Section: 7.5.1 Common procedures
Content: When on receipt of a message, a) an "imperative message part" error; or b) a "missing mandatory IE" error is diagnosed or when a message containing: a) a syntactically incorrect mandatory IE; b) an IE with an IEI unknown in the message, but encoded as "comprehension required" (see 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [11]); or c) an out of sequence IE encoded as "comprehension required" (see 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [11]) is received, the UE shall proceed as follows: If the message is not one of the messages listed in the UE procedures in subclause 7.5.3, item a), b) or c), the UE shall return a status message (5GMM STATUS or 5GSM STATUS depending on the EPD) with cause #96 "invalid mandatory information"; the network shall proceed as follows: If the message is not one of the messages listed in the network procedures in subclause 7.5.3, item a), b) or c), the network shall either: 1) try to treat the message (the exact further actions are implementation dependent); or 2) ignore the message except that it should return a status message (5GMM STATUS or 5GSM STATUS depending on the EPD) with cause #96 "invalid mandatory information".