Buffered Uplinks - Cabletron Systems 100BASE-FX Cabling Manual

The design and operation of these different repeater types result in different
operating characteristics and network limitations. Class I repeaters, by translating
the received signal, produce a stronger repeated transmission. The translation
process, however, takes up a number of microseconds. This additional delay
reduces the total distance a signal may travel before the allowable delay for that
transmission has elapsed. While Class II repeaters are faster, the signals they
produce are less precise, and they cannot connect to different media types.
These differences mean that, in any Fast Ethernet network, there may be a
maximum of one Class I or two Class II repeaters between any two end stations.
These implementations also result in different maximum network radii, as shown
in Table 7-1.

Buffered Uplinks

Several Fast Ethernet devices support the incorporation of buffered uplinks to
help alleviate the pressures placed on network design by the small network
radius of Fast Ethernet networks. The buffered uplink acts as a non-filtering
bridge, providing little more than retiming and regeneration of signals. In effect,
the buffered uplink provides only the distance characteristics of a bridged
connection. Fast Ethernet networks that incorporate a buffered uplink effectively
extend the maximum network radius. The multimode fiber optic buffered uplink
can be up to 400 m in length. The overall allowable network radius for Fast
Ethernet networks that incorporate buffered uplinks are also provided in
Table 7-1.
Repeater
Class
Class I 200 m
Class II 200 m
Hybrid Installations
Table 7-1. Fast Ethernet Maximum Network Radii
UTP & Fiber
UTP
Optics
260 m
N/A
Fast Ethernet Network Requirements
UTP &
Fiber Optics Buffered
Uplink
272 m 500 m
320 m N/A
Fiber Optics
and Buffered
Uplink
800 m
N/A
7-7