:

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 Session Initiation Protocol. Both H.323 and SIP can be referred to as "intelligent endpoint protocols". H.248/Megaco and MGCP can 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 Call Control Protocol (SCCP, or short Skinny).

Protocols[edit]

The “Device” Control protocols evolved through several versions. The Media Gateway Control Protocol (MGCP) emerged from a group now called the International SoftSwitch Consortium. This group started early with Level 3 Communications (through its acquisition of Xcom) and Telcordia (BellCore).

In July 1998, Telcordia (Bellcore) and Cisco Systems created a protocol called Simple Gateway Control Protocol (SGCP) for controlling Telephony Gateways from external call control elements.[8] 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.[9] IPDC was intended to used between Media Gateway and 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 Media Gateway Control Protocol (MGCP).[10]

MGCP was submitted to the IETF’s MeGaCo working group in October 1998.[11] 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.[12] IETF merged MGCP and MDCP and proposed a new and improved protocol named MeGaCo protocol (also known as H.248) in April 1999.[13]

Gateway Control Evolution. Current version of MGCP is informational as per RFC 3435. H.248/Megaco is standard as defined in RFC 3525.
Current version of H.248 - Gateway control protocol: Version 3 is standard and in force[14]

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 astandardized protocol. Therefore, the decision was made to release MGCP as an informational RFC in October 1999. Specification on MGCP has stopped, although companies continue to implement MGCP within their systems 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. 

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 development of Megaco/H.248 was the need to provide various requirements that were not addressed properly by MGCP. Megaco/H.248 is an evolution of MGCP. Megaco/H.248 is combination of MGCP and Media Device Control Protocol (MDCP) and was published as Standard in RFC 3015 in November 2000. The implementation of H.248/Megaco and MGCP is different and they are not directly compatible.

Currently H.248 (H.248.1 Gateway Control Protocol version 3 is published by International Telecommunication Union Telecommunication (ITU-T) as standard protocol. The ITU-T has published three versions of H.248.1. Media Gateway Control Protocol (MGCP) is defined Internet Engineering Task Force as informational by RFC 3525.

Both H.248 and MGCP are protocol for controlling Media Gateways using Media Gateway Controller or called Call Agents. In a VoIP system, H.248 and MGCP are used with SIP or H.323. SIP or H.323 will provide the call control functionality and MGCP can be used to manage media establishment in Media Gateways.[15]

RFCs[edit]

  • 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 (this 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[edit]

References[edit]

  1. ^ RFC 2805, Media Gateway Control Protocol Architecture and Requirements, N. Greene, M. Ramalho, B. Rosen, IETF, April 2000
  2. ^ "Understanding VoIP Protocols". packetizer.com. Retrieved 2012-06-07. 
  3. ^ RFC 3435, Media Gateway Control Protocol (MGCP) Version 1.0, F. Andreasen, B. Foster, The Internet Society (January 2003)
  4. ^ RFC 3525, Gateway Control Protocol Version 1, C. Groves, M. Pantaleo, T. Anderson, T. Taylor (editors), The Internet Society (June 2003)
  5. ^ RFC 5125, Reclassification of RFC 3525 to Historic, T. Taylor, The IETF Trust (February 2008)
  6. ^ title=Use of MEGACO vis-à-vis MGCP to build a Gateway Solution
  7. ^ "SIP core working group charter h2.48 history". packetizer.comg. Retrieved 2012-06-07. 
  8. ^ "Simple Gateway Control Protocol (SGCP". IETF. 30 July 1998. Retrieved 8 June 2012. 
  9. ^ "IPDC - Connection Control Protocol". IETF. August 1998. Retrieved 8 June 2012. 
  10. ^ "Level 3 Communications, Bellcore Announce Merger of Protocol Specifications for Voice Over IPe". Level 3 Communications. Retrieved 8 June 2012. 
  11. ^ "Media Gateway Control Protocol (MGCP)". IETF. 27 October 1998. Retrieved 8 June 2012. 
  12. ^ "Toward the PSTN/Internet Inter-Networking - MEDIA DEVICE CONTROL PROTOCOL". IETF. November 1998. Retrieved 8 June 2012. 
  13. ^ "MEGACO Protocol". IETF. 16 April 1999. Retrieved 8 June 2012. 
  14. ^ "H.248.1 : Gateway control protocol: Version 3". ITU Telecommunication. 
  15. ^ "Media Gateway Control Protocol". telecomspace.com. Retrieved 2012-06-07. 

External links[edit]