NAS Messages Compliance and Invalid Protocol Data Handling
SMF complies with the following sections of the 3GPP specifications for the NAS messages compliance with invalid protocol data handling feature:
Message Too Short
SMF discards a NAS message whose size doesn't meet the minimum limit.
Following table lists the minimum limit for NAS messages that SMF receives from UE:
Number | NAS Message | Minimum Limit |
---|---|---|
1 |
PDU Session Establishment Request |
6 octets |
2 |
PDU Session Authentication Complete |
4 octets |
3 |
PDU Session Modification Request |
4 octets |
4 |
PDU Session Modification Complete |
4 octets |
5 |
PDU Session Modification Command Reject |
5 octets |
6 |
PDU Session Release Request |
4 octets |
7 |
PDU Session Release Complete |
4 octets |
Message Too Long
SMF discards a NAS message whose size doesn't meet the maximum limit.
The maximum size of a NAS message for NR that is connected to 5G Core Network is 9000 bytes.
Unknown IEs
SMF ignores unknown IEs in a NAS message.
Note | SMF handles only the IEs relevant to a specific NAS message type. SMF ignores other IEs that are unknown to the message type. |
Out of Sequence IEs
SMF ignores IEs that have incorrect sequence of mandatory IEs in a NAS message.
Repeated IEs
Sometimes SMF can receive an IE multiple times in a NAS message with no information on the repetition of IE. In such a case, SMF considers only the first occurrence of the repeated IE and ignores all the subsequent occurrences of the IE.
Syntactically Incorrect IEs
SMF ignores syntactically incorrect optional IEs in a NAS message.
Missing or Unexpected Conditional IEs
SMF ignores the received NAS message with the following conditional IE errors:
-
Missing expected conditional IE
-
Unexpected conditional IE
-
Syntactically incorrect conditional IE