VoLTE端到端业务详解 | SDP协议

书籍来源：艾怀丽《VoLTE端到端业务详解》

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附上汇总贴：VoLTE端到端业务详解 | 汇总_COCOgsta的博客-CSDN博客

4.2.1 基础知识

会话描述协议（SDP，Session Description Protocol）是由IETF（Internet工程任务组）作为RFC4566颁布，描述流媒体初始化参数的格式。其目的就是在媒体会话中传递媒体流信息，允许会话描述的接收者去参与会话。该协议定义了会话描述的统一格式，但并不定义多播地址的分配和SDP消息的传输，也不支持媒体编码方案的协商，这些功能均由下层传送协议完成。

会话描述协议（SDP）为会话通知、会话邀请和其他形式的多媒体会话初始化等提供了多媒体会话描述。

SDP文本信息包括：

· 会话名称和意图；

· 会话持续时间；

· 构成会话的媒体；

· 有关接收媒体的信息（地址等）。

SDP协议字段

SDP信息是文本信息，采用UTF-8编码中的ISO 10646字符集。SDP会话描述如表4-5所示（标注*符号的表示可选字段）。

（1）V、o、s、t、m为必需的，其他项为可选；

（2）如果SDP语法分析器不能识别某一类型（Type），则整个描述丢失；

（3）如果“a=”的某属性值不理解，则予以丢失；

（4）整个协议区分大小写；

（5）“=”两侧不允许有空格；

（6）会话级的描述就是媒体级描述的默认值；

（7）所有格式均为=。

4.2.2 SIP电话中的应用

SDP用于构建Invite和200 OK响应消息的消息体，供主/被叫用户交换媒体信息。

1.媒体流的配置

（1）主/被叫的媒体描述必须完全与主/被叫的第m个媒体流（“m=”）对应，都包含“a=rtpmap”，目的是易于适应静态净荷类型到动态净荷类型的转换。

（2）如果被叫不想接收主叫提出的某个媒体流，则在响应中设置该媒体流的端口号为0，并且必须返回对应的媒体流行。

2.单播SDP值的设定

（1）若只发媒体流，端口号无意义，应设为0。

（2）每个媒体流的净载荷类型列表应传送两个信息：能接收/发送的编译码和用以标识这些编译码的RTP净载荷类型号。

（3）若某一媒体流，主/被叫没有公共的媒体格式，被叫仍然要求返回媒体流的“m=”行，端口号为0，同时，不列净载荷类型。

（4）如果所有媒体流均无公共的媒体格式，则被叫回送400响应（坏请求），并加入304警告头字段（无媒体类型）。

3.多播操作

（1）接收和发送的多播地址是相同的。

（2）被叫不允许改变媒体流的只发、只收或收/发特性。

（3）如果被叫不支持多播，则回送400响应和330警告（多播不可用）。

4.延时媒体流

由于主叫可能实际上是一个和其他协议（如H.323）互通的协议网关，与S要求呼叫建立后进行媒体协商，这样，主叫可以先发不带SDP的Invite，通过ACK或重新发一个Invite请求修改被叫的会话描述（SDP）。

5.媒体流保持

如果要求对方进入保持状态，即暂时停止发送一个或多个媒体流，则可以用Re-Invite，会话描述与原来的请求或响应中的描述相同，只是“c=”为“0.0.0.0”，并且Re_Invite中的Cseq需要递增。

6.对应于SIP中有三个实体字段

（1）Content-Type：指明消息体类型，有两种：①Application/SDP表示是SDP会话描述；②Text/HTML表示是普通文本或HTML格式的描述。

