RFC 5630
The Use of the SIPS URI Scheme in the Session Initiation Protocol (SIP)
6.3. Alice Calls Bob's SIP AOR Using TCP
Bob's registration has already occurred as per Section 6.1. In the second example, Alice calls Bob's SIP AOR instead (sip:bob@example.com), and she uses TCP as a transport. Registrar/ Authoritative Proxy B consults the binding in the registration database, and finds the two Contact header field bindings. Alice had addressed Bob with a SIP Request-URI (sip:bob@example.com), so Registrar/Authoritative Proxy B determines that the call needs to be routed both to bobpc (which registered with a SIP Contact header field) and bobphone (which registered with a SIPS Contact header field), and therefore the request is forked to sip:bob@bobpc.example.com and sip:bob@bobphone.example.com, through Edge Proxy B. Note that Registrar/Authoritative Proxy B preserved the SIP scheme of the Request-URI instead of replacing it with the SIPS scheme of the Contact header field that was used for registration. Both Registrar/Authoritative Proxy B and Edge Proxy B insert themselves in the Record-Route. Bob's phone's policy is to accept calls to SIP and SIPS (i.e., "best effort"), so both his PC client and his SIP phone ring simultaneously. Bob answers on his SIP phone, and the forked call leg to the PC client is canceled.
(eb) (pb)
Edge Registrar/
Bob@bobpc Proxy B Auth. Proxy B Proxy A Alice
| | | | |
| | | | INVITE F9 |
| | | INVITE F11 |<-----------|
| | INVITE F13'|<-----------| 100 F10 |
| INVITE F15' |<-----------| 100 F12 |----------->|
|<------------------| 100 F14' |----------->| |
| 180 F16' |----------->| | |
|------------------>| 180 F17' | | |
| |----------->| 180 F18' | |
| Bob@bobphone | |----------->| 180 F19' |
| | | INVITE F13 | |----------->|
| | INVITE F15 |<-----------| | |
| |<-----------| 100 F14 | | |
| | 180 F16 |----------->| | |
| |----------->| 180 F17 | | |
| | 200 F20 |----------->| 180 F18 | |
| |----------->| 200 F21 |----------->| 180 F19 |
| | |----------->| 200 F22 |----------->|
| | | |----------->| 200 F23 |
| | | | |----------->|
| | | | | ACK F24 |
| | | | ACK F25 |<-----------|
| | | ACK F26 |<-----------| |
| | ACK F27 |<-----------| | |
| |<-----------| | | |
| | CANCEL F26'| | |
| CANCEL F27' |<-----------| | |
|<------------------| | | |
| 200 F28' | | | |
|------------------>| 200 F29' | | |
| 487 F30' |----------->| | |
|------------------>| 487 F31' | | |
| |----------->| | |
Alice Calls Bob's SIP AOR
Message details
F9 INVITE Alice -> Proxy A
INVITE sip:bob@example.com SIP/2.0
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
Max-Forwards: 70
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Route: <sip:proxya.example.net;lr>
Contact: <sip:alice@alice-1.example.net>
Content-Type: application/sdp
Content-Length: {as per SDP}
{SDP not shown}
F10 100 (INVITE) Proxy A -> Alice
SIP/2.0 100 Trying
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Content-Length: 0
F11 INVITE Proxy A -> Registrar/Authoritative Proxy B
INVITE sip:bob@example.com SIP/2.0
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
Max-Forwards: 69
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route: <sip:proxya.example.net;lr>
Contact: <sip:alice@alice-1.example.net>
Content-Type: application/sdp
Content-Length: {as per SDP}
{SDP not shown}
F12 100 (INVITE) Registrar/Authoritative Proxy B -> Proxy A
SIP/2.0 100 Trying
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Content-Length: 0
F13' INVITE Registrar/Authoritative Proxy B -> Edge Proxy B
INVITE sip:bob@bobpc.example.com SIP/2.0
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
Max-Forwards: 68
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Route: <sip:laksdyjanseg237+fsdf+uy623hytIJ8@eb.example.com;lr;ob>
Record-Route: <sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:alice@alice-1.example.net>
Content-Type: application/sdp
Content-Length: {as per SDP}
{SDP not shown}
F14' 100 (INVITE) Edge Proxy B -> Registrar/Authoritative Proxy B
SIP/2.0 100 Trying
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Content-Length: 0
F15' INVITE Edge Proxy B -> Bob's PC Client
INVITE sip:bob@bobpc.example.com SIP/2.0
Via: SIP/2.0/TCP eb.example.com:5060;branch=z9hG4bKbiba
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
Max-Forwards: 67
