Chapter 4 computer network and the internet2

Chapter 4
Networking and Data Communications
What is Computer Network?
A computer network, or simply a network, is a collection of
Computers and other hardware interconnected by communication
channels that allow sharing of resources and information.
The computers on a network may be linked through cables,
telephone lines, radio waves, satellites, or infrared light beams.
Prepared by Feven T. 1

Basic components of a Computer Network
Following are the basic components of network.
1. Server:
Powerful computers that provides services to the other computers
on the network.
2. Client:
Computer that uses the services that a server provides.
3.Media:
A physical connection between the devices on a network.
4.Resources:
Any thing available to a client on the network is considered a
resource, Printers, data, fax devices and other network devices and
information are resources.

Con’t
5.Protocols:
These are written rules used for communications. They are the
languages that computers use to talk to each other on a network.
Advantages and Disadvantages of Networking
Advantages:
Computer networks have highly benefited various fields of
educational sectors, business world and many organizations.
Sharing of peripheral devices:
Each computer that is connected to the network can share the
same peripheral devices, such as a printer.
Sharing of Programs and data:
By sharing the software and data the usage of memory can be
minimized, thereby minimizing the expense.
Sharing a single Internet connection

Con’t
Better Communication:
Communication is one of the biggest advantages provided by the
computer networks. Information can be transferred within fraction of
a second over long distances. Example E-Mail
Security of information:
Data or information could be backed-up or duplicated on a network
storage device, shared by others.
Saves Cost
Building up links thorough the computer networks immediately
transfers files and messages to the other people which reduced
transportation and communication expense.

Con’t
Disadvantages:
Rapid Spread of Computer Viruses
When computers are connected by a network, the virus can spread
itself electronically, at computer speeds affecting badly the network
performance and the performance of the computers.
Difficult to secure information.
Confidential documents (files) can be accessed without the
knowledge and permission of the owner.
Needs initial investment

Types of Networks
Based on the size/scope, the Computer Networks are classified
into:
1.LAN (Local Area Network)
A LAN connects network devices over a relatively short distance.
Such as office building, school, or home and occasionally a LAN will
span a group of nearby buildings.
LAN connection is a high-speed connection.
Most connections are either Ethernet (10Mbps) or Fast Ethernet
6(100Mbps), and a few locations have Gigabit Ethernet (1000Mbps)
connections.
LANs typically use half-duplex communications.
Such computer networks are usually owned by one organization.

Con’t
2.MAN (Metropolitan Area Network)
A MAN is a larger network that usually spans several buildings in
the same city or town.
Also used to mean the interconnection of several LANs by bridging
them together.
MANs have the requirements of using telecommunication media
such as voice channels or data channels.
such computer networks are owned and operated by single
entities such as government bodies or large corporations.
Examples of Organizations that use MANs are; Universities and
Colleges, grocery chains, and Banks

Con’t
3.WAN (Wide Area Network)
WAN is a geographically-dispersed collection of LANs.
A network device called a Router connects LANs to a WAN.
Most WANs (like the Internet) are not owned by any one
organization but rather exist under collective or distributed
ownership and management.
WANs tend to use technology like ATM, Frame Relay and X.25 for
connectivity over the longer distances.
The Internet is an example of a worldwide public WAN.

Con’t
 A WAN differs from a LAN in several
important ways.
 WANs cover greater distance.
 WAN speeds are slower.
 WANs can be connected on demand or be
permanently connected. LANs have
permanent connections between stations.
 WANs can use public or private network
transports. LANs typically use private
transports.
 WANs can use either full- or half-duplex
communications. LANs typically use half-
duplex communications.

Other types of networks include;
Wireless Local Area Network (WLAN )
refer to LANs that are based on Wi-Fi wireless network technology.
Campus Area Network
A network spanning multiple LANs but smaller than a MAN, such as
on a university or local business campus.
Storage Area Network
connects servers to data storage devices through a technology like
Fiber Channel.
System Area Network
links high-performance computers with high-speed connections in
a cluster configuration. Also known as Cluster Area Network.

