UNIT-I

Computer Networks
Introduction

1. Define Computer Network? Need of computer Network?

A Group of computers which are communicated to each other for the purpose of
sharing their resources is Called computer network. These computers can exchange
information with each other through the Communication channels like copper wire,
fiber optics, microwaves, infrared, and communication satellites can also be used.
Need of computer Networking
 To shared a files and folders from one computer to another computer in network
 To shared a hardware equipment like printers, CD-Rom and so on
 To shared the software applications over network and this allows implementing
 Client server applications to improve the communication between to computers
 To improved speed and accuracy
 To reduce the cost of data transfer
 High reliability

Types of Networks

Local Area Network (LAN)

 A local area network is generally called as LANs; these are privately-owned networks
within a single Building or campus of up to a few kilometers in size.
 LANs are widely used to connect personal computers and work stations in company
Offices and factories to share resources like printers, and to exchange information.
 LANs are different from other networks by three characteristics (1).With their size,
(2).With their transmission technology. (3).their topology.
 LANs run at a speed of 10 to 100 Mbps (mega bits/sec)
 LANs use a transmission Technology consisting of a single cable to which all the
systems are attached, Like a telephone lines.
 Here it uses IEEE 802.3 popularly known as Ethernet, and IEEE 802.5 IBM Token ring
 Various Topologies are used for broadcasting the LANs. The most common LAN
topologies are bus, ring, and star.
 Metropolitan Area Network (MAN)

 A metropolitan area network (MAN) is a network with a size between a LAN and a WAN.
 Both the buses contain Head-End which initiates the tran*smission. The traffic of right
Side of the sender uses upper bus. And to send left side uses lower one.
 It is designed for customers who need a high-speed connectivity.
 The range of MAN is 100M to 10KM
 These are private and public owned networks

Wide Area Network (WAN)

 WAN spans large geographical area

 The range of WAN is different countries
 WAN provides long-distance transmission of data, voice, image and information over
Large geographical areas that may comprise a country, continent or even the
whole world. In WANs systems are connected by a communication subnet or
subnet.

 The job of the subnet is to carry messages from system to the system, just like a
Telephone which carries Words from speaker to speaker in most wide area networks
the subnet consists of two distinct components transmission lines and switching
elements. Transmission lines are also called as circuits, channels or trunks move bits
between machines. The switching elements are specialized computers used to connect
two or more transmission lines connecting multiple networks known as routers.
Network Topologies

Topology: The Physical arrangement of computers which are connected to each other
through via communication channel is called topology.

Bus Topology:

 Bus topology is a network type in which every computer and network device is
connected to single cable. When it has exactly two endpoints, then it is
called Linear Bus topology.

Features of Bus Topology

 It transmits data only in one direction.
 Every device is connected to a single cable

Advantages of Bus Topology

 It is cost effective.
 All nodes are easily add or remove
 Used in small network
 It is easy to understand.
 Easy to expand joining two cables together.

Disadvantages of Bus Topology

 Cables fails then whole network fails.
 If network traffic is heavy or nodes are more the performance of the network
decreases.
  Cable has a limited length.

2. RING Topology

It is called ring topology because it forms a ring as each computer is connected to

another computer, with the last one connected to the first. Exactly two neighbors for
each device.

Features of Ring Topology

 Numbers of repeaters are used for Ring topology with large number of nodes,
because if someone wants to send some data to the last node in the ring topology
with 100 nodes, then the data will have to pass through 99 nodes to reach the
100th node. Hence to prevent data loss repeaters are used in the network.
 The transmission is unidirectional
 Data is transferred in a sequential manner that is bit by bit

Advantages of Ring Topology

 Transmitting network is not affected by high traffic or by adding more nodes, as
only the nodes having tokens can transmit data.
 Cheap to install and expand
Disadvantages of Ring Topology
 Troubleshooting is difficult in ring topology.
 Adding or deleting the computers disturbs the network activity.
 Failure of one computer disturbs the whole network.