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:laksdyjanseg237+fsdf+uy623hytIJ8@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:alice@alice-1.example.net>
Content-Type: application/sdp
Content-Length: {as per SDP}
{SDP not shown}
F16' 180 (INVITE) Bob's PC Client -> Edge Proxy B
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP eb.example.com:5060;branch=z9hG4bKbiba
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=963258
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:laksdyjanseg237+fsdf+uy623hytIJ8@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobpc.example.com>
Content-Length: 0
F17' 180 (INVITE) Edge Proxy B -> Registrar/Authoritative Proxy B
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=963258
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:laksdyjanseg237+fsdf+uy623hytIJ8@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobpc.example.com>
Content-Length: 0
F18' 180 (INVITE) Registrar/Authoritative Proxy B -> Proxy A
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=963258
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:laksdyjanseg237+fsdf+uy623hytIJ8@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobpc.example.com>
Content-Length: 0
F19' 180 (INVITE) Proxy A -> Alice
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=963258
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:laksdyjanseg237+fsdf+uy623hytIJ8@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobpc.example.com>
Content-Length: 0
F13 INVITE Registrar/Authoritative Proxy B -> Edge Proxy B
INVITE sip:bob@bobphone.example.com SIP/2.0
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
Max-Forwards: 68
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Route: <sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>
Record-Route: <sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:alice@alice-1.example.net>
Content-Type: application/sdp
Content-Length: {as per SDP}
{SDP not shown}
F14 100 (INVITE) Edge Proxy B -> Registrar/Authoritative Proxy B
SIP/2.0 100 Trying
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Content-Length: 0
F15 INVITE Edge Proxy B -> Bob's Phone
INVITE sip:bob@bobphone.example.com SIP/2.0
Via: SIP/2.0/TLS eb.example.com:5061;branch=z9hG4bKtroubaba
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
Max-Forwards: 68
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:alice@alice-1.example.net>
Content-Type: application/sdp
Content-Length: {as per SDP}
{SDP not shown}
F16 180 (INVITE) Bob's Phone -> Edge Proxy B
SIP/2.0 180 Ringing
Via: SIP/2.0/TLS eb.example.com:5061;branch=z9hG4bKtroubaba
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobphone.example.com>
Content-Length: 0
F17 180 (INVITE) Edge Proxy B -> Registrar/Authoritative Proxy B
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobphone.example.com>
Content-Length: 0
F18 180 (INVITE) Registrar/Authoritative Proxy B -> Proxy A
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobphone.example.com>
Content-Length: 0
F19 180 (INVITE) Proxy A -> Alice
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobphone.example.com>
Content-Length: 0
F20 200 (INVITE) Bob's Phone -> Edge Proxy B
SIP/2.0 200 OK
Via: SIP/2.0/TLS eb.example.com:5061;branch=z9hG4bKtroubaba
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobphone.example.com>
Content-Length: 0
F21 200 (INVITE) Edge Proxy B -> Registrar/Authoritative Proxy B
SIP/2.0 200 OK
Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobphone.example.com>
Content-Length: 0
F22 200 (INVITE) Registrar/Authoritative Proxy B -> Proxy A
SIP/2.0 200 OK
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobphone.example.com>
Content-Length: 0
F23 200 (INVITE) Proxy A -> Alice
SIP/2.0 200 OK
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 INVITE
Record-Route:
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>,
<sip:pb.example.com;lr>, <sip:proxya.example.net;lr>
Contact: <sip:bob@bobphone.example.com>
Content-Length: 0
F24 ACK Alice -> Proxy A
ACK sip:bob@bobphone.example.com SIP/2.0
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
Max-Forwards: 70
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 ACK
Route: <sip:proxya.example.net;lr>, <sip:pb.example.com;lr>,
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@edge.example.com;lr;ob>
Content-Length: 0
F25 ACK Proxy A -> Registrar/Authoritative Proxy B
ACK sip:bob@bobphone.example.com SIP/2.0
Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet
Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout
Max-Forwards: 69
To: Bob <sip:bob@example.com>;tag=5551212
From: Alice <sip:alice@example.net>;tag=8675309
Call-ID: lzksjf8723k@sodk6587
CSeq: 1 ACK
Route: <sip:pb.example.com;lr>,
<sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob>
Content-Length: 0
F26 ACK Registrar/Authoritative Proxy B -> Edge Proxy B ACK sip:bob@bobphone.example.com SIP/2.0 Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1 Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout Max-Forwards: 69 To: Bob <sip:bob@example.com>;tag=5551212 From: Alice <sip:alice@example.net>;tag=8675309 Call-ID: lzksjf8723k@sodk6587 CSeq: 1 ACK Route: <sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob> Content-Length: 0 F27 ACK Proxy B -> Bob's Phone ACK sip:bob@bobphone.example.com SIP/2.0 Via: SIP/2.0/TLS eb.example.com:5061;branch=z9hG4bKtroubaba Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.1 Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout Max-Forwards: 68 To: Bob <sip:bob@example.com>;tag=5551212 From: Alice <sip:alice@example.net>;tag=8675309 Call-ID: lzksjf8723k@sodk6587 CSeq: 1 ACK Content-Length: 0 F26' CANCEL Registrar/Authoritative Proxy B -> Edge Proxy B CANCEL sip:bob@bobpc.example.com SIP/2.0 Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2 Max-Forwards: 70 To: Bob <sip:bob@example.com> From: Alice <sip:alice@example.net>;tag=8675309 Call-ID: lzksjf8723k@sodk6587 CSeq: 1 CANCEL Route: <sip:psodkfsj+34+kklsL+uJH-Xm816k09Kk@eb.example.com;lr;ob> Content-Length: 0
F27' CANCEL Edge Proxy B -> Bob's PC Client CANCEL sip:bob@bobpc.example.com SIP/2.0 Via: SIP/2.0/TCP eb.example.com:5060;branch=z9hG4bKtroubaba Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2 Max-Forwards: 69 To: Bob <sip:bob@example.com> From: Alice <sip:alice@example.net>;tag=8675309 Call-ID: lzksjf8723k@sodk6587 CSeq: 1 CANCEL Content-Length: 0 F28' 200 (CANCEL) Bob's PC Client -> Edge Proxy B SIP/2.0 200 OK Via: SIP/2.0/TCP eb.example.com:5060;branch=z9hG4bKtroubaba Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2 To: Bob <sip:bob@example.com> From: Alice <sip:alice@example.net>;tag=8675309 Call-ID: lzksjf8723k@sodk6587 CSeq: 1 CANCEL Content-Length: 0 F29' 200 (CANCEL) Edge Proxy B -> Registrar/Authoritative Proxy B SIP/2.0 200 OK Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2 To: Bob <sip:bob@example.com> From: Alice <sip:alice@example.net>;tag=8675309 Call-ID: lzksjf8723k@sodk6587 CSeq: 1 CANCEL Content-Length: 0
F30' 487 (INVITE) Bob's PC Client -> Edge Proxy B SIP/2.0 487 Request Terminated Via: SIP/2.0/TCP eb.example.com:5060;branch=z9hG4bKtroubaba Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2 Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout To: Bob <sip:bob@example.com> From: Alice <sip:alice@example.net>;tag=8675309 Call-ID: lzksjf8723k@sodk6587 CSeq: 1 INVITE Content-Length: 0 F31' 487 (INVITE) Edge Proxy B -> Registrar/Authoritative Proxy B SIP/2.0 487 Request Terminated Via: SIP/2.0/TCP pb.example.com:5060;branch=z9hG4bKbalouba.2 Via: SIP/2.0/TCP proxya.example.net:5060;branch=z9hG4bKpouet Via: SIP/2.0/TCP alice-1.example.net:5060;branch=z9hG4bKprout To: Bob <sip:bob@example.com> From: Alice <sip:alice@example.net>;tag=8675309 Call-ID: lzksjf8723k@sodk6587 CSeq: 1 INVITE Content-Length: 06.4. Alice Calls Bob's SIP AOR Using TLS
Bob's registration has already occurred as per Section 6.1. The third example is identical to the second one, except that Alice uses TLS as the transport for her connection to her proxy. Such an arrangement would be common if Alice's UA supported TLS and wanted to use a single connection to the proxy (as would be the case when using [RFC5626]). In the example below, Proxy A is also using TLS as a transport to communicate with Outbound Proxy B, but it is not necessarily the case. When using a SIP URI in the Request-URI but TLS as a transport for sending the request, the Via field indicates TLS. The Route header field (if present) typically would use a SIP URI (but it could also be a SIPS URI). The Contact header fields and To and From, however would also normally indicate a SIP URI. The call flow would be exactly as per the second example (Section 6.3). The only difference would be that all the Via header fields would use TLS Via parameters. The URIs would remain SIP URIs and not SIPS URIs.
