Section: 10.3.2 Transaction identifier
Content: Bits 5 to 8 of the first octet of every message belonging to the protocols "Call Control; call related SS messages" and "Session Management"contain the transaction identifier (TI). The transaction identifier and its use are defined in 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [20]. For the session management protocol, the extended TI mechanism may be used (see 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [20]). For the call control protocol, the extended TI mechanism shall be supported for the purpose of protocol error handling as specified in subclause 8.3.1