tech-invite   World Map     

IETF     RFCs     Groups     SIP     ABNFs    |    3GPP     Specs     Glossaries     Architecture     IMS     UICC    |    search

RFC 5359

 
 
 

Session Initiation Protocol Service Examples

Part 2 of 6, p. 19 to 57
Prev RFC Part       Next RFC Part

 


prevText      Top      Up      ToC       Page 19 
2.2.  Consultation Hold

           Alice            Proxy           Bob                Carol
             |                |              |                   |
             |    INVITE F1   |              |                   |
             |--------------->|   INVITE F2  |                   |
             |                |------------->|                   |
             |(100 Trying) F3 |              |                   |
             |<---------------|180 Ringing F4|                   |
             |                |<-------------|                   |
             | 180 Ringing F5 |              |                   |
             |<---------------|  200 OK F6   |                   |
             |                |<-------------|                   |
             |    200 OK F7   |              |                   |
             |<---------------|              |                   |
             |     ACK F8     |              |                   |
             |--------------->|     ACK F9   |                   |
             |                |------------->|                   |
             |     Both way RTP Established  |                   |
             |<=============================>|                   |
             |                |INVITE(hold) F10                  |
             |INVITE(hold) F11|<-------------|                   |
             |<---------------|              |                   |
             |    200 OK F12  |              |                   |
             |--------------->|   200 OK F13 |                   |
             |                |------------->|                   |
             |                |     ACK F14  |                   |
             |                |<-------------|                   |
             |    ACK F15     |              |                   |
             |<---------------|              |                   |
             |         No RTP Sent!          |                   |
             |                |   INVITE F16 |                   |
             |                |<-------------|                   |
             |                |              |    INVITE F17     |
             |                |--------------------------------->|
             |                |(100 Trying) F18                  |
             |                |------------->|                   |
             |                |              | 180 Ringing F19   |
             |                |<---------------------------------|
             |                | 180 Ringing F20                  |
             |                |------------->|                   |
             |                |              |    200 OK F21     |
             |                |<---------------------------------|
             |                |   200 OK F22 |                   |
             |                |------------->|                   |
             |                |    ACK F23   |                   |
             |                |<-------------|                   |
             |                |              |      ACK F24      |

Top      Up      ToC       Page 20 
             |                |--------------------------------->|
             |                |         Both way RTP Established |
             |                |              |<=================>|
             |                |   BYE F25    |                   |
             |                |<-------------|                   |
             |                |              |       BYE F26     |
             |                |--------------------------------->|
             |                |              |    200 OK F27     |
             |                |<---------------------------------|
             |                |   200 OK F28 |                   |
             |                |------------->|                   |
             |                |   INVITE F29 |                   |
             |    INVITE F30  |<-------------|                   |
             |<---------------|              |                   |
             |    200 OK F31  |              |                   |
             |--------------->|   200 OK F32 |                   |
             |                |------------->|                   |
             |                |     ACK F33  |                   |
             |                |<-------------|                   |
             |    ACK F34     |              |                   |
             |<---------------|              |                   |
             |     Both way RTP Established  |                   |
             |<=============================>|                   |
             |    BYE F35     |              |                   |
             |--------------->|    BYE F36   |                   |
             |                |------------->|                   |
             |                |   200 OK F37 |                   |
             |                |<-------------|                   |
             |  200 OK F38    |              |                   |
             |<---------------|              |                   |
             |                |              |                   |

   In this scenario, Alice calls Bob.  Bob places call on hold.  Bob
   calls Carol.  Bob then disconnects with Carol, then takes the call
   with Alice off hold.  The call ends when Alice hangs up.

   Also note the use of the rendering feature tag defined in RFC 4235
   [RFC4235] used in F10 to indicate that Bob's UA is no longer
   rendering media to Bob, i.e., that Bob has placed the call on hold.

