多媒体通信技术(第七章终端).ppt

一级标题1st level,二级标题2nd level,三级标题3rd level,*,*,*,本页PPT标题,第七章 多媒体通信终端,程控教研室,课堂主要内容,基于多媒体计算机的多媒体通信终端,基于特定网络的多媒体通信终端,多媒体通信终端概述,多媒体通信终端相关标准,视频会议,视频监控,概念,多媒体通信终端：是指接收、处理和集成各种媒体信息，并通过同步机制将多媒体信息同步地呈现给用户，同时具有交互功能的通信终端。,多媒体终端的构成,搜索模块,编解码模块,同步,模块,准备模块,执行模块,用户,网络,应用协议,同步协议,接口协议,输入交互部分,再编辑,接口,终端的特点,C,A,交互性,同步性,多媒体通信终端的特点,集成性,B,H.323,标准,H.323,是,ITU-T,的一个标准簇，它于,1996,年由,ITU-T,的第,15,研究组通过，最初叫做“工作于不保证服务质量的,LAN,上的多媒体通信终端系统”。,1997,年底通过了,H.323V2,，改名为“基于分组交换网络的多媒体通信终端系统”。,H.323V2,的图像质量明显提高，同时也考虑了与其他多媒体通信终端的互操作性。,1999,年,5,月,ITU-T,又提出了,H.323,的第三个版本,。,介于传输层与应用层之间,应 用 层,H323,层,传 输 层,网 络 层,数 据 链 路 层,物 理 层,协议体系,H.323,协议站,(,TCP/IP),Audio/Video Application,C&I,(,T.126,T.127),G.7xx,H.26x,RTP,RTCP,Q.931,(H.225.0),H.245,T.124,T.125,Unreliable Transport,(,UDP,),Reliable Transport,(,TPKP,+TCP,),Network(,IP,),Data Link,T.123,Physical,RAS,(H.225.0),LL1,L2,L3,L4,L6,L5,L7,音频/视频编解码器,音频编解码器,G.711,(mandatory),A-law,Mu-Law,64 kbit/s,G.723.1,5.3,6.3 kbit/s,G.729/G.729A,8 kbit/s(6.4,11.8 kbit/s),G.728,16 kbit/s,low delay,G.722,wide band,64 kbit/s,视频编解码器,H.261,(mandatory),QCIF,CIF,Frame per second according the available bandwidth,H.263,More efficient,Better quality at low bit rate,More robust to errors,Gatekeeper,Multipoint,Processor,H.323,Multipoint,Controller,Router,WAN/,Internet,Router,firewall,firewall,WAN/,Internet,H.323,Gateway,H.320,H.320,H.323,网络,H.323系统构成,终端,网关,网守,多点控制单元,信令与控制,实时通信,编解码,系统控制,网关提供了一,种电路交换网,络（,SCN,）和,包交换网络的,连接途径，它,在不同的网络,上完成呼叫的,建立和控制功,能。,网守也称为关,守、网闸，是,H.323,系统中,的信令单元，,管理一个区域,里的终端、,MCU,和网关等,设备,完成视频会议,的控制和管理,功能，它由,MC,和,MP,组成。,MCU,可以是独,立的设备，也,可以集成在终,端、网关或网,守中。,H323,终端,终端用于实现实时双向多媒体通信，,H.323,终端可以是运行了,H.323,协议栈软件的,PC,，也可以是内置了,H.323,协议栈功能的独立设备。,H.323,终端必须支持语音通信，视频与数据通信是可选实现功能。,H.323,终端必须支持：,用于交换终端能力和打开媒体通道的,H.245,用于呼叫建立和呼叫信令的,H.225.0,用于向,Gatekeeper,注册以及其余控制的,RAS,用于封装音频和视频包的,RTP/RTCP,Q.931 Call Signal,H.245 Multimedia Control,RAS Zone Control,G.711,G.722,G.728,G.723,G.729,H.261,H.263,T.120,RTP,/,RTCP,H.225.0,网路接口,PBN,Transport(Lev 4),TCP/IP,SPX/IPX,LAN(Eth,TR,),Internet,ISDN(+PPP),PSTN(+PPP),ADSL,Frame Relay,Audio,Video,Data,C&I,User,H.323 Scope,H.323,终端结构,SIP,协议,SIP,（,Session Initiation Protocol,）是,IETF,（,Internet Engineering Task Force,，互联网工程任务组）制定的多媒体通信协议，是基于,IP,的一个文本型应用层控制协议，独立于底层协议，用于建立、修改和终止,IP,网上的双方或多方的多媒体会话。,SIP协议概念,会话启动协议,SIP,（,Session Initiation Protocol,）是一个在,IP,网络上进行多媒体通信的应用层控制协议，它被用来创建、修改、和终结一个或多个参加者参加的会话进程。,SIP,协议可用于发起会话，也可以用于邀请成员加入已经用其它方式建立的会话。,SIP,协议透明地支持名字映射和重定向服务，便于实现,ISDN,、智能网以及个人移动业务。,SIP协议的特点,一个正在发展和不断研究中的协议。,简练、开放、兼容和可扩展等原则。,充分注意到因特网开放而复杂的网络环境下的安全问题。,充分考虑了对传统公共电话网的各种业务，包括,IN,业务和,ISDN,业务的支持。