一种基于H.323协议的VoIP语音网关软件设计
摘要
通过因特网进行语音通信是一个非常复杂的系统工程，其应用面很广，因此涉及的技术也特别多，其中最根本的技术是VoIP(Voice over IP)技术。而所谓的VoIP是以IP分组交换网络为传输平台，对模拟的语音信号进行压缩、打包等一系列的特殊处理，使之可以采用无连接的UDP协议进行传输。
H.323协议是1997年ITU-T第16工作组的建议，H.323由一组协议构成，其中有负责音频与视频信号的编码、解码和包装，有负责呼叫信令收发和控制的信令，还有负责能力交换的信令。H.323定义了4个主要部件构筑基于网络的通信系统：终端、网关、网守、多点控制单元(MCU)。
网关必须在传输格式之间(例如H.225.0／H.221)和通信过程之间(例如H.245／H.242)提供适当的转换。这些转换在H.246建议中规定。网关也必须能够在网络一侧和SCN一侧执行呼叫建立和清除。在网关中也可以执行视频、音频和数据格式的转换。一般而言，网关的作用(当不用做MCU时)是以透明方式将网络端点反映为SCN端点，反之亦然。
本论文主要为一款基于H.323协议的VoIP语音网关进行软件架构设计，定义了基于H.323协议的语音接入网关软件的模块划分及模块间的接口、数据流和控制流，详细进行了每个功能的过程分析，并对H.323在实际应用中的不足进行优化和改进。本文首先介绍了H.323协议的网络体系结构；接着介绍软件概要设计；第四章介绍了模块划分；第五章接口描述；第六章介绍了过程描述；第七章进行了全文总结。
Audio communication by internet is very complicated as a system, project which has been used in a widely ranges, and many technology has been used including VoIP (Voice over IP) which is the most basic technology. The called VoIP is packetisation and transport of classic public switched telephone system audio over an IP network .The analog audio steam is encoding in a digital format, with possible compression, and encapsulating it in IP for transport over your LAN/WAN or the public internet.
H.323 protocol has been suggested by ITU-T 16~(th) group since 1997 . It is consist by a group of protocol including some is used to encode and decode and packet audio signal and video signal ,some is used to accept and send control signal order, others is used to capacity exchange .four components is defined to consist communication system based network in H.323 such as terminals, Gateways, Gatekeepers, MCs and MCUs..
The Gateway shall provide the appropriate translation between transmission formats (for example H.225.0 to/from H.221) and between communications procedures (for example H.245 to/from H.242). This translation is specified in Recommendation H.246. The Gateway shall also perform call setup and clearing on both the network side and the SCN side. In general, the purpose of the Gateway (when not operating as an MCU) is to reflect the characteristics of a network endpoint to an SCN endpoint, and the reverse, in a transparent fashion.
In this thesis an audio gateway based on H.323 protocol is analyzed as blueprint and defined models classify and interfaces between models, then understand whole VoIP system and improve some lacks of H.323 in application.
The first chapter overviews the H.323 protocol system construction. Chapter two shows the summary design. Chapter four illustrates the model classify and chapter five outlines its interface details. Then chapter six discusses the process and the results. Finally chapter seven means the whole work
H.323协议是1997年ITU-T第16工作组的建议，H.323由一组协议构成，其中有负责音频与视频信号的编码、解码和包装，有负责呼叫信令收发和控制的信令，还有负责能力交换的信令。H.323定义了4个主要部件构筑基于网络的通信系统：终端、网关、网守、多点控制单元(MCU)。
网关必须在传输格式之间(例如H.225.0／H.221)和通信过程之间(例如H.245／H.242)提供适当的转换。这些转换在H.246建议中规定。网关也必须能够在网络一侧和SCN一侧执行呼叫建立和清除。在网关中也可以执行视频、音频和数据格式的转换。一般而言，网关的作用(当不用做MCU时)是以透明方式将网络端点反映为SCN端点，反之亦然。
本论文主要为一款基于H.323协议的VoIP语音网关进行软件架构设计，定义了基于H.323协议的语音接入网关软件的模块划分及模块间的接口、数据流和控制流，详细进行了每个功能的过程分析，并对H.323在实际应用中的不足进行优化和改进。本文首先介绍了H.323协议的网络体系结构；接着介绍软件概要设计；第四章介绍了模块划分；第五章接口描述；第六章介绍了过程描述；第七章进行了全文总结。
Audio communication by internet is very complicated as a system, project which has been used in a widely ranges, and many technology has been used including VoIP (Voice over IP) which is the most basic technology. The called VoIP is packetisation and transport of classic public switched telephone system audio over an IP network .The analog audio steam is encoding in a digital format, with possible compression, and encapsulating it in IP for transport over your LAN/WAN or the public internet.