Con’t
Based on the relationship among the computers, we can
categorize computer networks as:
A. peer-to-peer networks
Essentially, every computer on a peer-to-peer network can function
as both a server and a client; No hierarchy among computers.
Peer-to-peer networks are characterized by the following:
Security is not centralized; each computer is responsible to check
access rights for its resources.
Network is not scalable; it is good only for a few number of
computers (mostly 10).
No specialized operating system is required;
Each user is responsible for local backup

Con’t
Advantages
 It is usually less expensive.
 It is simple to design and maintenance.
Disadvantages
 Decentralized – No central repository for files and
applications.
 Security – Does not provide the security available
on peer-to-peer.

Con’t
B. Client/Server Networks
On a client/server network, every computer has a distinct role: that
of either a client or a server.
A server is designed to share its resources among the client
computers on the network.
A dedicated server computer often has faster processors, more
memory, and more storage space than a client.
A client system is a standard PC that uses resources available on
Server.
A client computer typically communicates only with servers, not with
other clients.

Con’t
Client/Server Networks
Client/server network is characterized by the following:
It has centralized, tighter security.
All user accounts are stored in the same database on the server.
The network is highly scalable;
you can have tens of thousands of workstations in the network.
Specialized networking operating systems are required
Backup is centralized
Accessibility : From various platforms in the network, server can
be accessed remotely.

Con’t
Disadvantages of client/ server
1) Congestion in Network :
Too many requests from the clients may lead to congestion.
Overload can lead to breaking-down of servers.
2) Client-Server architecture is not as robust as a P2P and if the
server fails, the whole network goes down.
3) Cost : It is very expensive to install and manage this type of
computing.
4) You need professional IT people to maintain the servers and
other technical details of network.

Network Topologies
Network Topologies
Network topologies describe the ways in which the elements of a
network are mapped.
They describe the physical and logical arrangement of the network
nodes.
• The physical topology of a network refers to the configuration of
cables, computers, and other peripherals
Logical topology of a network refers to the method used to pass
information between devices on the network.

Main Types of Physical Topologies
1.Bus Topology
A linear bus topology consists of a main run of cable with a
terminator at each end.
All nodes(file server, workstations, and peripherals) are connected
to the linear cable
Terminator
Terminato
Nodes

Con’t
Advantages of a Linear Bus Topology
Easy to connect a computer or peripheral to a linear
bus.
Requires less cable length than a star topology.
Failure of a single node does not terminate the
network.
If a cable that connect the nodes with the backbone
fails, the network does not fail.

Con’t
Disadvantages of a Linear Bus Topology
Entire network shuts down if there is a break in the
main cable (backbone).
Terminators are required at both ends of the backbone
cable.
Difficult to identify the problem if the entire network
shuts down.

Con’t
2. Star Topology
A star topology is designed with each node connected
directly to a central network concentrator , typically hub.
Data on a star network passes through the hub or
concentrator before continuing to its destination.
The hub or concentrator manages and controls all
functions of the network.
It also acts as a repeater for the data flow.
Concentrator
Hub
Nodes

Con’t
Advantages of a Star Topology
Easy to install and wire.
No disruptions to the network when connecting or
removing devices.
Easy to detect faults and to remove parts.
Easily scalable, i.e., you can add a node easily.
Failure of a single computer/cable does not affect the
rest of the network.

Con’t
Disadvantages of a Star Topology
Requires more cable length than a linear topology.
If the hub or concentrator fails, nodes attached are disabled.
More expensive than linear bus topologies because of the cost of
the concentrators and extra cost of the hub.
Broadcasting creates unnecessary network traffic.

Con’t
3. Ring Topology
A Ring topology is the one in which all computers and other
communication devices are connected in a continuous loop.
Electronic messages are passed around the ring in one direction,
with each node serving as the repeater, until they reach the right
destination.

Con’t
Advantages of a Ring Topology
There is less signal attenuation because each computer in the
network is used as a repeater.
More than one computer can send data at a time.
Disadvantages of a Ring Topology
Difficult to setup
If any computer/cable in the ring fails, the whole network goes
down.

Con’t
4. Mesh Topology
Each computer is directly connected to every other computer.
A mesh topology can become quite complex as wiring and
connections increase rapidly with the increase of computers to
connect.
For n computers, n(n-1)/2 cables are required.

