Wireless communication system for performing combined service between terminals having different communication environments

A method by a Combined Circuit-Switched and Internet protocol Multimedia Subsystem (CSI) User Equipment (UE) for communicating over a CSI session between an Internet protocol Multimedia Subsystem (IMS) UE and the CSI UE, the method comprising:

• receiving, by the CSI UE from a CSI Application Server (AS), a first message in a Circuit-Switched (CS) domain, wherein the first message including information about IMS registration status of the IMS UE and information about radio environment capability of the IMS UE is generated by the CSI AS when the CSI AS receives a request message from the IMS UE,
• wherein capability information of the IMS UE is added to the first message by the CSI AS, and
• wherein the radio environment capability indicates whether circuit-switched and packet-switched services are simultaneously supported;
• and
• sending, by the CSI UE to the CSI AS, a second message including capability information of the CSI UE in response to the first message.

A Combined Circuit-Switched and Internet protocol Multimedia Subsystem (CSI) Application Server (AS) for supporting a CSI session between an Internet protocol Multimedia Subsystem (IMS) User Equipment (UE) and a CSI UE, the CSI AS comprising:

• a transceiver;
• and
• a processor configured to:
• generate a first message including information about IMS registration status of the IMS UE and information about radio environment capability of the IMS UE,
• wherein the radio environment capability indicates whether circuit-switched and packet-switched services are simultaneously supported,
• control the transceiver to send the first message to the CSI UE in a Circuit-Switched (CS) domain, and
• control the transceiver to send a response message to the IMS UE.

A Combined Circuit-Switched and Internet protocol Multimedia Subsystem (CSI) User Equipment (UE) for communicating over a CSI session between an Internet protocol Multimedia Subsystem (IMS) UE and the CSI UE, the CSI UE comprising:

• a transceiver;
• and
• a processor configured to:
• control the transceiver to receive, from a CSI Application Server (AS), a first message in a Circuit-Switched (CS) domain,
• wherein the first message including information about IMS registration status of the IMS UE and information about radio environment capability of the IMS UE is generated by the CSI AS when the CSI AS receives a request message from the IMS UE,
• wherein capability information of the IMS UE is added to the first message by the CSI AS, and
• wherein the radio environment capability indicates whether circuit-switched and packet-switched services are simultaneously supported, and
• control the transceiver to send, to the CSI AS, a second message including capability information of the CSI UE in response to the first message.