Ethernet Passive Optical Networks
Clearly addressing efficiency, performance, and implementation issues, this book provides valuable, annotated insights into all engineering-critical EPON topics.
TABLE OF CONTENTS Ethernet Passive Optical Networks
Chapter 18: Cousin-Fair Hierarchical Scheduling in EPON
In Chap. 17 we found that the EPON scheduler faces two conflicting requirements: on one hand, the algorithm should be hierarchical to be scalable; on the other hand, it should be direct to be globally fair (or cousin-fair) to all subscribers. In this chapter, we will investigate a new algorithm, called fair queuing with service envelopes (FQSE), which successfully achieves both goals: it is hierarchical (each node knows only its immediate children) and it is cousin-fair. FQSE can be generalized to various remote scheduling systems, e.g., wireless networks or coax-tree networks; however, our focus will be on its application to EPON.
18.1 Fair Queuing with Service Envelopes
FQSE is a hierarchical remote scheduling algorithm that distributes service in accordance with Eq. (17.5). The algorithm is based on a concept of a service envelope (SE). A service envelope represents the amount of service (timeslot size) given to a node as a function of some nonnegative value which we call the satisfiability parameter (SP). SP is a measure of how much the demand for bandwidth can be satisfied for a given node.
In a scheduling hierarchy, each node has its associated SE function. We distinguish the construction of a service envelope for a leaf (denoted E *) from the construction of a service envelope for a nonleaf node (denoted E).
Envelope E * is a piecewise linear function consisting of at most two segments (Fig.18.1, plots 
and 
). The first segment begins at a point...
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