,SIP体系结构,用户代理,(User Agent),：,就是,SIP,终端，也可以说是,SIP,用户。,按功能分为两类：,用户代理客户端,UAC(User Agent Client),，负责发起呼叫；,用户代理,服务器,UAS,（,User Agent Server,），负责接受呼叫并做出响应。,重定向服务器（,Redirect server,）,重定向服务器将请求中的目的地址映射为零个或多个新的地址，然后返回给客户端，客户端直接再次向这些新的地址发起请求。,代理,服务器,（,Proxy Server,）：,可以当作一个客户端或者是一个服务器。具有解析能力，负责接收用户代理发来的请求，根据网络策略将请求发给相应的服务器，并根据应答对用户做出响应，也可以将收到的消息改写后再发出。,注册服务器,(Register Server),：,用来完成,UAS,的登录。在,SIP,系统中所有的,UAS,都要在网络上注册、登录，以便,UAC,通过服务器能找到。它的作用就是接收用户端的请求，完成用户地址的注册。,1,名字翻译和用户定位：确保呼叫达到位于网络的被叫方，执行描述信息到定位信息的映射。,特征协商：允许与呼叫有关的组在支持的特征上达成一致。,呼叫参与者管理：在通话中引入或取消其他用户的连接，转移或保持其他用户的呼叫。,SIP协议实现的功能,呼叫特征改变：用户能在呼叫过程中改变特征。,2,3,4,系统结构差异,不同,应用领域之分,SIP和H.323的不同,基于N-ISDN网的多媒体通信终端,H.320,协议栈,基于N-ISDN网的多媒体通信终端,基于,H.320,标准的多媒体电视会议系统终端结构示意图,基于计算机的多媒体通信终端,数据准,备软件,编辑软件,支持多媒体,的操作系统,应用软件,基于计算机的多媒体通信终端软件平台,Thank You!,程控教研室,網路電話,Session Initiation Protocol(SIP),Speaker:,王嘉裕,Date:2008/09/11,SIP-Session Initiation Protocol,前身,-MMUSIC(Multiparty Multimedia Session Control),Sep.1999,由,IETF,的,SIP Working Group,發展,開始於,1995,Proposed standard RFC2543,February 1999,New Version of SIP-RFC 3261,June 2002,SIP,A Signaling Protocol,Create,Modify,Terminate Multimedia Sessions,使用,IP,Client/Server,架構,相似於,HTTP,SMTP,Uniform Resource Locator(URL),sip:bobhit.edu.tw,sip:[phone]hit.edu.tw,也可以是,tel:[phone],Request and Response,回應訊息,SIP,藉由現成的,IETF,協定來提供,SIP,的訊息格式,(HTTP 1.1),RFC 2616,描述媒體的連線,(SDP)RFC 2327,媒體,(RTP),RFC 3550 and(RTSP)RFC 2326,定址方式,(URL),RFC 1738 and(URI)RFC 2396,名稱解析和位置的移動性,(DHCP)RFC 2131 and(DNS)RFCs 1034&1035,資料編碼方式,(MIME),RFC 2045,安全,(TLS),RFC 2246,IPsec,RFC 2401&2406,SIP,的封包格式,IHL,Total Length,Identification,Flags,Fragment Offset,Header Checksum,Protocol,Time to Live,Source Address,Destination Address,Padding,Options,Version,DSCP ECN,IPv4,的表頭,Source Port,Destination Port,Checksum,Length,UDP 8,個,Bytes,的表頭,(,這裡也可以是,TCP,或者,SCTP),SIP,表頭,以,US-ASCII,文字為基礎,變動長度,SIP,訊息主體,也是變動長度,視,Message-Type,的需要而存在,可以是任何形式的資料,Protocol Zoo,Source:Henning Schulzrinne,www.cs.columbia.edu/hgs/internet/,SIP,組成元件,User Agent,Proxy Server,Gateway,Proxy Server,Location Server,Redirect Server,Registrar Server,PSTN,PLMN,Gateway,SIP User Agents,User Agent(UA),用戶端,User Agent Client(UAC),送出,SIP,請求,伺服器端,User Agent Server(UAS),回應,SIP,請求 接受或拒絶,User Agent=UAC+UAS,UA 1,UA 2,LAN A,UA 3,UA 4,LAN B,SIP,訊息流程,Request,Response,Media Session,User Agent,Proxy Server,Redirect Server,Location Server,User Agent,Proxy Server,SIP Request methods,RFC 3261,REGISTER,INVITE,ACK,BYE,OPTIONS,CANCEL,其它的,RFC,SIP Request methods,INFO(RFC 2976),PRACK(RFC 3262),SUBSCRIBE and NOTIFY(RFC 3265),UPDATE(RFC 