3. STAR Topology
 In this type of topology all the computers are connected to a single hub through a
cable.
 This hub is the central node and all others nodes are connected to the central
node.

Features of Star Topology

 Every node has its own dedicated connection to the hub.
 Hub acts as a repeater for data flow.
  Can be used with twisted pair, Optical Fiber or coaxial cable.

Advantages of Star Topology

 Hub can be upgraded easily.
 Easy to troubleshoot.
 Easy to setup and modify.
 Only that node is affected which has failed, rest of the nodes can work smoothly.
Disadvantages of Star Topology
 Cost of installation is high.
 Expensive to use.
 If the hub fails then the whole network is stopped because all the nodes depend
on the hub.
4. MESH Topology
 It is point–to-point connection to other nodes traffic is carried only between two
devices to which it is connected. Mesh has n(n-2)/2 physical channels.

Figure: A fully connected mesh topology (five devices)

Feature of Mesh Topology

 Fully connected
 Robust
 Not flexible
Advantages of mesh topology:
 Each connection can carry its own data load
 It is robust
 Provides security and privacy
Disadvantages of mesh topology:
 Cable cost is more
 Installation and configuration is difficult
 Bulk wiring is required
HYBRID Topology
 It is two different types of topologies which is a mixture of two or more topologies.
 It is combination of two or more topologies
 Inherits the advantages and disadvantages of the topologies included
Advantages of Hybrid Topology Feature of Hybrid Topology

 Reliable as error detecting and trouble shooting is easy

 Effective
 Flexible
Disadvantages of Hybrid Topology
 Complex in design
  costly

Reference model
It describes how information from a software application in one computer moves
through a physical medium to the software application in other computer.
Reference models are two types 1. OSI 2.TCP/IP
OSI Reference Model
It stands for open system inter connection. It was developed by International standard
organization in 1984.It consist of 7 layers.
1. Application Layer 2.Presentation Layer 3.Session Layer 4.Transport Layer 5.Network
Layer 6.Data Link Layer 7.Physical Layer
Layers 1, 2, and 3-physical, data link, and network layers are known as
Networksupport layers
Layers 5, 6, and 7-session, presentation, and application layers are known as the
Usersupport layers
1. Physical Layer

 The main functionality of the physical layer is to transmit the individual bits from
one node to another node.
 It is the lowest layer of the OSI model.
 It establishes, maintains and deactivates the physical connection.
 It transmit the raw bits over a communication channel
 If system at one side sends one bit and other side receive one bit

Functions of a Physical layer:

 Representation of bit: This layer data consist of a bits with no interpretation.

 Data Rate: It represents how many number of bits can be transfer in each
second also defined by physical layer
 Synchronization: The sender and receiver both side must have to use the same
bit rate.
 Line configuration: It is concerned with connection of devices to the media in
point to point or multi configuration.
 Topology: It defines how devices are connected to make a network
 Transmission media: It defines the direction of transmission between the
devices as simplex, half duplex and full duplex.
2. Data Link Layer:

Functions of a Data Link layer:

 Framing: It divides the stream of bits received from network layer into data units
called Frame. It contains header, Data and trailer.

 Physical addressing: The data link layer adds a header to the frame that
 consists of a destination address.
 Flow control: It is the main function of the data link layer. The constant data
rate is maintained on both sender and receiver so no data get corrupted.
 Error Control: It is achieved by adding calculated value CRC (Cycle Redundancy
Check) it is placed to data link layer. The trailer which is added to message to
frame before it is sending to physical layer. if any error seems to occur the
receiver sends acknowledgement to retransmit of the corrupted frame.
 Access Control: When two or more devices are connected to the same
communication channel then the data link layer protocols are used to determine
which device control over the link at has given time.
3. Network Layer:

 It is the third layer of the OSI model

 The Data link layer is responsible for routing and forwarding the packets.
 This layer of data is transfer from source to destination through packet
Functions of a Network layer:

