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RFC 3665

Session Initiation Protocol (SIP) Basic Call Flow Examples

Pages: 94
Best Current Practice: 75
Errata
Part 4 of 4 – Pages 67 to 94
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Top   ToC   RFC3665 - Page 67   prevText

3.8. Unsuccessful No Answer

Alice Proxy 1 Proxy 2 Bob | | | | | INVITE F1 | | | |--------------->| INVITE F2 | | | 100 F3 |--------------->| INVITE F4 | |<---------------| 100 F5 |--------------->| | |<---------------| | | | | 180 F6 | | | 180 F7 |<---------------| | 180 F8 |<---------------| | |<---------------| | | | CANCEL F9 | | | |--------------->| | | | 200 F10 | | | |<---------------| CANCEL F11 | | | |--------------->| | | | 200 F12 | | | |<---------------| | | | | CANCEL F13 | | | |--------------->| | | | 200 F14 | | | |<---------------| | | | 487 F15 | | | |<---------------| | | | ACK F16 | | | 487 F17 |--------------->| | |<---------------| | | | ACK F18 | | | 487 F19 |--------------->| | |<---------------| | | | ACK F20 | | | |--------------->| | | | | | | In this scenario, Alice gives up on the call before Bob answers (sends a 200 OK response). Alice sends a CANCEL (F9) since no final response had been received from Bob. If a 200 OK to the INVITE had crossed with the CANCEL, Alice would have sent an ACK then a BYE to Bob in order to properly terminate the call. Note that the CANCEL message is acknowledged with a 200 OK on a hop by hop basis, rather than end to end.
Top   ToC   RFC3665 - Page 68
   Message Details

   F1 INVITE Alice -> Proxy 1

   INVITE sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com>
   Proxy-Authorization: Digest username="alice",
    realm="atlanta.example.com",
    nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="",
    uri="sip:bob@biloxi.example.com",
    response="b00b416324679d7e243f55708d44be7b"
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /*Client for Alice prepares to receive data on port 49172 from the
   network.*/


   F2 INVITE Proxy 1 -> Proxy 2

   INVITE sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com>
   Content-Type: application/sdp
   Content-Length: 151
Top   ToC   RFC3665 - Page 69
   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 1 -> Alice

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 INVITE Proxy 2 -> Bob

   INVITE sip:bob@client.biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   Max-Forwards: 68
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000
Top   ToC   RFC3665 - Page 70
   F5 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 180 Ringing Bob -> Proxy 2

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.biloxi.example.com>
   Content-Length: 0


   F7 180 Ringing Proxy 2 -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
Top   ToC   RFC3665 - Page 71
   Contact: <sip:bob@client.biloxi.example.com>
   Content-Length: 0


   F8 180 Ringing Proxy 1 -> Alice

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.biloxi.example.com>
   Content-Length: 0


   F9 CANCEL Alice -> Proxy 1

   CANCEL sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Route: <sip:ss1.atlanta.example.com;lr>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F10 200 OK Proxy 1 -> Alice

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 CANCEL
   Content-Length: 0
Top   ToC   RFC3665 - Page 72
   F11 CANCEL Proxy 1 -> Proxy 2

   CANCEL sip:alice@atlanta.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F12 200 OK Proxy 2 -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F13 CANCEL Proxy 2 -> Bob

   CANCEL sip:bob@client.biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F14 200 OK Bob -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
    ;received=192.0.2.222
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 CANCEL
   Content-Length: 0
Top   ToC   RFC3665 - Page 73
   F15 487 Request Terminated Bob -> Proxy 2

   SIP/2.0 487 Request Terminated
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F16 ACK Proxy 2 -> Bob

   ACK sip:bob@client.biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F17 487 Request Terminated Proxy 2 -> Proxy 1

   SIP/2.0 487 Request Terminated
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0
Top   ToC   RFC3665 - Page 74
   F18 ACK Proxy 1 -> Proxy 2

