呼叫等待（Communication Waiting）服务允许主叫终端告知被叫终端有没有可用于接入的通信资源。主叫（UA)可以选择接受、拒绝或忽略传入的通信。

1. IMS/SIP中呼叫等待信令流程

2.呼叫等待信令消息主要内容

2.1(A) INVITE sip:001010123456789@[2001::1:d279:3516:72e6:fa46]:39047 SIP/2.0

INVITE sip:001010123456789@[2001::1:d279:3516:72e6:fa46]:39047 SIP/2.0

Via: SIP/2.0/UDP [2001:0:0:1::2]:65211;branch=z9hG4bK7274b6a822524ffa...;transport=udp

Via: SIP/2.0/TCP [2001:0:0:1::2]:50626;branch=z9hG4bKe16b0a51e196416...;transport=tcp

Max-Forwards: 69

Call-ID: 1e73797a14b14c7eb85e33e3e4b628ea

CSeq: 30001 INVITE

To: sip:001010123456789@ims.mnc01.mcc001.3gppnetwork.org

From: sip:0123456789@ims.mnc01.mcc001.3gppnetwork.org;tag=1111111111

Feature-Caps: *;+g.3gpp.srvcc-alerting;+g.3gpp.mid-call

Allow: ACK, BYE, CANCEL, INVITE, PRACK, UPDATE

Accept-Contact: *;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";require;explicit

User-Agent: UA2/9dc040f

Content-Type: application/sdp

Content-Length: 727

Contact: <sip:0123456789@[2001:0:0:1::2]:50626;transport=tcp>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";video;+g.3gpp.srvcc-alerting;+g.3gpp.mid-call

Privacy: none

P-Asserted-Identity: <sip:0123456789@ims.mnc01.mcc001.3gppnetwork.org>

Record-Route: <sip:[2001:0:0:1::2]:65211;lr>

v=0

o=Sharetechnote 164 63164 IN IP6 2001:0:0:1::2

s=-

i=A VOIP Session

c=IN IP6 2001:0:0:1::2

t=0 0

m=audio 60000 RTP/AVP 96 97 98 99 100 8 0 101 102

b=AS:153

b=RS:800

b=RR:2400

a=ptime:20

a=maxptime:240

a=rtpmap:96 EVS/16000/1

a=fmtp:96 max-red=220

a=rtpmap:97 AMR-WB/16000/1

a=fmtp:97 mode-change-capability=2

a=rtpmap:98 AMR-WB/16000/1

a=fmtp:98 octet-align=1; mode-change-capability=2

a=rtpmap:99 AMR/8000/1

a=fmtp:99 mode-change-capability=2

a=rtpmap:100 AMR/8000/1

a=fmtp:100 octet-align=1; mode-change-capability=2

a=rtpmap:8 PCMA/8000/1

a=rtpmap:0 PCMU/8000/1

a=rtpmap:101 telephone-event/16000

a=fmtp:101 0-15

a=rtpmap:102 telephone-event/8000

a=fmtp:102 0-15

a=mid:0

a=rtcp:60001

a=sendrecv

2.2(B) INVITE sip:001010123456789@[2001::1:d279:3516:72e6:fa46]:39047 SIP/2.0

INVITE sip:001010123456789@[2001::1:d279:3516:72e6:fa46]:39047 SIP/2.0

Via: SIP/2.0/UDP [2001:0:0:1::2]:65211;branch=z9hG4bK7274b6a822524ffa838...;transport=udp

Via: SIP/2.0/TCP [2001:0:0:1::2]:50628;branch=z9hG4bK3234f01ce09b445aa5...;transport=tcp

Max-Forwards: 69

Call-ID: bf653744ce1d4b83ae0ccebdfad4e14d

CSeq: 52001 INVITE

To: sip:001010123456789@ims.mnc01.mcc001.3gppnetwork.org

From: sip:VirtualUA_2nd@test.3gpp.com;tag=2222222222

Feature-Caps: *;+g.3gpp.srvcc-alerting;+g.3gpp.mid-call

Allow: ACK, BYE, CANCEL, INVITE, PRACK, UPDATE

Accept-Contact: *;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";require;explicit

Privacy: none

User-Agent: UA3/9dc040f

Content-Type: application/sdp

Content-Length: 728

Contact: <sip:VirtualUA_2nd@[2001:0:0:1::2]:50628;transport=tcp>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";video;+g.3gpp.srvcc-alerting;+g.3gpp.mid-call

P-Asserted-Identity: <sip:UA3@test.3gpp.com>

Record-Route: <sip:[2001:0:0:1::2]:65211;lr>

v=0

o=Sharetechnote 960 775960 IN IP6 2001:0:0:1::2

s=-

i=A VOIP Session

c=IN IP6 2001:0:0:1::2

t=0 0

m=audio 60002 RTP/AVP 96 97 98 99 100 8 0 101 102

b=AS:153

b=RS:800

b=RR:2400

a=ptime:20

a=maxptime:240

a=rtpmap:96 EVS/16000/1

a=fmtp:96 max-red=220

a=rtpmap:97 AMR-WB/16000/1

a=fmtp:97 mode-change-capability=2

a=rtpmap:98 AMR-WB/16000/1

a=fmtp:98 octet-align=1; mode-change-capability=2

a=rtpmap:99 AMR/8000/1

a=fmtp:99 mode-change-capability=2

a=rtpmap:100 AMR/8000/1

a=fmtp:100 octet-align=1; mode-change-capability=2

a=rtpmap:8 PCMA/8000/1

a=rtpmap:0 PCMU/8000/1

a=rtpmap:101 telephone-event/16000

a=fmtp:101 0-15

a=rtpmap:102 telephone-event/8000

a=fmtp:102 0-15

a=mid:0

a=rtcp:60003

a=sendrecv 

2.3(C) INVITE sip:0123456789@[2001:0:0:1::2]:50626;transport=tcp SIP/2.0  

INVITE sip:0123456789@[2001:0:0:1::2]:50626;transport=tcp SIP/2.0

Max-Forwards: 70

Route: <sip:[2001:0:0:1::2]:65211;lr>

Via: SIP/2.0/TCP [2001::1:d279:3516:72e6:fa46]:39047;branch=z9hG4bK150087668-37dae110

