Section: 7.5.1 Common procedures
Content: When on receipt of a message, - an "imperative message part" error; or - a "missing mandatory IE" error is diagnosed or when a message containing: - a syntactically incorrect mandatory IE; - an IE unknown in the message, but encoded as "comprehension required" (see 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [12]); or - an out of sequence IE encoded as "comprehension required" (see 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [12]) is received, the UE shall proceed as follows: - If the message is not one of the messages listed in clause 7.5.3, item a, b, c, or d, the UE shall return a status message (EMM STATUS or ESM STATUS depending on the PD) with cause #96 "invalid mandatory information"; and the network shall proceed as follows: - If the message is not one of the messages listed in clause 7.5.3, item e, f, g or h, the network shall either: - try to treat the message (the exact further actions are implementation dependent); or - ignore the message except that it should return a status message (EMM STATUS or ESM STATUS depending on the PD) with cause #96 "invalid mandatory information".