 Internetworking: An internet working is the main responsibility of the network

layer. It provides a logical connection between different devices.
 Addressing: A Network layer adds the source and destination address to the
header of the frame. Addressing is used to identify the device on the internet.
 Routing: Routing is the major component of the network layer, and it determines
the best optimal path out of the multiple paths from source to the destination
 Packetizing: A Network Layer receives the packets from the upper layer and
converts them into packets. This process is known as Packetizing. It is achieved
by internet protocol (IP)

4. Transport Layer:
  The Transport layer is a fourth layer of OSI reference model.
 The main responsibility of the transport layer is to transfer the data completely.
 It receives the data from the upper layer and converts them into smaller units
known as segments.
 This layer can be termed as an end-to-end layer as it provides a point-to-point
connection between source and destination to deliver the data reliably. This
layer used two protocols are TCP and UDP
Functions of a Transport Layer:

 Segmentation: When the transport layer receives the message from the upper
layer, it divides the message into multiple segments, and each segment is
assigned with a sequence number that uniquely identifies each segment. When
the message has arrived at the destination, then the transport layer reassembles
the message based on their sequence numbers.
 Connection control: Transport layer provides two services Connection-oriented
service and connectionless service. A connectionless service treats each segment
as an individual packet, and they all travel in different routes to reach the
destination. A connection-oriented service makes a connection with the transport
layer at the destination machine before delivering the packets. In connection-
oriented service, all the packets travel in the single route.
 Flow control: The transport layer also responsible for flow control but it is
performed end-to-end rather than across a single link.
 Error control: The transport layer is also responsible for Error control. The
sender transport layer ensures that message reach at the destination without
any error.

5. Session Layer:

 It is a layer 5 in the OSI model.

 The Session layer is used to establish, maintain and synchronizes the interaction
between communicating devices.
 Functions of Session layer:

 Dialog control: Session layer acts as a dialog controller that creates a dialog
between two processes or we can say that it allows the communication between
two processes which can be either half-duplex or full-duplex.

 Synchronization: Session layer adds some checkpoints when transmitting the

data in a sequence. If some error occurs in the middle of the transmission of
data, then the transmission will take place again from the checkpoint. This
process is known as Synchronization and recovery.

6. Presentation Layer:

 A Presentation layer is mainly concerned with the syntax and semantics of the
information exchanged between the two systems.

 It acts as a data translator for a network.

 This layer is a part of the operating system that converts the data from one
presentation format to another format.
 The Presentation layer is also known as the syntax layer.

Functions of Presentation layer:

Encryption: Encryption is needed to maintain privacy. Encryption is a process of

converting the sender-transmitted information into another form and sends the
resulting message over the network.
Compression: Data compression is a process of compressing the data, i.e., it reduces
the number of bits to be transmitted. Data compression is very important in multimedia
such as text, audio, video

7. Application Layer
  It is the 7th and top most layer of OSI reference model
 It handles issues such as network transparency, resource allocation, etc.
 This layer provides the network services to the end-users.

Functions of Application layer:

 File transfer, access, and management: An application layer allows a user to

access the files in a remote computer, to retrieve the files from a computer and to
manage the files in a remote computer.
 Mail services: An application layer provides the facility for email forwarding and
storage
 Directory services. This application provides distributed database sources and
access for global information about various objects and services.
 Eg: HTTP, FTP, TELNET, SMTP etc...

Lack of OSI Models Success

Advantages
 It is a truly generic model
 The OSI model works as a standard model in data communication
 OSI model is helpful if you want to buy the required software or hardware to
build your own network
 Layers in the OSI model architectures can be distinguished and every layer has
its own importance according to their interfaces, services, and protocols.
 The OSI divides the all process of data communication into simpler and smaller
 The protocols are hidden in the OSI model, so any protocols can be implemented
in the OSI model. OSI model is a standard model, so it can adapt all features of
other protocols.
 The OSI model can facilitate the followings;
Component development
Concept of Modularity
 Design of the network
Troubleshooting of the network
 The OSI model increases the learn ability of the network.

