Fixed Access
Fixed access covers how broadband subscribers are connected over PON and point-to-point topologies and how services are mapped onto Nokia access nodes. The exam tests architecture rather than product memorization: subscriber identification, VLAN handling, QoS, multicast, authentication, and the split between an access controller and the access node.
Access architecture
Nokia's fixed access portfolio includes the 7360 ISAM FX family and the Altiplano Access Controller. GPON and XGS-PON share a passive optical splitter; each ONU/ONT is identified by a serial number and managed through OMCI or TR-069 depending on the deployment model. In a software-defined access network, the controller holds intent and the access node executes it. Service architecture must define how a subscriber is authenticated, which VLAN or pseudowire carries traffic, and where QoS and multicast replication occur.
Rules to apply
- GPON downstream is broadcast and upstream is scheduled; do not model both directions as shared broadcast.
- XGS-PON provides 10 Gbps symmetric capacity, but split ratio and optical loss still constrain reach.
- A subscriber service is not automatically one VLAN; VLAN-per-subscriber and shared-VLAN models have different forwarding and security implications.
- Multicast replication belongs as close to the subscriber as possible; the access node should not carry duplicate streams across the aggregation network.
Worked example
A GPON port offers 2.488 Gbps downstream. With a 1:64 split, the average downstream rate if all 64 subscribers are active at once is about 38.9 Mbps. If only 30 percent are active concurrently, the average active rate is about 129.6 Mbps. The architecture must not sell a committed rate above what the split and upstream scheduler can guarantee. The reasoning: capacity is shared, so oversubscription must be explicit in the SLA and in the QoS plan.
Traps that cost marks
Assuming split ratio affects only bandwidth and not optical loss; mixing OMCI and TR-069 responsibilities; forgetting upstream scheduling; and treating a VLAN as a security boundary without authentication or isolation policy.