H.323 protocol has been suggested by ITU-T 16~(th) group since 1997 . It is consist by a group of protocol including some is used to encode and decode and packet audio signal and video signal ,some is used to accept and send control signal order, others is used to capacity exchange .four components is defined to consist communication system based network in H.323 such as terminals, Gateways, Gatekeepers, MCs and MCUs..
The Gateway shall provide the appropriate translation between transmission formats (for example H.225.0 to/from H.221) and between communications procedures (for example H.245 to/from H.242). This translation is specified in Recommendation H.246. The Gateway shall also perform call setup and clearing on both the network side and the SCN side. In general, the purpose of the Gateway (when not operating as an MCU) is to reflect the characteristics of a network endpoint to an SCN endpoint, and the reverse, in a transparent fashion.
In this thesis an audio gateway based on H.323 protocol is analyzed as blueprint and defined models classify and interfaces between models, then understand whole VoIP system and improve some lacks of H.323 in application.
The first chapter overviews the H.323 protocol system construction. Chapter two shows the summary design. Chapter four illustrates the model classify and chapter five outlines its interface details. Then chapter six discusses the process and the results. Finally chapter seven means the whole work
引文
[1] ITU-T Recommendation H. 225.0, Call signalling protocols and media stream packetization for packet based multimedia communication systems. (1999)
[2] ITU-T Recommendation H. 245, Control protocol for multimedia communication. (2000)
[3] CCITT Recommendation G. 711, Pulse Code Modulation (PCM) of voice frequencies. (1988)
[4] CCITT Recommendation G. 722, 7 kHz audio-coding within 64 kbit/s. (1988)
[5] ITU-T Recommendation G. 723.1, Speech coders: Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbit/s. (1996)
[6] CCITT Recommendation G. 728, Coding of speech at 16 kbit/s using low-delay code excited linear prediction. (1992)
[7] ITU-T Recommendation G. 729, Coding of speech at 8 kbit/s using Conjugate Structure Algebraic-Code-Excited Linear-Prediction (CS-ACELP). (1996)
[8] ITU-T Recommendation H. 261, Video codec for audiovisual services at p×64 kbit/s. (1993)
[9] ITU-T Recommendation H. 263, Video coding for low bit rate communication. (1996)
[10] ITU-T Recommendation T. 120, Data protocols for multimedia conferencing. (1996)
[11] ITU-T Recommendation H. 320, Narrow-band visual telephone systems and terminal equipment. (1997)
[12] ITU-T Recommendation H. 321, Adaptation of H. 320 visual telephone terminals to B-ISDN environments. (1996)
[13] ITU-T Recommendation H. 322, Visual telephone systems and terminal equipment for local area networks which provide a guaranteed quality of service. (1996)
[14] ITU-T Recommendation H. 324, Terminal for low bit rate multimedia communication. (1996)
[15] ITU-T Recommendation H. 310. Broadband audiovisual communication systems and terminals. (1996)
[16] ITU-T Recommendation Q. 931, ISDN user-network interface layer 3 specification for basic call control. (1998)
[17] ITU-T Recommendation Q. 932, Generic procedures for the control of ISDN supplementary services. (1998)
[18] ITU-T Recommendation Q. 950, Supplementary services protocols, structure and general principles. (1997)
[19] ISO/IEC 10646-1: 1993, Information technology-Universal Multiple-Octet Coded Character Set (USC)-Part 1: Architecture and Basic Multilingual Plane.