（2）Content-Encoding：补充说明消息体类型，使用户可以采用压缩编码编辑消息体。

（3）Content-Length：给出消息体的字节数。

4.2.3 VoLTE实例

以下是典型VoLTE被叫用户振铃后主叫早释的呼叫流程。

主叫UE1：178XXXXXXXX，被叫UE2：760（家庭亲情号）且签约了视频彩铃业务，主叫用户登记在NJPSBC15BHW上。

呼叫过程：主叫拨号，被叫侧网络给主叫用户播放视频彩铃，主叫在收看视频彩铃过程中挂机、被叫未应答。

整体流程如图4-78所示。

1.主叫拨号


Session Initiation Protocol (Invite)
   Request-Line: Invite tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org SIP/2.0
   Method: Invite
   Request-URI: tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org Message Header
   From:　8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
   To: "760"760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>
   P-Preferred-Identity: @js.ims.mnc000.mcc460.3gppnetwork.org>
   Contact: 8617*****8860@[****:****:****:****:*:*:****:****]:31825>;+sip.instance="";+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";audio;video;+g.3gpp.mid-call;+g.3gpp.srvcc-alerting;+g.3gpp.ps2cs-srvcc-orig-pre-alerting
   Accept-Contact: *;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"
  P-Access-Network-Info:　3GPP-E-UTRAN-TDD;utran-cell-id-3gpp=4600051A1D546B03
  P-Preferred-Service: urn:urn-7:3gpp-service.ims.icsi.mmtel
 P-Early-Media: supported
  Supported:　100rel,histinfo,join,norefersub,precondition,replaces, timer,sec-agree
  Allow:　Invite,ACK,OPTIONS,BYE,CANCEL,UPDATE,INFO,PRACK,NOTIFY,MES SAGE,REFER
 Accept: application/sdp,application/3gpp-ims+xml
 Session-Expires: 1800
 Min-SE: 90
 Route:**********************************************************************************************************************
 Require: sec-agree
 Proxy-Require: sec-agree 
Security-Verify:　ipsec-3gpp;alg=hmac-sha-1-96;prot=esp;mod=　trans;ealg=null;spi-c=2545605770;spi-s=4136901965;port-c=9950; port-s=9900
    Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
    CSeq: 1 Invite
    Max-Forwards: 70
    User-Agent: IM-client/OMA1.0 HW-Rto/V1.0
    Via: SIP/2.0/UDP [****:****:****:****:*:*:****:****]:31825;branch=z9h G4bKbfjcb9LnjGLnjOfdamVm;rport
    Content-Type: application/sdp//表示是SDP会话描述、主叫用户侧媒体信息
    Content-Length: 814//消息体长度为814Byte Message Body
 Session Description Protocol
  Session Description Protocol Version (v): 0//版本为0
  Owner/Creator, Session Id (o): rue 3308 3308 IN IP6 ****:****:****:****:*:*:****:****　//会话源：用户名rue，会话标识3308，版本3308，网络类型internet，地址类型Ipv6，地址主叫ip****:****:****:****:*:*:****:****
  Session Name (s): -
  Connection Information (c): IN IP6 ****:****:****:****:*:*:****:****//连接数据：网络类型internet，地址类型Ipv6，连接地址****:****:****:****:*:*:****:***
  Bandwidth Information (b): AS:49//RTP流总带宽49Kbit/s
  Bandwidth Information (b): RR:1837//接收的RTCP流带宽1837bit/s
  Bandwidth Information (b): RS:612//发送的RTCP流带宽612bit/s
  Time Description, active time (t): 0 0//无开始和结束时间
  Media Description, name and address (m): audio 31016 RTP/AVP 107 106 105 104 101 102//媒体格式：媒体类型audio，端口号31016，传送层协议RTP/AVP，格式列表为 107 106 105 104 101 102
  Bandwidth Information (b): AS:49
  Bandwidth Information (b): RR:1837
  Bandwidth Information (b): RS:612
  Media Attribute (a): rtpmap:107 AMR-WB/16000/1
  Media Attribute (a): fmtp:107 mode-change-capability=2;max-red=0 //净荷类型107，编码名AMR-WB，抽样速度为16kHz
  Media Attribute (a): rtpmap:105 AMR/8000/1
  Media Attribute (a): fmtp:105 mode-change-capability=2;max- red=0
  Media Attribute (a): rtpmap:101 telephone-event/16000
  Media Attribute (a): fmtp:101 0-15
  Media Attribute (a): rtpmap:102 telephone-event/8000
  Media Attribute (a): fmtp:102 0-15
  Media Attribute (a): ptime:20//媒体打包的时长为20ms
  Media Attribute (a): maxptime:240//媒体打包的时长最大为240ms
  Media Attribute (a): sendrecv//收发模式为发送接收
  Media Attribute (a): curr:qos local none
  Media Attribute (a): curr:qos remote none//当前的状态是本地和远端均为没有资源
  Media Attribute (a): des:qos mandatory local sendrecv
  Media Attribute (a): des:qos optional remote sendrecv//请求的状态是本地一定为发送接收、远端的发送接收是可选的
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2.临时响应100 Trying消息


Status-Line: SIP/2.0 100 Trying
   Message Header
   Via: SIP/2.0/UDP [****:****:****:****:****:****:****:****]:31825;branc h=z9hG4bKbfjcb9LnjGLnjOfdamVm;rport=31409
   Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
   From: <sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
   To: "760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>
   CSeq: 1 Invite
   Content-Length: 0
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3.针对Invite的响应183消息