3311),MESSAGE(RFC 3428),REFER(RFC 3515),PUBLISH(RFC 3903),SIP Response,說明,範例,1xx,Informational,代表請求已收到,100 Trying,180 Ringing,181 Call is Being Forwarded,183 Session Progressing,2xx,Success,代表請求已被成功處理,200 OK,202 Acce,ptable,3xx,Redirection,代表重新導向,300 Multiple Choices,301 Moved Permanently,302 Moved Temporarily,4xx,Client Error,代表用互端錯誤,401 Unautho,rized,406,Not Acceptable,407 Proxy Auth,entication,Required,486 Busy Here,487 Request Terminated,4,88 Not Acceptable Here,5xx,Server Error,代表伺服器端錯誤,502 Bad Gateway,503 Service Unavailable,6xx,Global Failure,代表整體網路環境錯誤,600 Busy Everywhere,603 Decline,SIP,INVITE,100 Trying,INVITE,100 Trying,180 Ringing,180 Ringing,200 OK,200 OK,ACK,ACK,BYE,100 Trying,BYE,200 OK,200 OK,Call Setup,Call Teardown,Media Session,UAC,UAS,Server,連線過程,建立連線,通話,斷線,SIP,訊息,範例,SIP,SDP,INVITE sip:bobzzz.edu SIP/2.0,Via:SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:70,To:Bob,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 INVITE,Contact:,Content-Type:application/sdp,Content-Length:142,v=0,o=Alice 2897654321 2897654321 IN IP4 10.0.0.1,s=Phone Call,c=IN IP4 192.168.0.1,t=0 0,m=audio 49170 RTP/AVP 0,a=rtpmap:0 PCMU/8000,SIP Headers,INVITE,sip:bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,SIP Headers,INVITE,sip:bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,Method,即 命令,Request URI,SIP,協定版本,SIP Headers,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,所有經過的,SIP,設備都會被列在這裡,branch,用來識別不同的連線分支,在所有,SIP Requests,中都是必要的欄位,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,最多可以被幾個,Server,轉傳,SIP Headers,在所有,SIP Requests,之中除了,INFO,都是必要的欄位,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,目的地位址,SIP Headers,在所有,SIP Requests,中都是必要的欄位,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,來源位址 虛擬的隨機亂數,(,當作是,ID,使用,),SIP Headers,在所有,SIP Requests,中都是必要的欄位,James Polk 20050503,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,在網域內獨一無二的識別碼,SIP Headers,在所有,SIP Requests,中都是必要的欄位,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,遞增的序號,SIP Headers,在所有,SIP Requests,中都是必要的欄位,James Polk 20050503,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,直接可以路由到來源位址的完整網域名稱或,IP,位址,SIP Headers,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,用來描述附加的訊息主體格式,(,如果有的話,),SIP Headers,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,用來描述附加的訊息主體的內容長度,(Octets),SIP Headers,INVITE sip:,bobzzz.edu SIP/2.0,Via:,SIP/2.0/UDP pc33.yyy.edu;branch=z9hG4bK776asdhds,Max-Forwards:,70,To:,Bob,From:,Alice;tag=1928301774,Call-ID:,a84b4c76e66710pc33.yyy.edu,CSeq:,314159 