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RFC 3666

 
 
 

Session Initiation Protocol (SIP) Public Switched Telephone Network (PSTN) Call Flows

Part 3 of 4, p. 54 to 87
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3.  PSTN to SIP Dialing

   In these scenarios, Alice is placing calls from the PSTN to Bob in a
   SIP network.  Alice's telephone switch signals to a Network Gateway
   (NGW 1) using ANSI ISUP.

   Since the called SIP User Agent does not send in-band signaling
   information, no early media path needs to be established on the IP
   side.  As a result, the 183 Session Progress response is not used.
   However, NGW 1 will establish a one way speech path prior to call
   completion, and generate ringing for the PSTN caller.  Any tones or

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   recordings are generated by NGW 1 and played in this speech path.
   When the call completes successfully, NGW 1 bridges the PSTN speech
   path with the IP media path.

   To reduce the number of messages, only a single proxy server is shown
   in these flows, which means that the a.example.com proxy server has
   access to the b.example.com location service.

3.1.  Successful PSTN to SIP call

   Switch A          NGW 1          Proxy 1           Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      180 F5    |
     |                |    180 F6      |<---------------|
     |     ACM F7     |<---------------|                |
     |<---------------|                |                |
     |  One Way Voice |                |                |
     |<===============|                |                |
     |  Ringing Tone  |                |      200 F8    |
     |<===============|    200 F9      |<---------------|
     |                |<---------------|                |
     |                |     ACK F10    |                |
     |     ANM F12    |--------------->|     ACK F11    |
     |<---------------|                |--------------->|
     | Both Way Voice |        Both Way RTP Media       |
     |<==============>|<===============================>|
     |     REL F13    |                |                |
     |--------------->|                |                |
     |     RLC F14    |                |                |
     |<---------------|     BYE F15    |                |
     |                |--------------->|     BYE F16    |
     |                |                |--------------->|
     |                |                |     200 F17    |
     |                |     200 F18    |<---------------|
     |                |<---------------|                |
     |                |                |                |

   In this scenario, Alice from the PSTN calls Bob through a Network
   Gateway NGW1 and Proxy Server Proxy 1.  When Bob answers the call,
   the media path is setup end-to-end.  The call terminates when Alice
   hangs up the call, with Alice's telephone switch sending an ISUP
   RELease message that is mapped to a BYE by NGW 1.

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   Message Details

   F1 IAM Alice -> NGW 1

   IAM
   CgPN=314-555-1111,NPI=E.164,NOA=National
   CdPN=972-555-2222,NPI=E.164,NOA=National


   F2 INVITE Alice -> Proxy 1

   INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   s=-
   c=IN IP4 ngw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Based upon location analysis the call is forwarded to NGW
   1.  NGW 1  prepares to receive data on port 3456 from Alice.*/

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   F3 INVITE Proxy 1 -> Bob

   INVITE sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   s=-
   c=IN IP4 ngw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F4 100 Trying Bob -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 180 Ringing Bob -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals

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   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Length: 0


   F6 180 Ringing Proxy 1 -> NGW 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Length: 0


   F7 ACM NGW 1 -> Alice

   ACM


   F8 200 OK Bob -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   Contact: <sip:bob@client.b.example.com>
   CSeq: 1 INVITE
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=bob 2890844527 2890844527 IN IP4 client.b.example.com
   s=-
   c=IN IP4 client.b.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0

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   a=rtpmap:0 PCMU/8000


   F9 200 OK Proxy 1 -> NGW 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=bob 2890844527 2890844527 IN IP4 client.b.example.com
   s=-
   c=IN IP4 client.b.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F10 ACK NGW 1 -> Proxy 1

   ACK sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F11 ACK Proxy 1 -> Bob

   ACK sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159

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   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F12 ANM Bob -> NGW 1

   ANM

   /* RTP streams are established between A and B (via the GW) */

   /* Alice Hangs Up with Bob. */


   F13 REL Alice -> NGW 1

   REL
   CauseCode=16 Normal


   F14 RLC NGW 1 -> Alice

   RLC


   F15 BYE NGW 1-> Proxy 1

   BYE sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0


   F16 BYE Proxy 1 -> Bob

   BYE sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com

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   CSeq: 2 BYE
   Content-Length: 0


