Introduction and application of Session Initialization Protocol (SIP)

Next Generation Network (NGN) and SIP protocol

With the rapid development of mobile communication technology, we are brought into the colorful 3G multimedia Information age. In particular, the rapid development of the Internet, more and more users can use faster, cheaper Internet connection, which makes such as chat applications, video voice, online games, such as the need to continue online applications to achieve the possibility. The traditional telecom network is designed for the telephone business, the type of dialing a number and conversation mode has been far from meeting the needs of this multimedia applications, the need to design a new network structure to support. 3G Network as the Next Generation network (next Generation NETWORK,NGN) Its main goal is to provide users with a variety of multimedia services, including voice services and the Internet Digital Service, the main feature is the cable network, the Internet and wireless network seamless integration. Under this condition, the concept of SoftSwitch is born and bred. One of the focuses of the next generation network is to separate the call control function from the media gateway and realize the basic call control by sending the software package. In this way, the network system of NGN, which separates the service from the call control and the data bearer, makes the low coupling between the layers can effectively meet the diverse and changing demands of the users.

Figure 1. Next Generation network layered architecture

In many communication protocols of SoftSwitch devices, Session Initiation Protocol (SIP) is an important protocol for next generation network and IP Multimedia Subsystem (IMS) by virtue of its simplicity and easy realization. SIP protocol is a signaling protocol in the IETF (Internet Engineering Task Group), the main purpose of which is to establish, modify and terminate the Application layer protocol of multimedia session in IP network. Its main applications include but not limited to voice, message, video, call control and so on. SIP was originally used to publish multimedia content, because of its simplicity and scalability, which was called the IETF Standard [RFC2543] in 1999. With the enhancement of the SIP protocol interoperability and new features, the new standard [RFC3261] was formed in 2002.

The SIP protocol is a signaling protocol based on Hypertext Transfer Protocol (HTTP) and Simple Mail Transfer Protocol (SMTP), which describes the location of the SIP protocol in the protocol stack:

Figure 2. Protocol stack Structure

SIP protocol, although it belongs to the application layer protocol, does not provide any service in itself. But SIP is the basis of communication and can be used to build different services on the basis of SIP communication. SIP protocol in the establishment and maintenance of multimedia sessions, the main support for the following 5 features:

Check the location of the end user. Wherever the called party can ensure that the call reaches the called party, any description information to the positioning information conversion;

Check how willing the user is to participate in the session. Participants in the call can introduce other users to join or cancel the connection of other users;

Check media and media parameters to allow the group associated with the call to remain consistent on the support features;

In the call with the two sides to establish the session;

Send and terminate sessions, modify session parameters, and activate session management operations such as services;