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92    VoIP subscriber gateways 
Figure below shows 'Unattended calltransfer' service operation algorithm: 
 
’Local  calltransfer’  service  allows  you  to  transfer  call  through  a  gateway  without  sending  an  external 
REFER message if C subscriber is a local TAU client and its call was directly performed with ignoring of the proxy 
server.  If  C  subscriber  is  external  or  local  client  which  was  called  via  proxy  server,  ‘Local  calltransfer’  service 
operates like ‘Attended calltransfer’ service and call transfer is performed by sending REFER message to the B 
subscriber.  
5.2 Call Waiting 
 This service allows you to inform "busy" subscribers about new incoming calls with a special signal. 
Upon receiving this notification, user can answer or reject waiting call. 
Access to this service is established via subscriber line settings menu by selecting 'Attended calltransfer', 
'Unattended calltransfer' or 'Local calltransfer' in the 'Flash transfer' field and selecting 'Call waiting' checkbox.  
Service usage: 
If you receive a new call while being in a call state, you may do the following: 
  R 0—reject a new call.