   F17 200 OK Bob -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0


   F18 200 OK Proxy 1 -> NGW 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

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3.2.  Successful PSTN to SIP call, Fast Answer

   Switch A           NGW 1          Proxy 1           Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      200 F5    |
     |                |     200 F6     |<---------------|
     |                |<---------------|                |
     |                |     ACK F7     |                |
     |     ANM F9     |--------------->|     ACK F8     |
     |<---------------|                |--------------->|
     | Both Way Voice |        Both Way RTP Media       |
     |<==============>|<===============================>|
     |     REL F10    |                |                |
     |--------------->|                |                |
     |     RLC F11    |                |                |
     |<---------------|     BYE F12    |                |
     |                |--------------->|     BYE F13    |
     |                |                |--------------->|
     |                |                |     200 F14    |
     |                |     200 F15    |<---------------|
     |                |<---------------|                |
     |                |                |                |

   This "fast answer" scenario is similar to 3.1., except that Bob
   immediately accepts the call, sending a 200 OK (F5) without sending a
   180 Ringing response.  The Gateway then sends an Answer Message (ANM)
   without sending an Address Complete Message (ACM).  Note that for
   ETSI and some other ISUP variants, a CONnect message (CON) would be
   sent instead of the ANM.

   Message Details

   F1 IAM Alice -> NGW 1

   IAM
   CgPN=314-555-1111,NPI=E.164,NOA=National
   CdPN=972-555-2222,NPI=E.164,NOA=National


   F2 INVITE NGW 1 -> Proxy 1

   INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

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   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   s=-
   c=IN IP4 ngw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Based upon location analysis the call is forwarded to User
   B.  Bob  prepares to receive data on port 3456 from Alice.*/


   F3 INVITE Proxy 1 -> Bob

   INVITE bob@b.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   s=-
   c=IN IP4 ngw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

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   F4 100 Trying Proxy 1 -> NGW 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 200 OK Bob -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=bob 2890844527 2890844527 IN IP4 client.b.example.com
   s=-
   c=IN IP4 client.b.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F6 200 OK Proxy 1 -> NGW 1

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com;transport=tcp>

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   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=bob 2890844527 2890844527 IN IP4 client.b.example.com
   s=-
   c=IN IP4 client.b.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F7 ACK NGW 1 -> Proxy 1

   ACK bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F8 ACK Proxy 1 -> Bob

   ACK bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=130.131.132.14
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F9 ANM Bob -> NGW 1

   ANM

   /* RTP streams are established between A and B (via the GW) */

   /* Alice Hangs Up with Bob. */

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   F10 REL ser Alice -> NGW 1

   REL
   CauseCode=16 Normal


   F11 RLC NGW 1 -> Alice

   RLC


   F12 BYE NGW 1 -> Proxy 1

   BYE sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0


   F13 BYE Proxy 1 -> Bob

   BYE sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0


   F14 200 OK Bob -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com

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   CSeq: 2 BYE
   Content-Length: 0


   F15 200 OK Proxy 1 -> NGW 1

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

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3.3.  Successful PBX to SIP call

   PBX A            GW 1           Proxy 1           Bob
     |                |                |                |
     |    Seizure     |                |                |
     |--------------->|                |                |
     |      Wink      |                |                |
     |<---------------|                |                |
     |  MF Digits F1  |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      180 F5    |
     |                |    180 F6      |<---------------|
     |                |<---------------|                |
     |  One Way Voice |                |                |
     |<===============|                |                |
     |  Ringing Tone  |                |      200 F7    |
     |<===============|     200 F8     |<---------------|
     |                |<---------------|                |
     |                |     ACK F9     |                |
     |     Seizure    |--------------->|     ACK F10    |
     |<---------------|                |--------------->|
     | Both Way Voice |        Both Way RTP Media       |
     |<==============>|<===============================>|
     | Seizure Removal|                |                |
     |--------------->|                |                |
     | Seizure Removal|                |                |
     |<---------------|     BYE F11    |                |
     |                |--------------->|     BYE F12    |
     |                |                |--------------->|
     |                |                |     200 F13    |
     |                |     200 F14    |<---------------|
     |                |<---------------|                |
     |                |                |                |

   In this scenario, Alice dials from PBX A to Bob through GW 1 and
   Proxy 1.  This is an example of a call that appears destined for the
   PSTN but is instead routed to a SIP Client.

