DATA COMMUNICATION NETWORK CRITERIA PART - 1

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➢ Performance : include measurement of transit time
& response time.
➢ Transit time is the amount of time required for a
message to travel from one
device to another.
➢ Response time is the elapsed time between an inquiry
& response.

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➢ Performance of a n/w depends on :
- no. of users
- type of transmission medium
-capabilities of the connected h/w
- efficiency of the s/w
➢ Performance evaluated by two networking
metrics: throughput & delay.
➢ Reliability: measured by the frequency of failure,
the time it takes a link to recover from a failure, &
the n/w’s robustness in a catastrophe.
➢Security: N/w security issues include protecting
data from unauthorized access, protecting data
from damage & development, & implementing
policies and procedures.

Definition of Computer Network
●A computer network is an interconnected
collection of autonomous computers.
●Two computer are interconnected if they are able to
exchange information
●Two computer are autonomous if they are capable
of operating independently, that is, neither is
capable of forcibly starting, stopping, or controlling
the other
●Computer n/ws are created by different entities.
Standards are needed so that these heterogeneous
networks can communicate with one another.
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Network Model
●Local Area Networks (LANs) : The computers
are geographically close together (that is, in the
same building).
●Metropolitan Area Network (MAN) : The
Computer network designed for a town or city.
●Wide Area Networks (WANs) : The computers
are farther apart and are connected by telephone
lines or radio waves. (Across Countries)
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characteristics
●Topology : The geometric arrangement of a
computer system. Common topologies include a
bus, star, and ring.
●Architecture : Networks can be broadly classified
as using either a peer-to-peer or client/server
architecture
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Local Area Network (LAN)
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•A LAN is usually privately owned & links the devices in a single office,
building, or campus.
•Depending on the needs of an organization & the type of technology
used, a LAN can be simple as two PCs & a printer in someone’s home
office; or it can be extended throughout a company & include audio &
video peripherals

LAN
confined to:
●a single building or group of building
●Home, Office Building, Or School, Or University
●Either Wired or wireless media.
LAN size is limited to a few kilometers.
●Allow resources to be shared between personal
computers or workstations.(include h/w, s/w, or data)
●LANs are distinguished from other types of networks
by their transmission media & topology
●data rates: earlier 4 to 16 Mbps
now 100 or 1000 Mbps
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Metropolitan Area Network
(MAN)
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Metropolitan Area Network (MAN)
●For a town or city
●Consists of multiple LANs
●larger than local-area networks (LANs)
●but smaller than wide-area networks (WANs)
●characterized by very high-speed connections using
fiber optical cable or other digital media.
●Examples: part of telephone company n/w that can
provide a high speed DSL line to the customer.
●Cable TV n/w that originally was designed for cable
TV, but today can also be used for high-speed data
connection to the Internet.
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Wide Area Network (WAN)
●Covers a large Geographical area (Kilometers)
●Consists of two or more LANs
●The INTERNET (the largest WAN)
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●Provides long-distance transmission of data, image,
audio, & video information over large geographic areas
that may comprise a country, a continent, or even the
whole world.
●A WAN can be as complex as the backbone that
connect the Internet or as simple as a dial-up line that
connects a home computer to the Internet
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PAN:
●Personal devices of one individual:
●His/her PC, laptop, cell phone, PDA
●To allow devices to communicate and work together.
●To permit devices to become smarter: spontaneously,
network and work together.
●PANs feasibility growing with improvement of
wireless technology:
●Bluetooth enabling devices to communicate
automatically and wirelessly when they are in range.
●PANs can keep portable devices synchronized with a
desktop PC.
●E-clothing products (Jacket) equipped with a battery
pack and devices.
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Types of connection
In a n/w devices are connected through links.
Link → communication pathway → transfers data from one device to another.
Two types of connections: point-to-point & multipoint.
➢ Point-to-Point connection provides dedicated link b/w 2 devices.
→ entire capacity of the link is reserved for transmission b/w those 2
devices.
➢ Multipoint connection is one in which more than two specific devices share
a single link

●A network topology describes the configuration of a
network (how the network components are connected
together).
●The topology of a n/w is the geometric representation of
the relationship of all the links & linking devices to one
another.
●There are FIVE main topology's.
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Factors for selecting topologies
●Desired Performance-
●Desired Reliability-
●Size(No of nodes)-
●Expandability of the system-
●Cost of the components
●Delays involved in routing
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●The star topology uses a central hub through which
all components are connected.
Central device (hub)
●Contains multiple ports to connect the network
devices
●All network transmissions sent through it
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 Each device has a dedicated point-to-point link only to a
central controller, called a hub
 devices are not directly connected to one another.
 less expensive.
each device needs only one link & one I/O port to connect it to
any no. of others. easy to install & reconfigure.
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Star- Advantages:
●If any comp. fails the remaining N/W is unaffected
●Only n-1 lines are required for connecting n
nodes
Disadvantages:
●If the hub fails , the entire network fails.
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Ring A ring topology connecting six stations
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•The ring topology connects workstations in a closed loop.
• Each terminal is connected to TWO other terminals (the
next and the previous), with the last terminal being
connected to the first.
•Data is transmitted around the ring in one direction only,
each station passing on the data to the next station till it
reaches its destination.

●Faulty workstations can be isolated from the ring.
●When the workstation is powered on, it connects
itself into the ring. When power is off, it disconnects
itself from the ring and allows the information to
bypass the workstation.
●Information travels around the ring from one
workstation to the next.
●Each packet of data sent on the ring is prefixed by
the address of the station to which it is being sent to.
●When a packet of data arrives, the workstation
checks to see if the packet address is the same as its
own. If it is, it grabs the data in the packet.
●If the packet does not belong to it, it sends the
packet to the next workstation in the ring.
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●Ring systems use 4 pair cables (separate send/receive).
●The common implementation of this topology is token
ring.
● A break in the ring causes the entire network to fail.
●No central hub.
●No central cable.
●Network devices connected in a ring formation from
one
device to the next.
●Data travels from one device to another around the
ring in
one direction only.
●There's no danger of collisions because data always
flows
in one direction.
● If a connection is broken, the entire network goes
down.
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Ring Topology
●Advantage
1.Easy to install
2.Add or delete is easy
3.Fault isolation is simplified
Disadvantage
1.A break in the ring can disable the entire network
2.Addition of new nodes increases the delay
3.Requires more complicated control then star
network
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Bus topology
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•The bus topology connects workstations using a
single cable.
•Each workstation is connected to the next
workstation in a point to point fashion.
• All workstations connect to the same cable.

BUS:
●No central hub
●Central cable to which all devices are attached
●Data transmission down the line from one
device to another
● Only one device transmits at a time.
●Easy to implement and extend
●Requires less cable length than a star topology
BUT
●If there is a problem with the cable, the entire
network goes down.
● Performance degrades as additional computers
are added or on heavy traffic.
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Mesh:
●The mesh topology connects all computers to
each other.
●The cable requirements are high, but there are
redundant paths built in.
●Any failure of one computer allows all others
to continue, as they have alternative paths to
other computers.
●Mesh topology's are used in critical connection
of host computers (typically telephone
exchanges).
●Alternate paths allow each computer to
balance the load to other computer systems in
the network by using more than one of the
connection paths available.
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A hybrid topology:
a star backbone with three bus networks
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DATA COMMUNICATION NETWORK CRITERIA PART - 1

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DATA COMMUNICATION NETWORK CRITERIA PART - 1