Transport
Transport covers the optical and packet layer that connects access, core, and data center sites. The exam tests WDM/OTN architecture, Nokia 1830 Photonic Service Switch platforms, FP5-based packet transport, protection, and the mapping of client services onto wavelengths and ODU containers.
Layered transport model
Transport is built in layers: L0 photonic wavelengths, L1 OTN containers such as ODUk, and L2 packet services. A 100GbE client can be mapped into an OTN container and carried over a wavelength. Flexgrid WDM increases spectrum efficiency; CDC-F adds colorless, directionless, and contentionless add/drop. Protection must be defined per layer: optical protection, ODUk SNCP, or packet-level fast reroute. Synchronization and latency budgets are part of service design, not afterthoughts.
Rules to apply
- Choose protection at the layer that matches the failure and the required switch time.
- OTN framing adds overhead but provides strong OAM and tandem connection monitoring.
- WDM reach depends on optical margin, amplifier spacing, FEC, and fiber type; nominal reach is not guaranteed reach.
- Packet transport such as segment routing can provide service-level repair, but it does not replace optical restoration for fiber cuts.
- Client service mappings must preserve QoS and synchronization requirements.
Worked example
A 100GbE client is carried between two sites over a 400G-capable WDM line. The service is mapped into an OTN container and protected with ODUk SNCP. If the working fiber is cut, the protection path switches at the OTN layer, and the client does not need to re-signal at Layer 3. The reasoning: protection at the transport layer gives deterministic recovery for physical failures, while packet restoration handles logical or node failures.
Traps that cost marks
Quoting WDM reach without optical margin; confusing OTN protection with Ethernet ring protection; ignoring FEC and amplifier limits; and assuming packet fast reroute covers a fiber cut without an optical path.