   Signaling between PBX A and GW 1 is Feature Group B (FGB) circuit
   associated signaling, in-band Mult-Frequency (MF) outpulsing.  After
   the receipt of the 180 Ringing from Bob, GW 1 generates a ringing
   tone for Alice.

   Bob answers the call by sending a 200 OK.  The call terminates when
   Alice hangs up, causing GW1 to send a BYE.

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   The  Gateway can only identify the trunk group that the call came in
   on; it cannot identify the individual line on PBX A that is placing
   the call.  The SIP URI used to identify the caller is shown in these
   flows as sip:551313@gw1.a.example.com.

   Message Details

   PBX Alice -> GW 1

   Seizure

   GW 1 -> PBX A

   Wink

   F1 MF Digits PBX Alice -> GW 1

   KP 1 972 555 2222 ST


   F2 INVITE GW 1 -> Proxy 1

   INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
   Max-Forwards: 70
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:551313@gw1.a.example.com;user=phone>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   s=-
   c=IN IP4 gw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* Proxy 1 uses a Location Service function to determine where the
   phone number +19725552222 is located.  Based upon location
   analysis the call is forwarded to SIP Bob. */

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   F3 INVITE Proxy 1 -> Bob

   INVITE sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:551313@gw1.a.example.com;user=phone>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
   s=-
   c=IN IP4 gw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F4 100 Trying Proxy 1 -> GW 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 180 Ringing Bob -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com

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   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Length: 0


   F6 180 Ringing Proxy 1 -> GW 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Length: 0

   /* One way Voice path is established between GW and the PBX for
   ringing. */


   F7 200 OK Bob -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   Contact: <sip:bob@client.b.example.com>
   CSeq: 1 INVITE
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=bob 2890844527 2890844527 IN IP4 client.b.example.com
   s=-
   c=IN IP4 client.b.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

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   F8 200 OK Proxy 1 -> GW 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=bob 2890844527 2890844527 IN IP4 client.b.example.com
   s=-
   c=IN IP4 client.b.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F9 ACK GW 1 -> Proxy 1

   ACK sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
   Max-Forwards: 70
   Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F10 ACK Proxy 1 -> Bob

   ACK sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Max-Forwards: 69
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

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   /* RTP streams are established between A and B (via the GW) */

   /* Alice Hangs Up with Bob. */


   F11 BYE GW 1 -> Proxy 1

   BYE sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
   Max-Forwards: 70
   Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0


   F12 BYE Proxy 1 -> Bob

   BYE sip:bob@client.b.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Max-Forwards: 69
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0


   F13 200 OK Bob -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

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   F14 200 OK Proxy 1 -> GW 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

3.4.  Unsuccessful PSTN to SIP REL, SIP error mapped to REL

   Switch A            GW 1          Proxy 1           Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|                |
     |                |     604 F3     |                |
     |                |<---------------|                |
     |                |     ACK F4     |                |
     |                |--------------->|                |
     |     REL F5     |                |                |
     |<---------------|                |                |
     |     RLC F6     |                |                |
     |--------------->|                |                |
     |                |                |                |

   Alice attempts to place a call through Gateway GW 1 and Proxy 1,
   which is unable to find any routing for the number.  The call is
   rejected by Proxy 1 with a REL message containing a specific Cause
   value mapped by the gateway based on the SIP error.

   Message Details

   F1 IAM Alice -> GW 1

   IAM
   CgPN=314-555-1111,NPI=E.164,NOA=National
   CdPN=972-555-9999,NPI=E.164,NOA=National


   F2 INVITE Alice -> Proxy 1

   INVITE sip:+1972559999@ss1.a.example.com;user=phone  SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sip:+13145551111@gw1.a.example.com;user=phone>;tag=076342s

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   To: <sip:+1972559999@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Contact:
   <sip:+13145551111@gw1.a.example.com;user=phone;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 144

   v=0
   o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
   s=-
   c=IN IP4 gw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* Proxy 1 uses a Location Service to find a route to +1-972-555-
   9999.  A route is not found, so Proxy 1 rejects the call. */