Disadvantages
 The OSI model is a theoretical model. Sometimes it can be a difficulty if the
appropriate technology is not available.
 The OSI restricts its practical implementation.
 The OSI model is a very complex model.
 The initial implementation of the OSI model is slow.
 The initial implementation of the OSI model is costly.
 There is inter dependence among the OSI layers. OSI layers cannot work in
parallel. Each upcoming layer needs to wait to receive the data from its
predecessor layer. For an example the application layer receives the data from
the presentation layer and the presentation layer needs to wait to receive the
data from the session layer and so on.
 The duplication of services in various layers is a problem in the OSI model. Some
Services are offered by multiple layers. Some of these services are mentioned
below;
Flow control
Error control
Addressing etc.

TCP/IP Reference Model

TCP/IP stands for transmission control protocol and internet protocol .It was developed
Department of defense .It has 4 layers.
 These Layers are
 Application Layer
 Transport Layer
 Internet Layer
 Host- to –Network Layer
1. Host-to-Network Layer:
 This is the Lowest Layer
 Protocol is used to connect the host, so that the packets can besent over it.
 Varies host to host and network to network
2. Internet Layer:
 Selection of a packet switching network which is based on a connection less
 Internetwork layer is called internet layer.
 It helps the packets to travel independently to the destination
 It allows the host to insert the packets
 Internet protocol is used in this layer
 This layer holds the whole architecture
3. Transport Layer:
 It decides if data transmission should be on parallel path or single path
 It breaks the message into small units called segments. So that they are handled
more efficiently by the network layer.
 Functions of transport layer are same as the OSI model
 It also arranges the packets sent in sequence.
 This is a third layer of TCP/IP model
4. Application Layer:
Protocols used in this layer are high level protocols such as TELNET, FTP, SMTP, DNS
etc..
 TELNET is a two-way communication protocol, which allows connecting to a
remote machine and run applications on it.
 FTP (File Transfer Protocol) is a protocol that allows File transfer amongst
computer users connected over a network. It is reliable, simple and efficient.
 SMTP (Simple Mail Transport Protocol) is a protocol, which is used to transport
electronic mail between a source and destination, directed via a route.
 DNS (Domain Name Server) resolves an IP address into a textual address for
Hosts connected over a network. It allows peer entities to carry conversation.
 It defines two end-to-end protocols: TCP and UDP
 TCP (Transmission Control Protocol): It is a reliable connection-oriented protocol
which handles byte-stream from source to destination without error and flow
control.
 UDP (User-Datagram Protocol): It is an unreliable connection-less protocol that
do not wants TCPs, sequencing and flow control.

TCP/IP PROTOCOL SUITE

Compare OSI Reference model and TCP /IP

OSI TCP/IP

OSI represents Open System TCP/IP model represents the

Interconnection. Transmission Control Protocol /
Internet Protocol.

OSI is a generic, protocol independent TCP/IP model depends on standard

standard. protocols about which the computer
network has created.

The OSI model was developed first, and The protocols were created first and
then protocols were created to fit the then built the TCP/IP model.
network architecture’s needs.

It provides quality services. It does not provide quality services.

The OSI model represents defines It does not mention the services,
administration, interfaces and interfaces, and protocols.
conventions. It describes clearly which
layer provides services.

It provides both connection and It provides connectionless

connectionless oriented transmission in transmission in the network layer
the network layer

It uses a horizontal approach. It uses a vertical approach.

The smallest size of the OSI header is 5 The smallest size of the TCP/IP header
bytes. is 20 bytes.

