Section: 7.7.5 Unexpected GTP Message
Content: If a GTP entity receives an unexpected initial message (see clause 4.2 "Protocol stack"), for example a known message that is sent over an interface for which the message is not defined, or a message that is sent over an interface for which the message is defined, but the direction is incorrect, then the GTP entity shall silently discard the message and shall log an error. If a GTP entity receives an unexpected triggered message which is not a request message (see clause 4.2 "Protocol stack"), for example a message for which there is no corresponding outstanding request, it shall discard the message and may log an error. When a GTP entity receives an unexpected triggered message, which is a request message, triggered by a command message, i.e. the MSB of the sequence number is set "1", e.g. in Create/Update/Delete Bearer Request messages, the GTP entity may continue to handle the request, e.g. to accept the Delete Bearer Request message. NOTE: Whether to accept or reject such a message is implementation specific.