Interfaces & protocols

The 3GPP interfaces dflux TinyCore puts on the wire — their protocols, endpoints, and default ports — plus the ones that stay in-process.

Overview

dflux TinyCore implements the reference points that cross a process boundary as real protocols, and collapses the ones between co-located functions into in-process calls. The table below is the wire-level surface; the in-process interfaces follow.

Interface	Protocol	Between	Default
N1	NAS	UE ↔ AMF (DMF)	carried in NGAP over N2
N2	NGAP over SCTP	gNB ↔ AMF (DMF)	`:38412`
N4	PFCP (UDP)	SMF (DMF) ↔ UPF	`:8805/udp`
N3	GTP-U (UDP)	gNB ↔ UPF	`:2152` (userspace)
N6	IP via TUN	UPF ↔ data network	userspace datapath
SBI	HTTP/2 cleartext (h2c)	DMF ↔ DPF ↔ NRF	NRF `:8080`, DMF `:8081`, DPF `:8082`

N1 — NAS

N1 is the signaling between the UE and the AMF (NAS: registration, authentication, session-request messages). It has no transport of its own — NAS messages are tunneled inside NGAP over N2 between the gNB and the AMF.

N2 — NGAP over SCTP

N2 carries control signaling between the gNB and the AMF (DMF). The DMF binds an SCTP listener on :38412 by default and speaks NGAP. This is the interface a gNB or gNB simulator connects to first.

N4 — PFCP

N4 is how the SMF (inside the DMF) controls the UPF: session establishment, modification, and deletion, plus the forwarding rules that move UE packets. It uses PFCP over UDP on :8805. The DMF runs the PFCP client; the UPF runs the PFCP listener.

N3 — GTP-U

N3 carries user-plane packets between the gNB and the UPF, encapsulated in GTP-U over UDP. In the userspace datapath the UPF binds GTP-U on :2152.

N6 — data network

N6 connects the UPF to the data network. In the userspace datapath the UPF opens a TUN interface for N6 and forwards decapsulated UE traffic out through it; the kernel-side IP and routing on that TUN are left to the operator. See User plane.

SBI — HTTP/2 cleartext

The service-based interfaces between NFs (Namf, Nsmf, Nausf, Nudm, Npcf, Nnrf) run over HTTP/2 cleartext (h2c) in the lab. The DMF, DPF, and NRF each expose an SBI endpoint and call each other over it. The NRF can optionally require OAuth2 tokens and run with TLS/mTLS — see Securing NF communication.

In-process interfaces

Function calls, not wire protocols

Because the AMF and SMF share a process (DMF), and the AUSF, UDM, UDR, and PCF share a process (DPF), the interfaces between them are plain function calls — there is no socket to connect to and no port to scan.

N11 / Namf-Nsmf — AMF ↔ SMF, inside the DMF.
N8 / N10 / N12 / N13 — AUSF ↔ UDM ↔ UDR ↔ PCF, inside the DPF (UDM and PCF read the UDR store directly).

For how these interfaces are used during an attach, see Architecture.