   Message Details

      F1 INVITE Alice -> Proxy 1

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf9
      Max-Forwards: 70

Top      Up      ToC       Page 21 
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 INVITE Proxy 1 -> Bob

      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000

Top      Up      ToC       Page 22 
      F3 (100 Trying) Proxy 1 -> Alice

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F4 180 Ringing Bob -> Proxy 1
      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content Length:0


      F5 180 Ringing Proxy 1 -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content Length: 0

Top      Up      ToC       Page 23 
      F6 200 OK Bob -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

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


      F7 200 OK Proxy 1 -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

Top      Up      ToC       Page 24 
      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=
      c=IN IP4 client.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F8 ACK Alice -> Proxy 1

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf45
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F9 ACK Proxy 1 -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK837494.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf45
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0

Top      Up      ToC       Page 25 
      /* Bob places Alice on hold. */

      F10 INVITE Bob -> Proxy 1

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>;+sip.rendering="no"
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=
      c=IN IP4 client.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F11 INVITE Proxy 1 -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK837497.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>;+sip.rendering="no"
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

Top      Up      ToC       Page 26 
      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=
      c=IN IP4 client.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F12 200 OK Alice -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK837497.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      F13 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159

Top      Up      ToC       Page 27 
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      F14 ACK Bob -> Proxy 1

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashdsg
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F15 ACK Proxy 1 -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK8374.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashdsg
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567

Top      Up      ToC       Page 28 
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F16 INVITE Bob -> Proxy 1

      INVITE sips:carol@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds22
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844834 2890844834 IN IP4 client.biloxi.example.com
      s=
      c=IN IP4 client.biloxi.example.com
      t=0 0
      m=audio 50170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F17 INVITE Proxy 1 -> Carol

      INVITE sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749a.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY

Top      Up      ToC       Page 29 
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844834 2890844834 IN IP4 client.biloxi.example.com
      s=
      c=IN IP4 client.biloxi.example.com
      t=0 0
      m=audio 50170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F18 (100 Trying) Proxy 1 -> Bob

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F19 180 Ringing Carol -> Proxy 1
      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749a.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Content Length:0


      F20 180 Ringing Proxy 1 -> Bob

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds22

Top      Up      ToC       Page 30 
       ;received=client.chicago.example.com
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Content Length: 0


      F21 200 OK Carol -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749a.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844922 IN IP4 client.chicago.example.com
      s=
      c=IN IP4 client.chicago.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F22 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654

Top      Up      ToC       Page 31 
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844922 IN IP4 client.chicago.example.com
      s=
      c=IN IP4 client.chicago.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F23 ACK Bob -> Proxy 1

      ACK sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds24
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F24 ACK Proxy 1 -> Carol

      ACK sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749b.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds24
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 ACK

Top      Up      ToC       Page 32 
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F25 BYE Bob -> Proxy 1

      BYE sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7j
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F26 BYE Proxy 1 -> Carol

      BYE sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749k.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7j
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F27 200 OK Carol -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749k.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7j
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654

Top      Up      ToC       Page 33 
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F28 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7j
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      /* Bob takes the call off hold. */

      F29 INVITE Bob -> Proxy 1

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7b
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844529 IN IP4 client.biloxi.example.com
      s=
      c=IN IP4 client.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000

Top      Up      ToC       Page 34 
      F30 INVITE Proxy 1 -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749q.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7b
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844529 IN IP4 client.biloxi.example.com
      s=
      c=IN IP4 client.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F31 200 OK Alice -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK83749q.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7b
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

Top      Up      ToC       Page 35 
      v=0
      o=alice 2890844526 2890844528 IN IP4 client.atlanta.example.com
      s=
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F32 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7b
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844528 IN IP4 client.atlanta.example.com
      s=
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F33 ACK Bob -> Proxy 1

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7d7
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces

Top      Up      ToC       Page 36 
      Content-Length: 0

      F34 ACK Proxy 1 -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK8374.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7d7
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F35 BYE Alice -> Proxy 1

      BYE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf10
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F36 BYE Proxy 1 -> Bob

      BYE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK8379.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf10
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0

Top      Up      ToC       Page 37 
      F37 200 OK Bob -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061
       ;branch=z9hG4bK8379.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf10
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F38 200 OK Proxy 1 -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061
       ;branch=z9hG4bK74bf10
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0

