Patent ID: 7808928

Claim:
A network system to test user terminal status, the network system comprising: at least one user terminal adapted to transmit a status message in response to a Session Initiation Protocol (SIP)-based Options message; and a soft switch adapted to: transmit the Options message; determine whether or not the status message has been received; and recognize whether or not the at least one user terminal is in a Death state based on a result of the determination, wherein the status message comprises one of a 200 OK message, a 468 Busy message, and a 481 Not Exist message, and wherein the 200 OK message comprises at least one of: a successful response message from the user terminal indicating that the user terminal is in a normal Busy state in response to the received Options message containing a Call ID being identical to that of an Invite message; and a successful response message from the user terminal indicating that the user terminal is in a normal Idle state in response to the received Options message not containing a To Tag.