Download Network Devices

Itishree Mishra
Media
XII A
Media
Multiplexer
PC
PC
 Computer
networking devices are units
that mediate data in a computer
network. Computer networking devices
are also called network equipment,
Intermediate Systems (IS)or
Interworking Unit (IWU). Units which
are the last receiver or generate data are
called hosts or data terminal equipment.
•
Separating (connecting) networks or
expanding network
• e.g. repeaters, hubs, bridges, routers,
switches, gateways
•
Remote access
• e.g. 56K Modems and ADSL modems
•
Networks cannot be made larger by simply
adding new computers and more cables
•Less efficient !!
Can install components to
•segment (divide) large LAN to form smaller
LANs
•connect LANs
• Required components
•Repeaters, bridges, routers, switches or
gateways
•
 Modem
 RJ-45
 Ethernet
 Hub
 Switch
 Repeater
 Bridge
 Router
 Gateway
card
A
MODEM is a
computer
peripheral that
allows you to
connect and
communicate eith
other computers
via telephone
lines.
•MODEM stands for
modulation and
demodulation.
•Allow computers to
communicate over a
telephone line
•Enable
communication
between networks or
connecting to the
world beyond the
LAN
Cannot send digital signal directly to
telephone line
• Sending end: MODulate the computer’s
digital signal into analog signal and transmits
• Receiving end: DEModulate the analog signal
back into digital form
•
1.Internal modems:
The modems that
are fixed within the
computer.
2. EXTERNAL MODEMS:
The modems that
are connected externally
to the computer.

MODEM converts digital
signals to A/F (Audio
Frequency) tones which
are in the frequency
range that the
telephone lines can
transmit and also it can
convert transmitted
tones back to digital
information.
RJ 45 is the short for Registered
jack 45. RJ 45 is an eight wire
connector, which is commonly
used to connect computers on
the local area networks i.e.,
LAN’s especially Ethernets.
(Ethernet is a LAN
architechture developed by
Xerox Corp along with DEC and
Intel. It uses either bus or star
topologyand suports data
transfer rates upto 10 Mbps.)
RJ-45 jack.
Inserting an RJ-45 connector into its jack.
Ethernet is a LAN architecture
developed by Xerox corp. in
association with DEC and Intel.
Ethernet uses either bus or
star topology and supports
data transfer rates up to 10
mbps.
The computers that are part of
Ethernet, have to install a
special card called Ethernet
card .

An Ethernet card contains connections for either
coaxial or twisted pair cables or both.
Inserting Ethernet card in
its slot on motherboard
Hub can be defined as one
common point for connecting
all the network devices.
Various LAN segments are
connected to hub in order to
organize the working of the
network. A network hub connects the various
ports of the optic fiber cable and helps
establish a single network connection or
segment.
The
most common operation it performs is that it
repeats all the information it
receives and forward it to all
PC terminals attached to it.
This repetition of data
results in unnecessary
data traffic being sent to
the network. Therefore the data
is sent in bulk without the identification of its
destination.
Limitations and Features
• Cannot link unlike segments
• Cannot join segments with different access methods
(e.g. CSMA/CD and token passing)
• Do not isolate and filter packets
• Can connect different types of media
• The most economic way of expanding networks

A network switch is a small hardware device that
joins multiple computers together within one local
area network (LAN). Technically, network switches
operate at layer two (Data Link Layer) of the OSI
model.



Network switches appear nearly identical
to network hubs, but a switch generally contains
more intelligence (and a slightly higher price tag)
than a hub.
Unlike hubs, network switches are capable of
inspecting data packets as they are received,
determining the source and destination device of
each packet, and forwarding them appropriately.
By delivering messages only to the connected
device intended, a network switch
conserves network bandwidth and offers generally
better performance than a hub.

A switch is a telecommunication
device which receives a message
from any device connected to it
and then transmits the message
only to the device for which the
message was meant. This makes
the switch a more intelligent
device than a hub (which receives a
message and then transmits it to
all the other devices on its
network). The network switch
plays an integral part in most
modern Ethernet LANs.
Advantages of Switches
•Switches divide a network into several isolated
channels (or collision domains)
•Reduce the possibility of collision
• Collision only occurs when two devices try to get access to one
channel
• Can be solved by buffering one of them for later access
•Each channel has its own network capacity
• Suitable for real-time applications, e.g. video conferencing
•Since isolated, hence secure
• Data will only go to the destination, but not others
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Limitations of Switches
•Although contains buffers to accommodate
bursts of traffic, can become overwhelmed by
heavy traffic
•Device cannot detect collision when buffer
full
• CSMA/CD scheme will not work since the data channels are
isolated, not the case as in Ethernet
•Some higher level protocols do not detect
error
• E.g. UDP
•Those data packets are continuously
pumped to the switch and introduce more
problems
22

A repeater is
an electronic device that
receives
a signal and retransmits it
at a higher level or higher
power, or onto the other
side of an obstruction, so
that the signal can cover
longer distances.


In digital communication systems, a repeater is a device
that receives a digital signal on an electromagnetic or
optical transmission medium and regenerates the signal
along the next leg of the medium. In electromagnetic
media, repeaters overcome the attenuation caused by
free-space electromagnetic-field divergence or cable loss.
A series of repeaters make possible the extension of a
signal over a distance.
Repeaters remove the unwanted noise in an incoming
signal. Unlike an analog signal, the original digital
signal, even if weak or distorted, can be clearly perceived
and restored. With analog transmission, signals are
restrengthened with amplifiers which unfortunately also
amplify noise as well as information.
Has one input and one output
• Used to isolate network traffic and computers
• Has the intelligent to examine incoming packet
source and destination addresses.
•
• But cannot
interpret higherlevel information
• Hence cannot filter
packet according to
its protocol
Bridges work at the Media Access Control Sublayer of the OSI model.
Routing table is built
to record the segment
no. of address.
If destination address
is in the same segment
as the source address,
stop transmit.
Otherwise, forward to
the other segment.
Differences Between Bridges and
Repeaters
Repeaters
Bridges
OSI layer
Physical layer
Data link layer
Data
regeneration
Regenerate data at
the signal level
Regenerate data
at the packet
level
Yes
Reduce network No
traffic
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
In a common configuration, routers are
used to create larger networks by
joining two network segments.
A router can be a dedicated hardware
device or a computer system with more
than one network interface and the
appropriate routing software. All
modern network operating systems
include the functionality to act as a
router.
Routers will normally create, add, or
divide on the Network Layer as they are
normally IP-based devices.
•
•
•
•
•
As packets are passed from routers
to routers, Data Link layer source
and destination addresses are
stripped off and then recreated
Enables a router to route a packet
from a TCP/IP Ethernet network to
a TCP/IP token ring network
Only packets with known network
addresses will be passed - hence
reduce traffic
Routers can listen to a network and
identify its busiest part
Will select the most cost effective
path for transmitting packets
Distinguishing Between
Bridges and Routers
•Bridges forward everything
they don’t recognize
•Routers select the best path
• Routers are layer 3 devices
which recognize network
address
• Bridges are layer 2 devices
which look at the MAC
sublayer node address
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
Any device that translates one data format to
another is called a gateway.

A gateway is a network device that connects
dissimilar networks. It establishes an intelligent
connection between a local network and external
networks with completely. different structures.
•Some examples of gateways include a router that
translates data from one network protocol to another, a
bridge that converts between two networking systems,
and a software application that converts between two
dissimilar formats.
•The key point about a gateway is that only the data
format is translated, not the data itself. In many cases,
the gateway functionality is incorporated into another
device.
•The gateway often acts as a proxy server and a firewall.