ITUT协议H323中文.docx
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ITUT协议H323中文
国际电信联盟
ITU-TH.323
ITU的电信标准化区段（11/96）
H系列：
视听和多媒体系统
视听服务的基础-视听服务的系统和终端设备
为局域网提供无质量保证服务的可视电话系统和设备
ITU-T协议H.323
（早期由CCITT协议）
ITU-TH系列协议
视听和多媒体系统
用于除电话用途之外的传输信道的特性
H.10.19
用于音频报务的电话型电路的使用
H.20.29
用于各种类型的电报传输或同步传输电话电路或电缆
H.30.39
用于传真电报的电话型电路
H.40.49
数据信号的特性
H.50.99
可视电话系统的特性
H.100.199
视听服务的基础构架
H.200.399
通则
H.200.219
多路传输和同步传输
H.220.229
系统概况
H.230.239
通信过程
H.240.259
运动视频编码
H.260.279
相关系统概况
H.280.299
视听服务系统和终端设备
H.300.399
细节请参见ITU-T系列协议。
ITU-T协议H.323
为局域网提供无质量保证服务的可视电话系统和设备
摘要
H.323协议描述了基于无质量保证服务的局域网（LAN）上的多媒体通信的终端，设备和服务。
H.323终端和设备可以传输实时语音、数据和视频，或上述的任意组合，包括视频电话。
用于H.323终端通信的LAN，可以是单个网段或令牌环网，也可以是多个具有复杂拓补结构的段。
注意：
基于多个LAN网段上（包括Internet）的H.323的终端工作性能可能很低。
保证这种类型的LAN/互联网的服务质量的可能方法超出了本协议的范围。
H.323终端可以被集成进PC或在像视频电话这种独立设备上实现。
支持语音是必须的，而支持数据和视频是可选的，但是一旦支持的话，就必须具备使用特定通用方式的操作的能力，这样所有支持该媒体形式的终端就能互相协作。
本协议允许每种媒体类型的多通道同时使用。
H.323系列协议还包括：
H.225.0打包和同步，H.245控制，H.261和H.263视频编码器，G.711、G.722、G.728、G.729和G.723音频编码器，以及T.120系列多媒体通信协议。
本协议利用了H.245协议的逻辑信道信令进程，当通道打开时每个逻辑信道的内容已被描述好了。
对接收器和传送器能力的表示由进程提供，因此传输被限制什么接收器能译码上，这样接收器可以请求传送器的特定方式。
由于H.245协议的进程也用于ATM网的H.310协议以及GSTN和V.70的H.324协议中，因此与这些系统的协作应该不会要求H.225～H.245协议的传输达到与H.320系统相同的情况。
H.323终端可以用于多点配置，也可以和B-ISDN上的H.310终端，N-ISDN上的H.320终端，B-ISDN上的H.321终端，保证服务质量的LANs上的H.322终端，GSTN和无线网络上的H.324终端，以及GSTN上的V.70终端相互协作。
来源
ITU-T协议协议H.323是由ITU-T第15研究组（1993-1996）撰稿，并于1996年11月8日经WTSC决议的NO.1程序认可。
绪言
ITU（国际电信联盟）是联合国在电信领域中的专门机构。
ITU电信标准化区段（ITU-T）是ITU的永久性机构。
ITU-T负责研究技术，操作，征询问题以及在全球标准化通信方面制定标准协议。
世界电信标准化会议（WTSC），每四年召开一次，为ITU-T研究组的研究工作制定论题，然后ITU-T研究组为这些论题制定协议。
由ITU的成员核准的协议必须通过WTSC的NO.1解决方案的程序核实。
在信息技术的一些区域内，在ITU-T范围内，必要的标准由ISO和IEC共同制定。
说明
在本协议中，表达式管理机构是用于精确指示电信管理和识别操作机构的。
知识产权
ITU1997保留所有的权利。
1概况······································································1
2标准的参考································································2
3定义······································································3
4符号和缩写································································8
5常规······································································10
6系统描述··································································10
6.1信息流··································································10
6.2终端特性································································11
6.2.1本协议以外的终端元素··············································11
6.2.2本协议以内的终端元素··············································12
6.2.3LAN接口···························································12
6.2.4视频编码··························································12
6.2.5音频编码··························································13
6.2.6接收路径迟延······················································14
6.2.7数据通道··························································14
6.2.8H.245控制函数·····················································16
6.2.9RAS信号函数·······················································20
6.2.10呼叫信号函数·····················································20
6.2.11H.225.0层························································21
6.3网关特性································································21
6.4网闸特性································································24
6.5多点控制器特性··························································25