INVITE,Contact:,Content-Type:,application/sdp,Content-Length:,142,SIP Headers,Session Description Protocol(SDP),描述多媒體連線的協定,RFC 2327,簡單，可以擴充的，以文字為基礎,SIP Offer/Answer Model,RFC 3264,在每一行,欄位,=,值 值 值,欄位是一個字元,(,大小寫有差別,),等號兩旁不可以有空格,分為,Session,和,Media,層次,SDP,的結構內容,Session,層次,(,從,v=,這一行開始,),Session Name,主動發起的一端,活動時間,Media,層次,(,從,m=,這一行開始,),媒體形式,video,audio,Port number,傳輸層協定,RTP/UDP/IP,H.320,.,媒體格式,H.261 video,MPEG video,.,SDP,的範例,SDP,的欄位,v=(protocol version),例如,:v=0,o=(owner/creator and session identifier),o=,Username,不可以含有空格,Session id,和,version,建議使用,Network Time Protocol(NTP),的時間戳記來確保值的唯一性,例如,:o=john 2887654326 2887654307,IN,IP4,10.1.2.3,s=(session name string),例如,:s=SDP Seminar,t=(start time and stop time),例如,:t=2887654321 2887654310(,通常設為,0),為必要欄位,SDP,的欄位,m=(media name and transport address),m=,m=/,例如,:,m=video 49170/2 RTP/AVP 0,audio,video,application,data and control“,RTP/AVP-the,IETFs,Realtime,Transport Protocol using the Audio/Video profile carried over UDP,UDP,RTP/AVP,RFC 3551,e=(email address),例如,:,e=,johnyyy.edu,(John Doe),或者,e=John Doe,p=(phone number),例如,:p=[phone],或者,p=[phone],u-law PCM,single channel,audio sampled at 8KHz,SDP,的欄位,c=(connection information),c=,例如,:,c=,IN IP4,224.2.17.12/127,通常這個連線位址是一個,class D,的,IP,群播位址,/,例如,:c=IN IP4 224.2.1.1/127/3,指的是多個,c=IN IP4 224.2.1.1/127,c=IN IP4 224.2.1.2/127,c=IN IP4 224.2.1.3/127,如果這一個會議連線不是群播,則它可以搭配額外的屬性欄位決定是完整網域位址或單一,IP,位址等等,SDP,的欄位,i=(session information),u=(URI of description),b=(bandwidth information),z=(time zone adjustments),k=(encryption key),a=(zero or more session attribute lines),r=(zero or more repeat times),SIP Methods:,INVITE,ACK and BYE,Alice,Bob,INVITE,INVITE sip:bob192.168.10.20 SIP/2.0,Via:SIP/2.0/TCP pc33.yyy.edu,;branch=z9hG4bK776asdhds,Max-Forwards:70,To:Bob,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 INVITE,Contact:,Content-Type:application/sdp,Content-Length:142,(Alices SDP not shown),SIP Methods:,INVITE,ACK and BYE,INVITE,200 OK,Alice,Bob,SIP/2.0 200 OK,Via:SIP/2.0/TCP pc33.yyy.edu,;branch=z9hG4bKnashds8;received=10.1.3.33,To:Bob;tag=a6c85cf,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 INVITE,Contact:,Content-Type:application/sdp,Content-Length:131,(Bobs SDP not shown),SIP Methods:,INVITE,ACK,and BYE,INVITE,200 OK,Alice,Bob,ACK,ACK sip:bob192.168.10.20 SIP/2.0,Via:SIP/2.0/TCP pc33.yyy.edu;branch=z9hG4bKnashds8,Max-Forwards:70,To:Bob;tag=a6c85cf,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 ACK,Content-Length:0,SIP Methods:,INVITE,ACK,and BYE,INVITE,200 OK,Session Established,Alice,Bob,ACK,SIP