Section: 7.7.8 Semantically incorrect Information Element
Content: Apart from Echo Request message, the receiver of a GTP signalling message Request including a mandatory or a verifiable conditional information element with a semantically invalid Value shall discard the request, should log the error, and shall send a response with Cause set to "Mandatory IE incorrect" together with a type and instance of the offending IE. The receiver of a GTP signalling message Response including a mandatory or a verifiable conditional information element with a semantically invalid Value shall notify the upper layer that a message with this sequence number has been received and should log the error. If a GTP entity receives an information element with a value which is shown as reserved, it shall treat that information element as invalid and should log the error. If the invalid IE is received in a Request, and it is a mandatory IE or a verifiable conditional IE, the GTP entity shall send a response with Cause set to "Mandatory IE incorrect " together with a type and instance of the offending IE. The principle is: the use of reserved values invokes error handling; the use of spare values can be silently discarded and so in the case of IEs with spare values used, processing shall be continued ignoring the spare values. The receiver of a GTP signalling message including an optional information element with a Value that is not in the range defined for this information element value shall discard this IE, but shall treat the rest of the message as if this IE was absent and continue processing. The receiver shall not check the content of an information element field that is defined as 'spare". All semantically incorrect optional information elements in a GTP signalling message shall be treated as not present in the message.