Patent ID: 8184559

Claim:
A method of receiving and answering an incoming call for a representative group in a key telephone system using a session initiation protocol (SIP), the key telephone system comprising a main unit, a plurality of SIP telephones connected to the main unit via a LAN line, and a SIP server connected to the main unit via the LAN line, at least two of the SIP telephones forming the representative group, wherein the method comprising: a first transmitting step at which the main unit transmits, upon reception of the incoming call for the representative group, a first predetermined message to all of the SIP telephones forming the representative group to perform a calling operation; a second transmitting step at which a particular one of the SIP telephones, which answers the calling operation as an answering SIP telephone, transmits a second predetermined message to the main unit to notify the main unit that the calling operation is answered; a third transmitting step at which the main unit transmits a third predetermined message to the answering SIP telephone alone without via the SIP server to establish a call session with a calling telephone; and a fourth transmitting step at which the main unit transmits a fourth predetermined message to an unanswering SIP telephone to notify that the incoming call for the representative group has been answered; wherein the first predetermined message is selected from a group consisting of a “NOTIFY” message for event notification, a “MESSAGE” message for event notification, and an “INFO” message for event notification, and wherein the third predetermined message is an “INVITE” message for requesting session establishment.