It contains 7 layers It contain 4 Layers

 INTERNET HISTORY

ARPANET: Advanced Research Projects Agency

 It was started and developed by the United states

 It was wide area network linking many universities
 It was first to use packet switching which was suggested by Paul Baran and was
the beginning of what we consider the internet today
 It was created to make it easier for people to access computers ,improved computer
equipment
 It is used to have more effective communication method of military
 It was started when two nodes are established between UCLA(University of
California and Loss Angles) and Stanford Research Institute in 1969 .
 ARPANET completed its transits to TCP/IP on January 2,1983

 It consist of subnet host computers

 The subnet would consist of minicomputers called IMPs (Interface Message
Processors) connected by 56-kbps transmission lines.
 Each IMP would be connected to at least two other IMPs. The subnet was to be a
datagram subnet, so if some lines and IMPs were destroyed, messages could be
automatically rerouted along alternative paths.
 The software was split into two parts: subnet and host. The subnet software consisted
of the IMP end to the host IMP connection, the IMP-IMP protocol, and a source IMP to
 destination IMP protocol designed to improve reliability.

NSFNET (National Science Foundation)

 NSF (the U.S. National Science Foundation) saw the enormous impact that the
ARPANET was having on university research, allowing scientists across the country to
share data and collaborate on research projects. This lack of universal access
prompted NSF to set up a virtual network.
 NSF decided to build a backbone network to connect its six supercomputer centers;
each supercomputer was given a little brother, consisting of an LSI-11 microcomputer
called a fuzz ball. The fuzzballs were connected with 56-kbps leased lines and formed
the subnet, the same hardware technology as the ARPANET used. The software
technology was different however: the fuzzballs spoke TCP/IP right from the start,
making it as a first TCP/IP WAN.
 NSF also funded some 20 regional networks that connected to the backbone to allow
users at thousands of universities, research labs, libraries, and museums to access
any of the supercomputers and to communicate with one another. The complete
network, including the backbone and the regional networks, was called NSFNET. It
connected to the ARPANET through a link between an IMP and a fuzz ball.
 Consequently, NSF encouraged MERIT, MCI, and IBM to form a nonprofit corporation.
ANS (Advanced Networks and Services). In 1990, ANS took over NSFNET and
upgraded the 1.5-Mbps links to 45 Mbps to form ANSNET.
INTERNET:
The number of networks, machines, and users connected to the ARPANET grew rapidly
after TCP/IP became the only official protocol on January 1, 1983. When NSFNET and
the ARPANET were interconnected, the growth became exponential.
Traditionally the Internet and its predecessors had four main applications:
1. E-mail. The ability to compose, send, and receive electronic mail has been around
since the early days of the ARPANET and is enormously popular. Many people get
dozens of messages a day and consider it their primary way of interacting with the
outside world, far outdistancing the telephone and snail mail. E-mail programs are
available on virtually every kind of computer these days.
2. News. Newsgroups are specialized forums in which users with a common interest
can exchange messages. Thousands of newsgroups exist, devoted to technical and
nontechnical topics, including computers, science, recreation, and politics. Each
newsgroup has its own etiquette, style, and customs, and woe betide anyone violating
them.
3. Remote login. Using the telnet, rlogin, users anywhere on the Internet can log on to
any other machine on which they have an account.
4. File transfer. Using the FTP program, users can copy files from one machine on the
Internet to another. Vast numbers of articles, databases, and other information are
available this way.
Physical Layer

Transmission Media: It is the Physical path between the sender and

receiver in a data transmission system it is included in the Physical layer of the
OSI reference Model.

Introduction to Guided media

It is defined as the physical medium through which the signals are
transmitted. It is also known as Bounded media or Guided media.

Twisted pair:

 It is the simplest, oldest and low priced cable medium

 It is made up of two insulated copper wires about 1mm thick twisted
around each other.
 It is a lightweight cable.
 The frequency range for twisted pair cable is from 0 to 3.5 KHz.
 It was invented by Alexander Graham Bell

.
 It is used for transmitting either analog or digital signals
 The brand with depends upon the thickness of the wire and the distance
travel
 Twisted cables are two types 1.Unshield Twisted Pair
2. Shied twisted pair
Unshield Twisted Pair
 It is one of the most popular LAN cables
 It consist of 4 twisted pair of copper wires

 Installation of the unshielded twisted pair is easy.

