2426 CHAPTER 140: CALL S ERVICES CONFIGURATIONCurrently, the system supports four different types of call forwarding.■ Call forwarding unconditional: With this feature enabled on a voice subscriberline, incoming calls will be forwarded to the predetermined destination, nomatter whether the voice subscriber line is available.■ Call forwarding busy: With this feature enabled on a voice subscriber line, anincoming call will be forwarded to the predetermined destination when thevoice subscriber line is busy.■ Call forwarding no reply: With this feature enabled on a voice subscriber line,an incoming call will be forwarded to the predetermined destination when thevoice subscriber line is not answered within a period of time.■ Call forwarding unavailable: With this feature enabled on a voice subscriberline, an incoming call will be forwarded to the predetermined destination whenthe voice subscriber line is shut down.Call Transfer User A (originator) and User B (recipient) are in a conversation. User A presses theflash hook and the call is put on hold. User A dials another number to originate acall to User C (final recipient) so that the call between User B and User C isestablished.Call Backup After initiating a call to the terminating system, the originating system is unable toreceive a response. In this case, if there is another link (PSTN link or VoIP link) tothe terminating system, the originating system re-initiates a call to the terminatingsystem along the new route. This is call backup.Currently, the system supports two types of call backup:■ A PSTN link or VoIP link backs up a PSTN link■ A PSTN link backs up a VoIP linkHunt Group Multiple voice subscriber lines are configured for a called number. If the voicesubscriber line with the first priority is unavailable when the terminating systemreceives a call setup request from the originating system, the call will still beestablished between them. This is hunt group.Call Barring Call barring includes incoming call barring and outgoing call barring.Incoming call barring usually refers to the Do Not Disturb (DND) service. Whenincoming call barring is enabled on a voice subscribe line, calls originated to theattached phone will fail.When outgoing call barring is enabled on a voice subscriber line, calls originatedfrom the attached phone will fail, too.Support for FEATUREService of 3Com VoiceSystemTogether with a 3Com server, 3Com voice systems implement the application ofmultiple voice features such as Silent Monitor, Camp On, and FwdMail Toggle bymeans of the 3Com proprietary SIP FEATURE message. All these voice features arecalled FEATURE service.
