H.323

H.323 （简体）

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H.323協議是ITU-T提出的關於視頻電話及多媒體會議傳輸協議H.32x系列中的一部分。

第一版的 H.323 由 ITU 公布於1996年9月推出^[1]。ITU-T在完成了在ISDN 2Mbit/s上的視頻電話及多媒體會議傳輸協議H.320後，ITU-T又相繼發布了具有相似功能的H.310，H.321工作於ATM網路和使用了調製解調技術的H.324工作於公共交換電話網（PSTN）以及沒有來得急發布就淘汰的H.322工作在Isochronous Ethernet. 直到1995年ITU-T發布了迄今為止被廣泛採用的，最有前途的，也是在QoS（Quality of Service 服務質量）上克服了眾多困難，定義了完善的服務質量，提供較好的服務質量保證。H.323工作在區域網，H.323為現有的分組網路（如IP網路）提供多媒體通信標準。若和其它的IP技術如IETF的資源預留協議（RSVP）相結合，就可以實現IP網路的多媒體通信。它配合IP做為在IOS網路層的協議。。它的最主要的目的是提供PBN在不同的網路之間進行多媒體通信互連互通的標準。

關於H.323最初的版本是在1996年6月由ITU-T發布的，為各種通信行業提供了一個標準。最初的焦點只是在區域網上，因為當時Qos服務質量標準對於基於IP的廣域網，例如Internet，還沒有的很好的制定出。在1996年早期，H.323的應用明確的要求在廣域網中得到應用，將語音通信做為唯一的目標，所以基於IP技術的H.323誕生了。隨後，H.323繼續向前發展，做為一個以IP技術應用為基礎，集成了眾多關於語音通信技術協議的平台。第一次主要的對這個協議做出的修改和添加內容，是由ITU-T在1998年1月發布的H.323版本2。在1999年9月，ITU-T發布H.323v3，合併了眾多的長遠的功能，並擴展了它的概念，這些工作使得H.323成為全球範圍內數據IP電話及企業內部IP電話發展得基礎。而且隨後得時間更多得擴充被添加到H.323協議中，2000年11月17日H.323 的第4版問世，添加了在很多重要的領域的擴充和改進。其中包括可靠性，可測量性，和靈活性。新的特性使它在市場要求網關和MCU不斷升級中更加靈活的完成自身的升級。H.323 已經無異議的成了在網路傳輸聲音，視頻，數據會議的領導者^[2]。

ITU-T Recommendations of the H.323 System

ITU-T H.323 Core Recommendations

• ITU-T Recommendation H.323, Packet-based multimedia communications systems.
• ITU-T Recommendation H.225.0, Call signalling protocols and media stream packetization for packet-based multimedia communication systems.
• ITU-T Recommendation H.245, Control protocol for multimedia communication.
• ITU-T Recommendation H.246, Interworking of H-series multimedia terminals with H-series multimedia terminals and voice/voiceband terminals on GSTN and ISDN.
• ITU-T Recommendation H.283, Remote device control logical channel transport.
• ITU-T Recommendation H.341, Multimedia management information base.

ITU-T H.235 Series Recommendations

• ITU-T Recommendation H.235.1, H.323 security framework: Baseline security profile.
• ITU-T Recommendation H.235.2, H.323 security framework: Signature security profile.
• ITU-T Recommendation H.235.3, H.323 security: Hybrid security profile.
• ITU-T Recommendation H.235.4, H.323 security: Direct and selective routed call security.
• ITU-T Recommendation H.235.5, H.323 security: Framework for secure authentication in RAS using weak shared secrets.
• ITU-T Recommendation H.235.6, H.323 security framework: Voice encryption profile with native H.235/H.245 key management.
• ITU-T Recommendation H.235.7, H.323 security framework: Usage of the MIKEY key management protocol for the Secure Real Time Transport Protocol (SRTP) within H.235.
• ITU-T Recommendation H.235.8, H.323 security: Key exchange for SRTP using secure signalling channels.
• ITU-T Recommendation H.235.9, H.323 security: Security gateway support for H.323.

