OSS/BSS: from the customer's order to the configuration on the device and back to the invoice
Every mechanism has a step-by-step animation, the configuration explained line by line and the exam notes. Where a parameter changes the outcome, you get a simulator in which you change it yourself.
TL;DR
BSS are the systems the operator uses to talk to the customer: product catalog, CRM, orders, charging and billing. OSS are the ones it uses to talk to the network: inventory, activation, alarms, performance. An order isn't executed, it's decomposed — product → CFS → RFS → resources (SID) — and the state climbs back up the same ladder; TM Forum standardized the processes (eTOM), the data (SID) and the APIs (TMF620, 622, 641, 640, 642, 628, 678). At the bottom, the orchestrator (NSO) writes the configuration to the devices over NETCONF, in a transaction with rollback; alarms and telemetry come back up, are correlated through the inventory and become tickets, KQIs and SLA credits; usage (RADIUS, IPFIX, CDR) becomes an invoice, online or offline. Most incidents come from an inventory that lies, from orders stuck without an alert and from point-to-point integrations.
How to read the notes: red = critical for the exam, green = theory, blue = numbers, yellow = pitfalls, cyan = differences between platforms, standards and products. In the animations, the configuration lines used in the current step are highlighted automatically; the ← → arrows change the step when the animation is selected.
The analogy, in short
Think of a big restaurant: the dining room is BSS (the menu, the waiter, the bill), the kitchen is OSS (the pantry, the head chef, the stations), and the counter between them, with standardized tickets, is the TM Forum API layer. The “tasting menu” order comes apart into courses, preparations and ingredients; the smoke detector goes off once, the timers ten times; at the end, the waiter writes down what was consumed and the till applies the prices.
The model holds up to §10. From §11 onwards (asynchronous events, the closed loop, 5G slices) it breaks down; see the full analogy and its limits in §15.