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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 the 51.2 µsec slottime that is specified for
the round trip delay budget set by the IEEE 802.3 CSMA/CD protocol.
(Thus, point-to-point link distances are limited to a maximum of 4.2 km.)
This section describes how to define 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 Twisted Pair-to-the-Desk
❑ Fiber Backbone, Coaxial Connection
Fiber Backbone, Fiber-to-the-Desk
When designing an all-fiber network (Figure 2-5), keep the following rules
in mind:
1. Limit the longest path from one fiber optic transceiver 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 transceivers 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-FB Module in the path when
calculating fiber equivalent distances.