【正文】 rovide services including IP voice and fax service. Forrester Research estimates that longdistance IP telephone business in 2001 will reach $1 billion, many panies also according to their own development strategy for the experiments of IP phone and deployment, such as ATamp。T carried out IP phone experiment on the Internet in November May 1998, Atlanta, Boston and San Francisco launched IP phone services, and prepared to carry out theses services in large area in the next 12 to 18 months. Now in addition to directly provide the IP telephone business operator, there have been some operators who disposal, exchange and settle IP telephone business. The former install your own gateway equipment around, the latter usually has their own backbone of global network and settlement center, it is similar to a membership organization which responsible for the members with global IP phone roaming and billing. The panies who provide this service are ITXC, GRIC and VIP Calling, etc, By joining the organization can provide global IP telephone service.2. IP phone standardsThe international organization for standardization of IP phone are mainly the international telemunications union (ITUT) standardization department, the European telemunications standards institute (ETSI), the Internet engineering task force (IETF) and multimedia remote meeting group (IM TC), etc. (1) ITUT SG16The international telemunication union SG16 team engaged in the research of multimedia terminal and security problems, the main work is to develop series.(2) ETSITIPHON Engineering DivisionGroup39。s main goal of this project is a set of business interoperability requirements, determine the interface and functional aspects of architecture, the call control procedures, the traffic rules and protocols, study the endtoend service quality parameters and e. 164 conversion between address and IP address, and billing and security issues. TIPHON engineering team want to all kinds of network operators to provide businessoriented solution, its work is largely based on H. 323, a series of Suggestions and the existing circuit switched network standards.(3) IETFIETF formulate new signaling protocol, including the session initial protocol (SIP), Internert and PSTN network. IPTEL working group of IETF is overall responsible for the relevant agreements and framework, including call processing grammar, etc. The working group also writes some business model file, describing the syntax by call processing implementation of business and discussing the use of grammar.(4) IMTCIMTC is made up of more than 150 members from North America, Europe and the asiapacific region, its purpose is to establish an open international standard, to promote the application of interactive multimedia conferencing solutions and implementation. VoIP BBS (Voice over IP Forum) of IMTC aperiodically do some activities to make standard, promote the IP telephone business.Due to the rapid development of Internet, and the great prospects of the business of packet voice, the above organizations actively promote the standardization of IP phone positively driven by each of the manufacturers. According to the current situation and the key work of each standard organization, related to the IP phone protocol can be divided into two main categories: H. 323 protocol and SIP. At present each organization to carry on IP network realtime business (voice, video, etc.) is no different, all is the use of the derived from RTP protocol of IETF, but are different in terms of call setup and control scheme, its representative is the following, H. 323 and SIP protocol.(1) Protocol belongs to the ITU multimedia munication protocol series, , which provide packetbased network voice, video, data and control protocol. H. 323 support point to point munication and support point to multipoint munication protocol with the MCU (multipoint control unit). As a framework agreement, H. 323 provided the system and ponent description, call way description and call signaling program. H. 323 related protocols including H. 263, H. 261 video coding standard and G. 711, G. 723, G. 722, G. 728 audio coding standard, T. 120 multipoint data conference series standard, H. grouping and synchronous standard, H. 245 system control standard, etc. The protocol stack is shown in figure 1. protocol after years of development, the function, is supported by the broad masses of manufacturers. VoIP BBS of IMTC has been used H. 323 as the basis of Internet telephony. system structure including: H. 323 terminal, Gateway, Gatekeeper, and multipoint control unit (MCU). terminal: provide realtime twoway audio, video and data munications. But the H. 323 has not stipulated the audio or video equipment, data application and network interface.Gateway: provide call signaling control, channel information conversion, and h. 323 terminals and other ITU terminals interconnect technology.Gatekeeper: provide management mechanism and management for gateway resources。 Provide address conversion function, call control and network bandwidth management, etc.Multipoint control unit: provide conference control and media processing functions.H. 323 system position and exchanged with other terminals as shown in figure 2.In the system structure of H. 323, it is worth mentioning H. 323 domain. H. 323 domain was defined as a group of gateway collection under the unified control. The concept of domain not only the meaning of technology, also has the meaning of administration.(2) SIP ProtocolSIP is session initiation protocol provided by ISTF, is a kind of based on the text of the protocol, using the rules of the SIP resource location description language. It is not like which provides all of the munication protocols, but only provides the establishment of the call and the control function. It is applied to the IP phone, pared with , the characteristics of simple, flexible is stand out, unlike H. 323