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:

Minimum Limit for NAS Messages
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