Top      Up      ToC       Page 38 
2.3.  Music on Hold

           Alice             Bob       Music Server
             |                |              |
             |    INVITE F1   |              |
             |--------------->|              |
             | 180 Ringing F2 |              |
             |<---------------|              |
             |    200 OK F3   |              |
             |<---------------|              |
             |     ACK F4     |              |
             |--------------->|              |
             |       RTP      |              |
             |<==============>|              |
             |                |              |
             |   Bob places Alice on hold    |
             |                |              |
             | INVITE (hold) F5              |
             |<---------------|              |
             |    200 OK F6   |              |
             |--------------->|              |
             |     ACK F7     |              |
             |<---------------|              |
             |    no RTP      |              |
             |                |              |
             |  Bob initiates music on hold  |
             |                |              |
             |                |   REFER Refer-To: A F8
             |                |------------->|
             |                |    202 F9    |
             |                |<-------------|
             |                |   NOTIFY F10 |
             |                |<-------------|
             |                |    200 F11   |
             |                |------------->|
             |  INVITE F12 Replaces: B       |
             |<------------------------------|
             |          200 OK F13           |
             |------------------------------>|
             |           ACK F14             |
             |<------------------------------|
             |           RTP Music           |
             |<==============================|
             |     BYE F15    |              |
             |--------------->|  NOTIFY F17  |
             |  200 OK F16    |<-------------|
             |<---------------|  200 OK F18  |
             |                |------------->|

Top      Up      ToC       Page 39 
             |                |              |
             | The music on hold is complete |
             |                |              |
             |    Bob takes Alice off hold   |
             |                |              |
             |  INVITE Replaces: M F19       |
             |<---------------|              |
             |    200 OK F20  |              |
             |--------------->|              |
             |     ACK F21    |              |
             |<---------------|              |
             |       RTP      |              |
             |<==============>|              |
             |            BYE F22            |
             |------------------------------>|
             |          200 OK F23           |
             |<------------------------------|

   In this flow, Bob places Alice on hold with music.  This is performed
   by Bob sending a REFER to a Music Server that sends an INVITE with
   Replaces to Alice.  The Music Server then sends RTP music to Alice.
   Bob picks the call up from hold by sending an INVITE with Replaces to
   Alice.

   Note the use of the rendering feature tag defined in RFC 4235
   [RFC4235] used in F5 to indicate that Bob's UA is no longer rendering
   media to Bob, i.e., that Bob has placed the call on hold.  Feature
   tags are also used in F12 with the automaton (defined in RFC 3840
   [RFC3840]) and byeless feature tags (defined in RFC 4235 [RFC4235])
   to describe the capabilities of the Music Server.

   Should Alice not wish to receive music on hold, her UA could refuse
   F12 and she will remain on hold with Bob, but in silence.

   Message Details

     F1 INVITE Alice -> Bob

     INVITE sips:bob@biloxi.example.com SIP/2.0
     Via: SIP/2.0/TLS client.atlanta.example.com:5061
      ;branch=z9hG4bK74bf9
     Max-Forwards: 70
     From: Alice <sips:alice@atlanta.example.com>;tag=1234567
     To: Bob <sips:bob@biloxi.example.com>
     Call-ID: 12345600@atlanta.example.com
     CSeq: 1 INVITE
     Contact: <sips:a8342043f@atlanta.example.com;gr>
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY

Top      Up      ToC       Page 40 
     Supported: replaces, gruu
     Content-Type: application/sdp
     Content-Length: ...

     v=0
     o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
     s=
     c=IN IP4 client.atlanta.example.com
     t=0 0
     m=audio 49170 RTP/AVP 0
     a=rtpmap:0 PCMU/8000


     F2 180 Ringing Bob -> Alice

     SIP/2.0 180 Ringing
     Via: SIP/2.0/TLS client.atlanta.example.com:5061
      ;branch=z9hG4bK74bf9
      ;received=192.0.2.103
     From: Alice <sips:alice@atlanta.example.com>;tag=1234567
     To: Bob <sips:bob@biloxi.example.com>;tag=23431
     Call-ID: 12345600@atlanta.example.com
     CSeq: 1 INVITE
     Contact: <sips:bob@client.biloxi.example.com>
     Content-Length: 0