Call-ID: 1e73797a14b14c7eb85e33e3e4b628ea

CSeq: 1 INVITE

From: <sip:001010123456789@ims.mnc01.mcc001.3gppnetwork.org>;tag=5446714287d456-5e34ced8

To: <sip:0123456789@ims.mnc01.mcc001.3gppnetwork.org>;tag=1111111111

Contact: <sip:001010123456789@[2001::1:d279:3516:72e6:fa46]:39047>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";video;+g.3gpp.srvcc-alerting;+sip.instance="<urn:gsma:imei:35910506-000422-0>"

Accept-Contact: *;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";video

Allow: INVITE,BYE,CANCEL,ACK,PRACK,UPDATE,INFO,REFER,NOTIFY,MESSAGE

P-Preferred-Identity: <sip:001010123456789@ims.mnc01.mcc001.3gppnetwork.org>

P-Access-Network-Info: 3GPP-E-UTRAN-FDD;utran-cell-id-3gpp=0010100010000000

Security-Verify: ipsec-3gpp;q=0.1;alg=hmac-md5-96;prot=esp;mod=trans;ealg=null;spi-c=3854453982;spi-s=1494228412;port-c=65210;port-s=65211

Require: sec-agree

Supported: 100rel,timer

User-Agent: UA1

Proxy-Require: sec-agree

Content-Length: 648

Content-Type: application/sdp

v=0

o=sip:001010123456789@ims.mnc01.mcc001.3gppnetwork.org 3690753268 3690753269 IN IP6 2001:0:0:1::11

s=-

c=IN IP6 2001:0:0:1::11

t=0 0

m=audio 50010 RTP/AVP 97 98 99 100 101 102

b=AS:49

b=RS:0

b=RR:1200

a=rtpmap:97 AMR-WB/16000/1

a=fmtp:97 mode-change-capability=2

a=rtpmap:98 AMR-WB/16000/1

a=fmtp:98 octet-align=1; mode-change-capability=2

a=rtpmap:99 telephone-event/16000

a=fmtp:99 0-15

a=rtpmap:100 AMR/8000/1

a=fmtp:100 mode-change-capability=2

a=rtpmap:101 AMR/8000/1

a=fmtp:101 octet-align=1; mode-change-capability=2

a=rtpmap:102 telephone-event/8000

a=fmtp:102 0-15

a=mid:0

a=sendonly

a=ptime:20

a=maxptime:240

 2.4(D) SIP/2.0 200 OK

SIP/2.0 200 OK

Max-Forwards: 70

Via: SIP/2.0/TCP [2001::1:d279:3516:72e6:fa46]:39047;branch=z9hG4bK150087668-37dae110

From: <sip:001010123456789@ims.mnc01.mcc001.3gppnetwork.org>;tag=5446714287d456-5e34ced8

To: <sip:0123456789@ims.mnc01.mcc001.3gppnetwork.org>;tag=1111111111

Call-ID: 1e73797a14b14c7eb85e33e3e4b628ea

CSeq: 1 INVITE

Allow: ACK, BYE, CANCEL, INVITE, PRACK, UPDATE

Record-Route: <sip:[2001:0:0:1::2]:65211;lr>

User-Agent: UA2/9dc040f

Content-Type: application/sdp

Content-Length: 336

Contact: <sip:0123456789@[2001:0:0:1::2]:50626;transport=tcp>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";video;+g.3gpp.srvcc-alerting;+g.3gpp.mid-call

Privacy: none

P-Asserted-Identity: <sip:0123456789@ims.mnc01.mcc001.3gppnetwork.org>

v=0

o=Sharetechnote 164 63166 IN IP6 2001:0:0:1::2

s=-

i=A VOIP Session

c=IN IP6 2001:0:0:1::2

t=0 0

m=audio 60000 RTP/AVP 97 99

b=AS:49

b=RS:0

b=RR:1200

a=rtpmap:97 AMR-WB/16000/1

a=fmtp:97 mode-change-capability=2

a=rtpmap:99 telephone-event/16000

a=fmtp:99 0-15

a=mid:0

a=ptime:20

a=maxptime:240

a=recvonly

a=rtcp:60001 

2.5(E) ACK sip:0123456789@[2001:0:0:1::2]:50626;transport=tcp SIP/2.0

ACK sip:0123456789@[2001:0:0:1::2]:50626;transport=tcp SIP/2.0

Max-Forwards: 70

Route: <sip:[2001:0:0:1::2]:65211;lr>

Via: SIP/2.0/UDP [2001::1:d279:3516:72e6:fa46]:39047;branch=z9hG4bK15009b44d-410bdd5b

Call-ID: 1e73797a14b14c7eb85e33e3e4b628ea

CSeq: 1 ACK

From: <sip:001010123456789@ims.mnc01.mcc001.3gppnetwork.org>;tag=5446714287d456-5e34ced8

To: <sip:0123456789@ims.mnc01.mcc001.3gppnetwork.org>;tag=1111111111

Allow: INVITE,BYE,CANCEL,ACK,PRACK,UPDATE,INFO,REFER,NOTIFY,MESSAGE

Require: sec-agree

User-Agent: UA1

Proxy-Require: sec-agree

Content-Length: 0

原文来自：http://www.sharetechnote.com

整理：kangguoying20201020

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