在 IMS/SIP中的（呼叫）无条件前转（Communication Forwarding Unconditional -CFU) 的终端分别为UA1,UA2和UA3;其中UA1,UA3分别在IMS/SIP运行，UA2在网络中正常工作；

1.无条件前转流程

        根据3GPP TS24.604中的A.1.3（呼叫）无条件前转的主要流程如下：

2.无条件前转主要消息内容

2.1 SIP/SDP Request: INVITE sip:UA2@Sharetechnote-cscf.com | , with session description

INVITE sip:UA2@Sharetechnote-cscf.com SIP/2.0

Via: SIP/2.0/UDP 192.168.1.11:58475;branch=z9hG4bK250253573;rport

From: <sip:UA1@Sharetechnote-cscf.com>;tag=390680916

To: <sip:UA2@Sharetechnote-cscf.com>

Contact: <sip:UA1@192.168.1.11:58475;transport=udp>;+g.oma.sip-im;language="en,fr";+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"

Call-ID: 0452befc-bfd8-afe1-fff8-65286703bad9

CSeq: 1500260822 INVITE

Content-Type: application/sdp

Content-Length: 695

Max-Forwards: 70

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

P-Preferred-Service: urn:urn-7:3gpp-service.ims.icsi.mmtel

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

Privacy: none

P-Access-Network-Info: ADSL;utran-cell-id-3gpp=00000000

User-Agent: IM-client/OMA1.0 android-ngn-stack/v2.544.836 (doubango r836 - L-06D)

P-Preferred-Identity: <sip:user@Sharetechnote-cscf.com>

Supported: 100rel

 

v=0

o=doubango 1983 678901 IN IP4 192.168.1.11

s=-

c=IN IP4 192.168.1.11

t=0 0

a=tcap:1 RTP/AVPF

m=audio 11286 RTP/AVP 9 98 99 97 8 0 96 3 18 101

a=ptime:20

a=silenceSupp:off - - - -

a=rtpmap:9 G722/8000/1

a=rtpmap:98 SPEEX/16000/1

a=rtpmap:99 SPEEX/32000/1

a=rtpmap:97 SPEEX/8000/1

a=rtpmap:8 PCMA/8000/1

a=rtpmap:0 PCMU/8000/1

a=rtpmap:96 iLBC/8000/1

a=fmtp:96 mode=20

a=rtpmap:3 GSM/8000/1

a=rtpmap:18 g729/8000/1

a=fmtp:18 annexb=no

a=rtpmap:101 telephone-event/8000/1

a=fmtp:101 0-16

a=pcfg:1 t=1

a=sendrecv

a=rtcp-mux

a=ssrc:4050946750 cname:ldjWoB60jbyQlR6e

a=ssrc:4050946750 mslabel:6994f7d1-6ce9-4fbd-acfd-84e5131ca2e2

a=ssrc:4050946750 label:Doubango.Audio

2.2  SIP/SDP Request: INVITE sip:UA3@192.168.1.3:61657;transport=udp | , with session description

INVITE sip:UA3@192.168.1.3:61657;transport=udp SIP/2.0

Via: SIP/2.0/UDP 192.168.1.2:60971;branch=z9hG4bK07ec3b4acc4a4392a7bedaa6532051df8d;rport;transport=udp

Via: SIP/2.0/UDP 192.168.1.11:58475;branch=z9hG4bK250253573;rport=58475

From: <sip:UA1@Sharetechnote-cscf.com>;tag=390680916

To: <sip:UA2@Sharetechnote-cscf.com>

Contact: <sip:UA1@192.168.1.11:58475;transport=udp>;+g.oma.sip-im;language="en,fr";+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"

Call-ID: 0452befc-bfd8-afe1-fff8-65286703bad9

CSeq: 1500260822 INVITE

Content-Type: application/sdp

Content-Length: 695

Max-Forwards: 69

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

P-Preferred-Service: urn:urn-7:3gpp-service.ims.icsi.mmtel

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

Privacy: none

P-Access-Network-Info: ADSL;utran-cell-id-3gpp=00000000

User-Agent: IM-client/OMA1.0 android-ngn-stack/v2.544.836 (doubango r836 - L-06D)

Supported: 100rel

P-Asserted-Identity: <sip:user@Sharetechnote-cscf.com>

Record-Route: <sip:192.168.1.2;lr>

 

v=0

o=doubango 1983 678901 IN IP4 192.168.1.11

s=-

c=IN IP4 192.168.1.11

t=0 0

a=tcap:1 RTP/AVPF

m=audio 11286 RTP/AVP 9 98 99 97 8 0 96 3 18 101

a=ptime:20

a=silenceSupp:off - - - -

a=rtpmap:9 G722/8000/1

a=rtpmap:98 SPEEX/16000/1

a=rtpmap:99 SPEEX/32000/1

a=rtpmap:97 SPEEX/8000/1

a=rtpmap:8 PCMA/8000/1

a=rtpmap:0 PCMU/8000/1

a=rtpmap:96 iLBC/8000/1

a=fmtp:96

原文来自：http://www.sharetechnote.com

整理：kangguoying20201014

“5G中的软切换--双活协议栈（DAPS）介绍 ”已在微信公众号"跟着老康学5G"中推出，敬请关注！