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RFC 3666

 
 
 

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

Part 4 of 4, p. 88 to 118
Prev RFC Part

 


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3.8.  Unsuccessful PSTN->SIP, ACM timeout, stateless Proxy

   Switch A          NGW 1      Stateless Proxy 1     Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |   INVITE F4    |--------------->|
     |                |--------------->|   INVITE F5    |
     |                |   INVITE F6    |--------------->|
     |                |--------------->|   INVITE F7    |
     |                |   INVITE F8    |--------------->|
     |                |--------------->|   INVITE F9    |
     |                |   INVITE F10   |--------------->|
     |                |--------------->|   INVITE F11   |
     |                |   INVITE F12   |--------------->|
     |                |--------------->|   INVITE F13   |
     |                |                |--------------->|
     |     REL F14    |                |                |
     |--------------->|                |                |
     |     RLC F15    |                |                |
     |<---------------|                |                |


   In this scenario, Alice calls Bob through NGW 1 and Proxy 1.  Since
   Proxy 1 is stateless (it does not send a 100 Trying response), NGW 1
   re-sends the INVITE message after the expiration of SIP timer T1.
   Bob does not respond with 180 Ringing.  Alice's network disconnects
   the call with a release REL (CauseCode=102 Timeout).

   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/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

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   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=192.0.2.201
   Max-Forwards: 69
   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 INVITE NGW 1 -> Proxy 1

   Same as Message F2


   F5 INVITE Proxy 1 -> Bob

   Same as Message F3

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   F6 INVITE NGW 1 -> Proxy 1

   Same as Message F2


   F7 INVITE Proxy 1 -> Bob

   Same as Message F3


   F8 INVITE NGW 1 -> Proxy 1

   Same as Message F2


   F9 INVITE Proxy 1 -> Bob

   Same as Message F3


   F10 INVITE NGW 1 -> Proxy 1

   Same as Message F2


   F11 INVITE Proxy 1 -> Bob

   Same as Message F3


   F12 INVITE NGW 1 -> Proxy 1

   Same as Message F2


   F13 INVITE Proxy 1 -> Bob

   Same as Message F3

   /* A timer expires in Alice's access network. */


   F14 REL Alice -> NGW 1

   REL
   CauseCode=102 Timeout

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   F15 RLC NGW 1 -> Alice

   RLC

3.9.  Unsuccessful PSTN->SIP, Caller Abandonment

   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  |                |                |
     |<===============|                |                |
     |                |                |                |
     |     REL F8     |                |                |
     |--------------->|                |                |
     |     RLC F9     |                |                |
     |<---------------|   CANCEL F10   |                |
     |                |--------------->|                |
     |                |     200 F11    |                |
     |                |<---------------|                |
     |                |                |   CANCEL F12   |
     |                |                |--------------->|
     |                |                |     200 F13    |
     |                |                |<---------------|
     |                |                |     487 F14    |
     |                |                |<---------------|
     |                |                |     ACK F15    |
     |                |     487 F16    |--------------->|
     |                |<---------------|                |
     |                |     ACK F17    |                |
     |                |--------------->|                |
     |                |                |                |

   In this scenario, Alice calls Bob through NGW 1 and Proxy 1.  Bob
   does not respond with 200 OK.  NGW 1 plays ringing tone since the ACM
   indicates that interworking has been encountered.  Alice disconnects
   the call with a Release message REL which is mapped by NGW 1 to a

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   CANCEL.  Note that if Bob had sent a 200 OK response after the REL,
   NGW 1 would have sent an ACK and then a BYE to properly terminate the
   call.

