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(Redirected from Media Gateway Control Protocol (Megaco))
Gateway control protocol
Relationship between network elements in a media gateway control architecture
StatusIn Force
Year started2000
Latest version(13/03)
OrganizationITU-T, IETF
Related standardsH.248.2 .. H.248.98
Domainnetwork architecture

The Gateway Control Protocol (Megaco, H.248) is an implementation of the media gateway control protocol architecture for providing telecommunication services across a converged internetwork consisting of the traditional public switched telephone network (PSTN) and modern packet networks, such as the Internet. H.248 is the designation of the recommendations developed by the ITU Telecommunication Standardization Sector (ITU-T) and Megaco is a contraction of media gateway control protocol used by the earliest specifications by the Internet Engineering Task Force (IETF). The standard published in March 2013 by ITU-T is entitled H.248.1: Gateway control protocol: Version 3.[1]

Megaco/H.248 follows the guidelines published in RFC 2805 in April 2000, entitled Media Gateway Control Protocol Architecture and Requirements. The protocol performs the same functions as the Media Gateway Control Protocol (MGCP), is however a formal standard while MGCP has only informational status. Using different syntax and symbolic representation, the two protocols are not directly interoperable. They are both complementary to H.323 and the Session Initiation Protocol (SIP) protocols.[2][3]

Multimedia audio controller device driver

H.248 was the result of collaboration of the MEGACO working group of the Internet Engineering Task Force (IETF) and the International Telecommunication Union Telecommunication Study Group 16. The IETF originally published the standard as RFC 3015, which was superseded by RFC 3525. The term Megaco is the IETF designation. Megaco combines concepts from MGCP and the Media Device Control Protocol (MDCP).[4] MGCP originated from a combination of the Simple Gateway Control Protocol (SGCP) with the Internet Protocol Device Control (IPDC).[5]

After the ITU took responsibility of the protocol maintenance, the IETF reclassified its publications as historic in RFC 5125. The ITU has published three versions of H.248,[1] the most recent in September 2005. H.248 encompasses not only the base protocol specification in H.248.1, but many extensions defined throughout the H.248 sub-series.

Protocol overview[edit]

3GPP / TISPAN IMS Architectural Overview. H.248 messages are used between Media Gateway Control Function (MGCF) control IMS - Media Gateways (IMS-MGW). SIP is used by MGCF to interact with Call Session Control Function (CSCF) and Breakout Gateway Control Function (BGCF)

H.248/Megaco due to its master-slave nature does not describe the establishment of calls across domains or across media gateway controllers. H.248/Megaco is used for communication downward, to the media gateways and does not constitute a complete system. The architecture requires other protocols for communication between multiple MGCs.

The device that handles the call control function is referred to as an intelligent media gateway controller and the device that handles the media is referred to as a relatively unintelligent media gateway. H.248 defines the protocol for media gateway controllers to control media gateways for the support of multimedia streams across IP networks and the public switched telephone network (PSTN). It is typically used for providing Voice over Internet Protocol (VoIP) services like voice and fax between IP networks and the PSTN), or entirely within IP networks.

Because of the types of devices targeted for control by H.248/Megaco and the low level of its control structure, H.248 is generally viewed as complementary to H.323 and Session Initiation Protocol (SIP). While a media gateway controller (MGC) uses H.248/Megaco to manage media establishment and control with a number of media gateways (MGs), other VoIP protocols, such as SIP and H.323 are used for one communication between controllers.[3] From a SIP perspective, the combination of MGC and MGs are treated together as a SIP Gateway.

The H.248/Megaco model describes a connection model that contains the logical entities, or objects, within the Media Gateways (MGs) that can be controlled by the Media Gateway Controller. The main entities are Contexts and Terminations.

These source or sink one or more media streams or control streams. Terminations may be physical or ephemeral
h.248 Connection Model
These are star connections created by associating multiple terminations. A logical entity on an MG that is an association between a collection of Terminations. A NULL context contains all non-associated terminations. A Context is a logical entity on an MG that is an association between a collection of Terminations. A ContextID identifies a Context.
The normal, 'active' context might have a physical termination (say, one DS0 in a DS3) and one ephemeral one (the RTP stream connecting the gateway to the network). Contexts are created and released by the MG under command of the MGC. A context is created by adding the first termination, and it is released by removing (subtracting) the last termination.
A termination may have more than one stream, and therefore a context may be a multistream context. Audio, video, and data streams may exist in a context among several terminations.

In IP Multimedia Subsystem (IMS), Media Gateway Control Function (MGCF) control Media Gateways (MGW)s to send and receive call to / from the PSTNcircuit switched (CS) networks using. H.248. The MGCF uses SIP messages to interact with Call Session Control Function (CSCF) and Breakout Gateway Control Function (BGCF).

Although the modeling of the Media Gateway differs in H.248/Megaco when compared to MGCP, there is a similarity between the semantics of the commands in the two specifications. There is almost a one-to-one mapping between the commands of MEGACO and MGCP. For example, the Create connection command in MGCP has an equivalent ADD termination command in MEGACO, the Modify connection command in MGCP equates to the MODIFY termination command of MEGACO and the Delete connection command equates to the SUBTRACT termination command of MEGACO.[2]

Messages and commands[edit]

The Media Gateway Controller always manages the media channels available on the Media Gateway itself by managing specific contexts and terminations. When the call state changes, the MGC sends a corresponding message to the gateway and waits for an acknowledgment.