   F3 604 Does Not Exist Anywhere Proxy 1 -> GW 1

   SIP/2.0 604 Does Not Exist Anywhere
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   From: <sip:+13145551111@gw1.a.example.com;user=phone>;tag=076342s
   To: <sip:+1972559999@ss1.a.example.com;user=phone>;tag=6a34d410
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Error-Info: <sip:does-not-exist@ann.a.example.com>
   Content-Length: 0


   F4 ACK GW 1 -> Proxy 1

   ACK sip:+1972559999@ss1.a.example.com;user=phone SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sip:+13145551111@gw1.a.example.com;user=phone>;tag=076342s
   To: <sip:+1972559999@ss1.a.example.com;user=phone>;tag=6a34d410
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

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   F5 REL GW 1 -> Alice

   REL
   CauseCode=1


   F6 RLC Alice -> GW 1

   RLC

3.5.  Unsuccessful PSTN to SIP REL, SIP busy mapped to REL

   Switch A          NGW 1           Proxy 1          Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      600 F5    |
     |                |                |<---------------|
     |                |                |      ACK F6    |
     |                |     600 F7     |--------------->|
     |                |<---------------|                |
     |                |     ACK F8     |                |
     |                |--------------->|                |
     |   REL(17) F9   |                |                |
     |<---------------|                |                |
     |     RLC F10    |                |                |
     |<-------------->|                |                |
     |                |                |                |

   In this scenario, Alice calls Bob through Network Gateway NGW 1 and
   Proxy 1.  The call is routed to Bob by Proxy 1.  The call is rejected
   by Bob who sends a 600 Busy Everywhere response.  The Gateway sends a
   REL message containing a specific Cause value mapped by the gateway
   based on the SIP error.

   Since no interworking is indicated in the IAM (F1), the busy tone is
   generated locally by Alice's telephone switch.  In some scenarios,
   the busy signal is generated by the Gateway since interworking is
   indicated.  For more discussion on interworking, refer to [4].

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   Message Details

   F1 IAM Alice -> NGW 1

   IAM
   CgPN=314-555-1111,NPI=E.164,NOA=National
   CdPN=972-555-2222,NPI=E.164,NOA=National


   F2 INVITE Alice -> Proxy 1

   INVITE sip:+19725552222@ss1.a.example.com;user=phone  SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 144

   v=0
   o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
   s=-
   c=IN IP4 gw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* Proxy 1 uses a Location Service function to determine a route for
   +19725552222.  The call is then forwarded to Bob. */


   F3 INVITE F3 Proxy 1 -> Bob

   INVITE bob@b.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp

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   Content-Length: 144

   v=0
   o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
   s=-
   c=IN IP4 gw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F4 100 Trying Proxy 1 -> NGW 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 600 Busy Everywhere Bob -> Proxy 1

   SIP/2.0 600 Busy Everywhere
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 ACK Proxy 1 -> Bob

   ACK bob@b.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

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   F7 600 Busy Everywhere Proxy 1 -> NGW 1

   SIP/2.0 600 Busy Everywhere
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F8 ACK NGW 1 -> Proxy 1

   ACK bob@b.example.com SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F9 REL NGW 1 -> Alice

   REL
   CauseCode=17 Busy


   F10 RLC Alice -> NGW 1

   RLC

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3.6.  Unsuccessful PSTN->SIP, SIP error interworking to tones

   Switch A          NGW 1           Proxy 1          Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      600 F5    |
     |                |                |<---------------|
     |                |                |      ACK F6    |
     |                |     600 F7     |--------------->|
     |                |<---------------|                |
     |                |     ACK F8     |                |
     |     ACM F9     |--------------->|                |
     |<---------------|                |                |
     | One Way Voice  |                |                |
     |<===============|                |                |
     |    Busy Tone   |                |                |
     |<===============|                |                |
     |   REL(16) F10  |                |                |
     |--------------->|                |                |
     |     RLC F11    |                |                |
     |<---------------|                |                |
     |                |                |                |

   In this scenario, Alice calls Bob through Network Gateway NGW 1 and
   Proxy 1.  The call is routed to Bob by Proxy 1.  The call is rejected
   by the Bob client.  NGW 1 sets up a two way voice path to Alice and
   plays busy tone.  The caller then disconnects

   NGW 1 plays the busy tone since the IAM (F1) indicates the
   interworking is present.  In scenario 5.2.2., with no interworking,
   the busy indication is carried in the REL Cause value and is
   generated locally instead.