   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: 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/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>

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   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


   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=192.0.2.201
   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 180 Ringing Bob -> Proxy 1

   SIP/2.0 180 Ringing
   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-Length: 0


   F6 180 Ringing Proxy 1 -> NGW 1

   SIP/2.0 180 Ringing

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   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>
   Content-Length: 0


   F7 ACM NGW 1 -> Alice

   ACM

   /* Alice hangs up */


   F8 REL Alice -> NGW 1

   REL
   CauseCode=16 Normal


   F9 RLC NGW 1 -> Alice

   RLC


   F10 CANCEL NGW 1 -> Proxy 1

   CANCEL 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 CANCEL
   Content-Length: 0


   F11 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>

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


   F12 CANCEL Proxy 1 -> Bob

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


   F13 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
   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


   F14 487 Request Terminated Bob -> Proxy 1

   SIP/2.0 487 Request Terminated
   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


   F15 ACK Proxy 1 -> Bob

   ACK sip:bob@b.example.com SIP/2.0
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
   Max-Forwards: 70

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   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


   F16 487 Request Terminated Proxy 1 -> NGW 1

   SIP/2.0 487 Request Terminated
   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


   F17 ACK NGW 1 -> Proxy 1

   ACK 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>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

4.  PSTN to PSTN Dialing via SIP Network

   In these scenarios, both the caller and the called party are in the
   telephone network, either normal PSTN subscribers or PBX extensions.
   The calls route through two Gateways and at least one SIP Proxy
   Server.  The Proxy Server performs the authentication and location of
   the Gateways.

   Again it is noted that the intent of this call flows document is not
   to provide a detailed parameter level mapping of SIP to PSTN
   protocols.  For information on SIP to ISUP mapping, the reader is
   referred to other references [4].

   In these scenarios, the call is successfully completed between the
   two Gateways, allowing the PSTN or PBX users to communicate.  The 183
   Session Progress response is used to indicate that in-band alerting
   may flow from the called party telephone switch to the caller.

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4.1.  Successful ISUP PSTN to ISUP PSTN call

   Switch A       NGW 1         Proxy 1         GW 2         Switch C
    |              |              |              |              |
    |     IAM F1   |              |              |              |
    |------------->|              |              |              |
    |              |  INVITE F2   |              |              |
    |              |------------->|  INVITE F3   |              |
    |              |              |------------->|     IAM F4   |
    |              |              |              |------------->|
    |              |              |              |     ACM F5   |
    |              |              |   183 F6     |<-------------|
    |              |    183 F7    |<-------------|              |
    |    ACM F8    |<-------------|              |              |
    |<-------------|              |              |              |
    | One Way Voice|      Two Way RTP Media      | One Way Voice|
    |<=============|<===========================>|<=============|
    |              |              |              |    ANM F9    |
    |              |              |   200 F10    |<-------------|
    |              |    200 F11   |<-------------|              |
    |    ANM F12   |<-------------|              |              |
    |<-------------|              |              |              |
    |              |    ACK F13   |              |              |
    |              |------------->|    ACK F14   |              |
    |              |              |------------->|              |
    |Both Way Voice|     Both Way RTP Media      |Both Way Voice|
    |<=============|<===========================>|<=============|
    |              |              |              |    REL F15   |
    |              |              |              |<-------------|
    |              |              |   BYE F16    |              |
    |              |    BYE F18   |<-------------|    RLC F17   |
    |              |<-------------|              |------------->|
    |              |              |              |              |
    |              |    200 F19   |              |              |
    |              |------------->|    200 F20   |              |
    |              |              |------------->|              |
    |    REL F21   |              |              |              |
    |<-------------|              |              |              |
    |    RLC F22   |              |              |              |
    |------------->|              |              |              |
    |              |              |              |              |

   In this scenario, Alice in the PSTN calls Carol who is an extension
   on a PBX.  Alice's telephone switch signals via SS7 to the Network
   Gateway NGW 1, while Carol's PBX signals via SS7 with the Gateway GW
   2.  The CdPN and CgPN are mapped by GW 1 into SIP URIs and placed in
   the To and From headers.  Proxy 1 looks up the dialed digits in the
   Request-URI and maps the digits to the PBX extension of Carol, which

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   is served by GW 2.  The Proxy in F3 uses the host portion of the
   Request-URI to identify what private dialing plan is being
   referenced.  The INVITE is then forwarded to GW 2 for call
   completion.  An early media path is established end-to-end so that
   Alice can hear the ringing tone generated by PBX C.