Each message is a transport mechanism for transmitting commands, and not the command itself, unlike most other telecommunication protocols.

Protocol Commands:

  • Add
  • Move
  • Subtract
  • Notify
  • Modify
  • AuditValue
  • AuditCapabilites
  • ServiceChange

Typical MGC and MG message exchange[edit]

Message structure[edit]

Message {Transaction {Action {Context {Command {Termination {Descriptor {Package}}}}}}}

By analogy with the OSI model, the hierarchy of interworking levels from the point of view of transmission over the network (Ethernet or ATM) is following.


Comparison with MGCP[edit]

The H.248/Megaco model is more complex than the Media Gateway Control Protocol (MGCP) model and it provides more flexibility when defining media control. For example, in MGCP a call can use an endpoint mode conference to manage the stream mixing, but it cannot achieve the fine grain control of H.248/Megaco in managing the media streams.

The H.248/Megaco model simplifies connection setup within the MG and to entities outside the MG. It simplifies the mechanism by which the media gateway controller (MGC) can specify associated media streams as well as specify the direction of media flow. H.248/Megaco is therefore able to provide greater application level support than MGCP. For example, setting up a multi-party conference with H.248 merely involves adding several terminations to a context. In case o MGCP, however, the MGC needs to establish several connections to a special type of endpoint called the conference bridge.

Following are the main differences between Megaco/H.248 and MGCP:

A call is represented by terminations within a call contextA call is represented by endpoints and connections
Call types include any combination of multimedia and conferencingCall types include point-to-point and multipoint
Encoding is text or binaryEncoding is text
Transport protocol is TCP, UDP or SCTP.Transport protocol is UDP.
Standard protocol for media gateway controlIETF status is Informational. MGCP does not specify an Internet standard
Defined by ITU (formerly by IETF and ITU)Managed by implementors, many independent protocol extensions exists.

Standards documents[edit]

ITU-T H.248 Recommendations
  • ITU-T Recommendation H.248.1, Gateway control protocol: Version 3.
  • ITU-T Recommendation H.248.2, Gateway control protocol: Facsimile, text conversation and call discrimination packages.
  • ITU-T Recommendation H.248.4, Gateway control protocol: Transport over Stream Control Transmission Protocol (SCTP).
  • ITU-T Recommendation H.248.12, Gateway control protocol: H.248.1 packages for H.323 and H.324 interworking.
  • ITU-T Recommendation H.248.15, Gateway control protocol: SDP H.248 package attribute.
  • 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]

  • Session Initiation Protocol (SIP)


  1. ^ ab'H.248.1 : Gateway control protocol: Version 3'. International Telecommunication Union - Telecommunication. Retrieved 2016-07-12.
  2. ^ ab'Use of MEGACO vis-à-vis MGCP to build a Gateway Solution'(PDF).
  3. ^ ab'H2.48 history'. Retrieved 2012-06-07.
  4. ^'Toward the PSTN/Internet Inter-Networking - MEDIA DEVICE CONTROL PROTOCOL'. IETF. November 1998. Retrieved 8 June 2012.
  5. ^'Level 3 Communications, Bellcore Announce Merger of Protocol Specifications for Voice Over IPe'. Level 3 Communications. Retrieved 8 June 2012.

External links[edit]

Driver For Multimedia Audio Controller

  • 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.
  • H.248.1 Base protocol specification .
  • MEGACO vs MGCP White Paper from Hughes Software Systems
  • MEGACO 1st draft, IETF, April 1999]
  • Protocols of Megaco and MGCP by Doug Allen at Dynamix
Retrieved from ''
(Redirected from Media Gateway Controller)
Relationship of network components in a 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 Internet Protocol network and traditional analog facilities of the public switched telephone network (PSTN).[1] 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.

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.

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) 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.[2]


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[edit]

Media gateway[edit]

Multimedia Audio Controller Hp Drivers

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[edit]

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).


The device control protocols evolved through several versions. 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 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.[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 use 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]

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. Dmg mori nhx 4000 weight. 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 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.[15]

Standards documents[edit]

  • RFC 2805Media Gateway Control Protocol Architecture and Requirements, April 2000 (Informational)
  • RFC 2705Media Gateway Control Protocol (MGCP) Version 1.0, October 1999 (Informational)
  • RFC 3435Media Gateway Control Protocol (MGCP) Version 1.0, (supersedes RFC 2705) (Informational)
  • RFC 3015Megaco Protocol Version 1.0, November 2000, (Standard Track)
  • RFC 3525Gateway Control Protocol Version 1, June 2003 (Obsoletes: RFC 3015) (Standard)

See also[edit]


  1. ^ abRFC 2805, Media Gateway Control Protocol Architecture and Requirements, N. Greene, M. Ramalho, B. Rosen, IETF, April 2000
  2. ^'Understanding VoIP Protocols'. 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. ^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. ISBN0071363262.
  15. ^'Media Gateway Control Protocol'. Retrieved 2012-06-07.

External links[edit]

Multimedia Audio Controller Driver Install

  • 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
  • H.248.1 Base protocol specification , ITU-T
  • Implementing Media Gateway Control Protocols - A RADVISION White Paper
  • A Description of MGCP and SIP Michael Lamy, ADTRAN Enterprise Networks Division

Multimedia Audio Controller Device Driver

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