What is GTP-U?
GTP-U (GPRS Tunneling Protocol – User Plane) is a protocol that enables the transmission of user traffic between elements of a mobile network. It is part of the GTP family, alongside GTP-C (control) and GTP’ (charging).
Where is GTP-U used?
- LTE/4G: between eNodeB ↔ SGW ↔ PGW
- 5G (NSA): as a legacy technology within EPC
- UMTS/GPRS: for data transfer between SGSN and GGSN
GTP-U transmits IP packets inside UDP encapsulation through tunnels bound to a specific user (TEID).
How GTP-U works
Main functions:
- Encapsulation of user IP traffic in UDP (port 2152)
- Session identification via TEID
- Operation within a single tunnel between EPC elements
Packet structure:
| Field | Purpose |
|---|---|
| Version | GTP version (typically 1) |
| TEID | Tunnel Endpoint Identifier |
| Payload | User IP packet |
Advantages and limitations
Pros:
- Fast kernel-level processing
- Simple implementation
- Wide support in DPI, BNG, CGNAT
Cons:
- Does not encrypt traffic
- Vulnerable to spoofing and DDoS with poor filtering
- Requires correlation with GTP-C for session analysis
FAQ
Which port does GTP-U use?
UDP 2152.
Can DPI analyze GTP-U?
Yes, if it recognizes the TEID and decodes the encapsulated IP packets.
Is GTP-U supported in 5G?
In NSA — yes. In SA architecture, GTP may be replaced with other protocols (e.g., HTTP/2 in SBA).
Conclusion
GTP-U remains a core protocol for delivering user traffic in 3G/4G/5G networks. Its simplicity, scalability, and broad support make it a key component of mobile data transport.