 It can be used for high-speed LAN
 An unshielded twisted pair is widely used in telecommunication.
 The UTP cables are twisted both data and voice transmission commonly
used in telephone system
 They are also widely used in DSL lines ,10Base -T,100 Base-T LAN

The Electronic Industries Association divides UTP into 7 categories based on

some standards.

Category Data rate Max.Length Application

CAT1 UP to 1 Mbps - Old Telephone Cable
CAT2 UP to 4 Mbps - Token Ring Network
CAT3 UP to 10 Mbps 100m 10 Base-T Ethernet
CAT4 UP to 16 Mbps 100m Token Ring Network
CAT5 UP to 100 Mbps 100m Ethernet, Fast Ethernet
CAT5A UP to 1Gbps 100m Ethernet, Fast Ethernet, Giga Byte
CAT6 UP to 10 GBPS 100m Giga Byte Ethernet
CAT7 UP to 10 GBPS 100m Giga Byte Ethernet

Advantages of the UTP:

 It is a less costly and less expensive unshielded wire from another
network medium.
 It is designed to reduce crosstalk, RFI, and EMI.
 Its size is small, and hence the installation of the UTP is easier.
 It is mostly useful for short-distance network connections like home
and small organizations.
 It is the most commonly used networking cable in the market. It is
considered as faster copper-based data transmission cable.
 It is suitable for transmitting both data and voice via UTP cable.
Disadvantage of the UTP:
 It can only be used in length segment up to 100 meters.
 It has limited bandwidth for transmitting the data.
 It does not provide a secure connection for data transmitting over the
network.
Shied twisted pair
 IBM invented the shielded twisted pair (STP) cable for token ring networks,
including two independent wires coated in a foil shielding that prevents
electromagnetic interference and speeds up data transmission.

 A shielded twisted pair is a type of twisted pair cable that contains an

extra wrapping foil or copper braid jacket to protect the cable from
defects like cuts, losing bandwidth, noise, and signal to the
interference.
 It is a cable that is usually used underground, and therefore it is costly
than UTP.
 It supports the higher data transmission rates across the long distance.
We can also say it is a cable with metal sheath or coating that
surrounds each pair of the insulated conductor to protect the wire from
external users and prevent electromagnetic noise from penetrating.
Advantages of the STP cable
 It has lower noise and attenuation than UTP.
 It is shielded with a plastic cover that protects the STP cable from a harsh
environment and increases the data transmission rate.
 It reduces the chances of crosstalk and protects from external interference.
 A modular connection helps to terminate the connection of the STP cable.
Disadvantages of the STP cable
 It is the most expensive wire from UTP cables.
 It requires more maintenance to reduce the loss of data signals.
 There is no segment improvement in length despite its thick and heavier
connection.
 It is used only as a grounded wire.

Type of Connector Used in UTP and STP cable

RJ-45 JACK
 UTP cable is installed using RJ-45 connector .It is an eight wire
connector use commonly to connect computers on to LAN.
 It is also known as 8P8C connector
Coaxial Cable

 Coaxial cable is very commonly used transmission media, for example, TV

wire is usually a coaxial cable.
 It has a higher frequency as compared to twisted pair cable.
 The inner conductor of the coaxial cable is made up of copper, and the
 outer conductor is made up of copper mesh. The middle core is made up of
non-conductive cover that separates the inner conductor from the outer
conductor.
 The middle core is responsible for the data transferring whereas the
copper mesh prevents from the EMI (Electromagnetic interference).
 There are two types of coaxial cables are Thick Client and Thin Client.
 RG-11: used with thick Ethernet.
 RG-58 : used with thin Ethernet
 RG-59 : used with cable television
Applications of Coaxial Cable

 Coaxial cable was widely used in analog telephone networks, where a

single coaxial network could carry 10,000 voice signals.
 Cable TV networks also use coaxial cables. In the traditional cable TV
network, the entire network used coaxial cable. Cable TV uses RG-59
coaxial cable.
 In traditional Ethernet LANs. Because of it high bandwidth, and
consequence high data rate, coaxial cable was chosen for digital
transmission in early Ethernet LANs. The 10Base-2, or Thin Ethernet,
uses RG-58 coaxial cable with BNC connectors to transmit data at 10Mbps
with a range of 185 m.

