N9 (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 FS.07, FS.19, GGSN, GTP, GTP Firewall and HLR — each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

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