N4 (N4 Reference Point)

Also known as: N4 Reference Point

N4 is the 3GPP 5G reference point between the SMF and the UPF, carrying PFCP as defined in TS 23.501 and TS 29.244. Over N4 the SMF installs forwarding, QoS and usage-reporting rules into the UPF that control every user-plane packet. Exposure of N4 is a critical intra-operator attack surface: it can be abused to redirect traffic, drop lawful intercept or exfiltrate session context.

Categories: Core NetworkThreats and AttacksProtocols and Standards

N4 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.

Telecom threats range from opportunistic SMS phishing and SIM swap to nation-state grade location tracking. The common thread is that most attacks exploit the inherited trust model of legacy signaling protocols.

To place N4 in the wider telecom-security picture, review AES, AMPS, Attack Surface Mapping, Backhaul, BGP and BTS — each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

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