Status-Line: SIP/2.0 183 Session Progress 
Message Header
    Via: SIP/2.0/UDP [****:****:****:****:****:****:****:****]:31825;branch=z9hG4bKbfjcb9LnjGLnjOfdamVm;rport=31409
    Record-Route: 9900;lr;Hpt=8f52_116;CxtId=3;TRC=ffffffff-ffffffff;X-HwB2bUaCookie=4635>
    Record-Route URI: sip:[****:****:****:****:****:****:****:****]:9900;lr;Hpt=8f52_116;CxtId=3;TRC=ffffffff-ffffffff;X-HwB2bUaCookie=4635
    Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
    From: 8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
    To: "760"760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
    SIP to tag: 03k1lz2w
    CSeq: 1 Invite
    Allow:　Invite,UPDATE,BYE,PRACK,INFO,OPTIONS,CANCEL,SUBSCRIBE,A CK,REFER,NOTIFY,REGISTER,PUBLISH,MESSAGE
    Contact:　2409:8095:0500:0000:0000:0000:0000:012F]:9900;H pt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"
    Require: precondition,100rel
    RSeq: 1
    P-Early-Media: gated
    Feature-Caps: *;+g.3gpp.srvcc;+g.3gpp.mid-call;+g.3gpp.srvcc-alerting;+g.3gpp.ps2cs-srvcc-orig-pre-alerting
    Recv-Info: g.3gpp.state-and-event-info
    Content-Length: 522
    Content-Type: application/sdp//被叫侧的媒体信息
    Message Body
    Session Description Protocol
     Session Description Protocol Version (v): 0
     Owner/Creator,　Session　Id　(o):-125499876　125499876　IN　IP6 2409:8095:0500:0000:0000:0000:0000:0131
    Session Name (s): SBC call
    Connection Information (c): IN IP6 2409:8095:0500:0000:0000:0000:0000:0131
    Time Description, active time (t): 0 0
    Media Description, name and address (m): audio 25158 RTP/AVP 107 101
    Bandwidth Information (b): AS:49
    Bandwidth Information (b): RS:612
    Bandwidth Information (b): RR:1837
    Media Attribute (a): rtpmap:107 AMR-WB/16000
    Media Attribute (a): fmtp:107 mode-change-capability=2;max-red=0
    Media Attribute (a): ptime:20
    Media Attribute (a): maxptime:240
    Media Attribute (a): sendrecv
    Media Attribute (a): des:qos mandatory local sendrecv
    Media Attribute (a): curr:qos local none
    Media Attribute (a): des:qos mandatory remote sendrecv
    Media Attribute (a): curr:qos remote none
    Media Attribute (a): conf:qos remote sendrecv
    Media Attribute (a): rtpmap:101 telephone-event/16000
    Media Attribute (a): fmtp:101 0-15
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4.针对183的响应Prack消息


Request-Line: PRACK sip:[2409:8095:500::12f]:9900;Hpt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff SIP/2.0    
Message Header
From:　<sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
To:　"760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
 SIP to tag: 03k1lz2w
Route:*************************************************************************************************************
Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
CSeq: 2 PRACK
Max-Forwards: 70
User-Agent: IM-client/OMA1.0 HW-Rto/V1.0
Supported: 100rel,histinfo,join,norefersub,precondition,repla ces,timer
P-Access-Network-Info: 3GPP-E-UTRAN-TDD;utran-cell-id-3gpp=4600051A1D546B03
Via: SIP/2.0/UDP [****:****:****:****:*:*:****:****]:31825;branch=z9h G4bKcgjcb9LnjGLnjOfda0wo;rport
RAck: 1 1 Invite
Content-Length: 0
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5.Prack的应答消息


Status-Line: SIP/2.0 200 OK 
Message Header
  Via: SIP/2.0/UDP [****:****:****:****:****:****:****:****]:31825;branc h=z9hG4bKcgjcb9LnjGLnjOfda0wo;rport=31409
Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
 From:　<sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
To:　"760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
  SIP to tag: 03k1lz2w
CSeq: 2 PRACK
Content-Length: 0
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6.主叫用户的Update消息