[20] ITU-T Recommendation E. 164, The international public telecommunication numbering plan. (1997)
[21] ITU-T Recommendation H. 246, Interworking of H-Series multimedia terminals with H-Series multimedia terminals and voice/voiceband terminals on GSTNand ISDN. (1998)
[22] ITU-T Recommendation H. 235, Security and encryption for H-Series (H. 323 and other H. 245 based) multimedia terminals. (1998)
[23] ITU-T Recommendation H. 332, H. 323 extended for loosely-coupled conferences. (1998)
[24] ITU-T Recommendation H. 450.1, Generic functional protocol for the support of supplementary services in H. 323. (1998)
[25] ITU-T Recommendation I. 363.5, B-ISDN ATM adaptation layer specification: Type 5 AAL. (1996)
[26] ITU-T Recommendation Q. 2931, Digital subscriber signalling system No. 2 (DSS 2)-ser-network interface (UNI)-Layer 3 specification for basic call/connection control. (1995)
[27] ITU-T Recommendation I. 356, B-ISDN ATM layer cell transfer performance. (1996)
[28] ITU-T Recommendation I. 371, Traffic control and congestion control in B-ISDN. (1996)
[29] ITU-T Recommendation I. 371.1, Traffic control and congestion control in B-ISDN: Conformance definitions for ABT and ABR. (1997)
[30] ITU-T Recommendation Q. 2961.2, Digital Subscriber Signalling System No. 2-Additional traffic parameters: Support of ATM Transfer capability in the broadband bearer capability information element. (1997)
[31] ITU-T Recommendation H. 282, Remote Device Control Protocol for Multimedia Applications. (1999)
[32] ITU-T Recommendation H. 283, Remote Device Control Logical Channel Transport. (1999)
[33] ATM Forum Technical Committee, AF-SAA-0124.000, Gateway for H. 323 Media Transport Over ATM, 1999.
[34] ITU-T Recommendation Q. 2941.2, Digital Subscriber Signalling System No. 2-Generic Identifier Transport Extensions. (1999)
[35] ITU-T Recommendation H. 450.2, Call transfer supplementary service for H. 323. (1998)
[36] ITU-T Recommendation H. 450.4, Call Hold Supplementary Service for H. 323. (1999)
[37] ITU-T Recommendation H. 248, Gateway Control Protocol. (2000)
[38] ISO/IEC 11571:, Information technology-Telecommunications and information exchange between systems-Private Integrated Services Networks-Addressing. 1998
[39] ITU-T Recommendation Q. 951, Stage 3 Description for Number Identification Supplementary Services using DSS1. (1993)
[40] 孔祥营，柏桂枝．嵌入式实时操作系统VxWorks及其开发环境Tornado．中国电力出版社，2003，7
[41] 周启平，张扬．VxWorks下设备驱动程序及BSP开发指南．中国电力出版社 2004，9
[2] ITU-T Recommendation H. 245, Control protocol for multimedia communication. (2000)
[3] CCITT Recommendation G. 711, Pulse Code Modulation (PCM) of voice frequencies. (1988)
[4] CCITT Recommendation G. 722, 7 kHz audio-coding within 64 kbit/s. (1988)
[5] ITU-T Recommendation G. 723.1, Speech coders: Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbit/s. (1996)
[6] CCITT Recommendation G. 728, Coding of speech at 16 kbit/s using low-delay code excited linear prediction. (1992)
[7] ITU-T Recommendation G. 729, Coding of speech at 8 kbit/s using Conjugate Structure Algebraic-Code-Excited Linear-Prediction (CS-ACELP). (1996)
[8] ITU-T Recommendation H. 261, Video codec for audiovisual services at p×64 kbit/s. (1993)
[9] ITU-T Recommendation H. 263, Video coding for low bit rate communication. (1996)
[10] ITU-T Recommendation T. 120, Data protocols for multimedia conferencing. (1996)
[11] ITU-T Recommendation H. 320, Narrow-band visual telephone systems and terminal equipment. (1997)
[12] ITU-T Recommendation H. 321, Adaptation of H. 320 visual telephone terminals to B-ISDN environments. (1996)
[13] ITU-T Recommendation H. 322, Visual telephone systems and terminal equipment for local area networks which provide a guaranteed quality of service. (1996)
[14] ITU-T Recommendation H. 324, Terminal for low bit rate multimedia communication. (1996)
[15] ITU-T Recommendation H. 310. Broadband audiovisual communication systems and terminals. (1996)
[16] ITU-T Recommendation Q. 931, ISDN user-network interface layer 3 specification for basic call control. (1998)
[17] ITU-T Recommendation Q. 932, Generic procedures for the control of ISDN supplementary services. (1998)
[18] ITU-T Recommendation Q. 950, Supplementary services protocols, structure and general principles. (1997)
[19] ISO/IEC 10646-1: 1993, Information technology-Universal Multiple-Octet Coded Character Set (USC)-Part 1: Architecture and Basic Multilingual Plane.