   Carol answers the call and the media path is cut through in both
   directions.  Bob hangs up terminating the call.

   Message Details

   F1 IAM Switch Alice -> NGW 1

   IAM
   CgPN=314-555-1111,NPI=E.164,NOA=National
   CdPN=918-555-3333,NPI=E.164,NOA=National


   F2 INVITE NGW 1 -> Proxy 1

   INVITE sips:+19185553333@ss1.a.example.com;user=phone  SIP/2.0
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
   Max-Forwards: 70
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844526 2890844526 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 consults Location Service and translates the dialed number
   to a private number in the Request-URI*/


   F3 INVITE Proxy 1 -> GW 2

   INVITE sips:4443333@gw2.a.example.com SIP/2.0
   Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKwqwee65

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    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

   v=0
   o=GW 2890844526 2890844526 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 IAM GW 2 -> Switch C

   IAM
   CgPN=314-555-1111,NPI=E.164,NOA=National
   CdPN=444-3333,NPI=Private,NOA=Subscriber


   F5 ACM Switch C -> GW 2

   ACM

   /* Based on the ACM message, GW 2 returns a 183 response.  In-band
   call progress indications are sent to Alice through NGW 1. */


   F6 183 Session Progress GW 2 -> Proxy 1

   SIP/2.0 183 Session Progress
   Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:4443333@gw2.a.example.com>

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   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=GW 987654321 987654321 IN IP4 gw2.a.example.com
   s=-
   c=IN IP4 gw2.a.example.com
   t=0 0
   m=audio 14918 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F7 183 Session Progress Proxy 1 -> GW 1

   SIP/2.0 183 Session Progress
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:4443333@gw2.a.example.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=GW 987654321 987654321 IN IP4 gw2.a.example.com
   s=-
   c=IN IP4 gw2.a.example.com
   t=0 0
   m=audio 14918 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* NGW 1 receives packets from GW 2 with encoded ringback, tones or
   other audio.  NGW 1 decodes this and places it on the originating
   trunk. */


   F8 ACM NGW 1 -> Switch A

   ACM

   /* Bob answers */

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   F9 ANM Switch C -> GW 2

   ANM


   F10 200 OK GW 2 -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:4443333@gw2.a.example.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=GW 987654321 987654321 IN IP4 gw2.a.example.com
   s=-
   c=IN IP4 gw2.a.example.com
   t=0 0
   m=audio 14918 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F11 200 OK Proxy 1 -> NGW 1

   SIP/2.0 200 OK
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:4443333@gw2.a.example.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=GW 987654321 987654321 IN IP4 gw2.a.example.com
   s=-
   c=IN IP4 gw2.a.example.com

Top      Up      ToC       Page 102 
   t=0 0
   m=audio 14918 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F12 ANM NGW 1 -> Switch A

   ANM


   F13 ACK NGW 1 -> Proxy 1

   ACK sips:4443333@gw2.a.example.com SIP/2.0
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
   Max-Forwards: 70
   Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F14 ACK Proxy 1 -> GW 2

   ACK sips:4443333@gw2.a.example.com SIP/2.0
   Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Max-Forwards: 69
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

   /* RTP streams are established between NGW 1 and GW 2. */

   /* Bob Hangs Up with Alice. */


   F15 REL Switch C -> GW 2

   REL
   CauseCode=16 Normal

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   F16 BYE GW 2 -> Proxy 1

   BYE sips:ngw1@a.example.com SIP/2.0
   Via: SIP/2.0/TLS gw2.a.example.com:5061;branch=z9hG4bKtexx6
   Max-Forwards: 70
   Route: <sips:ss1.a.example.com;lr>
   From: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   To: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 4 BYE
   Content-Length: 0


   F17 RLC GW 2 -> Switch C

   RLC


   F18 BYE Proxy 1 -> NGW 1

   BYE sips:ngw1@a.example.com SIP/2.0
   Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TLS gw2.a.example.com:5061;branch=z9hG4bKtexx6
    ;received=192.0.2.202
   Max-Forwards: 69
   From: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   To: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 4 BYE
   Content-Length: 0


