Interface Dictionary (Interface / Reference Point)¶
A dictionary for looking up 5GC reference points by the two points they connect, the Protocol used, the Transport, and the purpose.
Related: NF Dictionary / Protocol Dictionary / Registration chapter
Interface List¶
| Interface | Connection Points | Protocol | Transport | Main Purpose | Individual Page | Spec |
|---|---|---|---|---|---|---|
| N1 | UE ⇔ AMF | NAS (5GMM / 5GSM) | Relayed over N2 | NAS signaling such as registration and session requests | N1 | TS 24.501 |
| N2 | (R)AN ⇔ AMF | NGAP | SCTP | Control between RAN and core (NG Setup, UE-associated signalling) | N2 | TS 38.413 |
| N3 | gNB ⇔ UPF | GTP-U | UDP | User plane packet forwarding | N3 | TS 29.281 / TS 23.501 |
| N4 | SMF ⇔ UPF | PFCP | UDP | Session control (setting UPF forwarding rules) | N4 | TS 29.244 |
| N6 | UPF ⇔ DN | IP (tunnel not specified) | — | Connection to the data network | N6 | TS 23.501 |
| N7 | SMF ⇔ PCF | SBI (HTTP/2 / TLS) | TCP | Session policy control (Npcf_SMPolicyControl, PCC rule retrieval) | N7 | TS 29.512 (to be confirmed: clause number) |
| N8 | AMF ⇔ UDM | SBI (HTTP/2 / TLS) | TCP | Subscriber data and registration management | N8 | TS 29.503 (to be confirmed: clause number) |
| N10 | SMF ⇔ UDM | SBI (HTTP/2 / TLS) | TCP | Session subscription information retrieval | N10 | TS 29.503 (to be confirmed: clause number) |
| N11 | AMF ⇔ SMF | SBI (HTTP/2 / TLS) | TCP | PDU session control coordination | N11 | TS 29.502 (to be confirmed: clause number) |
| N12 | AMF ⇔ AUSF | SBI (HTTP/2 / TLS) | TCP | Authentication (UE Authentication) | N12 | TS 29.509 (to be confirmed: clause number) |
| N13 | AUSF ⇔ UDM | SBI (HTTP/2 / TLS) | TCP | Authentication vector retrieval | N13 | TS 29.503 (to be confirmed: clause number) |
| N5 | AF ⇔ PCF | SBI (HTTP/2 / TLS) | TCP | Policy authorization of application requests (Npcf_PolicyAuthorization) | N5 | TS 29.514 (to be confirmed: clause number) |
| N9 | UPF ⇔ UPF | GTP-U | UDP | Inter-UPF user plane forwarding (between I-UPF/PSA, etc.) | N9 | TS 29.281 / TS 23.501 |
| N15 | AMF ⇔ PCF | SBI (HTTP/2 / TLS) | TCP | Access & mobility policy control (Npcf_AMPolicyControl) | N15 | TS 29.507 (to be confirmed: clause number) |
| N22 | AMF ⇔ NSSF | SBI (HTTP/2 / TLS) | TCP | Network slice selection (Nnssf_NSSelection) | N22 | TS 29.531 (to be confirmed: clause number) |
| N32 | SEPP ⇔ SEPP (inter-PLMN) | N32-c / N32-f (HTTP/2 / TLS, PRINS) | TCP | Protected relay of inter-PLMN SBI and topology hiding | N32 | TS 29.573 (to be confirmed: clause number) |
| N33 | NEF ⇔ AF | SBI (HTTP/2 / TLS) | TCP | Capability exposure (Nnef, Northbound API) | N33 | TS 29.522 (to be confirmed: clause number) |
| N14 | AMF ⇔ AMF | SBI (HTTP/2 / TLS) | TCP | Inter-AMF UE context transfer (Namf_Communication) | N14 | TS 29.518 (to be confirmed: clause number) |
| N20 | AMF ⇔ SMSF | SBI (HTTP/2 / TLS) | TCP | Invocation and delivery of SMS over NAS (Nsmsf_SMService) | N20 | TS 29.540 (to be confirmed: clause number) |
| N21 | SMSF ⇔ UDM | SBI (HTTP/2 / TLS) | TCP | SMS subscription data retrieval and SMSF registration (Nudm) | N21 | TS 29.503 (to be confirmed: clause number) |
| N35 | UDM ⇔ UDR | SBI (HTTP/2 / TLS) | TCP | Persistent access to subscription data (Nudr_DataRepository) | N35 | TS 29.504 / TS 29.505 (to be confirmed: clause number) |
| N36 | PCF ⇔ UDR | SBI (HTTP/2 / TLS) | TCP | Persistent access to policy data (Nudr_DataRepository) | N36 | TS 29.504 / TS 29.519 (to be confirmed: clause number) |
| N37 | NEF ⇔ UDR | SBI (HTTP/2 / TLS) | TCP | Storage access to structured data (Nudr_DataRepository) | N37 | TS 29.504 (to be confirmed: clause number) |
| N40 | SMF ⇔ CHF | SBI (HTTP/2 / TLS) | TCP | Converged charging (Nchf_ConvergedCharging) | N40 | TS 32.290 / TS 32.291 (to be confirmed: clause number) |
| N26 | AMF ⇔ MME (4G/5G) | GTPv2-C (GTP-C) | UDP | Mobility context transfer between 4G/5G (Interworking) | N26 | TS 23.501 / TS 23.502 / TS 29.274 (to be confirmed: clause number) |
| Xn | gNB ⇔ gNB (inter-RAN) | Xn-C: XnAP / Xn-U: GTP-U | SCTP / UDP | Inter-base-station HO coordination, UE context transfer, data forwarding | Xn | TS 38.420 / TS 38.423 (to be confirmed: clause number) |
About SBI
N7/N8/N10/N11/N12/N13/N5/N15/N22/N33/N14/N20/N21/N35/N36/N37/N40 are SBI (Service Based Interface) and use HTTP/2 over TLS as the common transport. For details, refer to the Protocol Dictionary. The Spec clause numbers of each SBI API differ by Release, so "to be confirmed" is noted. N9 is GTP-U (inter-UPF user plane), and N32 is inter-PLMN interconnection between SEPPs (N32-c/N32-f, PRINS), which are positioned differently from SBI (inter-NF service invocation). Note that N35/N36/N37 are all persistent access to the Nudr_DataRepository provided by the UDR (UDM/PCF/NEF each use the UDR data storage layer); the reference point names are distinguished by the different consuming NF for the same service. Also, N26 is the 4G/5G interface between AMF⇔MME and uses EPC-series GTPv2-C, not SBI (Interworking). Xn is the inter-RAN-node interface connecting gNB⇔gNB (Xn-C: XnAP/SCTP, Xn-U: GTP-U), which is a separate category from the 5GC reference points (Nx numbers) (Handover).