     F3 200 OK Bob -> Alice

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS client.atlanta.example.com:5061
      ;branch=z9hG4bK74bf9
      ;received=192.0.2.103
     From: Alice <sips:alice@atlanta.example.com>;tag=1234567
     To: Bob <sips:bob@biloxi.example.com>;tag=23431
     Call-ID: 12345600@atlanta.example.com
     CSeq: 1 INVITE
     Contact: <sips:bob@client.biloxi.example.com>
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
     Supported: replaces
     Content-Type: application/sdp
     Content-Length: ...

     v=0
     o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
     s=
     c=IN IP4 client.biloxi.example.com
     t=0 0

Top      Up      ToC       Page 41 
     m=audio 3456 RTP/AVP 0
     a=rtpmap:0 PCMU/8000


     F4 ACK Alice -> Bob

     ACK sips:bob@client.biloxi.example.com SIP/2.0
     Via: SIP/2.0/TLS client.atlanta.example.com:5061
      ;branch=z9hG4bK74bfd
     Max-Forwards: 70
     From: Alice <sips:alice@atlanta.example.com>;tag=1234567
     To: Bob <sips:bob@biloxi.example.com>;tag=23431
     Call-ID: 12345600@atlanta.example.com
     CSeq: 1 ACK
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
     Supported: replaces
     Content-Length: 0


     /* Bob places Alice on hold. */

     F5 INVITE Bob -> Alice

     INVITE sips:a8342043f@atlanta.example.com;gr SIP/2.0
     Via: SIP/2.0/TLS client.biloxi.example.com:5061
      ;branch=z9hG4bK874bk
     To: Alice <sips:alice@atlanta.example.com>;tag=1234567
     From: Bob <sips:bob@biloxi.example.com>;tag=23431
     Call-ID: 12345600@atlanta.example.com
     CSeq: 712 INVITE
     Contact: <sips:bob@client.biloxi.example.com>;+sip.rendering="no"
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
     Supported: replaces
     Content-Type: application/sdp
     Content-Length: ...

     v=0
     o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
     s=
     c=IN IP4 client.biloxi.example.com
     t=0 0
     m=audio 3456 RTP/AVP 0
     a=rtpmap:0 PCMU/8000
     a=sendonly

Top      Up      ToC       Page 42 
     F6 200 OK Alice -> Bob

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS client.biloxi.example.com:5061
      ;branch=z9hG4bK874bk
      ;received=192.0.2.105
     To: Alice <sips:alice@atlanta.example.com>;tag=1234567
     From: Bob <sips:bob@biloxi.example.com>;tag=23431
     Call-ID: 12345600@atlanta.example.com
     CSeq: 712 INVITE
     Contact: <sips:a8342043f@atlanta.example.com;gr>
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
     Supported: replaces, gruu
     Content-Type: application/sdp
     Content-Length: ...

     v=0
     o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
     s=
     c=IN IP4 client.atlanta.example.com
     t=0 0
     m=audio 49170 RTP/AVP 0
     a=rtpmap:0 PCMU/8000
     a=recvonly


     F7 ACK Bob -> Alice

     ACK sips:a8342043f@atlanta.example.com;gr SIP/2.0
     Via: SIP/2.0/TLS client.biloxi.example.com:5061
      ;branch=z9hG4bKq874b
     To: Alice <sips:alice@atlanta.example.com>;tag=1234567
     From: Bob <sips:bob@biloxi.example.com>;tag=23431
     Call-ID: 12345600@atlanta.example.com
     CSeq: 712 ACK
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
     Supported: replaces
     Content-Length: 0


     /* Bob REFERs Music Server to establish session with Alice
        which replaces the established session between Alice and Bob. */

     F8 REFER Bob -> Music Server

     REFER sips:music@server.example.com SIP/2.0
     Via: SIP/2.0/TLS client.biloxi.example.com:5061
      ;branch=z9hG4bKnashds9