 Request-Line: UPDATE sip:[2409:8095:500::12f]:9900;Hpt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff SIP/2.0
From: 8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
To: "760"760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
 SIP to tag: 03k1lz2w
Contact: 8617*****8860@[****:****:****:****:*:*:****:****]:31825>;+sip.instance="";+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";audio;video;+g.3gpp.mid-call;+g.3gpp.srvcc-alerting;+g.3gpp.ps2cs-srvcc-orig-pre-alerting
P-Access-Network-Info: 3GPP-E-UTRAN-TDD;utran-cell-id-3gpp=4600051A1D546B03
Supported: 100rel,histinfo,join,norefersub,precondition,repla ces,timer,sec-agree
Require: precondition,sec-agree
Allow: Invite,ACK,OPTIONS,BYE,CANCEL,UPDATE,INFO,PRACK,NOTIFY, MESSAGE,REFER
Proxy-Require: sec-agree
Security-Verify: ipsec-3gpp;alg=hmac-sha-1-96;prot=esp;mod=trans;ealg=null;spi-c=2545605770;spi-s=4136901965;port-c=9950;port-s=9900
Route:***************************************************************************************************************
Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
CSeq: 3 UPDATE
Max-Forwards: 70
User-Agent: IM-client/OMA1.0 HW-Rto/V1.0
Via: SIP/2.0/UDP [****:****:****:****:*:*:****:****]:31825;branch=z9h G4bKdhjcbDQ9IaQ9IwfdamUm;rport
 Transport: UDP
 Sent-by Address: ****:****:****:****:*:*:****:****
 Sent-by port: 31825
 Branch: z9hG4bKdhjcbDQ9IaQ9IwfdamUm
 RPort: rport
Content-Type: application/sdp//更新主叫用户侧的媒体信息
Content-Length: 503 
Message Body
Session Description Protocol
 Session Description Protocol Version (v): 0
 Owner/Creator, Session Id (o): rue 3308 3309 IN IP6 2409:8805:3024:2f13:1:1:54b5:17f5
 Bandwidth Information (b): AS:49
 Bandwidth Information (b): RR:1837
 Bandwidth Information (b): RS:612
 Time Description, active time (t): 0 0
 Media Description, name and address (m): audio 31016 RTP/AVP 107 101
 Bandwidth Information (b): AS:49
 Bandwidth Information (b): RR:1837
 Bandwidth Information (b): RS:612
 Media Attribute (a): rtpmap:107 AMR-WB/16000/1
 Media Attribute (a): fmtp:107 mode-change-capability=2;max- red=0
 Media Attribute (a): rtpmap:101 telephone-event/16000
 Media Attribute (a): fmtp:101 0-15
 Media Attribute (a): ptime:20
 Media Attribute (a): maxptime:240
 Media Attribute (a): sendrecv
 Media Attribute (a): curr:qos local sendrecv
 Media Attribute (a): curr:qos remote none//远端目前状态未知
Media Attribute (a): des:qos mandatory remote sendrecv//请求远端状态为发送接收
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7.Update的应答消息


 Status-Line: SIP/2.0 200 OK    
Status-Code: 200    
Resent Packet: False   
Message Header    
Via: SIP/2.0/UDP [****:****:****:****:****:****:****:****]:31825;branc h=z9hG4bKdhjcbDQ9IaQ9IwfdamUm;rport=31409
Transport: UDP
Sent-by Address: ****:****:****:****:****:****:****:****
Sent-by port: 31825
Branch: z9hG4bKdhjcbDQ9IaQ9IwfdamUm
RPort: 31409   
Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]   
From:　<sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L    SIP from address: sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org
SIP from address User Part: +8617*****8860
E.164 number (MSISDN): 8617*****8860
 Country Code: China (People’s Republic of) (86)
SIP　from　address　Host　Part:　js.ims.mnc000.mcc460.3gppnetwork.org    SIP from tag: aejcb9L   To:　"760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w    SIP to tag: 03k1lz2w   CSeq: 3 UPDATE    Sequence Number: 3    Method: UPDATE   Contact: <sip:[****:****:****:****:****:****:****:****]:9900;Hpt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"    Contact URI: sip:[2409:8095:0500:0000:0000:0000:0000:012F]:99 00;Hpt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff
Contact URI Host Part: [2409:8095:0500:0000:0000:0000:00 00:012F]
Contact URI Host Port: 9900
Contact URI parameter: Hpt=8f52_16
Contact URI parameter: CxtId=3
Contact URI parameter: TRC=ffffffff-ffffffff    
Contact　parameter:　+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"\r\n    
Require: precondition    Supported: 100rel,replaces,precondition    P-Early-Media: gated    Content-Length: 530    Content-Type: application/sdp//被叫侧更新的媒体信息   Message Body    Session Description Protocol
Session Description Protocol Version (v): 0
Owner/Creator, Session Id (o):-125499876 125499877 IN IP6 2409:8095:0500:0000:0000:0000:0000:0131
Session Name (s): SBC call
Connection Information (c): IN IP6 2409:8095:0500:0000:0000:0000:0000:0131
Time Description, active time (t): 0 0
Media Description, name and address (m): audio 25158 RTP/AVP 107 101
Bandwidth Information (b): AS:49
Bandwidth Information (b): RS:612
Bandwidth Information (b): RR:1837
Media Attribute (a): rtpmap:107 AMR-WB/16000
Media　Attribute　(a):　fmtp:107　mode-change-capability=2;max-red=0
Media Attribute (a): ptime:20
Media Attribute (a): maxptime:240
Media Attribute (a): sendrecv
Media Attribute (a): des:qos mandatory local sendrecv
Media Attribute (a): curr:qos local sendrecv
Media Attribute (a): des:qos mandatory remote sendrecv
Media Attribute (a): curr:qos remote sendrecv
Media Attribute (a): conf:qos remote sendrecv
Media Attribute (a): rtpmap:101 telephone-event/16000
Media Attribute (a): fmtp:101 0-15
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8.被叫侧的Update消息


