EPS ⇄ 5GS Interworking over N26
This is where the two references meet — from both ends of the wire. Part A is the Huawei EPC+ core (CloudUSN MME + CloudUGW); Part B is the Huawei 5GC SA core (UNC + UDG + UPCF + UDM). The N26 interface between the MME and the AMF, plus four combined network-element pairs, let a subscriber move seamlessly between 4G and 5G. This volume carries the CloudUSN side (WSFD-011117/110307/110308/110309) and the UNC side (WSFD-011137, EPS Fallback WSFD-102702/102703, the N26 signalling procedures and NE/NF discovery) — every feature ID, flow step, MML parameter, software-parameter impact level and counter extracted directly from the libraries. Nothing invented.
What the N26 Interface Connects
Verbatim — CloudUSN → Feature Guide → WSFD-011117 N26 interface. Definition, benefits and the application scenario, exactly as Huawei documents them.
Interworking Architecture — the N26 topology, live
The EPS and 5GS topologies fused into one. Switch the view: see the N26 signalling tunnel light up, watch the four combined NE pairs converge, or drop N26 to see what interworking without N26 looks like. Node placement, interfaces and the combined-node model are verbatim from WSFD-110307.
Interworking Principles & Network Requirements — the 5GC solution view
The UNC library's own 4G/5G Interworking Solution: how interworking signalling is processed, how PDU session establishment differs when N26 interworking must be supported, and the exact version each node — UE, eNodeB, gNodeB, MME, AMF, combined gateways — must run for the bridge to work. Verbatim.
WSFD-011117 — N26 interface
The full feature anatomy as a dossier: definition, benefits, scenarios, availability with supporting versions, application limitations, the implementation principle and 3GPP standards compliance — walk the rail, every section verbatim.
WSFD-110307 — Network Reselection Between LTE and 5G
Idle-mode (ECM-IDLE) mobility: EPS-to-5GS and 5GS-to-EPS cell reselection. Note the combined-node Overview — UDM+HSS, PCF+PCRF, SMF+PGW-C, UPF+PGW-U — and the licence control item.
WSFD-110308 — PS Handover Between LTE and 5G
Connected-mode (ECM-CONNECTED) mobility: the LTE-to-5G and 5G-to-LTE handovers that keep the data session alive across the RAT boundary — the feature that requires N26.
WSFD-110309 — VoLTE Continuity Assurance
Keeping a voice call up across the 4G/5G boundary during interworking — verbatim.
Interworking-5GS-Indicator — the subscription switch, on the wire
The Diameter AVP on S6a that tells the MME whether 5GS/EPS interworking is subscribed for an APN — watch it travel from the HSS/UDM to the MME, then read the verbatim IE description and the software parameter that controls how the CloudUSN decodes it (AVP code 1705).
WSFD-011137 — N26 Interface, seen from the AMF
The same wire, documented from the other end. The UNC library's own N26 feature: relevant NFs, definition, availability, feature interactions, system impacts, application limitations, the technical overview and standards compliance — verbatim from the UNC 25.1.0 Feature Guide.
WSFD-102702 — EPS Fallback: the biggest real-world N26 customer
When a VoNR call cannot be anchored in 5G, the network falls the UE back to LTE — over exactly the N26 handover and redirection machinery in this volume. The complete UNC feature: description, technical details, activation procedure, commissioning procedure, and the engineer references — every MML command, alarm, software parameter and measured counter Huawei lists for the feature.
WSFD-102703 — EPS Fallback Emergency Call
The emergency-call variant of EPS fallback — with its own activation, commissioning and engineer references, verbatim from the UNC Feature Guide.
Mobility Call Flows — the MME view, as message-sequence charts
The four interworking procedures as animated message-sequence charts. Pick a flow, press Play, and watch the UE move between the EPC and the 5GC across N26. Every step description is the exact sentence from Huawei's System Implementation section — nothing paraphrased.
N26 Signalling Procedures — the AMF view, step by verbatim step
The UNC library documents every N26 procedure with numbered signalling steps — handover both ways, idle-mode reselection, and the slice-selection reselection variants (AMF relocation, I-SMF / I-UPF insertion and relocation). Pick a procedure and walk it: Play steps through the exact Huawei sentences one message at a time.
NE/NF Discovery — who finds whom, before any message can flow
Every N26 procedure starts with a lookup: the AMF must find the peer MME, the MME must find the AMF, gateways and SMFs must be selected. These are the verbatim discovery mechanics — DNS and NRF queries per procedure — from the UNC Technical Implementation chapter.
Configuring & Commissioning N26 — both ends of the wire
One interface, two configurations. Left: Huawei's configuration and commissioning tasks for the N26 interface on the CloudUSN (MME). Right: the initial-configuration task for the same interface on the UNC (AMF) — including the S10/N26 same-IP rule and the GTP-C protocol stack. All verbatim.
N26 Policy MML Reference — every command, every parameter
The two managed objects that govern interworking on the CloudUSN: the local interworking policy (N26IWKPLCY) and the combined gateway selection policy (N26GWSELPLCY). Each command carries its verbatim Function, a real MML example, and every parameter with value range, default and configuration notes.
N26IWKPLCY — Local Policy for EPS/5GS Interworking
N26GWSELPLCY — N26 Combined Gateway Selection Policy
Interworking Software-Parameter Ladder — sorted by Huawei's own impact
The CloudUSN software parameters that tune EPS/5GS interworking — from the master switch for interworking without N26 to the fine control of authentication, security and indirect-forwarding tunnels on the 5GS-to-EPS path. Sorted by Huawei's Impact Level; each shows its recommended value, initial value and range. Filter by impact or phase.
The EPS ⇄ 5GS Counter Bridge — measure every crossing, per cause
The CloudUSN's two dedicated EPS and 5GS Interworking measurement units — Inter Node and Intra Node — as a live bridge board. Four lanes (handover and reselection, each direction), each carrying its request / success / per-cause failure counters: SUBDATA restrictions, licence & configuration blocks, Forward-Relocation timeouts, S-GW selection failures, handover cancels, VoLTE-restricted handovers. Click a lane to open its counters. Every name, description and measurement point is verbatim.
The 5GC Side of the Bridge — UNC interworking & EPS-fallback counters
The bridge measured from the 5G side: every UNC counter whose verbatim name concerns N26, EPS⇄5GS interworking or EPS fallback — AMF and SMF families, indexed straight from the UNC counter reference. Filter by measurement unit or search by name and ID.
Source Provenance
Where every string on this page comes from.
.hdx is a ZIP archive of
profile.xml, resources/navi.xml and per-topic HTML. Every string on this page was parsed
directly out of two libraries: CloudUSN V100R020C60SPC100 issue 04 (the MME side — features WSFD-011117 /
110307 / 110308 / 110309, the Interworking-5GS-Indicator IE, N26 configuration & commissioning tasks,
N26IWKPLCY / N26GWSELPLCY MML, the interworking software parameters, and the Inter/Intra Node EPS and 5GS
Interworking measurement units) and UNC 25.1.0 issue 02 (the AMF side — WSFD-011137, EPS Fallback
WSFD-102702 / 102703 with activation, commissioning and references, the 4G/5G Interworking Solution chapters,
the N26 signalling procedures with their numbered steps, NE/NF discovery, the AMF-side N26 configuration task,
and the 5GC-side counter index). The text here is the text in the libraries.
This page connects Part A · EPC/NSA and Part B · 5GC/SA.