5-micron (?µ) or 50-?µ
multimode ?¬?ber; 10 km if 10-?µ singlemode
?¬?ber
1000BASE-SX Gigabit Ethernet over ?¬?ber-optic
cable
250 m if 62.5-?µ multimode ?¬?ber; 550 m
if 50-?µ multimode ?¬?ber
1000BASE-CX Gigabit Ethernet over copper cabling 25 m
Understanding the Challenges of Shared LANs 141
Extending a LAN Segment
You can add devices to an Ethernet LAN to extend segments. This topic describes how
adding repeaters or hubs can overcome the distance limitation in an Ethernet LAN.
A repeater is a physical layer device that takes a signal from a device on the network and
acts as an ampli?¬?er. Adding repeaters to a network extends the segments of the network so
that data can be communicated successfully over longer distances. There are, however,
limits on the number of repeaters that can be added to a network.
A hub, which also operates at the physical layer, is similar to a repeater. Figure 2-1 shows
two users connected to a hub, each 100 meters from the hub and effectively 200 meters from
one another.
Figure 2-1 Extending the Segment Link with a Hub
When a hub receives a transmission signal, it ampli?¬?es the signal and retransmits it. Unlike
a repeater, however, a hub can have multiple ports to connect to a number of network
devices; therefore, a hub retransmits the signal to every port to which a workstation or
server is connected.
Pages:
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209