Unit - 1

Network Hardware
The computer networks can be discussed in two dimensions
i) Transmission technology ii) Scale
There are two types of transmission technology that are in widespread use:
Broadcast links
Point-to-point links.
Point-to-point links connect individual pairs of machines. To go from the source to the destination
on a network made up of point-to-point links, short messages, called packets in certain contexts,
may have to first visit one or more intermediate machines. Often multiple routes, of different
lengths, are possible, so finding good ones is important in point-to-point networks. Point-to-point
transmission with exactly one sender and exactly one receiver is sometimes called unicasting.
On a broadcast network, the communication channel is shared by all the machines on the network;
packets sent by any machine are received by all the others. An address field within each packet
specifies the intended recipient. Upon receiving a packet, a machine checks the address field. If the
packet is intended for the receiving machine, that machine processes the packet; if the packet is
intended for some other machine, it is just ignored. A wireless network is a common example of a
broadcast link, with communication shared over a coverage region that depends on the wireless
channel and the transmitting machine.
When a packet with this code is transmitted, it is received and processed by every machine on the
network. This mode of operation is called broadcasting. Some broadcast systems also support
transmission to a subset of the machines, which known as multicasting.
Scale
An alternative criterion for classifying networks is by scale. Distance is important as a
classification metric because different technologies are used at different scales.
Personal Area Network
PANs (Personal Area Networks) let devices communicate over the range of a person. A common
example is a wireless network that connects a computer with its peripherals. Almost every
computer has an attached monitor, keyboard, mouse, and printer. Without using wireless, this
connection must be done with cables. some companies have designed a short-range wireless
network called Bluetooth to connect these components without wires. The idea is that if our
devices have Bluetooth, then we need no cables. You just put them down, turn them on, and they
work together.
In the simplest form, Bluetooth networks use the master-slave paradigm. The system unit (the PC)
is normally the master, talking to the mouse, keyboard, etc., as slaves. The master tells the slaves
what addresses to use, when they can broadcast, how long they can transmit, what frequencies they
can use, and so on.

Local Area Networks

A LAN is a privately owned network that operates within and nearby a single building like a
home, office or factory. LANs are widely used to connect personal computers and consumer
electronics to let them share resources (e.g., printers) and exchange information. When LANs are
used by companies, they are called enterprise networks. Wireless LANs are also popular where
each computer communicates with the device called an AP (Access Point), wireless router, or base
station which relays packets between the wireless computers and also between them and the
Internet. There is a standard for wireless LANs called IEEE 802.11, popularly known as WiFi and
it runs at speed from 11 to hundreds of Mbps. Wired LANs use a range of different transmission
technologies. Most of them use copper wires, but some use optical fiber.
Metropolitan Area Network
A MAN (Metropolitan Area Network) covers a city. The best-known examples of MANs are the
cable television networks available in many cities. Recent developments in highspeed wireless
Internet access have resulted in another MAN, which has been standardized as IEEE 802.16 and is
popularly known as WiMAX.
Wide Area Network
A WAN (Wide Area Network) spans a large geographical area, often a country or continent. In
most WANs, the subnet consists of two distinct components: transmission lines and switching
elements. Transmission lines move bits between machines. They can be made of copper wire,
optical fiber, or even radio links. Most companies do not have transmission lines lying about, so
instead they lease the lines from a telecommunications company. Switching elements, or just
switches, are specialized computers that connect two or more transmission lines.
Internetworks
A collection of interconnected networks is called an internetwork or internet. A network is formed
by the combination of a subnet and its hosts. The machine that makes a connection between two or
more networks and provides the necessary translation, both in terms of hardware and software, is a
gateway.

Network Software
Protocol Hierarchies
To reduce their design complexity, most networks are organized as a stack of layers or levels, each
one built upon the one below it. The number of layers, the name of each layer, the contents of each
layer, and the function of each layer differ from network to network. The purpose of each layer is
to offer certain services to the higher layers while shielding those layers from the details of how
the offered services are actually implemented. In a sense, each layer is a kind of virtual machine,
offering certain services to the layer above it. When layer n on one machine carries on a
conversation with layer n on another machine, the rules and conventions used in this conversation
are collectively known as the layer n protocol. Basically, a protocol is an agreement between the
communicating parties on how communication is to proceed. Between each pair of adjacent layers
is an interface. The interface defines which primitive operations and services the lower layer
makes available to the upper one.
A set of layers and protocols is called a network architecture. A list of the protocols used by a
certain system, one protocol per layer, is called a protocol stack.
Design Issues for the Layers
Reliability is the design issue of making a network that operates correctly even though it is made
up of a collection of components that are themselves unreliable.
Mechanism for finding errors in received information uses codes for error detection. Information
that is incorrectly received can then be retransmitted until it is received correctly. More powerful
codes allow for error correction, where the correct message is recovered from the possibly
incorrect bits that were originally received.
Another issue is finding a working path through a network. Often there are multiple paths between
a source and destination, and in a large network, there may be some links or routers that are
broken. The network should automatically make this decision. This topic is called routing.
Since there are many computers on the network, every layer needs a mechanism for identifying the
senders and receivers that are involved in a particular message. This mechanism is called
addressing or naming, in the low and high layers.
The network should continue to work well even when the network gets large. It is said to be
scalable. Another design issue is resource allocation. Networks provide a service to hosts from
their underlying resources, such as the capacity of transmission lines. To do this well, they need
mechanisms that divide their resources so that one host does not interfere with another too much.
A service is formally specified by a set of primitives (operations) available to user processes to
access the service. These primitives tell the service to perform some action or report on an action
taken by a peer entity.

