6A Handling of unknown, unforeseen, and erroneous PC5 signalling protocol data

24.5873GPPProtocol aspectsRelease 16Stage 3TSVehicle-to-Everything (V2X) services in 5G System (5GS)

6A.1 General

The procedures specified in clause 6.1 apply to those messages which pass the checks described in clause 6A.

Clause 6A also specifies procedures for the handling of unknown, unforeseen, and erroneous PC5 signalling protocol data by the receiving entity. These procedures are called "error handling procedures", but in addition to providing recovery mechanisms for error situations they define a compatibility mechanism for future extensions of the PC5 signalling protocol.

Clauses 6A.1 to 6A.7 shall be applied in order of precedence.

Detailed error handling procedures in the peer UE are implementation dependent and may vary. However, when extensions of PC5 signalling protocol are developed, the peer UE are assumed to have the error handling which is indicated in this clause as mandatory ("shall") and that is indicated as strongly recommended ("should").

Also, the error handling of the peer UE is only considered as mandatory or strongly recommended when certain thresholds for errors are not reached during a dedicated connection.

For definition of semantical and syntactical errors see 3GPP TS 24.007 [26], clause 11.4.2.

6A.2 Message too short or too long

6A.2.1 Message too short

When a message is received that is too short to contain a complete message type information element, that message shall be ignored, cf. 3GPP TS 24.007 [26].

6A.2.2 Message too long

The maximum size of a PC5 signalling message is 65535 octets.

6A.3 Unknown or unforeseen message type

If the UE or the peer UE receives a PC5 signalling message with message type not defined for the PC5 signalling protocol or not implemented by the receiver, it shall ignore the PC5 signalling message.

NOTE: A message type not defined for the PC5 signalling protocol in the given direction is regarded by the receiver as a message type not defined for the PC5 signalling protocol, see 3GPP TS 24.007 [26].

If the UE receives a message not compatible with the PC5 signalling protocol state, the UE shall ignore the PC5 signalling message.

If the peer UE receives a message not compatible with the Pc5 signalling protocol state, the peer UE actions are implementation dependent.

6A.4 Non-semantical mandatory information element errors

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 unknown in the message, but encoded as "comprehension required" (see 3GPP TS 24.007 [26]); or

c) an out of sequence IE encoded as "comprehension required" (see 3GPP TS 24.007 [26]) is received,

the UE shall ignore the PC5 signalling message and the peer UE shall:

a) try to treat the message (the exact further actions are implementation dependent); or

b) ignore the message.

6A.5 Unknown and unforeseen IEs in the non-imperative message part

6A.5.1 IEIs unknown in the message

The UE shall ignore all IEs unknown in a message which are not encoded as "comprehension required" (see 3GPP TS 24.007 [26]).

The peer UE shall take the same approach.

6A.5.2 Out of sequence IEs

The UE shall ignore all out of sequence IEs in a message which are not encoded as "comprehension required" (see 3GPP TS 24.007 [26]).

The peer UE should take the same approach.

6A.5.3 Repeated IEs

If an information element with format T, TV, TLV, or TLV-E is repeated in a message in which repetition of the information element is not specified in clause 8.4, the UE shall handle only the contents of the information element appearing first and shall ignore all subsequent repetitions of the information element. When repetition of information elements is specified, the UE shall handle only the contents of specified repeated information elements. If the limit on repetition of information elements is exceeded, the UE shall handle the contents of information elements appearing first up to the limit of repetitions and shall ignore all subsequent repetitions of the information element.

The peer UE should follow the same procedures.

6A.6 Non-imperative message part errors

6A.6.1 General

This category includes:

a) syntactically incorrect optional IEs; and

b) conditional IE errors.

6A.6.2 Syntactically incorrect optional IEs

The UE shall treat all optional IEs that are syntactically incorrect in a message as not present in the message.

The peer UE shall take the same approach.

6A.6.3 Conditional IE errors

When upon receipt of a PC5 signalling message the UE diagnoses a "missing conditional IE" error or an "unexpected conditional IE" error, or when it receives a PC5 signalling message containing at least one syntactically incorrect conditional IE, the UE shall ignore the message.

When the peer UE receives a message and diagnoses a "missing conditional IE" error or an "unexpected conditional IE" error or when it receives a message containing at least one syntactically incorrect conditional IE, the peer UE shall either:

a) try to treat the message (the exact further actions are implementation dependent); or

b) ignore the message.

6A.7 Messages with semantically incorrect contents

When a message with semantically incorrect contents is received, the UE shall perform the foreseen reactions of the procedural part of clause 6.1. If, however no such reactions are specified, the UE shall ignore the message.

The peer UE should follow the same procedure.