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Written by Hemanshu Patel
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Thursday, 08 November 2007 |
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Page 11 of 17 3.5. Session Through a SIP ALG
Alice ALG Proxy 2 Bob
| | | |
| INVITE F1 | | |
|--------------->| INVITE F2 | |
| 100 F3 |--------------->| INVITE F4 |
|<---------------| 100 F5 |--------------->|
| |<---------------| 180 F6 |
| | 180 F7 |<---------------|
| 180 F8 |<---------------| |
|<---------------| | 200 F9 |
| | 200 F10 |<---------------|
| 200 F11 |<---------------| |
|<---------------| |
| ACK F12 | |
|--------------->| ACK F13 |
| |-------------------------------->|
| RTP Media | Both Way RTP Media |
|<==============>|<===============================>|
| BYE F14 | |
|--------------->| BYE F15 |
| |-------------------------------->|
| | 200 F16 |
| 200 F17 |<--------------------------------|
|<---------------| |
| | |
Alice completes a call to Bob through a ALG (Application Layer
Gateway) and a SIP Proxy. The routing through the ALG is
accomplished using a pre-loaded Route header in the INVITE F1. Note
that the media stream setup is not end-to-end - the ALG terminates
both media streams and bridges them. This is done by the ALG
modifying the SDP in the INVITE (F1) and 200 OK (F10) messages, and
possibly any 18x or ACK messages containing SDP.
In addition to firewall traversal, this Back-to-Back User Agent
(B2BUA) could be used as part of an anonymizer service (in which all
identifying information on Alice would be removed), or to perform
codec media conversion, such as mu-law to A-law conversion of PCM on
an international call.
Also note that Proxy 2 does not Record-Route in this call flow.
Message Details
F1 INVITE Alice -> SIP ALG
INVITE sip:
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SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
From: Alice <sip:
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>;tag=9fxced76sl
To: Bob <sip:
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>
Call-ID:
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CSeq: 1 INVITE
Contact: <sip:
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>
Route: <sip:alg1.atlanta.example.com;lr>
Proxy-Authorization: Digest username="alice",
realm="biloxi.example.com",
nonce="85b4f1cen4341ae6cbe5a3a9c8e88df9", opaque="",
uri="sip:
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",
response="b3f392f9218a328b9294076d708e6815"
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
/* Client for Alice prepares to receive data on port 49172 from the
network. */
F2 INVITE SIP ALG -> Proxy 2
INVITE sip:
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SIP/2.0
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Max-Forwards: 69
Record-Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Contact: <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Proxy-Authorization: Digest username="alice",
realm="biloxi.example.com",
nonce="85b4f1cen4341ae6cbe5a3a9c8e88df9", opaque="",
uri="sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
",
response="b3f392f9218a328b9294076d708e6815"
Content-Type: application/sdp
Content-Length: 150
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.128
t=0 0
m=audio 2000 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F3 100 Trying SIP ALG -> Alice
SIP/2.0 100 Trying
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
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>
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Content-Length: 0
/* SIP ALG prepares to proxy data from port 192.0.2.128/2000 to
192.0.2.101/49172. Proxy 2 uses a Location Service function to
determine where Bob is located. Based upon location analysis the call
is forwarded to Bob */
F4 INVITE Proxy 2 -> Bob
INVITE sip:
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SIP/2.0
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
;received=192.0.2.128
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Max-Forwards: 68
Record-Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
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>
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Contact: <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Content-Type: application/sdp
Content-Length: 150
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.128
t=0 0
m=audio 2000 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F5 100 Trying Proxy 2 -> SIP ALG
SIP/2.0 100 Trying
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
;received=192.0.2.128
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
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>
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Content-Length: 0
F6 180 Ringing Bob -> Proxy 2
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.222
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
;received=192.0.2.128
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
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>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Contact: <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Content-Length: 0
F7 180 Ringing Proxy 2 -> SIP ALG
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
;received=192.0.2.128
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Contact: <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Content-Length: 0
F8 180 Ringing SIP ALG -> Alice
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
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CSeq: 1 INVITE
Contact: <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Content-Length: 0
F9 200 OK Bob -> Proxy 2
SIP/2.0 200 OK
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.222
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
;received=192.0.2.128
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Contact: <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F10 200 OK Proxy 2 -> SIP ALG
SIP/2.0 200 OK
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
;received=192.0.2.128
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Contact: <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F11 200 OK SIP ALG -> Alice
SIP/2.0 200 OK
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 INVITE
Contact: <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.128
t=0 0
m=audio 1734 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* The ALG prepares to proxy packets from 192.0.2.128/
1734 to 192.0.2.201/3456 */
F12 ACK Alice -> SIP ALG
ACK sip:
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SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bhh
Max-Forwards: 70
Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
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CSeq: 1 ACK
Content-Length: 0
F13 ACK SIP ALG -> Bob
ACK sip:
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SIP/2.0
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bhh
;received=192.0.2.101
Max-Forwards: 69
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 1 ACK
Content-Length: 0
/* RTP streams are established between Alice and the ALG and
between the ALG and B*/
/* Alice Hangs Up with Bob. */
F14 BYE Alice -> SIP ALG
BYE sip:
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SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5
Max-Forwards: 70
Route: <sip:alg1.atlanta.example.com;lr>
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 2 BYE
Content-Length: 0
F15 BYE SIP ALG -> Bob
BYE sip:
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SIP/2.0
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5
;received=192.0.2.101
Max-Forwards: 69
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 2 BYE
Content-Length: 0
F16 200 OK Bob -> SIP ALG
SIP/2.0 200 OK
Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1
;received=192.0.2.128
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5
;received=192.0.2.101
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 2 BYE
Content-Length: 0
F17 200 OK SIP ALG -> Alice
SIP/2.0 200 OK
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5
;received=192.0.2.101
From: Alice <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=9fxced76sl
To: Bob <sip:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
>;tag=314159
Call-ID:
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
CSeq: 2 BYE
Content-Length: 0
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