 Request-Line: UPDATE sip:+8617*****8860@[****:****:****:****:****:****:****:****]:31825 SIP/2.0 Message Header
Via:　SIP/2.0/UDP　[****:****:****:****:****:****:****:****]:9900;bra nch=z9hG4bKefjhegs6fifgajsagkwg7eeid;Role=3;Hpt=8f52_ 36;TRC=ffffffff-ffffffff
Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
From: "760"760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
 SIP from tag: 03k1lz2w
To: 8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
CSeq: 1 UPDATE
Contact:　9900;Dpt=ed ca-200;Hpt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff>
Max-Forwards: 63
Supported: timer,precondition
P-Early-Media: sendrecv,gated
P-Asserted-Identity:　760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>
Content-Length: 1355
Content-Type: application/sdp//被叫侧更新的媒体信息 Message Body
Session Description Protocol
 Session Description Protocol Version (v): 0
 Owner/Creator, Session Id (o): - 125499876 125499878 IN IP6 2409:8095:0500:0000:0000:0000:0000:0131
 Session Name (s): SBC call
 Connection Information (c): IN IP6 2409:8095:0500:0000:0000:0000:0000:0131
 Time Description, active time (t): 0 0
  Session Start Time: 0
  Session Stop Time: 0
 Media Description, name and address (m): audio 25158 RTP/AVP 107 101 111 112 113 18 8 0 97
  Media Attribute (a): content:g.3gpp.cat//3GPP协议规定的彩铃业务属性
 Media Attribute (a): rtpmap:107 AMR-WB/16000
 Media Attribute (a): rtpmap:101 telephone-event/16000
 Media Attribute (a): ptime:20
 Media Attribute (a): fmtp:101 0-15
 Media Attribute (a): maxptime:240
Media Attribute (a): fmtp:107 mode-change-capability=2;max-red=0
Media Attribute (a): curr:qos remote none
Media Attribute (a): des:qos optional remote sendrecv
Media Attribute (a): conf:qos remote sendrecv
Media Attribute (a): curr:qos local sendrecv
Media Attribute (a): des:qos optional local sendrecv
Media Attribute (a): rtpmap:111 EVS/16000
 Media Attribute (a): fmtp:111 br=9.6-128;bw=swb;mode-change-capability=2;cmr=0;dtx=0;ch-aw-recv=-1;max-red=0
  Media Attribute (a): rtpmap:112 EVS/16000
 Media Attribute (a): fmtp:112 br=5.9-128;bw=wb;mode-change-capability=2;cmr=0;dtx=0;ch-aw-recv=-1;max-red=0
Media Attribute (a): fmtp:113 mode-change-capability=2;max-red=0
Media Attribute (a): rtpmap:18 G729/8000
Media Attribute (a): fmtp:18 annexb=no
Media Attribute (a): rtpmap:8 PCMA/8000
Media Attribute (a): rtpmap:0 PCMU/8000
Media Attribute (a): rtpmap:97 telephone-event/8000
Media Attribute (a): fmtp:97 0-15
Media Description, name and address (m): video 52784 RTP/AVP 114//被叫侧增加了视频媒体信息
Media Attribute (a): content:g.3gpp.cat
Media Attribute (a): rtpmap:114 H264/90000
Media Attribute (a): fmtp:114 max-br=960;profile-level-id=42C01E;packetization-mode=1;sprop-parameter-sets=Z0LAHtkAoD2hAAADAA EAAAMAPA8WLkg=,aMuAjLI=
Media Attribute (a): framerate:30
Media Attribute (a): framesize:114 640-480
Media Attribute (a): sendonly
Media Attribute (a): curr:qos remote none
Media Attribute (a): des:qos optional remote recv
Media Attribute (a): conf:qos remote recv
Media Attribute (a): curr:qos local send
Media Attribute (a): des:qos optional local send
复制代码