Protocol Layering
 In networking, a protocol defines the rules that both the sender and receiver and
 all intermediate devices need to follow to be able to communicate effectively.
 A protocol provides a communication service that the process use to exchange
messages.
 When communication is simple, we may need only one simple protocol.
 When the communication is complex, we may need to divide the task between
different layers, in which case we need a protocol at each layer, or protocol
layering.
 Protocol layering is that it allows us to separate the services from the
implementation.
 A layer needs to be able to receive a set of services from the lower layer and to
give the services to the upper layer.
 Any modification in one layer will not affect the other layers.

Basic Elements of Layered Architecture

 Service: It is a set of actions that a layer provides to the higher layer.
 Protocol: It defines a set of rules that a layer uses to exchange the information
with peer entity. These rules mainly concern about both the contents and order of
the messages used.
 Interface: It is a way through which the message is transferred from one layer to
another layer.

Features of Protocol Layering

1. It decomposes the problem of building a network into more manageable
components.
2. It provides a more modular design.

Principles of Protocol Layering

1. The first principle dictates that if we want bidirectional communication, we need
to make each layer so that it is able to perform two opposite tasks, one in each
 direction.
2. The second principle that we need to follow in protocol layering is that the two
objects under each layer at both sites should be identical.

OSI Reference Model

o OSI stands for Open System Interconnection.

o It is a reference model that describes how information from a software application
in one computer moves through a physical medium to the software application in
another computer.
o OSI consists of seven layers, and each layer performs a particular network
function.
o OSI model was developed by the International Organization for Standardization
(ISO) in 1984, and it is now considered as an architectural model for the inter-
computer communications.
o OSI model divides the whole task into seven smaller and manageable tasks. Each
layer is assigned a particular task.
o Each layer is self-contained, so that task assigned to each layer can be performed
independently.

ORGANIZATION OF THE OSI LAYERS

FUNCTIONS OF THE OSI LAYERS
1.PHYSICAL LAYER
The physical layer coordinates the functions required to transmit a bit stream over a
physical medium.
The physical layer is concerned with the following functions:
 Physical characteristics of interfaces and media - The physical layer defines
the characteristics of the interface between the devices and the transmission
medium.
 Representation of bits - To transmit the stream of bits, it must be encoded to
signals. The physical layer defines the type of encoding.
 Signals: It determines the type of the signal used for transmitting the information.
 Data Rate or Transmission rate - The number of bits sent each second –is also
defined by the physical layer.
 Synchronization of bits - The sender and receiver must be synchronized at the
bit level. Their clocks must be synchronized.
 Line Configuration - In a point-to-point configuration, two devices are
connected together through a dedicated link. In a multipoint configuration, a link
is shared between several devices.
 Physical Topology - The physical topology defines how devices are connected to
make a network. Devices can be connected using a mesh, bus, star or ring
topology.
 Transmission Mode - The physical layer also defines the direction of
transmission between two devices: simplex, half-duplex or full-duplex.

2.DATA LINK LAYER

It is responsible for transmitting frames from one node to the next node.
The other responsibilities of this layer are
 Framing - Divides the stream of bits received into data units called frames.
 Physical addressing – If frames are to be distributed to different systems on the
network , data link layer adds a header to the frame to define the sender and
receiver.
 Flow control- If the rate at which the data are absorbed by the receiver is less
 than the rate produced in the sender, t h e Data link layer imposes a flow
ctrl mechanism.
 Error control- Used for detecting and retransmitting damaged or lost frames and
to prevent duplication of frames. This is achieved through a trailer added at the
end of the frame.
 Medium Access control -Used to determine which device has control over the
link at any given time.