Top      Up      ToC       Page 43 
     Max-Forwards: 70
     From: Bob <sips:bob@biloxi.example.com>;tag=02134
     To: Music Server <sips:music@server.example.com>
     Call-ID: 4802029847@biloxi.example.com
     CSeq: 1 REFER
   <allOneLine>
     Refer-To: <sips:a8342043f@atlanta.example.com;gr?Replaces=
     12345600%40atlanta.example.com%3Bfrom-tag%3D23431
     %3Bto-tag%3D1234567&Require=replaces>
   </allOneLine>
     Referred-By: <sips:bob@biloxi.example.com>
     Contact: <sips:bob@client.biloxi.example.com>
     Content-Length: 0


     F9 202 Accepted Music Server -> Bob

     SIP/2.0 202 Accepted
     Via: SIP/2.0/TLS client.biloxi.example.com:5061
      ;branch=z9hG4bKnashds9
      ;received=192.0.2.105
     From: Bob <sips:bob@biloxi.example.com>;tag=02134
     To: Music Server <sips:music@server.example.com>;tag=56323
     Call-ID: 4802029847@biloxi.example.com
     Contact: <sips:music@server.example.com>
     CSeq: 1 REFER
     Content-Length: 0


     F10 NOTIFY Music Server -> Bob

     NOTIFY sips:bob@client.biloxi.example.com SIP/2.0
     Via: SIP/2.0/TLS server.example.com:5061
      ;branch=z9hG4bK74bT6
     To: Bob <sips:bob@biloxi.example.com>;tag=02134
     Max-Forwards: 70
     From: Music Server <sips:music@server.example.com>;tag=56323
     Call-ID: 4802029847@biloxi.example.com
     CSeq: 1 NOTIFY
     Event: refer
     Subscription-State: active;expires=60
     Contact: <sips:music@server.example.com>
     Content-Type: message/sipfrag
     Content-Length: ...

     SIP/2.0 100 Trying

Top      Up      ToC       Page 44 
     F11 200 OK Bob -> Music Server

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS server.example.com:5061
      ;branch=z9hG4bK74bT6
      ;received=192.0.2.103
     To: Bob <sips:bob@biloxi.example.com>;tag=02134
     From: Music Server <sips:music@server.example.com>;tag=56323
     Call-ID: 4802029847@biloxi.example.com
     CSeq: 1 NOTIFY
     Content-Length: 0


     /* Music Server places call to Alice to replace session
        between Alice and Bob. */

     F12 INVITE Music Server -> Alice

     INVITE sips:a8342043f@atlanta.example.com;gr SIP/2.0
     Via: SIP/2.0/TLS server.example.com:5061
      ;branch=z9hG4bK74rf
     Max-Forwards: 70
     From: <sips:music@server.example.com>;tag=0111
     To: <sips:a8342043f@atlanta.example.com;gr>
     Call-ID: a5-75-34-12-76@server.example.com
     CSeq: 1 INVITE
     Referred-By: <sips:bob@biloxi.example.com>
     Contact: <sips:music@server.example.com>;automaton
      ;+sip.byeless;+sip.rendering="no"
     Require: replaces
     Replaces: 12345600@atlanta.example.com
      ;from-tag=23431;to-tag=1234567
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
     Supported: replaces
     Content-Type: application/sdp
     Content-Length: ...

     v=0
     o=MusicServer 2890844576 2890844576 IN IP4 server.example.com
     s=
     c=IN IP4 server.example.com
     t=0 0
     m=audio 49170 RTP/AVP 0
     a=rtpmap:0 PCMU/8000
     a=sendonly

Top      Up      ToC       Page 45 
     F13 200 OK Alice -> Music Server

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS server.example.com:5061
      ;branch=z9hG4bK74rf
      ;received=192.0.2.103
     From: <sips:music@server.example.com>;tag=0111
     To: <sips:a8342043f@atlanta.example.com;gr>;tag=098594
     Call-ID: a5-75-34-12-76@server.example.com
     CSeq: 1 INVITE
     Contact: <sips:a8342043f@atlanta.example.com;gr>
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
     Supported: replaces, gruu
     Content-Type: application/sdp
     Content-Length: ...