9.Update的响应200 OK消息


 Status-Line: SIP/2.0 200 OK   Message Header    From: "760"760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
SIP from tag: 03k1lz2w    To: 8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L    Contact: 8617*****8860@[****:****:****:****:*:*:****:****]:31825>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";audio;video;+g.3gpp.mid-call;+g.3gpp.srvcc-alerting;+g.3gpp.ps2cs-srvcc-orig-pre-alerting    P-Access-Network-Info: 3GPP-E-UTRAN-TDD;utran-cell-id-3gpp=4600051A1D546B03    Supported: 100rel,histinfo,join,norefersub,precondition,repla ces,timer    Allow: Invite,ACK,OPTIONS,BYE,CANCEL,UPDATE,INFO,PRACK,NOTIFY, MESSAGE,REFER    Require: precondition    Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]    CSeq: 1 UPDATE
Sequence Number: 1
Method: UPDATE    User-Agent: IM-client/OMA1.0 HW-Rto/V1.0    Via: SIP/2.0/UDP [****:****:***::***]:9900;branch=z9hG4bKefjhegs6昀fgajsagkwg7eeid;Role=3;Hpt=8f52_36;TRC=ffffffff-ffffffff
Transport: UDP
Sent-by Address: ****:****:***::***
Sent-by port: 9900
Branch: z9hG4bKefjhegs6昀fgajsagkwg7eeid
Role=3
Hpt=8f52_36
TRC=ffffffff-ffffffff    Content-Type: application/sdp    Content-Length: 862   Message Body    Session Description Protocol
Session Description Protocol Version (v): 0
Owner/Creator, Session Id (o): rue 3308 3310 IN IP6 ****:****:****:****:*:*:****:****
Session Name (s): -
Connection Information (c): IN IP6 ****:****:****:****:*:*:****:****
Bandwidth Information (b): AS:995//视频和音频媒体的总RTP带宽为995kbit/s
Bandwidth Information (b): RR:7837//视频和音频媒体的总RTCP接收带宽为7837bit/s
Bandwidth Information (b): RS:8612//视频和音频媒体的总RTCP发送带宽为8612bit/s
Time Description, active time (t): 0 0
Media Description, name and address (m): audio 31016 RTP/AVP 107 101
Bandwidth Information (b): AS:49//音频媒体的RTP带宽为49kbit/s
Bandwidth Information (b): RR:1837//音频媒体的RTCP接收带宽为1837bit/s
Bandwidth Information (b): RS:612//音频媒体的RTCP发送带宽为612bit/s
Media Attribute (a): rtpmap:107 AMR-WB/16000/1
Media　Attribute　(a):　fmtp:107　mode-change-capability=2;max-red=0
Media Attribute (a): rtpmap:101 telephone-event/16000
Media Attribute (a): fmtp:101 0-15
Media Attribute (a): ptime:20
Media Attribute (a): maxptime:240
Media Attribute (a): sendrecv
Media Attribute (a): curr:qos local none
Media Attribute (a): curr:qos remote sendrecv
Media Attribute (a): des:qos mandatory local sendrecv
Media Attribute (a): des:qos optional remote sendrecv
Media Description, name and address (m): video 37078 RTP/ AVP 114//主叫用户的视频媒体信息
Bandwidth　Information　(b):　AS:946//视频媒体的RTP带宽为946kbit/s
Bandwidth Information (b): RR:6000//视频媒体的RTCP接收带宽为6000bit/s
Bandwidth Information (b): RS:8000//视频媒体的RTCP发送带宽为8000bit/s
Media Attribute (a): rtpmap:114 H264/90000
Media Attribute (a): fmtp:114 pro昀le-level-id=42C01E; packetization-mode=1; max-br=960; sprop-parameter-sets=Z0LAHtsCgPRA, aMqPIA==
Media Attribute (a): recvonly//模式修改为仅接收Media Attribute (a): curr:qos local none//本地目前的状态是无资源
Media Attribute (a): curr:qos remote send
Media Attribute (a): des:qos mandatory local sendrecv//请求本地的状态是一定要发送接收
Media Attribute (a): des:qos optional remote send//请求远端的状态是可以发送
Media Attribute (a): des:qos mandatory remote recv//请求远端的状态是一定要为接收
复制代码

10.主叫用户的Update消息


   Request-Line:　UPDATE　sip:[****:****:****::***]:9900;Dpt=edca-200;Hpt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff SIP/2.0    Message Header     From:　8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L     To:　"760"760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
SIP to tag: 03k1lz2w     Contact:　8617*****8860@[****:****:****:****:*:*:****:****]:31825>;+sip.instance="";+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";audio;video;+g.3gpp.mid-call;+g.3gpp.srvcc-alerting;+g.3gpp.ps2cs-srvcc-orig-pre-alerting     P-Access-Network-Info:　3GPP-E-UTRAN-TDD;utran-cell-id-3gpp=4600051A1D546B03     Supported:　100rel,histinfo,join,norefersub,precondition,repla ces,timer,sec-agree     Allow:　Invite,ACK,OPTIONS,BYE,CANCEL,UPDATE,INFO,PRACK,NOTIFY, MESSAGE,REFER     Require: sec-agree     Proxy-Require: sec-agree
Security-Verify:　ipsec-3gpp;alg=hmac-sha-1-96;prot=esp;mod=trans;ealg=null;spi-c=2545605770;spi-s=4136901965;port-c=9950;port-s=9900     Route:********************************************************* **************************************************************     Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]     CSeq: 4 UPDATE     Max-Forwards: 70     User-Agent: IM-client/OMA1.0 HW-Rto/V1.0     Via: SIP/2.0/UDP [****:****:****:****:*:*:****:****]:31825;branch=z9h G4bKaijcbDQ9IaQ9IwfdaeMo;rport     Content-Type: application/sdp//主叫用户再次更新自己的媒体信息     Content-Length: 870    Message Body     Session Description Protocol
Session Description Protocol Version (v): 0
Owner/Creator, Session Id (o): rue 3308 3311 IN IP6 2409:8805:3024:2f13:1:1:54b5:17f5
Session Name (s): -
Connection Information (c): IN IP6 ****:****:****:****:*:*:****:****
Bandwidth Information (b): AS:995
Bandwidth Information (b): RR:7837
Bandwidth Information (b): RS:8612
Time Description, active time (t): 0 0
Media Description, name and address (m): audio 31016 RTP/AVP 107 101
Bandwidth Information (b): AS:49
Bandwidth Information (b): RR:1837
Bandwidth Information (b): RS:612
Media Attribute (a): rtpmap:107 AMR-WB/16000/1
Media　Attribute　(a):　fmtp:107　mode-change-capability=2;max-red=0
Media Attribute (a): rtpmap:101 telephone-event/16000
Media Attribute (a): fmtp:101 0-15
Media Attribute (a): ptime:20
Media Attribute (a): maxptime:240
Media Attribute (a): sendrecv
Media Attribute (a): curr:qos local sendrecv
Media Attribute (a): curr:qos remote sendrecv
Media Attribute (a): des:qos mandatory local sendrecv
Media Attribute (a): des:qos optional remote sendrecv
Media Description, name and address (m): video 37078 RTP/AVP 114
Bandwidth Information (b): AS:946
Bandwidth Information (b): RR:6000
Bandwidth Information (b): RS:8000
Media Attribute (a): rtpmap:114 H264/90000
Media　Attribute　(a):　fmtp:114　profile-level-id=42C01E;packetization-mode=1;　max-br=960;　sprop-parameter-sets=Z0LAHtsCgPRA, aMqPIA==
Media Attribute (a): recvonly
Media Attribute (a): curr:qos local sendrecv//目前本地的状态是发送接收
Media Attribute (a): curr:qos remote send//目前远端的状态是发送
Media Attribute (a): des:qos mandatory local sendrecv
Media Attribute (a): des:qos optional remote send
Media Attribute (a): des:qos mandatory remote recv
复制代码