   F19 200 OK NGW 1 -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TLS gw2.a.example.com:5061;branch=z9hG4bKtexx6
    ;received=192.0.2.202
   From: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   To: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 4 BYE
   Content-Length: 0

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   F20 200 OK Proxy 1 -> GW 2

   SIP/2.0 200 OK
   Via: SIP/2.0/TLS gw2.a.example.com:5061;branch=z9hG4bKtexx6
    ;received=192.0.2.202
   From: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   To: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 4 BYE
   Content-Length: 0


   F21 REL Switch C -> GW 2

   REL
   CauseCode=16 Normal


   F22 RLC GW 2 -> Switch C

   RLC

Top      Up      ToC       Page 105 
4.2.  Successful FGB PBX to ISDN PBX call with overflow

   PBX A       GW 1        Proxy 1        GW 2         GW 3        PBX C
     |            |            |            |            |            |
     |  Seizure   |            |            |            |            |
     |----------->|            |            |            |            |
     |    Wink    |            |            |            |            |
     |<-----------|            |            |            |            |
     |MF Digits F1|            |            |            |            |
     |----------->|            |            |            |            |
     |            | INVITE F2  |            |            |            |
     |            |----------->| INVITE F3  |            |            |
     |            |            |----------->|            |            |
     |            |            |   503 F4   |            |            |
     |            |            |<-----------|            |            |
     |            |            |   ACK F5   |            |            |
     |            |            |----------->|            |            |
     |            |            |  INVITE F6              |            |
     |            |            |------------------------>|  SETUP F7  |
     |            |            |          100  F8        |----------->|
     |            |            |<------------------------|CALL PROC F9|
     |            |            |                         |<-----------|
     |            |            |                         | ALERT F10  |
     |            |            |          180 F11        |<-----------|
     |            |  180 F12   |<------------------------|            |
     |            |<-----------|                         |            |
     | Ringtone   |            |                         |OneWay Voice|
     |<===========|            |                         |<===========|
     |            |            |                         | CONNect F13|
     |            |            |         200 F14         |<-----------|
     |            |  200 F15   |<------------------------|            |
     |  Seizure   |<-----------|                         |            |
     |<-----------|  ACK F16   |                         |            |
     |            |----------->|         ACK F17         |            |
     |            |            |------------------------>|CONN ACK F18|
     |            |            |                         |----------->|
     |BothWayVoice|          Both Way RTP Media          |BothWayVoice|
     |<==========>|<====================================>|<==========>|
     |            |            |                         |  DISC F19  |
     |            |            |                         |<-----------|
     |            |            |         BYE F20         |            |
     |            |  BYE F21   |<------------------------|  REL F22   |
     |Seiz Removal|<-----------|                         |----------->|
     |<-----------|  200 F23   |                         |            |
     |Seiz Removal|----------->|         200 F24         |            |
     |----------->|            |------------------------>| REL COM F25|
     |            |            |                         |<-----------|
     |            |            |                         |            |

Top      Up      ToC       Page 106 
   PBX Alice calls PBX Carol via Gateway GW 1 and Proxy 1.  During the
   attempt to reach Carol via GW 2, an error is encountered - Proxy 1
   receives a 503 Service Unavailable (F4) response to the forwarded
   INVITE.  This could be due to all circuits being busy, or some other
   outage at GW 2.  Proxy 1 recognizes the error and uses an alternative
   route via GW 3 to terminate the call.  From there, the call proceeds
   normally with Carol answering the call.  The call is terminated when
   Carol hangs up.

