User equipment, telecommunications system and message recovery method

A message recovery method used in a user equipment, wherein the user equipment supports messages of both the circuit switched (CS) domain and the packet switched (PS) domain in a wireless telecommunications system, comprising:

• receiving a Non-Access stratum (NAS) message comprising a domain identifier and a protocol discriminator while performing a call setup procedure;
• determining whether the domain identifier and the protocol discriminator are of the same domain;
• if the domain identifier and the protocol discriminator are of the same domain, proceeding with processes corresponding to the NAS message;
• if the domain identifier and the protocol discriminator indicate different domains, assessing the NAS message as an error message, and modifying the domain identifier of the NAS message to generate a recovered NAS message.

A user equipment, wherein the user equipment supports messages of both a circuit switched (CS) domain and a packet switched (PS) domain in a wireless telecommunications system, comprising:

• a first means for receiving a Non-Access stratum (NAS) message comprising a domain identifier and a protocol discriminator while performing a call setup procedure;
• a second means for determining whether the domain identifier and the protocol discriminator are of the same domain;
• a third means for proceeding with processes corresponding to the NAS message if the domain identifier and the protocol discriminator are of the same domain;
• a fourth means for assessing the NAS message as an error message, and modifying the domain identifier of the NAS message to generate a recovered NAS message, if the domain identifier and the protocol discriminator indicate different domains.