6 GTP-U Message Formats
29.2813GPPGeneral Packet Radio System (GPRS) Tunnelling Protocol User Plane (GTPv1-U)Release 17TS
6.1 General
GTP-U defines a set of messages between the two ends of the user plane of the interfaces Iu, Gn, Gp, S1-U, S11-U, S2a, S2b, S4, S5, S8, S12, X2, M1, Sn, Xn, N3, N9 and N19.
GTP-U messages are sent across a GTP user plane tunnel. A GTP-U message may be either a signalling message across the user plane tunnel, or a G-PDU message.
– GTP-U signalling messages are used for user plane path management, or for user plane tunnel management.
– G-PDU is a vanilla user plane message, which carries the original packet (T-PDU). In G-PDU message, GTP-U header is followed by a T-PDU.
A T-PDU is an original packet, for example an IP datagram, Ethernet frame or unstructured PDU Data, from an UE, or from a network node in an external packet data network.
The complete range of message types defined for GTPv1 is defined in 3GPP TS 29.060 [6]. The table below includes those applicable to GTP user plane. The three columns to the right define which of the three protocols sharing the common header of GTPv1 (GTP-C, GTP-U or GTP’) might implement the specific message type.
Table 6.1-1: Messages in GTP-U
|
Message Type value (Decimal) |
Message |
Reference |
GTP-C |
GTP-U |
GTP’ |
|---|---|---|---|---|---|
|
1 |
Echo Request |
X |
X |
x |
|
|
2 |
Echo Response |
X |
X |
x |
|
|
3-25 |
Reserved in 3GPP TS 32.295 [8] and 3GPP TS 29.060 [6] |
||||
|
26 |
Error Indication |
X |
|||
|
27-30 |
Reserved in 3GPP TS 29.060 [6] |
||||
|
31 |
Supported Extension Headers Notification |
X |
X |
||
|
32-252 |
Reserved in 3GPP TS 29.060 [6] |
||||
|
253 |
Tunnel Status |
X |
|||
|
254 |
End Marker |
X |
|||
|
255 |
G-PDU |
X |
6.2 Presence requirements of Information Elements
As specified in 3GPP TS 29.060 [6], clause 7.1.1.