   Message Details

   PBX Alice -> GW 1

   Seizure

   GW 1 -> PBX A

   Wink

   F1 MF Digits PBX Alice -> GW 1

   KP 444 3333 ST


   F2 INVITE GW 1 -> Proxy 1

   INVITE sip:4443333@ss1.a.example.com 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>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:551313@gw1.a.example.com>
   Content-Type: application/sdp
   Content-Length: 155

   v=0
   o=GW 2890844526 2890844526 IN IP4 gw1.a.example.com
   s=-
   c=IN IP4 gw1.a.example.com
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

Top      Up      ToC       Page 107 
   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Response is returned listing alternative routes, GW2 and
   GW3, which are then tried sequentially. */


   F3 INVITE Proxy 1 -> GW 2

   INVITE sip:4443333@gw2.a.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>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:551313@gw1.a.example.com>
   Content-Type: application/sdp
   Content-Length: 155

   v=0
   o=GW 2890844526 2890844526 IN IP4 gw1.a.example.com
   s=-
   c=IN IP4 gw1.a.example.com
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F4 503 Service Unavailable GW 2 -> Proxy 1

   SIP/2.0 503 Service Unavailable
   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>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 ACK Proxy 1 -> GW 2

   ACK sip:4443333@ss1.a.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

Top      Up      ToC       Page 108 
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Max-Forward: 70
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F6 INVITE Proxy 1 -> GW 3

   INVITE sip:+19185553333@gw3.a.example.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2
   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>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:551313@gw1.a.example.com>
   Content-Type: application/sdp
   Content-Length: 155

   v=0
   o=GW 2890844526 2890844526 IN IP4 gw1.a.example.com
   s=-
   c=IN IP4 gw1.a.example.com
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F7 SETUP GW 3 -> PBX C

   Protocol discriminator=Q.931
   Message type=SETUP
   Bearer capability: Information transfer capability=0 (Speech) or 16
   (3.1 kHz audio)
   Channel identification=Preferred or exclusive B-channel
   Progress indicator=1 (Call is not end-to-end ISDN; further call
   progress information may be available inband)
   Called party number:
   Type of number and numbering plan ID=33 (National number in ISDN
   numbering plan)
   Digits=918-555-3333

Top      Up      ToC       Page 109 
   F8 100 Trying GW 3 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F9 CALL PROCeeding PBX C -> GW 3

   Protocol discriminator=Q.931
   Message type=CALL PROC


   F10 ALERT PBX C -> GW 3

   Protocol discriminator=Q.931
   Message type=PROG

   /* Based on ALERT message, GW 3 returns a 180 response. */


   F11 180 Ringing GW 3 -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2
    ;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>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:+19185553333@gw3.a.example.com;user=phone>
   Content-Length: 0


   F12 180 Ringing Proxy 1 -> GW 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

Top      Up      ToC       Page 110 
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:+19185553333@gw3.a.example.com;user=phone>
   Content-Length: 0


   F13 CONNect PBX C -> GW 3

   Protocol discriminator=Q.931
   Message type=CONN


   F14 200 OK GW 3 -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2
    ;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>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:+19185553333@gw3.a.example.com;user=phone>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=GW 987654321 987654321 IN IP4 gw3.a.example.com
   s=-
   c=IN IP4 gw3.a.example.com
   t=0 0
   m=audio 14918 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F15 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>;tag=63412s

Top      Up      ToC       Page 111 
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:+19185553333@gw3.a.example.com;user=phone>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=GW 987654321 987654321 IN IP4 gw3.a.example.com
   s=-
   c=IN IP4 gw3.a.example.com
   t=0 0
   m=audio 14918 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   GW 1 -> PBX A

   Seizure


   F16 ACK GW 1 -> Proxy 1

   ACK sip:+19185553333@gw3.a.example.com;user=phone 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>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F17 ACK Proxy 1 -> GW 3

   ACK sip:+19185553333@gw3.a.example.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2
   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>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

Top      Up      ToC       Page 112 
   F18 CONNect ACK GW 3 -> PBX C

   Protocol discriminator=Q.931
   Message type=CONN ACK

   /* RTP streams are established between GW 1 and GW 3. */

   /* Bob Hangs Up with Alice. */


   F19 DISConnect PBX C -> GW 3

   Protocol discriminator=Q.931
   Message type=DISC
   Cause=16 (Normal clearing)


