Overview of the SIP AG

SIP AG

A SIP AG is a voice gateway that exchanges SIP signals with other devices between the PSTN/ISDN and IP network. It can implement VoIP functions.

The packet switched network (PSN) development brings revolutionary changes to the voice phone system and many new technologies emerge. VoIP transmits voice services such as telephony services on an IP network, and the IP multimedia subsystem (IMS) promotes development of VoIP applications. An IMS network is a standard next generation carrier network that provides mobile or fixed-line multimedia services. It supports traditional packet switched and circuit switched telephony systems. Compared with the public switched telephone network (PSTN), VoIP features higher resource utilization and VoIP calls do not occupy telephone lines exclusively. VoIP has been applied for commercial use. The line switched PSTN has developed for many years and currently there are a large number of devices. Replacing the PSTN with VoIP takes high costs. A device can function as the SIP AG to connect the PSTN to IP networks with low costs.

As shown in Figure 3-1, the device functions as a SIP AG to integrate voice networks with IP networks.

Figure 3-1 SIP AG as a voice gateway

Terms

• IMS

  The IP Multimedia Core Network Subsystem (IMS) is an architectural framework for providing IP multimedia services, including audio, video, text, and instant messages. It was designed by the wireless standards body 3rd Generation Partnership Project (3GPP) in Release 5.

• SIP

  SIP is a text-based signaling protocol. SIP messages are classified into Request and Response messages. As an application layer protocol, SIP establishes, modifies, or terminates multimedia sessions and creates and controls multimedia sessions among two or more parties. SIP can work with specified protocols to complete session setup and media negotiation, such as Real-Time Transport Protocol (RTP), Real-Time Transport Control Protocol (RTCP), Session Description Protocol (SDP), Real-time Stream Protocol (RTSP), Domain Name System (DNS), Stream Control Transmission Protocol (SCTP), and Transmission Control Protocol (TCP).