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 12: Baseline Efficiency
EPON efficiency depends on many parameters, such as packet size distribution, configuration of the scheduler, and the speed of the laser driver and clock recovery circuits. Making unrealistic assumptions about any of these parameters can result in efficiency numbers being far off from the true value. It is, therefore, clear that to answer the question of EPON efficiency, one has to come up with a realistic and unambiguous set of EPON operational parameters and traffic characteristics. In this chapter, we attempt to identify all the parameters affecting the efficiency and to justify the chosen values for these parameters.
By network efficiency we usually mean the throughput efficiency, also called utilization. Throughput is a measure of how much user data (application-level data) the network can carry through in a unit of time. Throughput efficiency is the ratio of maximum throughput to the network bit rate.
Perhaps, the easiest way to calculate the efficiency is to find the overhead components associated with frame encapsulation, scheduling, and optional FEC.
12.1 Encapsulation Overhead
The encapsulation (framing) overhead was briefly considered in Sec. 3.2.1. This overhead is a property of all Ethernet architectures (not specific to EPONs); it is a result of adding an 8-byte frame preamble, 14-byte Ethernet header, and 4-byte FCS field to MAC service data units (m_sdu) comprised of user s data. Additionally, at least a 12-byte (96-ns) minimum interframe gap (IFG) should be left between two adjacent frames. Thus, the absolute overhead per frame is constant and equal to...
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