3.NETWORK LAYER

This layer is responsible for the delivery of packets from source to destination.
It determines the best path to move data from source to the destination based on the
network conditions, the priority of service, and other factors.
The other responsibilities of this layer are
 Logical addressing - If a packet passes the network boundary, we need another
addressing system for source and destination called logical address. This
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.

4.TRANSPORT LAYER

It is responsible for Process to Process delivery. That is responsible for source-to-

destination (end-to-end) delivery of the entire message, It also ensures whether the
message arrives in order or not.
The other responsibilities of this layer are
 Port addressing / Service Point addressing - The header includes an address
called port address / service point address. This layer gets the entire message to
the correct process on that computer.
  Segmentation and reassembly - The message is divided into segments and each
segment is assigned a sequence number. These numbers are arranged correctly on
the arrival side by this layer.

 Connection control - This can either be connectionless or connection oriented.

 The connectionless treats each segment as an individual packet

and delivers to the destination.
 The connection-oriented makes connection on the destination side
before the delivery. After the delivery the termination will be terminated.
 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 - Error control is performed end-to-end rather than across the
single link..

5.SESSION LAYER

This layer establishes, manages and terminates connections between applications.

The other responsibilities of this layer are
 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

It is concerned with the syntax and semantics of information exchanged between two
systems.
The other responsibilities of this layer are
  Translation – Different computers use different encoding system, this layer is
responsible for interoperability between these different encoding methods. It will
change the message into some common format.
 Encryption and decryption-It means that sender transforms the original
information to another form and sends the resulting message over the n/w. and
vice versa.
 Compression and expansion-Compression reduces the number of bits contained
in the information particularly in text, audio and video.

7.APPLICATION LAYER
This layer enables the user to access the network. It handles issues such as network
transparency, resource allocation, etc. This allows the user to log on to remote user.
The other responsibilities of this layer are
 FTAM (File Transfer, Access, Management) - Allows user to access files in a
remote host.
 Mail services - Provides email forwarding and storage.
 Directory services - Provides database sources to access information about
various sources and objects.

TCP / IP Protocol
 The TCP/IP architecture is also called as Internet architecture.
 It is developed by the US Defense Advanced Research Project Agency (DARPA)
for its packet switched network (ARPANET).
 TCP/IP is a protocol suite used in the Internet today.
 It is a 4-layer model. The layers of TCP/IP are
1. Application layer
2. Transport Layer (TCP/UDP)
3. Internet Layer
4. The Host - to - Network Layer
APPLICATION LAYER
 An application layer incorporates the function of top three OSI layers. An
application layer is the topmost layer in the TCP/IP model.
 It is responsible for handling high-level protocols, issues of representation.
 This layer allows the user to interact with the application.
 When one application layer protocol wants to communicate with another
application layer, it forwards its data to the transport layer.
 Protocols such as FTP, HTTP, SMTP, POP3, etc running in the application layer
provides service to other program running on top of application layer
TRANSPORT LAYER
 The transport layer is responsible for the reliability, flow control, and correction
of data which is being sent over the network.
 The two protocols used in the transport layer are User Datagram protocol and
Transmission control protocol.
o UDP – UDP provides connectionless service and end-to-end delivery of
transmission. It is an unreliable protocol as it discovers the errors but not
specify the error.
o TCP – TCP provides a full transport layer services to applications. TCP is
a reliable protocol as it detects the error and retransmits the damaged
frames.
INTERNET LAYER
 The internet layer is the second layer of the TCP/IP model.
 An internet layer is also known as the network layer.
 The main responsibility of the internet layer is to send the packets from any
network, and they arrive at the destination irrespective of the route they take.
 Internet layer handle the transfer of information across multiple networks through
router and gateway .
 IP protocol is used in this layer, and it is the most significant part of the entire
TCP/IP suite.

HOST - TO - NETWORK LAYER

 The network interface layer is the lowest layer of the TCP/IP model.
 This layer is the combination of the Physical layer and Data Link layer defined in
the OSI reference model.
 It defines how the data should be sent physically through the network.
 This layer is mainly responsible for the transmission of the data between two
devices on the same network.
 The functions carried out by this layer are encapsulating the IP datagram into
frames transmitted by the network and mapping of IP addresses into physical
addresses.
 The protocols used by this layer are Ethernet, token ring, FDDI, X.25, frame
relay.
ARPANET
At the height of the Cold War, the U.S in 1950s, DoD wanted a command-and-control network
that could survive a nuclear war. At that time, all military communications used the public
telephone network, which was considered vulnerable.