Methods:,INVITE,ACK,and,BYE,INVITE,200 OK,Session Established,Alice,Bob,ACK,BYE,BYE sip:alicepc33.yyy.edu SIP/2.0,Via:SIP/2.0/TCP 10.1.3.33;branch=z9hG4bKnashds8,Max-Forwards:70,From:Bob;tag=a6c85cf,To:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:231 BYE,Content-Length:0,SIP Methods:,INVITE,ACK,and,BYE,INVITE,200 OK,Session Established,Alice,Bob,ACK,BYE,200 OK,SIP/2.0 200 OK,Via:SIP/2.0/TCP 192.168.10.20,From:Alice;tag=1928301774,To:Bob;tag=a6c85cf,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:231 BYE,Content-Length:0,Alice,Bob,SIP Proxy“server.zzz.edu”,透過,Proxy Server,INVITE,INVITE sip:bobzzz.edu/TCP SIP/2.0,Via:SIP/2.0/TCP pc33.yyy.edu,;branch=z9hG4bK776asdhds;received=10.1.3.33,Max-Forwards:70,To:Bob,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 INVITE,Contact:,Content-Type:application/sdp,Content-Length:142,(Alices SDP not shown),INVITE,INVITE,Alice,Bob,透過,Proxy Server,SIP Proxy“server.zzz.edu”,INVITE sip:bob192.168.10.20/TCP SIP/2.0,Via:SIP/2.0/TCP server.zzz.edu,;branch=z9hG4bK4b43c2ff8.1;received=192.168.10.1,Via:SIP/2.0/TCP pc33.yyy.edu,;branch=z9hG4bK776asdhds;received=10.1.3.33,Max-Forwards:69,To:Bob,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 INVITE,Contact:,Content-Type:application/sdp,Content-Length:142,(Alices SDP not shown),Via Header for,Alices phone,Via Header for,zzz server,Max-Forwards,decreases 1,James Polk 20050503,INVITE,INVITE,Alice,Bob,透過,Proxy Server,SIP Proxy“server.zzz.edu”,200 OK,SIP/2.0 200 OK,Via:SIP/2.0/TCP server.zzz.edu,;branch=z9hG4bK4b43c2ff8.1;received=192.168.10.1,Via:SIP/2.0/TCP pc33.yyy.edu,;branch=z9hG4bKnashds8;received=10.1.3.33,To:Bob;tag=a6c85cf,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 INVITE,Contact:,Content-Type:application/sdp,Content-Length:131,(Bobs SDP not shown),Notice,both,Via,headers,INVITE,INVITE,200 OK,Alice,Bob,透過,Proxy Server,SIP Proxy“server.zzz.edu”,200 OK,SIP/2.0 200 OK,Via:SIP/2.0/TCP pc33.yyy.edu,;branch=z9hG4bKnashds8;received=10.1.3.33,To:Bob;tag=a6c85cf,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 INVITE,Contact:,Content-Type:application/sdp,Content-Length:131,(Bobs SDP not shown),Notice,one,Via,header,INVITE,INVITE,200 OK,200 OK,Alice,Bob,透過,Proxy Server,ACK,ACK sip:bob192.168.10.20 SIP/2.0,Via:SIP/2.0/TCP pc33.yyy.edu,;branch=z9hG4bKnashds8,Max-Forwards:70,To:Bob;tag=a6c85cf,From:Alice;tag=1928301774,Call-ID:a84b4c76e66710pc33.yyy.edu,CSeq:314159 ACK,Content-Length:0,SIP Proxy“server.zzz.edu”,INVITE,INVITE,200 OK,200 OK,Session Established,Alice,Bob,透過,Proxy Server,ACK,SIP Proxy“server.zzz