11.被叫侧针对主叫Update的响应200 OK消息


 Status-Line: SIP/2.0 200 OK Message Header    Via: SIP/2.0/UDP [****:****:****:****:****:****:****:****]:31825;    Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]    From:　8617*****8860@js.ims.mnc000.mcc460.3gppnetwork. org>;tag=aejcb9L    To:　"760"760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
SIP to tag: 03k1lz2w    CSeq: 4 UPDATE    Contact: 9900;Hpt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff>    Supported: 100rel,replaces,precondition,histinfo    P-Early-Media: sendrecv,gated    Content-Length: 739    Content-Type: application/sdp//被叫侧更新后的媒体信息   Message Body    Session Description Protocol
Session Description Protocol Version (v): 0
Owner/Creator, Session Id (o): - 125499876 125499879 IN IP6 2409:8095:0500:0000:0000:0000:0000:0131
Session Name (s): SBC call
Connection Information (c): IN IP6 ****:****:****:****:****:****:****:****
Time Description, active time (t): 0 0
Media Description, name and address (m): audio 25158 RTP/AVP 107 101
Media Attribute (a): content:g.3gpp.cat
Media Attribute (a): rtpmap:107 AMR-WB/16000
Media Attribute (a): ptime:20
Media Attribute (a): maxptime:240
Media　Attribute　(a):　fmtp:107　mode-change-capability=2;max-red=0
Media Attribute (a): curr:qos remote sendrecv//目前远端的状态为发送接收
Media Attribute (a): des:qos mandatory remote sendrecv//请求远端的状态是一定为发送接收
Media Attribute (a): curr:qos local sendrecv//目前本地的状态为发送接收
Media Attribute (a): des:qos optional local sendrecv//请求的本地状态为发送接收可选
Media Attribute (a): rtpmap:101 telephone-event/16000
Media Attribute (a): fmtp:101 0-15
Media Description, name and address (m): video 52784 RTP/AVP 114
Media Attribute (a): content:g.3gpp.cat
Media Attribute (a): rtpmap:114 H264/90000
Media　Attribute　(a):　fmtp:114　max-br=960;profile-level-id=42C01E;packetization-mode=1;sprop-parameter-sets=Z0LAHtkAoD2hAAADAA EAAAMAPA8WLkg=,aMuAjLI=
Media Attribute (a): framerate:30
Media Attribute (a): framesize:114 640-480
Media Attribute (a): sendonly
复制代码