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F19 487 Request Terminated Proxy 1 -> Alice

   SIP/2.0 487 Request Terminated
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE


   F20 ACK Alice -> Proxy 1

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   Proxy-Authorization: Digest username="alice",
    realm="atlanta.example.com",
    nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="",
    uri="sip:bob@biloxi.example.com",
    response="b00b416324679d7e243f55708d44be7b"
   CSeq: 1 ACK
   Content-Length: 0
Top   ToC   RFC3665 - Page 75

3.9. Unsuccessful Busy

Alice Proxy 1 Proxy 2 Bob | | | | | INVITE F1 | | | |--------------->| INVITE F2 | | | 100 F3 |--------------->| INVITE F4 | |<---------------| 100 F5 |--------------->| | |<---------------| | | | | 486 F6 | | | |<---------------| | | | ACK F7 | | | 486 F8 |--------------->| | |<---------------| | | | ACK F9 | | | 486 F10 |--------------->| | |<---------------| | | | ACK F11 | | | |--------------->| | | | | | | In this scenario, Bob is busy and sends a 486 Busy Here response to Alice's INVITE. Note that the non-2xx response is acknowledged on a hop-by-hop basis instead of end-to-end. Also note that many SIP UAs will not return a 486 response, as they have multiple line and other features. Message Details F1 INVITE Alice -> Proxy 1 INVITE sip:bob@biloxi.example.com SIP/2.0 Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 Route: <sip:ss1.atlanta.example.com;lr> From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl To: Bob <sip:bob@biloxi.example.com> Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com CSeq: 1 INVITE Contact: <sip:alice@client.atlanta.example.com;transport=tcp> Proxy-Authorization: Digest username="alice", realm="atlanta.example.com", nonce="dc3a5ab2530aa93112cf5904ba7d88fa", opaque="", uri="sip:bob@biloxi.example.com", response="702138b27d869ac8741e10ec643d55be" Content-Type: application/sdp Content-Length: 151
Top   ToC   RFC3665 - Page 76
   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /*Client for Alice prepares to receive data on port 49172 from the
   network.*/


   F2 INVITE Proxy 1 -> Proxy 2

   INVITE sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 1 -> Alice

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0
Top   ToC   RFC3665 - Page 77
   F4 INVITE Proxy 2 -> Bob

   INVITE sip:bob@client.biloxi.example.com SIP/2.0
   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 486 Busy Here Bob -> Proxy 2

   SIP/2.0  486 Busy Here
   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
    ;received=192.0.2.222
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
Top   ToC   RFC3665 - Page 78
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F7 ACK Proxy 2 -> Bob

   ACK sip:bob@client.biloxi.example.com SIP/2.0
   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F8 486 Busy Here Proxy 2 -> Proxy 1

   SIP/2.0  486 Busy Here
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F9 ACK Proxy 1 -> Proxy 2

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Content-Length: 0
Top   ToC   RFC3665 - Page 79
   F10 486 Busy Here Proxy 1 -> Alice

   SIP/2.0  486 Busy Here
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F11 ACK Alice -> Proxy 1

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Proxy-Authorization: Digest username="alice",
    realm="atlanta.example.com",
    nonce="dc3a5ab2530aa93112cf5904ba7d88fa", opaque="",
    uri="sip:bob@biloxi.example.com",
    response="702138b27d869ac8741e10ec643d55be"
   Content-Length: 0
Top   ToC   RFC3665 - Page 80

