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Figure 6.19 illustrates the use of the bridge in a network. Suppose node A on LAN segment 1 wishes to send a packet
to node G on segment 3. On receiving this packet from node A, the bridge will examine its destination address and
forward it only to LAN segment 3.
A B LAN
Segment 2
LAN
Segment 1 BRIDGE
G I
C LAN
Segment 3
H
Figure 6.19 Bridge
6.5.6 Switch
Like hubs, switches also connect individual computers. Each computer is connected to a unique port on a switch.
However, it does not transmit an incoming frame to all the computers attached to it. When a switch receives a frame
from a LAN segment, it examines the incoming frame’s destination address and forwards it to the appropriate node.
However, on receiving a corrupted packet, the switch asks the sender to transmit it again. A store and forward switch
would wait until it receives a complete frame and then transmits it to the destination. Alternatively, a cut-through
switch initiates the process of forwarding the data as soon as it receives the frame’s destination address. Figure 6.20
shows the use of a switch in a network. If node A wishes to send a message to node G, it will pass the message to the
switch, which will transmit it on the line that connects to node G.
A L
B K
C J
D E F G H I
Figure 6.20 Switch
6.5.7 Modem
Whereas computers store and process data digitally, traditional telephone lines deal with analog signals. A modem
connects a computer to the Internet using telephone lines. It combines the modulation and demodulation functions
by transforming a digital signal to an analog signal and vice-versa. Digital data to be sent from a computer is modulated
for transmission over telephone lines. Similarly, at the receiving end, analog data is demodulated to digital form. A
modem’s speed is expressed in bits per second or in terms of baud rate.
A modem may be placed internally in an expansion slot of a computer, or it may be connected externally to a port.
Nowadays, wireless modems are also in use that do not require a physical connection with a computer. Figure 6.21
explains the use of modems in a network. Suppose node A wishes to send data to node B, digital data sent by node A
passes through the modem, which converts it into an analog signal. The analog signal generated is transmitted via the
telephone network. At the other end, a modem converts the signal back into digital form, which is sent to node B. A
modem also compresses the data before sending and uncompresses it at the receiving end.
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