Structure of Coaxial Cable

Advantages of Coaxial cable:

 The data can be transmitted at high speed.
 It has better shielding as compared to twisted pair cable.
 It provides higher bandwidth.
Disadvantages of Coaxial cable
 It is more expensive as compared to twisted pair cable.
 If any fault occurs in the cable causes the failure in the entire network.

Type of Connector Used in Coaxial cable

 To connect coaxial cable to devices, we need coaxial connectors. The most
common type of connector used today is the Bayonet Neill-Concelman
(BNC) connector.
 The BNC connector is used to connect the end of the cable to the device,
 such as a TV set. The BNC T connector is used in Ethernet networks to
branch out to a connection to a computer or other device.

Optical Fiber

 A fiber optic cable is made of glass or plastic and transmits signals in the
structure of light signals. In fiber optics, semiconductor lasers transmit
data in the form of light along with hair-thin glass (optical) fibers at the
speed of light (186,000 miles second) with no significant loss of intensity
over very long distances. The system includes fiber optic cables that are
made of tiny threads of glass or plastic.

 Fiber optic cable support two modes of propagating light ,They are
Multimode: In this mode many beams from a light source traverse along
multiple paths and multiple angles.

Single mode: The beams propagate almost horizontally LED or Laser acts
as the source converting electric pulse to light pluses and photodiode acts
as receiver doing vice versa.

Structure of Fiber Optical Cable

Core: The optical fiber consists of a narrow strand of glass or plastic known as a
core. A core is a light transmission area of the fiber. The more the area of the
core, the lighter will be transmitted into the fiber.
Cladding: The concentric layer of glass is known as cladding. The main
functionality of the cladding is to provide the lower refractive index at the core
interface as to cause the reflection within the core so that the light waves are
transmitted through the fiber.

Jacket: The protective coating consisting of plastic is known as a jacket. The

main purpose of a jacket is to preserve the fiber strength, absorb shock and
extra fiber protection.
Characteristics of Optical Fiber Cables
 Fiber optic cabling can support too high bandwidths in the range from 100
Mbps to 2 gigabytes because light has a much greater frequency than
electricity.
 Fiber optic cable is not concerned by EMI effects and can be used in
locations where high voltages pass.
 The value of fiber optic cable is more distinguished to twisted pair and co-
axial.
 The setup of fiber optic cables is complex and endless.
Advantages of Optical Fibers
 Small Size and lightweight − the size (diameter) of the optical fibers is
minimal (comparable to the diameter of a human hair).
 Easily available and low cost − the material used for producing the
optical fibers is silica glass. This material is readily applicable. Therefore,
the optical fibers cost lower than the cables with metallic conductors.
 No electrical or electromagnetic interface − since the transmission
occurs in light rays, the signal is not affected by electrical or
electromagnetic interference.

 Large Bandwidth − As the light arrays have a very high frequency in the
GHz range, the optical fiber bandwidth is vast. This allows the
transmission of more numbers of channels. Therefore, the information-
carrying capacity of an optical fiber is much higher than that of a Co-axial
cable.

Disadvantages of Optical Fibers

High Cost − The cable and the interfaces are associatively more expensive than
those of other guided media.
Unidirectional light propagation − since the optical transmission is inherently
unidirectional two-way communication requires either two fibers or two
frequency bands on one fiber.
Installation and Maintenance − Fiber is different technology requiring skills
most engineers do not occupy.

Type of Connector Used in Optical Fiber

 SC connector and ST connector are used in Fiber optical
Unguided Media

 An unguided transmission transmits the electromagnetic waves without

using any physical medium. Therefore it is also known as wireless
transmission.
 In unguided media, air is the media through which the electromagnetic
energy can flow easily.

