04.083GPPMobile radio interface Layer 3 specificationRelease 1998TS
10.3.1 Skip indicator
Bits 5 to 8 of the first octet of every Radio Resource management message and Mobility Management message and GPRS MobilityManagement message contains the skip indicator. A message received with skip indicator different from 0000 shall be ignored. A message received with skip indicator encoded as 0000 shall not be ignored (unless it is ignored for other reasons). A protocol entity sending a Radio Resource management message or a Mobility Management message or a GPRS Mobility Management message shall encode the skip indicator as 0000.
10.3.2 Transaction identifier
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 04.07 .