1-bit value that states whether there is a N-PDU number optional field. Message Type an 8-bit field that indicates the type of GTP message. Different types of messages are defined in 3GPP TS 29.060 section 7.1 Message Length a 16-bit field that indicates the length of the payload in bytes (rest of the packet following the mandatory 8-byte GTP header). Includes the optional fields. Tunnel endpoint identifier (TEID) A 32-bit(4-octet) field used to multiplex different connections in the same GTP tunnel. Sequence number an (optional) 16-bit field. This field exists if any of the E, S, or PN bits are on. The field must be interpreted only if the S bit is on. N-PDU number an (optional) 8-bit field. This field exists if any of the E, S, or PN bits are on. The field must be interpreted only if the PN bit is on. Next extension header type an (optional) 8-bit field. This field exists if any of the E, S, or PN bits are on. The field must be interpreted only if the E bit is on. Next Extension Headers are as follows: Extension length an 8-bit field. This field states the length of this extension header, including the length, the contents, and the next extension header field, in 4-octet units, so the length of the extension must always be a multiple of 4. Contents extension header contents. Next extension header an 8-bit field. It states the type of the next extension, or 0 if no next extension exists. This permits chaining several next extension headers. GTP version 2 It is also known as evolved-GTP or eGTP. GTPv2-C headers contain the following fields: There is no GTPv2-U protocol, GTP-U in LTE also uses GTPv1-U. Version It is a 3-bit field. For GTPv2, this has a value of 2. Piggybacking flag If this bit is set to 1 then another GTP-C message with its own header shall be present at the end of the current message. There are restrictions as to what type of message can be piggybacked depending on what the toplevel GTP-C message is. TEID flag If this bit is set to 1 then the TEID field will be present between the message length and the sequence number. All messages except Echo and Echo reply require TEID to be present. Message length This field shall indicate the length of the message in octets excluding the mandatory of