7. Further Considerations
SIP [RFC3261] itself introduces some complications with using SIPS, for example, when Record-Route is not used. When a SIPS URI is used in a Contact header field in a dialog-initiating request and Record- Route is not used, that SIPS URI might not be usable by the other end. If the other end does not support SIPS and/or TLS, it will not be able to use it. The last-hop exception is an example of when this can occur. In this case, using Record-Route so that the requests are sent through proxies can help in making it work. Another example is that even in a case where the Contact header field is a SIPS URI, no Record-Route is used, and the far end supports SIPS and TLS, it might still not be possible for the far end to establish a TLS connection with the SIP originating end if the certificate cannot be validated by the far end. This could typically be the case if the originating end was using server-side authentication as described below, or if the originating end is not using a certificate that can be validated. TLS itself has a significant impact on how SIPS can be used. Server- side authentication (where the server side provides its certificate but the client side does not) is typically used between a SIP end- user device acting as the TLS client side (e.g., a phone or a personal computer) and its SIP server (proxy or registrar) acting as the TLS server side. TLS mutual authentication (where both the client side and the server side provide their respective certificates) is typically used between SIP servers (proxies, registrars), or statically configured devices such as PSTN gateways or media servers. In the mutual authentication model, for two entities to be able to establish a TLS connection, it is required that both sides be able to validate each other's certificates, either by static configuration or by being able to recurse to a valid root certificate. With server-side authentication, only the client side is capable of validating the server side's certificate, as the client side does not provide a certificate. The consequences of all this are that whenever a SIPS URI is used to establish a TLS connection, it is expected to be possible for the entity establishing the connection (the client) to validate the certificate from the server side. For server-side authentication, [RFC5626] is the recommended approach. For mutual authentication, one needs to ensure that the architecture of the network is such that connections are made between entities that have access to each other's certificates. Record-Route [RFC3261] and Path [RFC3327] are very useful in ensuring that previously established TLS connections can be reused. Other mechanisms might also be used in certain circumstances: for example, using root certificates that are widely recognized allows for more easily created TLS connections.
8. Security Considerations
Most of this document can be considered to be security considerations since it applies to the usage of the SIPS URI. The "last-hop exception" of [RFC3261] introduced significant potential vulnerabilities in SIP, and it has therefore been deprecated by this specification. Section 26.4.4 of [RFC3261] describes the security considerations for the SIPS URI scheme. These security considerations also applies here, as modified by Appendix A.9. IANA Considerations
This specification registers two new warning codes, namely, 380 "SIPS Not Allowed" and 381 "SIPS Required". The warning codes are defined as follows, and have been included in the Warning Codes (warn-codes) sub-registry of the SIP Parameters registry available from http://www.iana.org. 380 SIPS Not Allowed: The UAS or proxy cannot process the request because the SIPS scheme is not allowed (e.g., because there are currently no registered SIPS contacts). 381 SIPS Required: The UAS or proxy cannot process the request because the SIPS scheme is required. Reference: RFC 5630 The note in the Warning Codes sub-registry is as follows: Warning codes provide information supplemental to the status code in SIP response messages.10. Acknowledgments
The author would like to thank Jon Peterson, Cullen Jennings, Jonathan Rosenberg, John Elwell, Paul Kyzivat, Eric Rescorla, Robert Sparks, Rifaat Shekh-Yusef, Peter Reissner, Tina Tsou, Keith Drage, Brian Stucker, Patrick Ma, Lavis Zhou, Joel Halpern, Hisham Karthabil, Dean Willis, Eric Tremblay, Hans Persson, and Ben Campbell for their careful review and input. Many thanks to Rohan Mahy for helping me with the subtleties of [RFC5626].