3.10. Unsuccessful No Response from User Agent

Alice Proxy 1 Proxy 2 Bob | | | | | INVITE F1 | | | |--------------->| INVITE F2 | | | 100 F3 |--------------->| INVITE F4 | |<---------------| 100 F5 |--------------->| | |<---------------| INVITE F6 | | | |--------------->| | | | INVITE F7 | | | |--------------->| | | | INVITE F8 | | | |--------------->| | | | INVITE F9 | | | |--------------->| | | | INVITE F10 | | | |--------------->| | | | INVITE F11 | | | 480 F12 |--------------->| | |<---------------| | | | ACK F13 | | | 480 F14 |--------------->| | |<---------------| | | | ACK F15 | | | |--------------->| | | | | | | In this example, there is no response from Bob to Alice's INVITE messages being re-transmitted by Proxy 2. After the sixth re-transmission, Proxy 2 gives up and sends a 480 No Response to Alice. Message Details F1 INVITE Alice -> Proxy 1 INVITE sip:bob@biloxi.example.com SIP/2.0 Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 Route: <sip:ss1.atlanta.example.com;lr> From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl To: Bob <sip:bob@biloxi.example.com> Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com CSeq: 1 INVITE Contact: <sip:alice@client.atlanta.example.com> Proxy-Authorization: Digest username="alice", realm="atlanta.example.com",
Top   ToC   RFC3665 - Page 81
    nonce="cf5904ba7d8dc3a5ab2530aa931128fa", opaque="",
    uri="sip:bob@biloxi.example.com",
    response="7afc04be7961f053c24f80e7dbaf888f"
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /*Client for Alice prepares to receive data on port 49172 from the
   network.*/


   F2 INVITE Proxy 1 -> Proxy 2

   INVITE sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 1 -> Alice

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
Top   ToC   RFC3665 - Page 82
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 INVITE Proxy 2 -> Bob

   INVITE sip:bob@client.biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
   <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0
Top   ToC   RFC3665 - Page 83
   F6 INVITE Proxy 2 -> Bob

   Resend of Message F4


   F7 INVITE Proxy 2 -> Bob

   Resend of Message F4


   F8 INVITE Proxy 2 -> Bob

   Resend of Message F4


   F9 INVITE Proxy 2 -> Bob

   Resend of Message F4


   F10 INVITE Proxy 2 -> Bob

   Resend of Message F4


   F11 INVITE Proxy 2 -> Bob

   Resend of Message F4

   /* Proxy 2 gives up */


   F12 480 No Response Proxy 2 -> Proxy 1

   SIP/2.0 480 No Response
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0
Top   ToC   RFC3665 - Page 84
   F13 ACK Proxy 1 -> Proxy 2

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F14 480 No Response Proxy 1 -> Alice

   SIP/2.0 480 No Response
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F15 ACK Alice -> Proxy 1

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Proxy-Authorization: Digest username="alice",
    realm="atlanta.example.com",
    nonce="cf5904ba7d8dc3a5ab2530aa931128fa", opaque="",
    uri="sip:bob@biloxi.example.com",
    response="7afc04be7961f053c24f80e7dbaf888f"
   Content-Length: 0
Top   ToC   RFC3665 - Page 85

3.11. Unsuccessful Temporarily Unavailable

Alice Proxy 1 Proxy 2 Bob | | | | | INVITE F1 | | | |--------------->| INVITE F2 | | | 100 F3 |--------------->| INVITE F4 | |<---------------| 100 F5 |--------------->| | |<---------------| 180 F6 | | | 180 F7 |<---------------| | 180 F8 |<---------------| | |<---------------| | 480 F9 | | | |<---------------| | | | ACK F10 | | | 480 F11 |--------------->| | |<---------------| | | | ACK F12 | | | 480 F13 |--------------->| | |<---------------| | | | ACK F14 | | | |--------------->| | | | | | | In this scenario, Bob initially sends a 180 Ringing response to Alice, indicating that alerting is taking place. However, then a 480 Unavailable is then sent to Alice. This response is acknowledged then proxied back to Alice. Message Details F1 INVITE Alice -> Proxy 1 INVITE sip:bob@biloxi.example.com SIP/2.0 Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 Route: <sip:ss1.atlanta.example.com;lr> From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl To: Bob <sip:bob@biloxi.example.com> Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com CSeq: 1 INVITE Contact: <sip:alice@client.atlanta.example.com> Proxy-Authorization: Digest username="alice", realm="atlanta.example.com", nonce="aa9311cf5904ba7d8dc3a5ab253028fa", opaque="", uri="sip:bob@biloxi.example.com", response="59a46a91bf1646562a4d486c84b399db" Content-Type: application/sdp
Top   ToC   RFC3665 - Page 86
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /*Client for Alice prepares to receive data on port 49172 from the
   network.*/


