Designing and Expanding the Network 2 -17
10BASE-FB Module Configurations
The theoretical maximum diameter of an all fiber Ethernet network is
limited to 4.2 km as defined by th e 51.2 µsec slottime that is specified for
the round trip delay budget set by the IEEE 802.3 CSMA/CD p rotocol.
(Thus, point-to-point link distance s are limited to a maximum of 4.2 km.)
This section describes how to de fine total network size based on the limits
of IEEE 802.3 collision detection.
This section describes the following scenarios:
❑Fiber Backbone, Fiber-to-the-Desk
❑Fiber Backbone, Unshielded Twiste d Pair-to-the-Desk
❑Fiber Backbone, Coaxial Connection

Fiber Backbone, Fiber-to-the-Desk

When designing an all-fiber network (Fi gure2-5), keep the following rules
in mind:
1. Limit the longest path from one fiber optic transcei ve r to another to
4.2 km (2.6 miles).
2. Each 10BASE-FB Module in a serial path between two transceivers
reduces the maximum cable distance between the tra nsceivers by
190 meters (623 feet). The equivalence is:
❑140 meters for signals that externally enter a 10BASE-FB Module
port
❑50 meters for signals that internally enter a 10BASE-FB Module
from the concentrator backplane
For simplicity, use 190 meters per 10BASE-F B Module in the path when
calculating fiber equivalent distances.