     v=0
     o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
     s=
     c=IN IP4 client.atlanta.example.com
     t=0 0
     m=audio 49170 RTP/AVP 0
     a=rtpmap:0 PCMU/8000
     a=recvonly


     F14 ACK Music Server -> Alice

     ACK sips:a8342043f@atlanta.example.com;gr SIP/2.0
     Via: SIP/2.0/TLS server.example.com:5061
      ;branch=z9hG4bK7rfF
     Max-Forwards: 70
     From: <sips:music@server.example.com>;tag=0111
     To: <sips:a8342043f@atlanta.example.com;gr>;tag=098594
     Call-ID: a5-75-34-12-76@server.example.com
     CSeq: 1 ACK
     Content-Length: 0


     F15 BYE Alice -> Bob

     BYE sips:bob@client.biloxi.example.com SIP/2.0
     Via: SIP/2.0/TLS client.atlanta.example.com:5061
      ;branch=z9hG4bKnashds7
     Max-Forwards: 70
     From: Alice <sips:alice@atlanta.example.com>;tag=1234567
     To: Bob <sips:bob@biloxi.example.com>;tag=23431
     Call-ID: 12345600@atlanta.example.com

Top      Up      ToC       Page 46 
     CSeq: 2 BYE
     Content-Length: 0


     F16 200 OK Bob -> Alice

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS client.atlanta.example.com:5061
      ;branch=z9hG4bKnashds7
      ;received=192.0.2.105
     From: Alice <sips:alice@atlanta.example.com>;tag=1234567
     To: Bob <sips:bob@biloxi.example.com>;tag=23431
     Call-ID: 12345600@atlanta.example.com
     CSeq: 2 BYE
     Content-Length: 0


     /* Music Server reports success back to Bob by returning
        a 200 OK response.  Bob obtains the dialog identifiers
        from the headers included in the response. */

     F17 NOTIFY Music Server -> Bob

     NOTIFY sips:bob@client.biloxi.example.com SIP/2.0
     Via: SIP/2.0/TLS server.example.com:5061
      ;branch=z9hG4bK74bf9
     To: Bob <sips:bob@biloxi.example.com>;tag=02134
     Max-Forwards: 70
     From: Music Server <sips:music@server.example.com>;tag=56323
     Call-ID: 4802029847@biloxi.example.com
     CSeq: 2 NOTIFY
     Event: refer
     Subscription-State: terminated;reason=noresource
     Contact: <sips:music@server.example.com>
     Content-Type: message/sipfrag
     Content-Length: ...

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS server.example.com:5061
      ;branch=z9hG4bK74rf
      ;received=192.0.2.103
     From: <sips:music@server.example.com>;tag=0111
     To: <sips:a8342043f@atlanta.example.com;gr>;tag=098594
     Call-ID: a5-75-34-12-76@server.example.com
     CSeq: 1 INVITE
     Contact: <sips:a8342043f@atlanta.example.com;gr>

Top      Up      ToC       Page 47 
     F18 200 OK Bob -> Music Server

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS server.example.com:5061
      ;branch=z9hG4bK74bf9
      ;received=192.0.2.103
     To: Bob <sips:bob@biloxi.example.com>;tag=02134
     From: Music Server <sips:music@server.example.com>;tag=56323
     Call-ID: 4802029847@biloxi.example.com
     CSeq: 2 NOTIFY
     Content-Length: 0


     /* Alice is now parked at the Music Server. */

     /* Bob picks up the call by sending an INVITE to Alice, who
        replaces the existing session with the Music Server. */

     F19 INVITE Bob -> Alice

     INVITE sips:a8342043f@atlanta.example.com;gr SIP/2.0
     Via: SIP/2.0/TLS client.biloxi.example.com:5061
      ;branch=z9hG4bK74bf9
     From: Bob <sips:bob@biloxi.example.com>;tag=4i323pr
     To: Alice <sips:a8342043f@atlanta.example.com;gr>
     Call-ID: uioewrjk2k2were
     CSeq: 42121 INVITE
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER,
      SUBSCRIBE, NOTIFY
     Replaces: a5-75-34-12-76@server.example.com
      ;to-tag=098594;from-tag=0111
     Contact: <sips:bob@client.biloxi.example.com>
     Supported: replaces
     Content-Type: application/sdp
     Content-Length: ...

