USER EQUIPMENT IN IMS SERVICE NETWORK WITH SHORTENED PTT CALL SETUP TIME AND IMS SERVICE NETWORK AND METHOD FOR SETUP OF PTT CALL IN THE SAME

摘要

A User Equipment (UE) in an Internet Protocol Multimedia Subsystem (IMS) service network with a shortened Push-To-Talk (PTT) call setup time, an ISM service network, and a PTT call setup method therein are provided. In the UT, a transmitter requests from a Domain Name Server (DNS) an address of a Push-to-talk over Cellular (PoC) server. A receiver receives the address of the PoC server from the DNS. A controller directly provides a PTT call to the PoC server using the address. In the IMS service network, the PoC server directly receives the PTT call from an originating subscriber and delivers the PTT call to a destination subscriber. A Serving Call Session Control Function (S-CSCF) entity provides information about the destination subscriber to the PoC server. A home subscriber server stores subscriber addresses and provides the information about the destination subscriber. The DNS provides the address of the PoC server to the originating subscriber.