   Again, note that for ETSI or ITU ISUP, a CONnect message would be
   sent instead of the Answer Message.

   Message Details

   F1 IAM Alice -> NGW 1

   IAM
   CgPN=314-555-1111,NPI=E.164,NOA=National
   CdPN=972-555-2222,NPI=E.164,NOA=National
   Interworking=encountered

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   F2 INVITE NGW1 -> Proxy 1

   INVITE sip:+19725552222@ss1.a.example.com;user=phone  SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   s=-
   c=IN IP4 ngw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* Proxy 1 uses a Location Service function to determine a route for
   +19725552222.  The call is then forwarded to Bob. */


   F3 INVITE Proxy 1 -> Bob

   INVITE bob@b.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   s=-
   c=IN IP4 ngw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0

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   a=rtpmap:0 PCMU/8000


   F4 100 Trying Bob -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 600 Busy Everywhere Bob -> Proxy 1

   SIP/2.0 600 Busy Everywhere
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 ACK Proxy 1 -> Bob

   ACK bob@b.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

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   F7 600 Busy Everywhere Proxy 1 -> NGW 1

   SIP/2.0 600 Busy Everywhere
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F8 ACK NGW 1 -> Proxy 1

   ACK sip:ngw1@a.example.com SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F9 ACM NGW 1 -> Alice

   ACM

   /* A one way speech path is established between NGW 1 and Alice. */

   /* Call Released after Alice hangs up. */


   F10 REL Alice -> NGW 1

   REL
   CauseCode=16


   F11 RLC NGW 1 -> Alice

   RLC

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3.7.  Unsuccessful PSTN->SIP, ACM timeout

   Switch A          NGW 1           Proxy 1          Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |   INVITE F5    |
     |                |                |--------------->|
     |                |                |   INVITE F6    |
     |                |                |--------------->|
     |                |                |   INVITE F7    |
     |                |                |--------------->|
     |                |                |   INVITE F8    |
     |                |                |--------------->|
     |                |                |   INVITE F9    |
     |                |                |--------------->|
     |     REL F10    |                |                |
     |--------------->|                |                |
     |     RLC F11    |                |                |
     |<---------------|                |                |
     |                |   CANCEL F12   |                |
     |                |--------------->|                |
     |                |     200 F13    |                |
     |                |<---------------|                |

   Alice calls Bob through NGW 1 and Proxy 1.  Proxy 1 re-sends the
   INVITE after the expiration of SIP timer T1 without receiving any
   response from Bob.  Bob never responds with 180 Ringing or any other
   response (it is reachable but unresponsive).  After the expiration of
   a timer, Alice's network disconnects the call by sending a Release
   message REL.  The Gateway maps this to a CANCEL.

   Message Details

   F1 IAM Alice -> NGW 1

   IAM
   CgPN=314-555-1111,NPI=E.164,NOA=National
   CdPN=972-555-2222,NPI=E.164,NOA=National


   F2 INVITE Alice -> Proxy 1

   INVITE sip:+19725552222@ss1.a.example.com;user=phone  SIP/2.0
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

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   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   s=-
   c=IN IP4 ngw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* Proxy 1 uses a Location Service function to determine a route for
   +19725552222.  The call is then forwarded to Bob. */


   F3 INVITE Proxy 1 -> Bob

   INVITE sip:bob@b.example.com  SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
   c c=IN IP4 ngw1.a.example.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

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   F4 100 Trying Proxy 1 -> NGW 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 INVITE Proxy 1 -> Bob

   Same as Message F3


   F6 INVITE Proxy 1 -> Bob

   Same as Message F3


   F7 INVITE Proxy 1 -> Bob

   Same as Message F3


   F8 INVITE Proxy 1 -> Bob

   Same as Message F3


   F9 INVITE Proxy 1 -> Bob

   Same as Message F3

   /* Timer expires in Alice's access network. */


   F10 REL Alice -> NGW 1

   REL
   CauseCode=16 Normal


   F11 RLC NGW 1 -> Alice

   RLC

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   F12 CANCEL NGW 1 -> Proxy 1

   CANCEL sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F13 200 OK Proxy 1 -> NGW 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 CANCEL
   Content-Length: 0


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