ITU-T H.450 Series Recommendations

• ITU-T Recommendation H.450.1, Generic functional protocol for the support of supplementary services in H.323.
• ITU-T Recommendation H.450.2, Call transfer supplementary service for H.323.
• ITU-T Recommendation H.450.3, Call diversion supplementary service for H.323.
• ITU-T Recommendation H.450.4, Call hold supplementary service for H.323.
• ITU-T Recommendation H.450.5, Call park and call pickup supplementary service for H.323.
• ITU-T Recommendation H.450.6, Call waiting supplementary service for H.323.
• ITU-T Recommendation H.450.7, Message waiting indication supplementary service for H.323.
• ITU-T Recommendation H.450.8, Name identification supplementary service for H.323.
• ITU-T Recommendation H.450.9, Call completion supplementary service for H.323.
• ITU-T Recommendation H.450.10, Call offering supplementary service for H.323.
• ITU-T Recommendation H.450.11, Call intrusion supplementary service for H.323.
• ITU-T Recommendation H.450.12, Common Information Additional Network Feature for H.323.

ITU-T H.460 Series Recommendations

• ITU-T Recommendation H.460.1, Guidelines for the user of the generic extensible framework.
• ITU-T Recommendation H.460.2, Number Portability interworking between H.323 and SCN networks.
• ITU-T Recommendation H.460.3, Circuit maps within H.323 systems.
• ITU-T Recommendation H.460.4, Call priority designation and country/international network of call origination identification for H.323 priority calls.
• ITU-T Recommendation H.460.5, H.225.0 transport of multipl Q.931 information elements of the same type.
• ITU-T Recommendation H.460.6, Extended Fast Connect feature.
• ITU-T Recommendation H.460.7, Digit maps within H.323 systems.
• ITU-T Recommendation H.460.8, Queirying for alternate routes within H.323 systems.
• ITU-T Recommendation H.460.9, Support for online QoS-monitoring reporting within H.323 systems.
• ITU-T Recommendation H.460.10, Call party category within H.323 systems.
• ITU-T Recommendation H.460.11, Delayed call establishment within H.323 systems.
• ITU-T Recommendation H.460.12, Called user release control.
• ITU-T Recommendation H.460.13, Support for Multi-Level Precedence and Preemption (MLPP) within H.323 systems.
• ITU-T Recommendation H.460.14, Call signalling transport channel suspension and redirection within H.323 systems.
• ITU-T Recommendation H.460.15, Multiple message release sequence capability.
• ITU-T Recommendation H.460.16, Using H.225.0 call signalling connection as transport for H.323 RAS messages.
• ITU-T Recommendation H.460.17, Traversal of H.323 signalling across network address translators and firewalls.
• ITU-T Recommendation H.460.18, Traversal of H.323 signalling across network address translators and firewalls.
• ITU-T Recommendation H.460.19, Traversal of H.323 media across network address translators and firewalls.
• ITU-T Recommendation H.460.20, Location number within H.323 systems.
• ITU-T Recommendation H.460.21, Message broadcast for H.323 systems.
• ITU-T Recommendation H.460.22, Negotiation of security protocols to protect H.225.0 Call Signalling Messages.

ITU-T H.500 Series Recommendations

• ITU-T Recommendation H.501, Protocol for mobility management and intra/inter-domain communication in multimedia systems.
• ITU-T Recommendation H.510, Mobility for H.323 multimedia systems and services.
• ITU-T Recommendation H.530, Symmetric security procedures for H.323 mobility in H.510.

參考資料

1. ^ ITU-T Recommendation H.323 (11/1996), first version of H.323.
2. ^ IP telephony cookbook 2004

參見

• GNU Gatekeeper

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