     v=0
     o=bob 2890844631 2890844631 IN IP4 client.biloxi.example.com
     s=
     c=IN IP4 client.biloxi.example.com
     t=0 0
     m=audio 3458 RTP/AVP 0
     a=rtpmap:0 PCMU/8000
     a=sendrecv

Top      Up      ToC       Page 48 
     F20 200 OK Alice -> Bob

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS client.biloxi.example.com:5061
      ;branch=z9hG4bK74bf9
      ;received=192.0.2.105
     From: Bob <sips:bob@biloxi.example.com>;tag=4i323pr
     To: Alice <sips:a8342043f@atlanta.example.com;gr>;tag=6654323
     Call-ID: uioewrjk2k2were
     CSeq: 42121 INVITE
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER,
      SUBSCRIBE, NOTIFY
     Contact: <sips:alice@client.atlanta.example.com>
     Supported: replaces
     Content-Type: application/sdp
     Content-Length: ...

     v=0
     o=alice 2890844576 2890844576 IN IP4 client.atlanta.example.com
     s=
     c=IN IP4 client.atlanta.example.com
     t=0 0
     m=audio 49170 RTP/AVP 0
     a=rtpmap:0 PCMU/8000
     a=sendrecv


     F21 200 ACK Bob -> Alice

     ACK sips:alice@client.atlanta.example.com SIP/2.0
     Via: SIP/2.0/TLS client.biloxi.example.com:5061
      ;branch=z9hG4bKj974bf9
     From: Bob <sips:bob@biloxi.example.com>;tag=4i323pr
     To: Alice <sips:a8342043f@atlanta.example.com;gr>;tag=6654323
     Call-ID: uioewrjk2k2were
     CSeq: 42121 ACK
     Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER,
      SUBSCRIBE, NOTIFY
     Supported: replaces
     Content-Length: 0


     F22 BYE Alice -> Music Server

     BYE sips:music@server.example.com SIP/2.0
     Max-Forwards: 70
     Via: SIP/2.0/TLS client.atlanta.example.com:5061
      ;branch=z9hG4bK74rf

Top      Up      ToC       Page 49 
     To: <sips:music@server.example.com>;tag=0111
     From: <sips:a8342043f@atlanta.example.com;gr>;tag=098594
     Call-ID: a5-75-34-12-76@server.example.com
     CSeq: 15 BYE
     Content-Length: 0


     F23 200 OK Music Server -> Alice

     SIP/2.0 200 OK
     Via: SIP/2.0/TLS client.atlanta.example.com:5061
      ;branch=z9hG4bK74rf
      ;received=192.0.2.103
     To: <sips:music@server.example.com>;tag=0111
     From: <sips:a8342043f@atlanta.example.com;gr>;tag=098594
     Call-ID: a5-75-34-12-76@server.example.com
     CSeq: 15 BYE
     Content-Length: 0


     /* Normal media session between Alice and Bob is resumed. */

Top      Up      ToC       Page 50 
2.4.  Transfer - Unattended


          Alice                 Bob                 Carol
            |      INVITE F1     |                    |
            |<-------------------|                    |
            |   180 Ringing F2   |                    |
            |------------------->|                    |
            |      200 OK F3     |                    |
            |------------------->|                    |
            |        ACK F4      |                    |
            |<-------------------|                    |
            |        RTP         |                    |
            |<==================>|                    |
            |                    |                    |
            |  Alice performs unattended transfer     |
            |                    |                    |
            | REFER Refer-To:C F5|                    |
            |------------------->|                    |
            |  202 Accepted F6   |                    |
            |<-------------------|                    |
            |      NOTIFY F7     |                    |
            |<-------------------|                    |
            |      200 OK F8     |                    |
            |------------------->|                    |
            |       BYE F9       |                    |
            |------------------->|                    |
            |     200 OK F10     |                    |
            |<-------------------|                    |
            |   No RTP Session   | INVITE Referred-By: A F11
            |                    |------------------->|
            |                    |   180 Ringing F12  |
            |                    |<-------------------|
            |                    |     200 OK F13     |
            |                    |<-------------------|
            |                    |       ACK F14      |
            |                    |------------------->|
            |                    |        RTP         |
            |                    |<==================>|
            |      NOTIFY F15    |                    |
            |<-------------------|                    |
            |      200 OK F16    |                    |
            |------------------->|                    |
            |                    |                    |

