State and compare internetworking devices used to connect different LAN
segments
Ans
Various devices are used to connect network of a computer The
most common devices are:
1) Routers
2) Gateways
3) Repeaters
4) Bridges
5) Hub
6) Modem
ROUTER
Routers are devices which connect two are more networks that
use similar protocol. A router consists of hard ware and software.
Hard ware can be a computer is specific device.
Software consists of special management program that controls
flow of data between networks.
Routers operate at a network layer of O.S.I model.
Routers use logical and physical address to connect two or
more logically separate network. They make this connection by organizing the
large network into logical network segment (some times small sub network or sub
nets). Each of these sub nets is given a logical address. Data is grouped into
packets or block of data.
Each packet in addition to having a physical device address,
has a logical address. The network address allows routers to calculate more
accurately and efficiently the path of the computer.
GATEWAYS
Gateways are devices which connect two are more networks that
use different protocols. They are similar in function to routes but they are
more powerful and intelligent devices. A gateway can actually convert data so
that network with an application on a computers on the other side of the
gateway e.g a get way can receive email messages in one format in convert them
into another format. Gateway can operate at all seven layer of OSI model. Since
Gateway perform data conversion so they are slower in speed and very expensive
devices.
REPEATERS
Repeaters are used within network to extend the length of
communication.
Data process through transmission media in the farm of waves
or signals. The transmission media weaken signals that move through it. The
weakening of signal is called attenuation. If the data is to be transmitted
beyond the maximum length of a communication media, signals have amplified. The
devices that are used to amplify the signals are called repeaters. Repeaters
work at the physical layer of OSI model.
Repeaters are normally two ports boxes that connect two
segments. As a signal comes in one port , it is Regenerated and send out to the
other port.
The signal is read as 1s and 0s. As 1s and 0s are
transmitted, the noise can be cleaned out.
BRIDGES
Bridges are used to connect similar network segments.
A bridge does not pass or signals it receives. When a bridge
receive a signal , it determines its destination by looking at its destination
and it sends the signals towards it. For example in a above figure a bridge has
been used to join two network segments A AND B.
When the bridge receives the signals it read address of both
sender and receiver. If the sender is a computer in segment A and the receiver
is also segment A, it would not pass the signals to the segments B. It will
however pass signals if the sender is in one segment and the receiver in other
segment. Bridge works at the data link layer of O.S.I model.
HUB
Hubs are basically multi ports repeaters for U.T.P cables.
Some hubs have ports for other type of cable such as coaxial cable. Hubs range
in size from four ports up to and for specific to the network types. These are
some hubs which are
I. Passive Hub
II. Active Hub
III. Switch/ Intelligent Hub
Passive Hub
It provides no signal regeneration. They are simply cables
connected together so that the signal is broken out to other nodes with out
regeneration. These are not used often today because of loss of cable length
that is allowed.
Active Hub
It acts as repeaters and regenerates the data signals to all
ports. They have no real intelligence to tell weather the signal needs to go to
all ports that is blindly repeated.
Switch Hub
Switches are multi ports bridges. They filter traffic between
the ports on the switch by using the address of computers transmitting to them.
Switches can be used when data performance is needed or when
collision need to be reduce.
MODEM
The device that converts digital signals into analog signals
and analog signals to digital signals is called Modem. The word modem stands
for modulation and demodulation. The process of converting digital signals to
analog signals is called modulation. The process of converting analog signals
to digital signals is called demodulation. Modems are used with computers to
transfer data from one computer to another computer through telephone lines.
Modems have two connections these are.
- Analog connection
- Digital connection
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