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简 评 Multimedia Agreement H.323 and Sipwww.aspsky.Net 2004-3-30
Abstract: The two technologies of the industry's multimedia business in the industry --H.323 and SIP have been discussed and practical in nearly 7-8 years. This article reviews, reviews, and comparisons on the development and evolution of its protocol. Finally, this paper briefly looks forward to its future prospect. Keywords: H.323 SIP Multimedia IP Phone 1. A main challenge for the next generation IP packet network technology is how to provide real-time multimedia business, including telephone and video services in IP packet network. At present, the development of multimedia business technology on the next-generation IP group online has two major directions. First, follow the ITU-H.323 protocol standards and the other is the SIP protocol standard for the Internet Engineering Task Force IETF. The concepts and standards of these two multimedia technologies are almost all proposed in the mid-1990s, and will be accompanied by people's general attention from the successful popularity of IP phone markets. Although people are accustomed to describing the terms of VoIP to describe the H.323 and SIP protocol standards, the concepts of these two technical representatives and the multimedia business they can provide far more than established a call. As a technique of multimedia services on IP packets, they have many common features, for example, they are all peer-to-peer communication protocols, and they have advocated distributed control and intelligent terminals, all of which use the same real-time media protocol. People's requirements not only provide familiar traditional telephone services and features, but also to provide support for supporting and integrating new business and functions. However, these two protocol systems have the same purpose, similar to the starting time, but due to standard organizations that belong to different sectors, under different standards, the principles of different concepts, and their content, progress and development direction It has been very different. After nearly 7 to 8 years of discussions, revisions and practices, both protocol systems become very complicated. In addition, for a long time, due to different backgrounds and interest factors, people have caused some misunderstandings of standards. From different perspectives, the review of two protocols may produce non-objective views and prejudice, plus two protocol systems are constantly developing, evolving, and perfect, so it is necessary to review these two multimedia agreements. Comment and comparison. Second, about the H.323 protocol system ITU-T Signaling Agreement on multimedia conferences from May 1995, December 1996, the 16th Research Group (SG16) responsible for multimedia signaling (SG16) A version of H.323-V1. The H.323 protocol group standard describes a system architecture consisting of a multimedia network consisting of endpoint EP and other NEs (gateways GK, gateway GW, and multi-point control unit MCU) on the packet network. It refers to a multimedia protocol group. Including the call control signaling H.225 and responsible for media control signaling H.245. Media Control Signaling is responsible for capacity exchange, media channel establishment / release and conference control protocols. The H.323 system architecture also includes data conferencing T.120 protocols and fax T.38 protocols, as well as real-time media stream protocol RTP and its control protocol RTCP. H.323 Support Voice Code Decoding G.711, G.723, G.729 and Video Codes H.261, H.263, etc. H.323 not only systematically standardizes a group of voices, but also a complete data and video conferencing standards. Although H.323-V1 was originally designed to group LAN LANs, people used H.323 for a wide-area Internet from the beginning, and the H.323 has achieved success and immediately received extensive attention. The H.323 standard emphasizes the complete interconnection of the traditional public telephone PSTN network, where the call control section and H.245 in H.225 are borrowed the narrowband video H.320, H.324 protocol group of existing ITUs. H.221 and H.242. However, the registration of the registration in H.225, allows admin, status status and address parsing mechanism (RAS), has to be designed from the header. The basic call program consists of RAS signaling (endpoint registration, grant control, and address analysis) and call signaling (connection establishment, power exchange, open logical channel). H.323 The meeting is performed by multipoint control unit MCU. The real-time media stream protocol of H.323 and its existing IETF standard RTP and RTCP respectively.
