Section: 8.1 Information Element Types
Content: A GTP control plane (signalling) message may contain several information elements. In order to have forward compatible type definitions for the GTPv2 information elements, all of them shall be TLIV (Type, Length, Instance, Value) coded. GTPv2 information element type values are specified in the Table 8.1-1. The last column of this table indicates whether the information element is: - Fixed Length: the IE has a fixed set of fields, and a fixed number of octets. - Variable Length: the IE has a fixed set of fields, and has a variable number of octets. For example, the last octets may be numbered similar to "5 to (n+4)". In this example, if the value of the length field, n, is 0, then the last field is not present. - Extendable: the IE has a variable number of fields, and has a variable number of octets. The last fields are typically specified with the statement: "These octet(s) is/are present only if explicitly specified". The legacy receiving entity shall ignore the unknown octets. In order to improve the efficiency of troubleshooting, it is recommended that the information elements should be arranged in the signalling messages as well as in the grouped IEs, according to the order the information elements are listed in the message definition table or grouped IE definition table in clause 7. However the receiving entity shall be prepared to handle the messages with information elements in any order. Within information elements, certain fields may be described as spare. These bits shall be transmitted with the value set to 0. To allow for future features, the receiver shall not evaluate these bits. GTPv2-C information elements that have similar semantics in GTPv1-C shall be converted into GTPv1-C format, as specified in TS 29.060[ General Packet Radio Service (GPRS); GPRS Tunnelling Protocol (GTP) across the Gn and Gp interface ]  [4], before sending them to a pre-R8 GSN. Table 8.1-1: Information Element types for GTPv2