   F20 BYE GW 3 -> Proxy 1

   BYE sip:551313@gw1.a.example.com SIP/2.0
   Via: SIP/2.0/UDP gw3.a.example.com:5060;branch=z9hG4bKkdjuwq
   Max-Forwards: 70
   Route: <sip:ss1.a.example.com;lr>
   From: <sip:4443333@ss1.a.example.com>;tag=123456789
   To: <sip:551313@gw1.a.example.com>;tag=63412s
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 BYE
   Content-Length: 0


   F21 BYE Proxy 1 -> GW 1

   BYE sip:551313@gw1.a.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2
   Via: SIP/2.0/UDP gw3.a.example.com:5060;branch=z9hG4bKkdjuwq
    ;received=192.0.2.203
   Max-Forwards: 69
   From: <sip:4443333@ss1.a.example.com>;tag=123456789
   To: <sip:551313@gw1.a.example.com>;tag=63412s
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 BYE
   Content-Length: 0

   GW 1 -> PBX A

   Seizure removal

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   F22 RELease GW 3 -> PBX C

   Protocol discriminator=Q.931
   Message type=REL


   F23 200 OK GW 1 -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw3.a.example.com:5060;branch=z9hG4bKkdjuwq
    ;received=192.0.2.203
   From: <sip:4443333@ss1.a.example.com>;tag=123456789
   To: <sip:551313@gw1.a.example.com>;tag=63412s
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 BYE
   Content-Length: 0


   F24 200 OK Proxy 1 -> GW 3

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP gw3.a.example.com:5060;branch=z9hG4bKkdjuwq
    ;received=192.0.2.203
   From: <sip:4443333@ss1.a.example.com>;tag=123456789
   To: <sip:551313@gw1.a.example.com>;tag=63412s
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 BYE
   Content-Length: 0


   F25 RELease COMplete PBX C -> GW 3

   Protocol discriminator=Q.931
   Message type=REL COM

   PBX Alice -> GW 1

   Seizure removal

5.  Security Considerations

   This document provides examples of mapping from SIP to ISUP and ISUP
   to SIP.  The gateways in these examples are compliant with the
   Security Considerations Section of RFC 3398 [4] which is summarized
   here.

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   There are few security concerns relating to the mapping of ISUP to
   SIP besides privacy considerations in the calling party number
   passing.  Some concerns relating to the mapping from tel URI
   parameters to ISUP include the user creation of parameters and codes
   relating to called number and local number portability (LNP).  An
   operator of a gateway should use policies similar to those present in
   PSTN switches to avoid security problems.

   The mapping from a SIP response code to an ISUP Cause Code presents a
   theoretical risk, so a gateway operator may implement policies
   controlling this mapping.  Gateways should also not rely on the
   contents of the From header field for identity information, as it may
   be arbitrarily populated by a user.  Instead, some sort of
   cryptographic authentication and authorization should be used for
   identity determination.  These flows show both HTTP Digest for
   authentication of users, although for brevity, the challenge is not
   always shown.

   The early media cut-through shown in some flows is another potential
   security risk, but it is also required for proper interaction with
   the PSTN.  Again, a gateway operator should use proper policies
   relating to early media to prevent fraud and misuse.  Finally, a user
   agent (even a properly authenticated one) can launch multiple
   simultaneous requests through a gateway, constituting a denial of
   service attack.  The adoption of policies to limit the number of
   simultaneous requests from a single entity may be used to prevent
   this attack.

   As discussed in the SIP-T framework [7], SIP/ISUP interworking can be
   employed as an interdomain signaling mechanism that may be subject to
   pre-existing trust relationships between administrative domains.  Any
   administrative domain implementing SIP-T or SIP/ISUP interworking
   should have an adequate security apparatus (including elements that
   manage any appropriate policies to manage fraud and billing in an
   interdomain environment) in place to ensure that the translation of
   ISUP information does not result in any security violations.

   Although no examples of this are shown in this document, transporting
   ISUP in SIP bodies may provide opportunities for abuse, fraud, and
   privacy concerns, especially when SIP-T requests can be generated,
   inspected or modified by arbitrary SIP endpoints.  ISUP MIME bodies
   should be secured (preferably with S/MIME as detailed in RFC 3261
   [2]) to alleviate this concern.  Authentication properties provided
   by S/MIME would allow the recipient of a SIP-T message to ensure that
   the ISUP MIME body was generated by an authorized entity.  Encryption
   would ensure that only carriers possessing a particular decryption
   key are capable of inspecting encapsulated ISUP MIME bodies in a SIP
   request.