In January 1998, the second edition H.323V2 overcome and improved some of the shortcomings of the first edition, increasing the tunnel mechanism of fast-connect mechanism FAST-Connect and H.245. Supplementary Business Architecture H.450 Series Protocol and Security Architecture H.235 protocols are proposed, as well as improvements in other PSTN interconnected signaling mechanisms. In September 1999, the third version of H.323-V3 only had small-scale addition and correction. Annex for UDP, attachments G, and some H.323 / H.245 is added and H.450.4-H.450.7 protocol. In November 2000, the fourth edition H.323-V4 added an important function required for telecom operations: this includes the reliability, scalability and flexibility of the H.323 system. Annex M and Accessories R provide the transmission and robustness of SS7 messages. This makes the H.323 system in fullness and systematic to maturity in the fourth edition. In September 2003, the goal of the fifth Edition H.323-V5 was to pursue the stability of the agreement and the balance of universal extension. The fifth edition along with the General Expansion Architecture GEF model of the fourth edition, the H.460 series standard is the embodiment of this universal expansion. The ITU's H.323 system is basically a cost-effective open standard system that is both a traditional PSTN call process and IP network characteristics, representing a big trend of telecommunications multimedia business. Its specialty is to learn from the network, interconnection and operation experience of the telecommunications network, can communicate with the PSTN network, interconnect with narrowband video services and other data services and application networks. This is exactly an important reason why Multimedia business has been widely used in the world since 1996. With the H.323 technical system, VoIP operators can basically inherit the management and operational model of traditional operators, which is especially important for China, Southeast Asia. H.323 VoIP and video service networks in China, operators are all national big nets, and the extensibility and stability requirements of the network are extremely high, and the networking must be multi-storey multi-domain, and more than hundreds of people in the recovery city. Every month is several hundreds of millions of traffic. For the formation of such a large network, H.323 technology is suitable and successful. Second, the SIP standard SIP is the abbreviation of session initiation protocol, and the domestic literature is translated into session start protocol or session initial protocol. The concept of SIP appeared in 1996 in the Internet in the Internet and is first proposed by Multimedia Control (MMUSIC) of IETF. After years of research, discussion and agreement, MMUSIC Working Group officially proposed RFC2543's recommendations for the basic principles and mechanisms of SIP, and discussed in the Internet industry. The MMusic Working Group is a research team with considerable history and reputation, which also proposes the RFC2327 session description protocol SDP and SIP MIME type format. In September 1999, a large amount of interest and work, IETF divided SIP's research and development work from MMUSIC and established a SIP Working Group, published SIP draft in July 2000. Subsequently, the SIPPING Working Group and SIMPLE Working Group are established to pay special attention to SIP extension and multimedia application and SIP instant messages and online services. In June 2002, ITEF's SIP Working Group issued a new version of the SIP basic skeleton and mechanism RFC3261 proposal to replace RFC2543. The concept of SIP has been proposed and sought after in the Internet and telecommunications industry. IETF proposed in 1999 RFC2543 in a network environment based on an IP network, particularly in a network environment such as Internet, implements real-time multimedia communication applications. The so-called session refers to the data exchange between the application level users, SIP is the session operation protocol. The SIP standard specifies the basic mechanism of establishing, modifying, and ending multimedia sessions. These multimedia sessions include multimedia conferences, distance education, IP phones, and other similar applications.
In applications based on the SIP protocol, each session can be a variety of different types of application content, which may be ordinary text data, or digitally processed audio, video data, and data such as a game, etc. Therefore, the SIP application has huge flexibility and potential space. The SIP standard defines a multimedia communication and conference signaling mechanism, and borrows the following IETF protocol: Message HTTP 1.1, Media Description (SDP), SIP message encoding based on ASCII text format for application and error correction, application encoding ( MIME), SIP's media stream and its control protocols are RTP and RTCP, respectively. SIP recommends that the Internet is similar to the Internet structure, providing services through the intelligent SIP terminal, and SIP can use the URI to dynamically network. Typically, the SIP terminal includes a UAC (user agent client) and UAS (user proxy server), UAC is used to initiate requests, UAS is used to land request. SIP's terminal registration and positioning available network resources: registration server, proxy server, and relocation server. SIP terminal name and address parsing can use network resources: positioning servers, DHCP, ENUM, TRIP, and DNS servers. The main function of SIP is the start of session objects and resources, and the startup of the application, and the agreement between session parameters. In order to achieve this, SIP provides independent operation of a set of text messages between peers (user terminal EP User Agents UA) in the SIP mesh. Thus, the basic call of the SIP can be provided with a SIP's INVITE request message signaling operation and other operations. The session itself includes two-layer meanings, the SIP protocol includes the characteristics of the address of the object and protocol processing, and its own session content is not necessarily associated. The exchange of multimedia flows between session objects is limited by another specification. IETF recommends using a session description protocol SDP, strictly said that SDP is not a protocol, but a texture description of a text format included in the SIP message. The session description transmitted by the SIP message is transparent for SIP, so the SIP supported session