Hi all:
There is a question confused me.
In a session lanched by INVITE request, before replied a final status
response, we can cancel this by a CANCEL request followed.
Callid、FromTag、ToTag and Request-Url are enough to separate which
INVITE request that the CANCEL request cancel.
Why copy the number part of Cseq headfield?
What is that surppose to?
Here comes a example inferred by rfc3665:
----------------------------Callflow
Start--------------------------------------------------------
Alice Proxy 1
| |
| INVITE |
|--------------->|
| 100 |
|<---------------|
| 180 |
|<---------------|
| CANCEL |
|--------------->|
----------------------------Callflow
End------------------------------------------------------------
----------------------------INVITE Message
Start----------------------------------------------
INVITE sip:[EMAIL PROTECTED] SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
Route: <sip:ss1.atlanta.example.com;lr>
From: Alice <sip:[EMAIL PROTECTED]>;tag=9fxced76sl
To: Bob <sip:[EMAIL PROTECTED]>
Call-ID: [EMAIL PROTECTED]
CSeq: 1 INVITE
Contact: <sip:[EMAIL PROTECTED]>
Proxy-Authorization: Digest username="alice",
realm="atlanta.example.com",
nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="",
uri="sip:[EMAIL PROTECTED]",
response="b00b416324679d7e243f55708d44be7b"
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
----------------------------INVITE Message
End----------------------------------------------------
----------------------------CANCEL Message
Start-------------------------------------------------
CANCEL sip:[EMAIL PROTECTED] SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
From: Alice <sip:[EMAIL PROTECTED]>;tag=9fxced76sl
To: Bob <sip:[EMAIL PROTECTED]>
Route: <sip:ss1.atlanta.example.com;lr>
Call-ID: [EMAIL PROTECTED]
CSeq: 1 CANCEL
Content-Length: 0
----------------------------CANCEL Message
End--------------------------------------------------
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