音乐保持

In this scenario:
 
 
  – Alice calls Bob: (1) to (4) 
 
  – Bob, acting as a 3pcc – third party call controller – places Alice on hold with music: 
 
 
  – Bob INVITEs a Music Server, without an SDP offer: (5) 
 
  – The Music Server replies with an SDP offer: (6) 
 
  – Bob takes the call with Alice on hold: (7) to (9) 
 
  – Bob acknowledges the Music Server with Alice's SDP answer: (10) 
 
  – The Music Server sends music to Alice 
 
 
  – Bob picks the call up from hold: 
 
 
  – Bob disconnects with the Music Server: (11) to (12) 
 
  – Bob takes the call with Alice off hold: (13) to (15)