Dynamic wavelength assignment in WDM passive optical networks.
This thesis is concerned with the study of dynamic wavelength assignment in wavelength
division multiplexed (WDM) passive optical networks (PONs), which is one option for
implementing WDM in access networks.
A discrete event simulation is developed using the Block Oriented Network Simulator
(BONeS) package to compare a WDM PON using dynamic wavelength allocation with
one utilizing fixed wavelengths. The model is used in conjunction with a traffic profile
constructed using market research data to show bandwidth savings for dynamic assignment
of between 4 and 20 % depending on the number of customers and the services distributed.
It is shown that the alternative approach of using the Erlang laws underestimates these
An upstream protocol for real-time services with a Fibre To The Cabinet (FTTCab)
configuration is developed for single wavelength PONs. It is shown that using connectionbased
information does not improve the performance of such a protocol. A segment based
protocol which provides timing information on cell arrivals to reduce CDV is modelled
and optimized. The results show that a frame of 766 ps divided into 10 segments allows
the International Telecommunication Union (ITU) delay and cell delay variation (CDV)
targets to be met.
The protocol and modelling process is then extended to a WDM system with multiple
service classes and non-negligible tuning times. A mechanism for masking tuning latencies
which achieves a throughput efficiency of over 98% is designed and modeled. An
improvement in performance is then demonstrated for rapid retuning at frame level
compared with wavelength assignment at connection set-up.
Finally, a new architecture for transferring the tunable devices from the optical network
units (ONUs) to the optical line termination (OLT) is proposed. The reduction in the
number of tunable components enables cost savings. The efficient transmission of
broadcast and multicast traffic is demonstrated using this architecture.