SIP Introduction SIP (Session Initiation Protocol, session initiation protocol) is the IP phone signaling protocol proposed by the IETF (Internet Engineering Task Group). Its main purpose is to resolve signaling controls in the IP network, and communication with SoftSwitch, thereby constitute a better value-added business platform for telecommunications, banks, finance and other industries. The structural diagram is shown below.
SIP features and features, as hidden by their name, SIP is used to initiate sessions, which control the establishment and end of multimedia sessions participating in multiple participants, and dynamically adjust and modify session properties, such as session bandwidth requirements, transfer Media type (voice, video and data, etc.), media codec format, support for multicast and unicast, etc. SIP is designed to take into account extended adaptability to other protocols. It supports many address descriptions and addressing, including: username @ host address, called number @PSTN gateway address and such as Tel: 010-62281234 Such ordinary telephone numbers, etc. In this way, the SIP call is called by the called address, you can identify whether the called is on the traditional telephone network, and then passed through a gateway connected to the traditional telephone network and established a call. The most powerful SIP is the user positioning. The SIP itself contains functions registered with the registration server, or other locating servers such as DNS, LDAP, such as DNS, LDAP, etc. to enhance their positioning function.
There are clients and servers in the classification and functionality of the servers in SIP. The client refers to an application that establishes a connection with the server in order to send a request to the server. User Agent and Proxy (Proxy) contain clients. The server is an application for providing services to the client and returning a response. A total of 4 basic servers: • User proxy server: Contacts users when receiving SIP requests and returning responders on behalf of the user. · Proxy server: Represents other clients to initiate a request, which acts both the server that acts as a client. It may rewrite the contents of the original request message before the forwarding request. · Right to the server: Receive the SIP request, map the original address in the request into zero or more new addresses, return to the client. · Registration server: Receive the client's registration request to complete the registration of the user address. User terminal programs often need to include user agency clients and user proxy servers. Proxy servers, redirect servers and registration servers can be seen as a public network server. The Concept of "Location Server" is often mentioned in SIP, but the location server is not part of the SIP server. The way the SIP server requests the location service is not within the discussion of the SIP. Its implementation in the IP network is as follows.