[20] ITU-T Recommendation E. 164, The international public telecommunication numbering plan. (1997)
[21] ITU-T Recommendation H. 246, Interworking of H-Series multimedia terminals with H-Series multimedia terminals and voice/voiceband terminals on GSTNand ISDN. (1998)
[22] ITU-T Recommendation H. 235, Security and encryption for H-Series (H. 323 and other H. 245 based) multimedia terminals. (1998)
[23] ITU-T Recommendation H. 332, H. 323 extended for loosely-coupled conferences. (1998)
[24] ITU-T Recommendation H. 450.1, Generic functional protocol for the support of supplementary services in H. 323. (1998)
[25] ITU-T Recommendation I. 363.5, B-ISDN ATM adaptation layer specification: Type 5 AAL. (1996)
[26] ITU-T Recommendation Q. 2931, Digital subscriber signalling system No. 2 (DSS 2)-ser-network interface (UNI)-Layer 3 specification for basic call/connection control. (1995)
[27] ITU-T Recommendation I. 356, B-ISDN ATM layer cell transfer performance. (1996)
[28] ITU-T Recommendation I. 371, Traffic control and congestion control in B-ISDN. (1996)
[29] ITU-T Recommendation I. 371.1, Traffic control and congestion control in B-ISDN: Conformance definitions for ABT and ABR. (1997)
[30] ITU-T Recommendation Q. 2961.2, Digital Subscriber Signalling System No. 2-Additional traffic parameters: Support of ATM Transfer capability in the broadband bearer capability information element. (1997)
[31] ITU-T Recommendation H. 282, Remote Device Control Protocol for Multimedia Applications. (1999)
[32] ITU-T Recommendation H. 283, Remote Device Control Logical Channel Transport. (1999)
[33] ATM Forum Technical Committee, AF-SAA-0124.000, Gateway for H. 323 Media Transport Over ATM, 1999.
[34] ITU-T Recommendation Q. 2941.2, Digital Subscriber Signalling System No. 2-Generic Identifier Transport Extensions. (1999)
[35] ITU-T Recommendation H. 450.2, Call transfer supplementary service for H. 323. (1998)
[36] ITU-T Recommendation H. 450.4, Call Hold Supplementary Service for H. 323. (1999)
[37] ITU-T Recommendation H. 248, Gateway Control Protocol. (2000)
[38] ISO/IEC 11571:, Information technology-Telecommunications and information exchange between systems-Private Integrated Services Networks-Addressing. 1998
[39] ITU-T Recommendation Q. 951, Stage 3 Description for Number Identification Supplementary Services using DSS1. (1993)
[40] 孔祥营，柏桂枝．嵌入式实时操作系统VxWorks及其开发环境Tornado．中国电力出版社，2003，7
[41] 周启平，张扬．VxWorks下设备驱动程序及BSP开发指南．中国电力出版社 2004，9