Con’t
Advantages of Mesh topology
Data can be transmitted from different devices simultaneously.
 Even if one of the components fails there is always an alternative
present. So data transfer doesn’t get affected.
Expansion and modification in topology can be done without
disrupting other nodes.

Con’t
Disadvantages of Mesh topology
 There are high chances of redundancy in many of the network
connections.
Overall cost of this network is too high as compared to other
network topologies
Set-up and maintenance of this topology is very difficult. Even
administration of the network is tough.

Con’t
5. Tree topology
Tree Topology integrates the characteristics of Star and Bus
topology.
In Tree Topology, the number of Star networks are connected using
Bus.
This main cable seems like a main stem of a tree, and other star
networks as the branches. It is also called Expanded Star
Topology.

Con’t
Advantages of Tree Topology
 It is an extension of Star and bus Topologies, so in networks
where these topologies can't be implemented individually for
reasons related to scalability, tree topology is the best
alternative.
Expansion of Network is possible and easy.
Here, we divide the whole network into segments (star
networks), which can be easily managed and maintained.
Each segment is provided with dedicated point-to-point
wiring to the central hub.
If one segment is damaged, other segments are not
affected.

Con’t
Disadvantages of Tree Topology
Because of its basic structure, tree topology, relies heavily on the
main bus cable, if it breaks whole network is crippled.
As more and more nodes and segments are added, the
maintenance becomes difficult.
Scalability of the network depends on the type of cable used.

Con’t
6. Hybrid Topology
• A combination of any two or more network topologies.
• It is a mixture of above mentioned topologies. Usually, a central
computer is attached with sub-controllers which in turn participate in
a variety of topologies

Con’t
Advantages of a Hybrid Topology
• It is extremely flexible.
• It is very reliable.
Disadvantages of a Hybrid Topology
• Expensive

Con’t…
Considerations When Choosing a Topology:
Cost.
A linear bus network may be the least expensive way to install a
network; you do not have to purchase concentrators.
Length of cable needed.
The linear bus network uses shorter lengths of cable.
Future growth.
With a star topology, expanding a network is easily done by adding
another concentrator.
Cable type.
The most common cable in schools is unshielded twisted pair, which is
most often used with star topologies.
Ease of installation
Ease of maintenance
Cable fault tolerance

Transmission Modes
There are three ways for transmitting data from one point to another
1.Simplex:
In simplex mode the communication can take place only in one
direction.
The receiver receives the signal from the transmitting device.
This mode of flow of information is Unidirectional.
One station is transmitter and the other is receiver.
Example: Radio, T.V..

Con’t…
2. Half-duplex:
In half-duplex mode the communication channel is used in both
directions, but only in one direction at a time.
Thus a half-duplex line can alternately send and receive data.
Example is the wireless communication, Police radio (wacky talky)
or talk back radio

Con’t…
3.Full-duplex:
In full duplex the communication channel is used in both directions
at the same time.
Use of full-duplex line improves the efficiency as the line turn-
around time required in half-duplex arrangement is eliminated.
Example of this mode of transmission is the telephone line.

Transmission Medias
The means through which data is transformed from one place to
another is called transmission or communication media.
There are two categories of transmission media used in computer
communications.
A. BOUNDED/GUIDED MEDIA
Bounded media are the physical links through which signals are
confined to narrow path.
Bounded media are made up o a external conductor (Usually
Copper) bounded by jacket material
Three common types of bounded media are used of the data
transmission. These are
1.Coaxial Cable
2.Twisted Pairs Cable
3.Fiber Optics Cable

B. Unbounded/Unguided Media
The unguided media is the wireless media.
It simply transports electromagnetic waves without using any
physical conductor.
Unguided media employ an antenna for transmitting through air,
vacuum, or water.
Three common types of unguided media are;
(i) Radio wave
(ii) Microwave
(iii) Infrared

Con’t…
A number of design factors relating to the transmission medium and the signal
determine the data rate and distance such as;
Bandwidth:
All other factors remaining constant, the greater the bandwidth of a signal, the
higher the data rate that can be achieved.
Transmission impairments: Impairments, such as attenuation, limit the
distance.
Interference: Interference from competing signals in overlapping frequency
bands can distort or wipe out a signal.
Number of receivers:
A guided medium can be used to construct a point-to point link or a shared
link with multiple attachments.
In the latter case, each attachment introduces some attenuation and distortion
on the line, limiting distance and/or data rate.