6.6多点处理器特性··························································26
6.7多点控制单元特性························································27
6.8多点能力································································27
6.8.1中心多点能力······················································27
6.8.2非中心多点能力····················································27
6.8.3混合多点-中心音频·················································28
6.8.4混合多点-中心视频·················································28
6.8.5建立常规模型······················································28
6.8.6多点速率匹配······················································29
6.8.7多点边缘同步······················································29
6.8.8多点加密··························································30
6.8.9级联多点控制单元··················································30
7呼叫信号·······························································30
7.1地址····································································30
7.1.1LAN地址···························································30
7.1.2TSAP标识符························································30
7.1.3别名地址··························································30
7.2注册，管理和状态通道····················································31
7.2.1网闸的发现························································31
7.2.2端点注册··························································32
7.2.3端点定位··························································33
7.2.4许可，带宽改变，状态，断开········································34
7.3呼叫信号通道····························································34
7.3.1呼叫信号通道路由选择··············································34
7.3.2控制信道路由选择··················································35
7.4呼叫基准值······························································36
7.5会议ID和会议目标·······················································37
8呼叫信令过程····························································37
8.1A阶段-建立呼叫··························································37
8.1.1基本呼叫建立-双方没有端点注册·····································37
8.1.2双方端点注册到同一网闸············································38
8.1.3只有主叫方端点有网闸··············································39
8.1.4只有被叫方端点有网闸··············································41
8.1.5双方端点注册到不同网闸············································42
8.1.6通过网关建立呼叫··················································46
8.1.7通过MCU建立呼叫··················································47
8.1.8呼叫转发··························································47
8.1.9建立广播呼叫······················································48
8.2B阶段-初始化通信和交换能力··············································48
8.3C阶段-建立视听通信······················································48
8.3.1模式转换··························································48
8.3.2双方协议的视频转换················································48
8.3.3媒体流地址分布····················································49
8.4D阶段-呼叫服务··························································49
8.4.1带宽改变··························································49
8.4.2状态······························································51
8.4.3特别多点会议扩展····················································51
8.4.4附加服务··························································58