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6.  References

6.1.  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M. E. and Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

   [3]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
        the Session Description Protocol (SDP)", RFC 3264, June 2002.

   [4]  Camarillo, G., Roach, A. B., Peterson, J. and L. Ong,
        "Integrated Services Digital Network (ISDN) User Part (ISUP) to
        Session Initiation Protocol (SIP) Mapping", RFC 3398, December
        2002.

   [5]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
        Leach, P., Luotonen, A. and L. Stewart, "HTTP Authentication:
        Basic and Digest Access Authentication", RFC 2617, June 1999.

   [6]  Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806, April
        2000.

   [7]  Vemuri, A. and J. Peterson, "Session Initiation Protocol for
        Telephones (SIP-T): Context and Architectures", BCP 63, RFC
        3372, September 2002.

   [8]  Zimmerer, E., Peterson, J., Vemuri, A., Ong, L., Audet, F.,
        Watson, M. and M. Zonoun, "MIME media types for ISUP and QSIG
        Objects", RFC 3204, December 2001.

   [9] Faltstrom, P., "E.164 number and DNS", RFC 2916, September 2000.

6.2.  Informative References

   [10] Johnston, A., Donovan, S., Sparks, R., Cunningham, C. and K.
        Summers, "Session Initiation Protocol (SIP) Basic Call Flow
        Examples", RFC 3665, December 2003.

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7.  Acknowledgments

   Thanks to Rohan Mahy, Adam Roach, Gonzalo Camarillo, Cullen Jennings,
   and Tom Taylor for their detailed comments during the final review.
   Thanks to Dean Willis for his early contributions to the development
   of this document.  Thanks to Jon Peterson for his help on the
   security section.

   The authors wish to thank Kundan Singh for performing parser
   validation of messages.

   The authors wish to thank the following individuals for their
   participation in a detailed review of this call flows document: Aseem
   Agarwal, Rafi Assadi, Ben Campbell, Sunitha Kumar, Jon Peterson, Marc
   Petit-Huguenin, Vidhi Rastogi, and Bodgey Yin Shaohua.

   The authors also wish to thank the following individuals for their
   assistance: Jean-Francois Mule, Hemant Agrawal, Henry Sinnreich,
   David Devanatham, Joe Pizzimenti, Matt Cannon, John Hearty, the whole
   MCI WorldCom IPOP Design team, Scott Orton, Greg Osterhout, Pat
   Sollee, Doug Weisenberg, Danny Mistry, Steve McKinnon, and Denise
   Ingram, Denise Caballero, Tom Redman, Ilya Slain, Pat Sollee, John
   Truetken, and others from MCI WorldCom, 3Com, Cisco, Lucent and
   Nortel.

8.  Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

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9.  Authors' Addresses

   All listed authors actively contributed large amounts of text to this
   document.

   Alan Johnston
   MCI
   100 South 4th Street
   St. Louis, MO 63102
   USA

   EMail: alan.johnston@mci.com

   Steve Donovan
   dynamicsoft, Inc.
   5100 Tennyson Parkway
   Suite 1200
   Plano, Texas 75024
   USA

   EMail: sdonovan@dynamicsoft.com

   Robert Sparks
   dynamicsoft, Inc.
   5100 Tennyson Parkway
   Suite 1200
   Plano, Texas 75024
   USA

   EMail: rsparks@dynamicsoft.com

   Chris Cunningham
   dynamicsoft, Inc.
   5100 Tennyson Parkway
   Suite 1200
   Plano, Texas 75024
   USA

   EMail: ccunningham@dynamicsoft.com

   Kevin Summers
   Sonus
   1701 North Collins Blvd, Suite 3000
   Richardson, TX 75080
   USA

   EMail: kevin.summers@sonusnet.com

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10.  Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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Acknowledgement

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