NGAP Dictionary (NGAP / N2)¶
A dictionary for looking up the key procedures and messages of NGAP (NG Application Protocol), which handles the control between (R)AN and AMF (N2). It runs over SCTP.
Related: Protocol Dictionary / Interface Dictionary (N2) / N2 page / Registration chapter
NGAP key procedures/messages¶
| Procedure/Message | Category | Direction | Purpose | Related | Spec |
|---|---|---|---|---|---|
| NG Setup Request / Response / Failure | Non-UE-associated | RAN⇔AMF | Initialization/establishment of the N2 interface (Procedure Code, etc. to be confirmed) | N2 page | TS 38.413 |
| Initial UE Message | UE-associated | RAN→AMF | Carries the UE's first NAS (Registration Request, etc.) to the core | Registration chapter | TS 38.413 |
| Downlink / Uplink NAS Transport | UE-associated | Bidirectional | Carries NAS-PDU over N2 | Protocol Dictionary | TS 38.413 |
| Initial Context Setup Request / Response | UE-associated | AMF→RAN | Setup of UE context, security, and DRB | Registration chapter | TS 38.413 |
| PDU Session Resource Setup / Modify / Release | UE-associated | AMF→RAN | Setup/modification/release of PDU session resources (DRB, etc.) | PDU Session chapter | TS 38.413 |
| UE Context Release Command / Complete | UE-associated | Bidirectional | Release of UE context (Service Request/Paging related) | Service Request chapter / Paging chapter | TS 38.413 |
| Paging | Non-UE-associated | AMF→RAN | Paging the UE on incoming | Paging chapter | TS 38.413 |
| Handover Required / Request / Command / Notify, etc. | UE-associated | Bidirectional | N2-based handover control | Handover chapter | TS 38.413 |
(Numeric values such as the Procedure Code / IE values of each procedure are to be confirmed)
NGAP's two categories and transport
NGAP procedures are broadly divided into "UE-associated (tied to a specific UE)" and "non-UE-associated (involving the whole interface, such as NG Setup / Paging)". NAS messages are carried to the AMF with NGAP (Initial UE Message / NAS Transport) as the carrier. The transport is SCTP, and the destination port 38412 is the registered value (TS 38.412).