8.5E阶段-呼叫结束··························································59
8.5.1不带网闸的呼叫清除················································59
8.5.2带网闸的呼叫清除··················································59
8.5.3使用网闸的呼叫清除················································60
8.6协议失败处理····························································61
9与其他终端类型的协作····················································61
9.1只有话音的终端··························································61
9.2基于ISDN（H.320）的可视电话终端·········································62
9.3基于GSTN（H.324）的可视电话终端·········································62
9.4基于无线移动（H.324/M）的可视电话终端·································62
9.5基于ATM（H.324）的可视电话终端··········································62
9.6基于质量保证的LANs服务（H.322）的可视电话终端··························63
9.7基于GSTN（V.70）的同步语音和数据终端····································63
9.8LAN上的T.120终端·······················································63
10可选扩展································································63
10.1加密···································································63
11维护···································································64
11.1保护性回退·····························································64
11.2监测方法·······························································65
附件A-H.323端点使用的H.245消息···········································65
附录I-网关中Q.931消息的处理过程···········································65
ITU-T协议H.323
为局域网提供无质量保证服务的可视电话系统和设备
（Geneva，1996）
1概述
本协议囊括了H.200/AV.120系列协议中定义的在传输路径包含一个或多个局域网（LAN）的条件下的窄带可视电话服务的技术要求，这些局域网也许不能提供与N-ISDN相同的质量保证服务的。
这种类型的局域网有：
-以太网（IEEE802.3）；
-快速以太网（IEEE802.10）；
-FDDI（无质量保证服务方式）；
-令牌环网（IEEE802.5）。
本协议囊括了在传输路径包含一个或多个局域网（LAN）的条件下的可视电话服务的情况，这些局域网被配置成能够提供与N-ISDN相同的质量保证服务（QOS）从而使终端无需提供任何H.320协议要求之外的附加保护性或恢复性机制的。
相关的参数是数据错误和丢失属性以及传输延迟的变化。
一个恰当的LAN的例子是：
综合服务（IS）局域网：
IEEE802.9A具有载波侦听多路访问及冲突监测（CSMA/CD）媒体访问控制（MAC）服务的同步服务。
H.323终端可以用于多点配置，也可以和B-ISDN上的H.310终端，N-ISDN上的H.320终端，B-ISDN上的H.321终端，有质量保证服务的LAN上的H.322终端，GSTN和无线网络上的H.324终端，以及GSTN上的V.70终端相互协作。
参见图1。
本协议范围不包含LAN本身，或可以用于连接不同局域网的传送层。
本协议范围仅包含与交换电路网交互（SCN）所需的元素。
H.323网关，H.323终端，以及外围LAN的组合在SCN上以H.320，H.310，H.324，或V.70终端的形式出现。
本协议描述了H.323系统的组件。
其中包含终端（terminals），网关（Gateways），网闸（Gatekeepers），多点控制器（MultipointControllers），多点处理器（MultipointProcessors）和多点控制单元（MultipointControlUnits）。
本协议中的控制消息（messages）和进程（procedures）定义了这些组件如何通信。
这些组件的详细描述参见条款（clause）6。
本协议中描述的组件由H.323的端点（endpoints）和实体（entities）组成。
端点能通过条款8的建立呼叫进程（callset-upprocedures）呼叫（call）或被叫（callable）。
然而实体是不能被叫的，他们能被寻址（beaddressed）到从而执行他们的专用功能。
例如，虽然终端不能呼叫网闸，但网闸被寻址到作为呼叫建立进程（callestablishmentprocedures）的一部分。
图1/hH.323-H.323终端协作
2参考标准
下列ITU-T协议和其他参考包含构成本协议的条款。
在出版时，版本提示是有效的。
所有协议和其他参考易受修订；本协议的所有使用者最好查找下列协议和参考文献的最近版本。
近期有效的ITU-T协议应该定期出版。
〖见H.323协议〗
3定义
出于本协议的忠旨，H.225.0[1]的条款3和H.245[2]的条款3给出的定义同样适用于本协议。
这些定义只适用于LAN方面。
其他用于交换电路网络（SCN）方面的术语应该会重点指出。
3.1活动MC（activeMC）：
一种在主/从决定进程（master-slavedeterminationprocedure）中获胜的MC，目前为会议提供多点控制功能。
3.2特别多点会议（adhocmultipointconference）：
特别多点会议是一种在呼叫的某一时刻已经扩展为多点会议的点对点（point-to-point）会议。
如果初始的点对点会议的一个或多个终端包含MC，或者呼叫是通过使用包含MC功能的网闸实现的，或初始呼叫是通过一个在两个终端之间作为多点呼叫的MCU实现的，则特别多点会议就会发生。
3.3可寻址（addressable）：
在LAN上的H.323实体有相应的传送地址。
这与可被叫不同。
终端或MCU是可寻址且可被叫的。
网闸是可寻址但不可被叫的。
MC和MP是不可寻址也不可被叫的，但却被包含在可寻址或可被叫的端点或网闸中。
3.4静音抑制（audiomute）：
对单个或所有声源（s）的音频信号的抑制。
发送静音是指音频数据流发生器削减自身的麦克风的噪声和/或根本不传送任何音频信号。
接收静音是指接收终端忽略某种特别的音频数据流或
升级会员 