Managing software failures and capacity assignment to control interval availability in PONs

Dependability in Time Division Multiplexed Passive Optical Networks (TDM PONs) is becoming crucial as end-users not only expect access networks to provide high bandwidth, but also to be dependable. While hardware failures in steady state assumptions have been extensively studied, little can be found regarding software failures in literature. Hence, it is the aim of this paper to study software failures in TDM PONs, as well as how to manage the PON available capacity to gain control over the interval availability of a client. Based on empirical data, failures of the Optical Line Terminal (OLT) software in TDM PONs are characterized, including their impact on PONs available capacity. Then, a fault-tolerance mechanism, protecting against both OLT hardware and software failures, is proposed, as well as a dependability-aware capacity assignment scheme. Both mechanisms are analyzed by means of Markov models, solved through simulations. These mechanisms not only improve the interval availability of PON clients with respect to an unprotected case, but also reduce its variability. Besides, the capacity assignment scheme reveals to be self-regulating, and can be used either as a fairness method regarding dependability, or to implement differentiated dependability in PONs by efficiently using the PON available capacity.