application is not limited to the ability of the telephone or conference, depending on the description of the session, SIP can also support information extraction, broadcast or subscription. Session. SIP's reference skeleton and principles are RFC3261 recommendations. In addition, there are also a range of RFCs and vast structure of SIP-related drafts to improve and supplement SIP applications, business, programming, conference, routing, regulatory, and interconnect structures. In this sense, SIP's IP phones and conference criteria are still in "to be completed", and a series of workgroups of ITEF are also stepped up revision and complete the baseline RFC, other RFCs, and expands. Third, the comparison of the two agreements H.323 and SIP are the results of the two standard camps (telecommunications field and Internet areas) along the results of their respective traditions and philosophy. H.323 is proposed in ITU, which focuses on compatibility with the IP phone and well-known traditional telephone services; while SIP is called to use an IP phone as an application on the Internet. Table 1 H.323 and SIP architecture comparison system architecture H.323 SIP standard organization ITU International Telecommunications Alliance SG16 leads IETF Internet Engineering Task Force SIP Working Group leads design concept according to the experience and requirements of telecommunications network, systematically design IP online Multimedia voice, video and data conferences and components, protocols, and procedures required for communication. According to the experience and requirements of the Internet, the module design IP network builds the components, protocols, and procedures required for "session" communication. The protocol architectural protocol architecture includes multimedia conferences and various business areas of communication, such as endpoint capacity exchange, meeting control, signaling interoperability, QoS control, registration, and business discovery. The protocol system includes basic signaling, user registration and location in the form of modules. Other related and independent features and services are provided through other related and independent protocol systems.
Architecture End Point EP, Gateway GW and Netleave GK Multipoint Control Unit MCU User Agent UA and Various Server Main Standards H.323 V1-V5 Architecture H.225 V1-V5RAS and Call Signaling, H.245 V2-V9 Multimedia Control Protocol H.235 V1-V3 Security Mechanism Agreement H.350 Multimedia Conference Directory Architecture H.450 Supplementary Business Architecture Series Protocol H.460 General Extension Architecture Series Protocol H.246 Interoperability Series Protocol H.248 Media Gateway Control Protocol RFC3261 is replaced by RFC2543. RFC2327 (SDP) RFC3266 (Model of SDP) RFC2068 HTTPRFC2045 MIMERFC2396 URIRFC2234 ABNF 2002, more than 300 SIP-related recommendations Waiting for discussion. The ITU-T uses from top to bottom to formulate standards, which defines specific content ranges from the overall macro uniform rules. From the system of IP phones and multimedia communication, H.323 standards are more relatively relatively relatively systematic, relatively complete, and relative, standardized, multimedia communication protocols, state mechanisms, and message flow architectures. This system also includes some specialized solutions across topic, such as QoS and mobility. On the other hand, the IETF's SIP has more tends to set the standard from the downward approach. The general model of abstract and deducting communication operations by simple basic requirements. Because the IETF is highly admined by the system and application, the agreement established by the basic operation module is transparent to specific applications, so it is strictly, RFC3261 is only SIP's reference skeleton and Module principles, rather than the complete system system of SIP applications or services, SIP applications or services require other RFCs and many SIP expansion RFCs and combinations of recommendations to be mature. This ability to generate applications and services depending on the general standard module is not only the basic applications will be very easy to use, but it is more open, more flexible, more conducive to innovation and more vitality. But it is also clear that the standard module and its operation have the versatility and generality of multimedia communication? The standard process is too long, and the standard category is easy to lack system and integrity, and the distributed multi-complicated network application and business compatibility and interoperability are not easy to guarantee. In 2002, it was an arduous year of the SIP protocol standardization task, with more than 300 SIP-related recommendations waiting for discussion. IETF has recently been admitted: SIP protocol standards may take 6 to 7 years. The SIP Protocol Standards need to be improved, mainly with traditional PSTN interconnection, accounting means, and processing of emergency calls. Table 2 H.323 and SIP system system Compare system system H.323 SIP system reliability network element fault tolerance defines some mechanisms, such as backup network elements (gatekeepers, endpoints). No. The load equalization endpoint can be registered into a set of GK. SIP itself is not yet. However, it can borrow DNS servers or HTTP load balancing mechanisms. System Scalability Multi-domain / Multi-Domain Debut and Accessories G Internet Support Address Resolution, Interconnect and Call Use Report. Support address parsing / addressing via the relocation server. No status keeps support, direct call mode of the gatekeeper network. Support, non-bifurcation SIP agent servers can be stateless. Address parsing LRQ or attachments G, TRIP, ENUM, or DNS. Relocate the server, or TRIP, ENUM, or DNS server. The gateway separation h.323v4 defines H.248. No. Commercial scale large-scale commercial 4 ~ 5 years small-scale commercial 1 ~ 2 years system security authentication support, H.235 support, HTTP, SSL, PGP, S / MIME or others. Encryption support, adopt H.235 support, SSL, PGP, S / MIME, or other. Many people think that H.323 standards are too traditional thinking, making H.323 protocols too complicated, while SIP is simple. However, people supporting H.323 believe that the communication system itself is not simple, SIP will simplify communication. It is actually short-sighted and the demand for telecom operators lacks full understanding. The H.323 protocol is complex but it meets many requirements for telecom operators.