   F2 INVITE Proxy 1 -> Proxy 2

   INVITE sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 1 -> Alice

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
Top   ToC   RFC3665 - Page 87
   Content-Length: 0


   F4 INVITE Proxy 2 -> Bob

   INVITE sip:bob@client.biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.atlanta.example.com>
   Content-Type: application/sdp
   Content-Length: 151

   v=0
   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0
Top   ToC   RFC3665 - Page 88
   F6 180 Ringing Bob -> Proxy 2

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.biloxi.example.com>
   Content-Length: 0


   F7 180 Ringing Proxy 2 -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.biloxi.example.com>
   Content-Length: 0


   F8 180 Ringing Proxy 1 -> Alice

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.example.com;lr>,
    <sip:ss1.atlanta.example.com;lr>
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.biloxi.example.com>
Top   ToC   RFC3665 - Page 89
   Content-Length: 0


   F9 480 Temporarily Unavailable Bob -> Proxy 2

   SIP/2.0 480 Temporarily Unavailable
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F10 ACK Proxy 2 -> Bob

   ACK sip:bob@client.biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F11 480 Temporarily Unavailable Proxy 2 -> Proxy 1

   SIP/2.0 480 Temporarily Unavailable
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0
Top   ToC   RFC3665 - Page 90
   F12 ACK Proxy 1 -> Proxy 2

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 ACK
   Content-Length: 0


   F13 480 Temporarily Unavailable Proxy 1 -> Alice

   SIP/2.0 480 Temporarily Unavailable
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   CSeq: 1 INVITE
   Content-Length: 0


   F14 ACK Alice -> Proxy 1

   ACK sip:bob@biloxi.example.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
   To: Bob <sip:bob@biloxi.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
   Proxy-Authorization: Digest username="alice",
    realm="atlanta.example.com",
    nonce="aa9311cf5904ba7d8dc3a5ab253028fa", opaque="",
    uri="sip:bob@biloxi.example.com",
    response="59a46a91bf1646562a4d486c84b399db"
   CSeq: 1 ACK
   Content-Length: 0
Top   ToC   RFC3665 - Page 91

4. Security Considerations

Since this document contains examples of SIP session establishment, the security considerations in RFC 3261 [1] apply. RFC 3261 describes the basic threats including registration hijacking, server impersonation, message body tampering, session modifying or teardown, and denial of service and amplification attacks. The use of HTTP Digest as shown in this document provides one-way authentication and protection against replay attacks. TLS transport is used in registration scenarios due to the lack of integrity protection in HTTP Digest and the danger of registration hijacking without it, as described in RFC 3261 [1]. A full discussion of the weaknesses of HTTP Digest is provided in RFC 3261 [1]. The use of TLS and the Secure SIP (sips) URI scheme provides a better level of security including two-way authentication. S/MIME can provide end-to-end confidentiality and integrity protection of message bodies, as described in RFC 3261.

5. References

5.1. Normative References

[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [2] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with SDP", RFC 3264, April 2002. [3] 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. [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

5.2. Informative References

[5] Johnston, A., Donovan, S., Sparks, R., Cunningham, C. and K. Summers, "Session Initiation Protocol (SIP) Public Switched Telephone Network (PSTN) Call Flows", BCP 76, RFC 3666, December 2003.

6. 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
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   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
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   this standard.  Please address the information to the IETF Executive
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7. Acknowledgments

This document is has been a group effort by the SIP and SIPPING WGs. The authors wish to thank everyone who has read, reviewed, commented, or made suggestions to improve this document. 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. 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 the 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.
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8. 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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9. Full Copyright Statement

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