Top      Up      ToC       Page 51 
   In this scenario, Bob calls Alice.  Alice then transfers Bob to
   Carol, then Alice disconnects with Bob.  Bob establishes the session
   to Carol then reports the success back to Alice in the NOTIFY in F15.
   If the transfer fails, Bob can send a new INVITE back to Alice to re-
   establish the session.

   Despite the BYE sent by Alice in F9, the dialog between Alice and Bob
   still exists until the subscription created by the REFER has
   terminated (either due to a NOTIFY containing a Subscription-State:
   terminated;reason=noresource header field, as in F15, or a 481
   response to a NOTIFY).

   For more about call transfer, see the transfer document [TRANSFER].

   Message Details

      F1 INVITE Bob -> Alice

      INVITE sips:alice@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

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


      F2 180 Ringing Alice -> Bob

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159

Top      Up      ToC       Page 52 
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Length: 0


      F3 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds7
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F4 ACK Bob -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds2
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /* Session is established between Alice and Bob. */

Top      Up      ToC       Page 53 
      /* Alice performs unattended transfer of Bob to Carol. */


      F5 REFER Alice -> Bob

      REFER sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds8
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 101 REFER
      Refer-To: <sips:carol@chicago.example.com>
      Referred-By: <alice@atlanta.example.com>
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Length: 0


      F6 202 Accepted Bob -> Alice

      SIP/2.0 202 Accepted
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds8
       ;received=192.0.2.105
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      Contact: <sips:bob@client.biloxi.example.com>
      CSeq: 101 REFER
      Content-Length: 0


      F7 NOTIFY Bob -> Alice

      NOTIFY sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds32
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 NOTIFY
      Event: refer
      Subscription-State: active;expires=60
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Type: message/sipfrag
      Content-Length: ...

Top      Up      ToC       Page 54 
      SIP/2.0 100 Trying


      F8 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds32
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 NOTIFY
      Content-Length: 0


      /* Alice now disconnects with Bob. */


      F9 BYE Alice -> Bob

      BYE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds43
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 102 BYE
      Content-Length: 0


      F10 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds43
       ;received=192.0.2.105
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 102 BYE
      Content-Length: 0

      /* Bob attempts the transfer to Carol. */

Top      Up      ToC       Page 55 
      F11 INVITE Bob -> Carol

      INVITE sips:carol@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds1
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Referred-By: <alice@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844539 2890844539 IN IP4 client.biloxi.example.com
      s=
      c=IN IP4 client.biloxi.example.com
      t=0 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F12 180 Ringing Carol -> Bob

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds1
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Content-Length: 0


      F13 200 OK Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds1
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287

Top      Up      ToC       Page 56 
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890944542 2890844542 IN IP4 client.chicago.example.com
      s=
      c=IN IP4 client.chicago.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F14 ACK Bob -> Carol

      ACK sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds9
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /* Bob and Carol now have established a session.  Bob reports
         success to Alice, which Alice probably ignores. */


      F15 NOTIFY Bob -> Alice

      NOTIFY sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds67
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 3 NOTIFY
      Event: refer
      Subscription-State: terminated;reason=noresource
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Type: message/sipfrag

Top      Up      ToC       Page 57 
      Content-Length: ...

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds1
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Content-Type: application/sdp
      Content-Length: ...


      F16 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061
       ;branch=z9hG4bKnashds6
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 3 NOTIFY
      Content-Length: 0


Next RFC Part