Download Local Area Networks

Data Communication
Ch 10
By: M.Nadeem Akhtar
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Networks?
 LAN
 MAN
 WAN
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Local Area Networks
(LAN)
 A local area network (LAN) is a group of computers and
other devices (such as printers) that are connected together
by a common medium.
 LANs typically join computers that are physically close
together, such as in the same room or building.
 Only a limited number of computers and other devices can
be connected on a single LAN.
 The limitations vary based upon the medium connecting
the computers and devices as well as upon the LAN
software being used.
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Local Area Networks
(LAN)
 As a general rule, a LAN will cover a total distance of only
about one-half mile.
 The distance between computers linked by the
communications medium is typically at least two feet and
no more than 60 feet.
 These distances are only guidelines since the specifications
imposed by the type of communications medium, the
network interface card used, and the LAN software dictate
actual distances.
 The current transmission speed of data along a LAN
generally runs from 10 Mbps to100 Mbps.
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Metropolitan Area Networks
(MAN)
 A metropolitan area network (MAN) covers an area large
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enough to include a whole city or several small, contiguous
cities.
The physical distance is roughly 30 miles.
The MAN came about as the need to link computers grew
past the distance limits of LANs.
Linking several buildings of an organization, such as
building on a campus, is the most common application of a
MAN.
MANs use the topologies described for LANs as well as
some protocols associated with wide area networks.
Common MANs transfer data at speeds of 100 Mbps
because they frequently use fiber optics as the
communications medium
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Wide Area Networks
 Wide area networks (WANs) are used to connect
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computers and other devices when the distances exceed
constraints of LANs and MANs.
The public telephone system, or common carrier, is used
for wide area networks.
The great disadvantage of using the public telephone
system is the reduction in transmission speed. The speed
limitations are due to protocols for telephone equipment.
Most data is currently transmitted on the public telephone
system at between 9,600 bits per second (the speed at
which fax machines operate) and 1 Mbps.
However, an advantage of wide area network is that, unlike
LANs, multiple network protocols can be used over a
single WAN.
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LAN Topologies:
LAN use one of the following physical layout designs.
These designs are referred to as 'topologies
 BUS TOPOLOGY
 STAR TOPOLOGY
 RING TOPOLOGY
 TREE TOPOLOGY
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BUS TOPOLOGY
 For the bus, all stations attach, through appropriate
hardware interfacing known as a tap, directly to a linear
transmission medium, or bus.
 Full-duplex operation between the station and the tap
allows data to be transmitted onto the bus and received
from the bus.
 A transmission from any station propagates the length of
the medium in both directions and can be received by all
other stations.
 At each end of the bus is a terminator, which absorbs any
signal, removing it from the bus.
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BUS TOPOLOGY
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STAR NETWORK
 In the star topology, each station is directly connected to a
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common central node/ hub.
Typically, each station attaches to a central node, referred to as
the star coupler, via two point-to-point links, one for
transmission and one for reception.
A transmission of a frame from one station to the node is
retransmitted on all of the outgoing links.
In this case, although the arrangement is physically a star, it is
logically a bus.
A transmission from any station is received by all other stations,
and only one station at a time may successfully transmit.
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STAR NETWORK
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3-RING TOPOLOGY
 In this the network consists of a set of repeaters joined by point-to
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point links in a closed loop.
The repeater is a comparatively simple device, capable of
receiving data on one link and transmitting them, bit by bit, on the
other link as fast as they are received, with no buffering at the
repeater.
The links are unidirectional; that is, data are transmitted in one
direction only and all are oriented in the same way. Thus, data
circulate around the ring in one direction (clockwise or
counterclockwise).
Each station attaches to the network at a repeater and can transmit
data onto the network through that repeater.
A data frame circulates past all the other stations, the destination
station recognizes its address and copies the frame into a local
buffer as it goes by.
The frame continues to circulate until it returns to the source
station, where it is removed.
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RING TOPOLOGY
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4-TREE TOPOLOGY
 The tree topology is a generalization of the bus topology.
 The transmission medium is a branching cable with no closed
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loops
The tree layout begins at a point known as the head end,
where one or more cables start, and each of these may have
branches.
The branches in turn may have additional branches to allow
quite complex layouts.
Again, a transmission from any station propagates throughout
the medium and can be received by all other stations.
Two problems present themselves in this arrangement.
First, because a transmission from any one station can be
received by all other stations, there needs to be some way of
indicating for whom the transmission is intended.
Second, a mechanism is needed to regulate transmission.
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TREE TOPOLOGY
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OSI reference Model
In the 1980s, the European-dominated International Standards
Organization (ISO), began to develop its Open Systems
Interconnection (OSI) networking suite
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OSI reference Model
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OSI reference Model
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OSI reference Model
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OSI reference Model
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OSI reference Model
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Communications Hardware
 Modem
 Hub
 Router
 Switch
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Modem
 Modem: A hardware device that converts
analog signals to digital signals and vice
versa.
 Data rates for various communications
systems:
– Telephone lines: 56 kbps
– Cable modem: up to 2 Mbps
– Local Area Networks: 10 to 100 Mbps
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Hub
 A hub is a device that receives a data packet from a
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computer at the end of one spoke of the star topology and
copies the contents to all other devoices.
Hubs are not sophisticated/ intelligent communication
equipment.
A device not physically connected to the hub via a wire can
be excluded from the hub network.
Hubs are becoming more complicated. When the term hub
is used in communications it generally refers to a passive
device that simply copies and passes along data.
As vendors try to differentiate their product from others
they have added features to the simple hub.
Hubs are also known as manageable hubs even they are
capable of monitoring the data flowing through the hub
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Router
 A router is a device that connects many LANs.
 This is the basis for establishing a wide area network.
 An earlier, less sophisticated communications device was
bridge, which simply connects two LANs.
 Routers extend the communications management facility.
 Unlike hubs that only disperse data to a connection port,
routers can process the header information of a packet and
determine to which LAN the data should be
communicated.
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Switch
 Equipment that filters out data communications not
destined for a computer on a particular network and
performs routing control to the receiving computer is
called switch.
 Switches, like routers, are associated with wide area
networks.
 A switch can improve the communications transmission
rates on a network by filtering out (disallowing) data
communications to go down paths of a network that cannot
contain the computer destination.
 By limiting unnecessary data communications, more
communication transmission capacity is made available for
other communications.
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