12.被叫侧的振铃消息180 Ringing


 Status-Line: SIP/2.0 180 Ringing Message Header
Via: SIP/2.0/UDP [****:****:****:****:****:****:****:****]:31825;branc h=z9hG4bKbfjcb9LnjGLnjOfdamVm;rport=31409
Record-Route: <sip:[****:****:****:****:****:****:****:****]:9900;lr;Hpt=8f52_116;CxtId=3;TRC=ffffffff-ffffffff;X-HwB2bUaCookie=4635>
 Record-Route URI: sip:[****:****:****:****:****:****:****:****]:99 00;lr;Hpt=8f52_116;CxtId=3;TRC=ffffffff-ffffffff;X-HwB2bUaCookie= 4635
Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
From:　<sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
To:　"760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
 SIP to tag: 03k1lz2w
CSeq: 1 Invite
Allow:　Invite,UPDATE,BYE,PRACK,INFO,OPTIONS,CANCEL,SUBSCRIBE,A CK,REFER,NOTIFY,REGISTER,PUBLISH,MESSAGE
Contact: <sip:[****:****:****:****:****:****:****:****]:9900;Hpt=8f52_16;CxtId=3;TRC=ffffffff-ffffffff>
P-Early-Media: sendrecv
Feature-Caps: *;+g.3gpp.srvcc;+g.3gpp.mid-call;+g.3gpp.srvcc-alerting;+g.3gpp.ps2cs-srvcc-orig-pre-alerting
Recv-Info: g.3gpp.state-and-event-info
Content-Length: 0
复制代码

13.主叫用户收看视频彩铃8s后主动挂机


 Request-Line:　CANCEL　tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org SIP/2.0 Message Header
From:　<sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
To: "760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>
Route:*******************************************************************************************************
Reason: SIP;cause=487;text="request terminated"
Supported: 100rel,histinfo,join,norefersub,precondition,replac es,timer,sec-agree
Security-Verify: ipsec-3gpp;alg=hmac-sha-1-96;prot=esp; mod=trans;ealg=null;spi-c=2545605770;spi-s=4136901965;port-c=9950;port-s=9900
Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
CSeq: 1 CANCEL
Max-Forwards: 70
User-Agent: IM-client/OMA1.0 HW-Rto/V1.0
Via: SIP/2.0/UDP [****:****:****:****:*:*:****:****]:31825;branch= z9 hG4bKbfjcb9LnjGLnjOfdamVm;rport
Content-Length: 0
复制代码

14.Cancel的响应200 OK消息


 Status-Line: SIP/2.0 200 OK Message Header    Via: SIP/2.0/UDP [****:****:****:****:****:****:****:****]:31825;branc h=z9hG4bKbfjcb9LnjGLnjOfdamVm;rport=31409    Call-ID: ddjcb9Lnj@[2409:8805:3024:2f13:1:1:54b5:17f5]    From: <sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L    To: "760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=c6ehgiha
SIP to tag: c6ehgiha    CSeq: 1 CANCEL    Content-Length: 0
复制代码

15.网络侧终止了本次通话


 Status-Line: SIP/2.0 487 Request Terminated Message Header
Via: SIP/2.0/UDP [****:****:****:****:****:****:****:****]:31825;branc h=z9hG4bKbfjcb9LnjGLnjOfdamVm;rport=31409
Call-ID: ddjcb9Lnj@[2409:8805:3024:2f13:1:1:54b5:17f5]
From:　<sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
To:　"760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
 SIP to tag: 03k1lz2w
CSeq: 1 Invite
Warning: 399 [****:****:****:****:****:****:****:****] "SS250200F156L921 [00000] Cancel received on initial invite"
Content-Length: 0
复制代码

16.主叫用户确认终止通话


 Request-Line: ACK tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org SIP/2.0 Message Header
To:　"760"<tel:760;phone-context=ims.mnc007.mcc460.3gppnetwork.org>;tag=03k1lz2w
 SIP to tag: 03k1lz2w
From:　<sip:+8617*****8860@js.ims.mnc000.mcc460.3gppnetwork.org>;tag=aejcb9L
CSeq: 1 ACK
Call-ID: ddjcb9Lnj@[****:****:****:****:*:*:****:****]
Route:*******************************************************************************************************************
Max-Forwards: 70
Via: SIP/2.0/UDP [****:****:****:****:*:*:****:****]:31825;branch=z9h G4bKbfjcb9LnjGLnjOfdamVm;rport
Supported:　100rel,histinfo,join,norefersub,precondition,repla ces,timer
Content-Length: 0
复制代码

4.2.4 现网案例

SDP协议对于我们掌握VoLTE语音质量问题的处理有着至关重要的作用，理论知识是实践的前提，同时实践又会进一步加深我们对理论的理解。下面就用一个语音质量问题的案例来帮助我们更好地了解SDP协议。

一用户通话过程中突然听不到对方的声音了，我们从他的信令流程可以看到，在被叫应答之后他给网络侧重新发起了一个Invite消息，流程如图4-79所示。

第二条Invite消息都带了什么信息？如图4-80所示，这个参数是本次主叫用户听不到声音的根本原因。

这条消息是告诉网络侧，现在将主叫侧的媒体修改为“只发送”模式，此时主叫用户的感知是听不到声音。

我们可能第一次遇到这样的信令，也许看不到这样一个细节。随着经验的积累和理论学习，我们在SDP中的各个参数中可以立即锁定能解决问题的参数。

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原文地址：https://blog.csdn.net/guolianggsta/article/details/126367110