Of course, if traditional PSTN's interoperability and telecom operators existing business model or not for IP phones and PSTN applications, SIP simple and easy to use should be popular, for example, PC to PC calls and communications . However, if you use SIP for telecommunications operator IP phone or multimedia communication business, the reality will make SIP to face challenges. The SIP protocol definition itself is not as good as H.323. The SIP structure has many ways to openly explain the space of any explanation, and some of the SIP protocol networks require many supplementary protocols. There are hundreds of SIP expansion standards and drafts, which not only makes the SIP "System" protocol, but more serious is due to the unaptuous, interoperability of the expansion standards and draft progress. SIP advocacy mode combination application design is flexible, but sometimes it brings problems, and complex communication systems do not have better overall architectures and "unified" standards, how can network element components work well? In addition, H.323 capabilities exchange and negotiation mechanisms facilitate control of multimedia services: such as turning any media channels (voice, video or data) without affecting other channels. Table 3 H.323 and SIP Protocol Characteristics H.323 SIP extension and compatibility passed the ITU standard period release, new features adopted a general expansion architecture GEF to expand new features, and safeguards backward compatibility. Add a new extension module to the release of the IETF's normally independent RFC. Guarantee the basic function and compatible. Vendor specific function design vendors reserve fields to avoid conflicts. The different header lines that can be added to add SIP are used for vendors. But interoperability is compatible. Message definition ASN.1 ABNF-RFC2234 message encoding compact binary ASCII text format Message Package long call setup RAS / H225 / Q.931 RFC3261 Media Control H.245 SDP RFC2327 1998.4 Transfer Protocol Most TCP or UDP Most UDP or TCP Media Transport RTP / RTCP RTP / RTCP codec CODEC supports all standard or non-standard codes. Static or dynamic settings. IANA registered codec or mutual agreed codeword name. Static or dynamic settings. Business load speech, video phone business, voice, video and data conferences and communications. Voice, video telephone traffic, and instant messaging in integrated Internet, online conversation. Message Type RAS-ARQ / RRQ / LRQSetUP / Alert / ProgressConnect / ReleaseComplete Inviteokack / PrackbyE Addressing Multiple Forms, E.164 or H H.225 H.323 alias or URI, where E164 can be H323ID, transmission address, Email address or called number. Only the URI format is supported, and E.164 can be converted to a URI format. Basic call creation -> setup <-ustom -> Connect / Ack -> Invite <-200 OK-> ACK Call removal line is similar to the PSTN mode. BYE message can be used to remove lines, but the demolition process is not complete enough. The PSTN protocol is borrowed with PSTN, and the interoperability is better. The abnormal situation is weak, depending on the new protocol module to improve. SS7 Transmission Ability Additional M SIP-T / SIP-I Billing Ability Adopt Returning Mode Neighborhood and Gateway Ways can be charged. The proxy server that maintains the call status can be charged. Fax T38 T38DTMF dual-tone multi-frequency support benchmark specification and additional band RFC2833. Only supported RFC2833. The external specification is also a draft, there is no reference specification. Capacity negotiation network elements can be flexibly exchanged and negotiated: such as opening or closing any media channel (voice, video or data) without affecting the normal operation of other channels. Net elements do not perform capacity exchange and negotiation, and in shortly, it is "suggested / accept" model. Because of this, although the concepts and standards of H.323 and SIP are almost start at the same time, the applications and services of the same multimedia communications are almost at the same time, but because of their ideas, their results and market effects, their results and market role, The effect is also significant.
