Overview of the H.248 AG

Definition

H.248 is a recommendation from the International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) and was first published (version 1) in June 2000. It is a gateway control protocol that is used by a Media Gateway Controller (MGC) to control Media Gateways (MGs) to enable the transmission of various media data.

Compared with the Media Gateway Control Protocol (MGCP), H.248 has the following advantages:

• Supports access of varied data types.
• Enhances the description capability of the MGCP, supports a broader range of networks, and provides far greater flexibility when defining media control.
• Supports various transport layer protocols such as the User Datagram Protocol (UDP) and Stream Control Transmission Protocol (SCTP).

Figure 4-1 shows the process of setting up and releasing an H.248-based VoIP call.

Figure 4-1 Application of H.248 in VoIP

Terms

• MG

  A core network device for converting the media format of a network to the required format of another network. It can process audio, video, and data services, and convert the media format in full duplex mode. It can also play certain audio and video signals and provide the interactive voice response (IVR) function and media conference.

• MGC

  In the ITU-T H.323 architecture, the MGC is responsible for call control on MGs.

• MGCP

  This protocol defines a call control architecture for signaling processing and session management in multimedia conferences. In this architecture, call control is separated from data transmission. MGCP is a master/slave protocol that allows a call control device such as an MCG or Call Agent (CA) to take control of a specific port on a Media Gateway.

• UDP

  UDP is one of the core members of the Internet protocol suite. It allows applications on a computer to send datagrams to other computers on an IP network. UDP is a message-based connectionless protocol that provides unreliable connections for applications. It provides no guarantees for message delivery. UDP messages may be discarded, repeated, delayed, or transmitted in an incorrect sequence. When data is transmitted using UDP, the destination does not actively inform the source of the transmission result.

• SCTP

  A transport layer protocol used between the SCTP user application and a connectionless packet network. In the SIGTRAN protocol stack, the upper layer of SCTP is the adaptation module of the SCN signaling, for example, M2UA and M2UA, and the lower layer of SCTP is the IP network. The SCTP protocol delivers the higher reliability, optimum real-time performance, and multi-homing feature for signaling transmission.

• H.248

  A media gateway control protocol used for communications between the media gateway controller (MGC) and the media gateway (MGW) in the detached gateway architecture so that the MGC can control the MGW. In Universal Mobile Telecommunications System (UMTS) networks, the interface between the MGC and the MGW is the MC interface and the 3GPP defines specific usage of H.248 over the MC interface.

• VoIP

  VoIP is a group of technologies used for the delivery of voice communications and multimedia sessions over IP networks, such as the Internet. The VoIP service is cheaper and is available on smartphones, personal computers, and Internet access devices. VoIP calls are free for Internet users.