1.Twisted Pair cable
The least expensive and most widely used guided transmission
medium is twisted pair.
A twisted pair consists of two insulated copper wires arranged in
a regular spiral pattern.
A wire pair acts as a single communication link. Typically, a
number of
these pairs are bundled together into a cable by wrapping them
in a tough protective sheath.
The twisting tends to decrease the crosstalk interference
between adjacent pairs in a cable.

Con’t…
Twisted pair cabling comes in two varieties:
shielded and unshielded.
i.Unshielded Twisted Pair (UTP) Cable
Unshielded twisted Pair(UTP) is ordinary telephone wire.
This is the least expensive of all the transmission media
commonly used for local area networks and is easy to work with
and easy to install.
The cable has four pairs of wires inside the jacket. Each pair is
twisted with a different number of twists per inch to help
eliminate interference from adjacent pairs and other electrical
devices.

Con’t…
The EIA/TIA (Electronic Industry
Association/Telecommunication Industry Association) has
established standards of UTP and rated five categories of wire.
Category 6 is relatively new and is used for gigabit connections.
Category 1:
Two twisted-pair (four wires).
Voice grade (not rated for data communications).
Category 2:
Four twisted-pair (eight wires). Suitable for up to 4Mbps.
Category 3:
Four twisted-pair (eight wires), with three twists per foot.
Acceptable for 10Mbps.

Con’t…
Category 4:
Four twisted-pair (eight wires) and rated for 16Mbps.
Category 5:
Category 6:
The standard connector for unshielded twisted pair cabling is an
RJ-45 connector.

ii. Shielded Twisted Pair (STP) Cable
STP is a twisted pair shielded with a metallic braid or sheathing
that reduces interference.
This shielded twisted pair (STP) provides better performance at
higher data rates.
However, it is more expensive and more difficult to work with
than unshielded twisted pair.

2.Coaxial Cable
Coaxial cabling has a single copper conductor at its center.
A plastic layer provides insulation between the center conductor
and a braided metal shield
The metal shield helps to block any outside interference from
fluorescent lights, motors, and other computers.

Con’t…
Although coaxial cabling is difficult to install, it is highly resistant
to signal interference.
It can support greater cable lengths between network devices
than twisted pair cable.
The two types of coaxial cabling are
1. Thin coaxial cable is also referred to as thinnet.
It is 10Base2.
10Base2 refers to the specifications for thin coaxial cable
carrying Ethernet signals.
The 2 refers to the approximate maximum segment length being
200 meters.
In actual fact the maximum segment length is 185 meters.

Con’t…
2. Thick coaxial cable is also referred to as thicknet.
It is 10Base5.
Thick coaxial cable has an extra protective plastic cover that
helps keep moisture away from the center conductor.
However, One disadvantage of thick coaxial is that it does not
bend easily and is difficult to install.
.

Coaxial Cable Connectors
(BNC) connector:
The most common type of connector used with ThinNet coaxial
cables is the Bayone-Neill-Concelman (BNC) connector
D-type Connectors:
The first type of networking connector was the D-type
connector.
The Attachment Unit Interface (AUI) connector is a D-type
connector used to connect your computer to ThickNet coaxial
cable.
.

3.Fiber Optic Cable
An optical fiber is a thin flexible medium capable of guiding an
optical ray.
Various glasses and plastics can be used to make optical fibers.
An optical fiber cable has a cylindrical shape and consists of
three concentric sections:

Fiber Optic Cable
a. The core
It is the innermost section and consists of one or more very thin
strands, or fibers, made of glass or plastic
b. The Cladding
a glass or plastic coating that has optical properties different
from those of the core that surrounds the fiber .
The interface between the core and cladding acts as a reflector
to confine light that would otherwise escape the core.
c. Jacket
The outermost layer, surrounding one or a
bundle of cladded fibers.
The jacket is composed of plastic and other
material layered to protect against moisture,
abrasion, crushing, and other environmental
dangers.