H.323 puts the attention of the basic functions of multimedia services, supplementing business, interconnection (such as PSTN), so H.323 will soon provide a variety of vertical solutions and enter the commercial market in multimedia communication. For example, the H.323 IP phone and video and data conferences and communication schemes are complete. However, for simple calls, the process of H.323 is unnecessarily complex, and the subsequent version of H.323 adds the FAST-Connect / Start to make H.323 simple call flows similar to SIP. Currently, the H.323 is transferred to a solution to solving such as security, mobile, and QoS issues. The SIP has left another road, and SIP starts to focus on an universal protocol for abstract and defining business sessions. The SIP's reference skeleton may only complete basic calls for IP telephony services. Since the IP phone must face the burden on traditional PSTN, the current SIP has to consider considering adding SIP's scales and its operations to address IP phones, including complement business and traditional PSTN Internet. So, from this point of view, although the H.323 leads to SIP, H.323, and SIPs are different in the standardization of SIP, H.323, and SIP in IP phones and videos and data conferences and communication applications, the H.323 and SIP operations are mutually fused. For example, H.323 is standardized for each supplementary service, while SIP is standardizing the operation of the protocol to support supplementary services. In addition, H.323 can support video calls and video conferencing, as well as data conferencing business, and SIP has no complete protocol. Table 4 H.323 and SIP Supplementary Service Capability Supplementary Service Capability H.323 SIP Call Transfer H.450.2 Available RFC3515 Set Call Turn H.450.3 Available RFC3261 Set Call H.450.4 Available RFC3264 Set Call Answers / Call Shelves H.450.5 Available RFC3515 Waiting Waiting H.450.6 Available RFC3261 Setting RFC3261 to set the message H.450.7 Draft to be discussed Name Show / Limit H.450.8 No Music Spread H.450.9 Draft Waiting for Discussion Musk H.450.10 No busy inserting H.450.11 No advanced function multicast signaling can, use LRQ and GRQ. Yes, send hair with a set of INVITEs. Third-party calls can, pause and weight routing function with H.323. Complex features can use the standards and extensions of H.450. Yes, the extra SIP expansion standard is used. The call assignment standard is not described, but if necessary, the gatekeeper can support it. The SIP proxy server can send a call bifurcation to any multiple network elements. Support for phone conference. stand by. Complete support of video conferencing. Includes some support for narrowband video conferencing. No synchronous and control mechanism. Data conference uses T.120 full support. No. Click Dial Support. stand by. Loop monitoring support. It is necessary to use the roundabout of the online inspection of LRQ. stand by. Monitor VIA Header. Open source code, such as OpenH323. Yes, such as Cisco vovida.org. Fourth, the end language is just because the idea and progress of the H.323 and SIP standards may vary, and their application prospects may vary, and the SIP design goals are universal session establishment and demolition of universal operation protocols. IP phones and multimedia communications are only one of the two applications of SIP. Other applications for SIP may not be IP phones and multimedia communications. In that case, the SIP session process will be very simple. On the other hand, the H.323 design goal is to focus on system control protocol groups for multimedia communication applications. The functional system of H.323 IP phones and multimedia communications will be more complete and comprehensive. Therefore, the development of H.323 will tend to tend to systematically, and the development of SIP will be more versatile. It is particularly worth mentioning that although the media communication between simple SIP video phones is intact, SIP video and H.323 video and narrowband videos cannot be compatible with interoperability. SIP has no complete video conferencing and data conferencing system protocol framework. Therefore, H.323 may lead video calls and video conferencing and multimedia services in a considerable period of time.
SIP can play a simple and efficient advantage in the service that controls non-IP phone types, which can be combined with other applications of PCs, such as with instant messages and online, and Email can form a more creative new business. Although the standards of H.323 and SIP are gradually integrated, their role is still complementary in a considerable period, and it is still not possible to completely replace another standard signs. In a long time in the future, in different environments and practices, H.323 and SIP standards will coexist in the industry. Please refer to the magazine of this issue, please refer to the Japanese magazine.