Radio Waves:

 These are electromagnetic waves that may be transmitted in all directions

in free space.
 Radio waves are omnidirectional, which means that signals travel in all
directions.
 Radio waves have frequencies ranging from 3 KHz to 1 KHz.
 In the case of radio waves, the sending and receiving antennas are not
aligned, thus the wave sent by the sending antenna can be received by any
receiving antenna.
 FM radio is one example of a radio wave.
Applications of Radio Waves:
 When there is only one transmitter and numerous recipients, a radio wave
is helpful for multicasting.
 Radio waves are used by FM radio, television, and cordless phones.
Advantages of Radio Waves:
 Radio transmission is mostly utilized for wide area networks and mobile
phones.
 Radio waves may penetrate barriers and cover a vast area.
 A greater transmission rate is provided through radio transmission.
Microwaves

 Electromagnetic waves having frequencies between 1 and 300 GHz are

called micro waves.
 Micro waves are unidirectional. When an antenna transmits microwaves,
they can be narrowly focused. This means that the sending and receiving
antennas need to be aligned. The unidirectional property has an obvious
advantage. A pair of antennas can be aligned without interfering with
another pair of aligned antennas.
Characteristics of microwaves propagation
 Microwave propagation is line-of-sight. Since the towers with the mounted
antennas need to be in direct sight of each other, towers that are far apart
need to be very tall.
 Very high-frequency microwaves cannot penetrate walls. This
characteristic can be a disadvantage if receivers are inside the buildings.
 The microwave band is relatively wide, almost 299 GHz. Therefore, wider
sub-bands can be assigned and a high date rate is possible.
 Use of certain portions of the band requires permission from authorities.

Terrestrial Transmission:
 Terrestrial microwave transmission is a method of transmitting a
concentrated and focused beam of a radio signal from one ground-based
microwave transmission antenna to another.
 Microwaves are electromagnetic waves with frequencies ranging from 1GHz
to 1000GHz.
 Microwaves are unidirectional because the transmitting and receiving
antennas must be aligned, resulting in narrowly focused waves produced
by the sending antenna.
 Antennas are installed on towers in this example to deliver a beam to
another antenna located kilometers distant.
 It is based on line-of-sight transmission, which means that the antennas
installed on the towers are in direct sight of each other.
Satellite Transmission
 A satellite is a physical entity that orbits the Earth at a fixed altitude.
 Satellite communication is more dependable now a day since it is more
adaptable than cable and fiber optic technologies.
 Using satellite communication, we can connect with any location on the
planet.
Advantages of Satellite Microwave Transmission:
 A satellite microwave has a larger coverage area than a terrestrial
microwave.
  The satellite’s transmission cost is independent of the distance from the
centre of the coverage region.
 In mobile and wireless communication applications, satellite
communication is employed.
 It is simple to set up.
 It is utilized in many different applications, including weather forecasting,
radio/TV signal transmission, mobile communication, and so on.
Disadvantages of Satellite Microwave Transmission:
 Satellite design and development need more time and money.
 The satellite must be monitored and operated on a regular basis in order
to remain in orbit.
 The satellite has a lifespan of 12-15 years. As a result, another launch of
the satellite is required before it becomes inoperable.

Infrared Waves

 Infrared transmission is a wireless technique used for short-range

communication.
 The frequency range for infrared wave transmission varies from 300 GHz
to 400 THz.
 It is used for short-range communication, such as data transmission
between two cell phones, TV remote control operation, and data transfer
between a computer and a mobile phone that are both in the same
confined area.
Characteristics of Infrared Transmission
 It has a large bandwidth; therefore the data rate will be quite high.
 Infrared waves are unable to permeate the walls. As a result, infrared
communication in one room cannot be disturbed by infrared signals from
nearby rooms.
 Infrared communication gives greater security while causing the least
amount of disturbance.
 Outside the building, infrared communication is unreliable because the
sun’s rays interfere with the infrared signals.