Con’t….
Fiber optic transmits light rather than electronic signals eliminating
the problem of electrical interference.
Fiber optic cable has the ability to transmit signals over much longer
distances than coaxial and twisted pair.
It also has the capability to carry information at vastly greater
speeds.
however, it is more difficult to install and modify.
Fiber Optic Connector
The most common connector used with fiber
optic cable are an ST connector and SC, connector

Ethernet Cable Summary
Specification Cable Type Maximum length
10BaseT Unshielded Twisted Pair 100 meters
10Base2 Thin Coaxial 185 meters
10Base5 Thick Coaxial 500 meters
10BaseF Fiber Optic 2000 meters

Networking Devices
The Network Interface Card (NIC)
The network interface card (NIC) provides the physical connection
between the network cable and the computer.
The role of the NIC is to:
Prepare data from the computer for the network cable.
Send the data to another computer.
Control the flow of data between the computer and the cabling
system.
Receive incoming data from the cable and translate it into bytes
that can be understood by the computer's central processing unit
(CPU).

I. Hub
A hub joins multiple computers (or other network devices) together
to form a single network segment.
A hub is the central device in a star topology.
Most hubs are simple multiport repeaters. That is, they receive a
signal on one port and repeat it to all other ports.
Hubs can be active or passive.
An active hub strengthens and regenerates the incoming signals
before sending the data on to its destination.
Passive hubs do nothing with the signal.

II. Repeaters
The repeater electrically amplifies the signal it receives and
rebroadcasts it.
They are used when the total length of your network cable exceeds
the
standards set for the type of cable being used.

III. Switch
Most switches are active, that is they electrically amplify the signal
as it moves from one device to another.
Switches no longer broadcast network packets as hubs did in the
past, they memorize addressing of computers and send the
information to the correct location directly.
Switches are:
Usually configured with 8, 12, or 24 RJ-45 ports Often used in a star
or star-wired ring topology
Sold with specialized software for port management

IV. Bridges
A bridge is a device that allows you to segment a large network into
two smaller, more efficient networks.
The main reason for putting a bridge in a network is to connect two
segments together, or to divide a busy network into two segments.
Most bridges can "listen" to the network and automatically figure out
the address of each computer on both sides of the bridge.
The bridge manages the traffic to maintain optimum performance on
both sides of the network.

V. Router
A router translates information from one network to another
Routers select the best path to route a message, based on the
destination address and origin.
While bridges know the addresses of all computers on each side of
the network, routers know the addresses of computers, bridges, and
other routers on the network.
Routers can even "listen" to the entire network to determine which
sections are busiest -- they can then redirect data around those
sections until they clear up.

Con’t…
Router also determines the best route to send the data over
the Internet.
Routers can:
Direct signal traffic efficiently
Route messages between any two protocols
Route messages between linear bus, star and ring
topologies
Route messages across fiber optic, coaxial and twisted-pair
cabling

VI. MODEM
A modem is a device that changes digital data into an analog form
for transmission over an analog medium and then back to digital
again at the receiving end.
A modem is a device that makes it possible for computers to
communicate over telephone lines.
The term “modem” is actually an acronym that stands for
MOdulator/DEModulator.
Modems connect to the phone line using
standard telephone RJ-11 connectors.

Protocol
These are written rules used for communications.
Communications thus between computers on a network is done
through protocol suits.
A protocol suit consists of a layered architecture where each layer
depicts some functionality which can be carried out by a protocol.
The most widely used and most widely available protocol suite is
TCP/IP protocol suite.

Chapter 4
Introduction to Computer Networks and the Internet
TCP/IP Protocol
TCP/IP is a large collection of different communication protocols
based upon the two original protocols TCP and IP.
TCP(Transmission Control Protocol)
IP (Internet Protocol)
TCP/IP is normally considered to be a 4 layer system.
Application layer
Transport Layer
TCP
UDP
Network Layer
Data Link Layer

THANK YOU!!

Chapter 4 computer network and the internet2

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