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [RFC5626] Jennings, C., "Managing Client-Initiated Connections in the Session Initiation Protocol (SIP)", RFC 5626, October 2009.11.2. Informative References
[RFC2543] Handley, M., Schulzrinne, H., Schooler, E., and J. Rosenberg, "SIP: Session Initiation Protocol", RFC 2543, March 1999. [RFC3327] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) Extension Header Field for Registering Non-Adjacent Contacts", RFC 3327, December 2002. [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer Method", RFC 3515, April 2003. [RFC3608] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) Extension Header Field for Service Route Discovery During Registration", RFC 3608, October 2003. [RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo, "Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April 2004. [RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation Protocol (SIP) "Replaces" Header", RFC 3891, September 2004. [RFC3893] Peterson, J., "Session Initiation Protocol (SIP) Authenticated Identity Body (AIB) Format", RFC 3893, September 2004.
[RFC3911] Mahy, R. and D. Petrie, "The Session Initiation Protocol (SIP) "Join" Header", RFC 3911, October 2004. [RFC4168] Rosenberg, J., Schulzrinne, H., and G. Camarillo, "The Stream Control Transmission Protocol (SCTP) as a Transport for the Session Initiation Protocol (SIP)", RFC 4168, October 2005. [RFC4244] Barnes, M., "An Extension to the Session Initiation Protocol (SIP) for Request History Information", RFC 4244, November 2005. [RFC4474] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006. [RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User Agent URIs (GRUU) in the Session Initiation Protocol (SIP)", RFC 5627, October 2009.
Appendix A. Bug Fixes for RFC 3261
In order to support the material in this document, this section makes corrections to RFC 3261. The last sentence of the fifth paragraph of Section 8.1.3.5 is replaced by: The client SHOULD retry the request, this time, using a SIP URI unless the original Request-URI used a SIPS scheme, in which case the client MUST NOT retry the request automatically. The fifth paragraph of Section 10.2.1 is replaced by: If the Address of Record in the To header field of a REGISTER request is a SIPS URI, then the UAC MUST also include only SIPS URIs in any Contact header field value in the requests. In Section 16.7 on p. 112 describing Record-Route, the second paragraph is deleted. The last paragraph of Section 19.1 is reworded as follows: A SIPS URI specifies that the resource be contacted securely. This means, in particular, that TLS is to be used on each hop between the UAC and the resource identified by the target SIPS URI. Any resources described by a SIP URI (...) In the third paragraph of Section 20.43, the words "the session description" in the first sentence are replaced with "SIP". Later in the paragraph, "390" is replaced with "380", and "miscellaneous warnings" is replaced with "miscellaneous SIP-related warnings". The second paragraph of Section 26.2.2 is reworded as follows: (...) When used as the Request-URI of a request, the SIPS scheme signifies that each hop over which the request is forwarded, until the request reaches the resource identified by the Request-URI, is secured with TLS. When used by the originator of a request (as would be the case if they employed a SIPS URI as the address-of- record of the target), SIPS dictates that the entire request path to the target domain be so secured. The first paragraph of Section 26.4.4 is replaced by the following: Actually using TLS on every segment of a request path entails that the terminating UAS is reachable over TLS (by registering with a SIPS URI as a contact address). The SIPS scheme implies
transitive trust. Obviously, there is nothing that prevents
proxies from cheating. Thus, SIPS cannot guarantee that TLS usage
will be truly respected end-to-end on each segment of a request
path. Note that since many UAs will not accept incoming TLS
connections, even those UAs that do support TLS will be required
to maintain persistent TLS connections as described in the TLS
limitations section above in order to receive requests over TLS as
a UAS.
The first sentence of the third paragraph of Section 26.4.4 is
replaced by the following:
Ensuring that TLS will be used for all of the request segments up
to the target UAS is somewhat complex.
The fourth paragraph of Section 26.4.4 is deleted.
The last sentence of the fifth paragraph of Section 26.4.4 is
reworded as follows:
S/MIME or, preferably, [RFC4474] may also be used by the
originating UAC to help ensure that the original form of the To
header field is carried end-to-end.
In the third paragraph of Section 27.2, the phrase "when the failure
of the transaction results from a Session Description Protocol (SDP)
(RFC 2327 [1]) problem" is deleted.
In the fifth paragraph of Section 27.2, "390" is replaced with "380",
and "miscellaneous warnings" is replaced with "miscellaneous SIP-
related warnings".
Author's Address
Francois Audet
Skype Labs
EMail: francois.audet@skypelabs.com