Wire the O-RAN
into your head.
The chapter where the disaggregated RAN stops being a buzzword. Four radio nodes, two intelligent controllers, one cloud — and every seam between them standardized. Built verbatim from O-RAN.WG1.TS.OAD-R005-v17.00: every node you see below is clickable, every flow animates, every claim carries its clause.
The O-RAN architecture — every node, every interface, one story
The player screen is a live animation stage — nodes assemble, interfaces draw themselves and control loops spin exactly as the narration reaches them. Karaoke subtitles in English + Persian, four subtitle modes, fullscreen.
The full O-RAN logical architecture — click every node & every interface
Placed verbatim from O-RAN.WG1.TS.OAD-R005-v17.00. Hover a node to trace what it connects to · click a node or an edge for its spec-verbatim card · filter a plane · or play an end-to-end flow.
The three control loops — why timing defines the architecture
Loops are named by their controlling entity. The stability law: an outer loop must run significantly slower than the inner loop it steers — so O-RAN's split into SMO / Near-RT RIC / E2 Node is really a split by timescale. Pick a loop to trace it on the wire.
"Typical execution time for use cases involving the Non-RT control loops is 1 second or more; Near-RT control loops are in the order of 10 milliseconds or more; control loops in the E2 Nodes can operate below 10 milliseconds (e.g., O-DU radio scheduling)." … "a stable solution would require the loop time in the Non-RT RIC and/or SMO management plane processes to be significantly longer than the loop time for the same use case in the Near-RT and RT control loops."
Every seam, its job, its spec
Learn these and you can read any O-RAN diagram ever drawn. Definitions per OAD §3.1 / §5.1.
| Interface | Connects | Carries | Owner spec |
|---|---|---|---|
| Open FH CUS | O-DU ↔ O-RU | C-plane sections, U-plane IQ, S-plane timing over eCPRI — the 7.2x split | WG4 CUS.0 v21.00 → Ch 2–5, 7 |
| Open FH M | O-DU ↔ O-RU (+SMO in hybrid) | NETCONF/YANG O-RU management — "generally driven from the O-DU but in the hybrid topology also driven from the SMO" (OAD §3.1) | WG4 MP.0 v21.01 → Ch 6 |
| F1-c / F1-u | O-DU ↔ O-CU-CP / O-CU-UP | F1AP (UE context, setup) / GTP-U — the midhaul | 3GPP TS 38.470–475 |
| E1 | O-CU-CP ↔ O-CU-UP | E1AP bearer-context management | 3GPP TS 37.483 |
| E2 | Near-RT RIC ↔ E2 Nodes | E2AP subscriptions, indications, control — service models KPM & RC | WG3 E2SM-KPM v08 · E2SM-RC v10 → Ch 8 |
| A1 | Non-RT RIC ↔ Near-RT RIC | Policies, enrichment info, ML model management | WG2 A1TD v12 → Ch 8 |
| O1 | SMO ↔ all NFs except O-RU | FCAPS — "All O-RAN NFs, except O-RU, are managed via the O1 interface" (OAD §5.1) | WG10 OAM / IM-DM → Ch 6 |
| O2 | SMO ↔ O-Cloud | Infrastructure + deployment lifecycle (IMS/DMS) | WG6 O2-IMS v12 → Ch 10 |
| R1 | rApps ↔ Non-RT RIC framework | Service-based R1 services | WG2 R1GAP v14 → Ch 8 |
| Y1 | Near-RT RIC → Y1 consumers | RAN analytics exposure | WG3 Y1GAP v01 → Ch 8 |
| D2 | O-DU ↔ peer O-DU | D2-c/D2-u — inter-O-DU carrier aggregation | WG5 D2AP v02 |
| Uu / NG / Xn | UE↔RAN / RAN↔5GC / gNB↔gNB | Unchanged 3GPP — O-RAN extends, never replaces | 3GPP TS 38.300 / 38.41x |
O-CU-CP: "logical node hosting the RRC and the control plane part of the PDCP protocol" · O-CU-UP: "logical node hosting the user plane part of the PDCP protocol and the SDAP protocol" · O-DU: "logical node hosting RLC/MAC/High-PHY layers based on a lower layer functional split" · O-RU: "logical node hosting Low-PHY layer and RF processing based on a lower layer functional split" — four lines, whole stack.
The O-RAN ALLIANCE working groups — who owns which seam
Every interface and node in the map above is standardized by exactly one working group. Grouped by the part of the architecture they own — pick a WG for its mandate, the specs it writes, and where this course covers it. WG4 writes the Open Fronthaul — the spine of this course.
🛠 Engineer detail block — what you'll actually meet in the field
- Hierarchical vs hybrid M-plane decides your whole management design (OAD §5.1). Get it wrong and NETCONF sessions fight each other. Full treatment in Chapter 6.
- "All O-RAN NFs, except O-RU, are managed via O1" (OAD §5.1) — the O-RU is the odd one out: Open FH M-plane, not O1. Exam favourite, field favourite.
- O-RU virtualization is not supported (OAD §5.1) — the O-RU is always a physical box.
- E2 Node ≠ Near-RT RIC. E2 Nodes are O-CU-CP, O-CU-UP, O-DU, O-eNB — the things the RIC controls, each still running its own <10 ms loops.
- Control-loop stability rule (OAD §5.2): when an xApp and the O-DU scheduler fight, this is the clause to quote.