在 IMS/SIP中的未注冊前轉(zhuǎn)（Communication Forwarding on Not Logged-in -CFNL) 是指被叫未完成在CSCF中注冊的呼叫前轉(zhuǎn)；如下圖所示：參與終端UA1,UA2和UA3中UA1,UA3已完成注冊，UA2未注冊；
1.未注冊前轉(zhuǎn)流程
根據(jù)3GPP TS24.604中的A.1.3（呼叫）未注冊前轉(zhuǎn)的主要流程如下：
2.未注冊前轉(zhuǎn)主要消息
2.1 (A) INVITE sip:UA2@test.3gpp.com SIP/2.0
Via: SIP/2.0/UDP [2001:0:0:1::2]:50329;branch=z9hG4bK996978744;rport
From: <sip:UA1@test.3gpp.com>;tag=996990843
To: <sip:UA2@test.3gpp.com>
Contact: <sip:UA1@[2001:0:0:1::2]:50329;transport=udp>;+g.oma.sip-im;language="en,fr";+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"
Call-ID: 8c8faa31-bf9c-3adf-fb9e-1571d98e4073
CSeq: 8139 INVITE
Content-Type: application/sdp
Content-Length: 740
Max-Forwards: 70
Route: <sip:[2001:0:0:1::2]:5060;lr;transport=udp>
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 Boghe/v2.0.112.744
P-Preferred-Identity: <sip:123456789@test.3gpp.com>
Supported: 100rel
v=0
o=doubango 1983 678901 IN IP6 2001:0:0:1::2
s=-
c=IN IP6 2001:0:0:1::2
t=0 0
m=audio 26306 RTP/AVP 112 111 3 8 0 9 97 98 99 101
a=ptime:20
a=rtpmap:112 AMR/8000/1
a=imageattr:112 octet-align=1
a=fmtp:112 octet-align=1
a=rtpmap:111 AMR/8000/1
a=imageattr:111 octet-align=0
a=fmtp:111 octet-align=0
a=rtpmap:3 GSM/8000/1
a=rtpmap:8 PCMA/8000/1
a=rtpmap:0 PCMU/8000/1
a=rtpmap:9 G722/8000/1
a=rtpmap:97 SPEEX/8000/1
a=rtpmap:98 SPEEX/16000/1
a=rtpmap:99 SPEEX/32000/1
a=rtpmap:101 telephone-event/8000/1
a=fmtp:101 0-15
a=tcap:1 RTP/AVPF
a=pcfg:1 t=1
a=sendrecv
a=rtcp-mux
a=ssrc:1146886926 cname:ldjWoB60jbyQlR6e
a=ssrc:1146886926 mslabel:6994f7d1-6ce9-4fbd-acfd-84e5131ca2e2
a=ssrc:1146886926 label:Doubango
2.2(B) 181 Call Is Being Forwarded
Max-Forwards: 70
Via: SIP/2.0/UDP [2001:0:0:1::2]:50329;branch=z9hG4bK996978744;rport=50329
From: <sip:UA1@test.3gpp.com>;tag=996990843
To: <sip:UA2@test.3gpp.com>;tag=987654321
Call-ID: 8c8faa31-bf9c-3adf-fb9e-1571d98e4073
CSeq: 8139 INVITE
History-Info: <sip:223456789@test.3gpp.com>; index=1
Content-Length: 0
2.3(C) INVITE sip:UA3@[2001:0:0:1::11]:5060;cause=404 SIP/2.0
Via: SIP/2.0/UDP [2001:0:0:1::2]:5060;branch=z9hG4bKe5a451b9d19443a79242368f24597c6111d;rport;transport=udp
Via: SIP/2.0/UDP [2001:0:0:1::2]:50329;branch=z9hG4bK996978744;rport=50329
From: <sip:UA1@test.3gpp.com>;tag=996990843
To: <sip:UA3@ims.mnc246.mcc081.3gppnetwork.org>
Contact: <sip:UA1@[2001:0:0:1::2]:50329;transport=udp>;+g.oma.sip-im;language="en,fr";+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"
Call-ID: 8c8faa31-bf9c-3adf-fb9e-1571d98e4073
CSeq: 8139 INVITE
Content-Type: application/sdp
Content-Length: 740
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 Boghe/v2.0.112.744
Supported: 100rel
P-Asserted-Identity: <sip:123456789@test.3gpp.com>
History-Info: <sip:223456789@test.3gpp.com>; index=1
History-Info: <sip:001010123456789@ims.mnc246.mcc081.3gppnetwork.org?cause=404>; index=1.1; MP=1
Record-Route: <sip:[2001:0:0:1::2]:5060;lr>
v=0
o=doubango 1983 678901 IN IP6 2001:0:0:1::2
s=-
c=IN IP6 2001:0:0:1::2
t=0 0
m=audio 26306 RTP/AVP 112 111 3 8 0 9 97 98 99 101
a=ptime:20
a=rtpmap:112 AMR/8000/1
a=imageattr:112 octet-align=1
a=fmtp:112 octet-align=1
a=rtpmap:111 AMR/8000/1
a=imageattr:111 octet-align=0
a=fmtp:111 octet-align=0
a=rtpmap:3 GSM/8000/1
a=rtpmap:8 PCMA/8000/1
a=rtpmap:0 PCMU/8000/1
a=rtpmap:9 G722/8000/1
a=rtpmap:97 SPEEX/8000/1
a=rtpmap:98 SPEEX/16000/1
a=rtpmap:99 SPEEX/32000/1
a=rtpmap:101 telephone-event/8000/1
a=fmtp:101 0-15
a=tcap:1 RTP/AVPF
a=pcfg:1 t=1
a=sendrecv
a=rtcp-mux
a=ssrc:1146886926 cname:ldjWoB60jbyQlR6e
a=ssrc:1146886926 mslabel:6994f7d1-6ce9-4fbd-acfd-84e5131ca2e2
a=ssrc:1146886926 label:Doubango
原文來自：http://www.sharetechnote.com
整理：kangguoying20201018
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