N9 Reference Point

Also known as: N9 Reference Point

N9 is the 3GPP 5G reference point between two UPFs, defined in TS 23.501. It is used for inter-UPF traffic in home-routed roaming (V-UPF to H-UPF), for UPF chaining in complex SMF-managed session paths and for uplink classifier / branching-point deployments. N9 carries GTP-U and is a documented attack surface for inter-operator user-plane manipulation.

Categories: Core NetworkSignalingRoaming and Interconnect

N9 in context

The mobile core carries subscriber sessions, mobility and policy. In 4G it is the EPC (MME, HSS, S/PGW); in 5G it is the Service-Based Architecture with AMF, SMF, UPF, AUSF, UDM and the NRF.

Signaling protocols carry the control-plane messages that set up calls, register subscribers and route SMS. SS7, Diameter, GTP-C and SIP are the four dominant families, and interconnect exposure of any of them is treated by GSMA as top-tier telecom risk.

To place N9 in the wider telecom-security picture, review GTP, IPUPS, GTP-C, GTP Firewall, GTP-U Smuggling and NGAP: each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

Related topic hubs

  • 5G Security 5G SBA, SEPP, SUCI, 5G-AKA, N32 and service-based interface security.
  • GTP Security GTP-C/GTP-U threats across S5/S8, N3/N9 and GRX/IPX borders under GSMA FS.20.
  • GTP Firewall GSMA FS.20 GTP-C/GTP-U screening on GRX/IPX borders.
  • Signaling Firewall Unified SS7/Diameter/GTP/SMS signaling firewall framework.

More from the TelcoSec Glossary

Browse the full TelcoSec Glossary, the Ultimate Guide to Mobile Network Security, or the P1 Arsenal of telecom-security tools.