Here the black dots represent telephone switching offices, each of which was connected to
thousands of telephones. These switching offices were, in turn, connected to higher-level
switching offices (toll offices), to form a national hierarchy with only a small amount of
redundancy. The vulnerability of the system was that the destruction of a few key toll offices
could fragment it into many isolated islands.
In 1957, a single defense research organization, ARPA, the Advanced Research Projects Agency
was created. ARPA had no scientists or laboratories; in fact, it had nothing more than an office and
a small (by Pentagon standards) budget. It did its work by issuing grants and contracts to
universities and companies whose ideas looked promising to it. Later, suggested building a packet-
switched subnet, connecting each host to its own router.
The subnet would consist of minicomputers called IMPs (Interface Message Processors)
connected by 56-kbps transmission lines. For high reliability, 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. Each node of the
network was to consist of an IMP and a host, in the same room, connected by a short wire. A host
could send messages of up to 8063 bits to its IMP, which would then break these up into packets of
at most 1008 bits and forward them independently toward the destination. Each packet was
received in its entirety before being forwarded, so the subnet was the first electronic store and-
forward packet-switching network.

During the 1980s, additional networks, especially LANs, were connected to the ARPANET. As
the scale increased, finding hosts became increasingly expensive, so DNS (Domain Name
System) was created to organize machines into domains and map host names onto IP addresses.

Transmission Media
o Transmission media is a communication channel that carries the information from
the sender to the receiver.
o Data is transmitted through the electromagnetic signals.
 o The main functionality of the transmission media is to carry the information in
the form of bits (Either as Electrical signals or Light pulses).
o It is a physical path between transmitter and receiver in data communication.
o The characteristics and quality of data transmission are determined by the
characteristics of medium and signal.
o Transmission media is of two types : Guided Media (Wired) and UnGuided
Media (wireless).
o In guided (wired) media, medium characteristics are more important whereas, in

unguided (wireless) media, signal characteristics are more important.

o Different transmission media have different properties such as bandwidth, delay,

cost and ease of installation and maintenance.

o The transmission media is available in the lowest layer of the OSI reference

model, i.e., Physical layer.

FACTORS FOR DESIGNING THE TRANSMISSION MEDIA

o Bandwidth: All the factors are remaining constant, the greater the bandwidth of a

medium, the higher the data transmission rate of a signal.

o Transmission impairment: When the received signal is not identical to the

transmitted one due to the transmission impairment. The quality of the signals
will get destroyed due to transmission impairment.
o Interference: An interference is defined as the process of disrupting a signal

when it travels over a communication medium on the addition of some unwanted

signal.

GUIDED MEDIA
 It is defined as the physical medium through which the signals are transmitted.
  It is also known as Bounded media.
 Types of Guided media: Twisted Pair Cable, Coaxial Cable, Fibre Optic Cable

TWISTED PAIR CABLE

 Twisted pair is a physical media made up of a pair of cables twisted with each
other.
 A twisted pair cable is cheap as compared to other transmission media.
 Installation of the twisted pair cable is easy, and it is a lightweight cable.
 The frequency ranges for twisted pair cable is from 0 to 3.5KHz.
 A twisted pair consists of two insulated copper wires arranged in a regular spiral
pattern.

Unshielded Twisted Pair

An unshielded twisted pair is widely used in telecommunication.
Following are the categories of the unshielded twisted pair cable:
o Category 1: Suports low-speed data.
o Category 2: It can support upto 4Mbps.
 o Category 3: It can support upto 16Mbps.
o Category 4: It can support upto 20Mbps.
o Category 5: It can support upto 200Mbps.

Advantages :
o It is cheap.
o Installation of the unshielded twisted pair is easy.
o It can be used for high-speed LAN.

Disadvantage:
o This cable can only be used for shorter distances because of attenuation.

Shielded Twisted Pair

A shielded twisted pair is a cable that contains the mesh surrounding the wire that allows
the higher transmission rate.

Advantages :
o The cost of the shielded twisted pair cable is not very high and not very low.
o Installation of STP is easy.
 o It has higher capacity as compared to unshielded twisted pair cable.
o It has a higher attenuation.
o It is shielded that provides the higher data transmission rate.

Disadvantages:
o It is more expensive as compared to UTP and coaxial cable.
o It has a higher attenuation rate.

COAXIAL CABLE

o Coaxial cable(Coax) is a very commonly used transmission media, for example,

TV wire is usually a coaxial cable.

o The name of the cable is coaxial as it contains two conductors parallel to each
other.
o It has a higher frequency as compared to Twisted pair cable.
o The inner conductor of the coaxial cable is made up of copper, and the outer
conductor is made up of copper mesh.
o The middle core is made up of non-conductive cover that separates the inner
conductor from the outer conductor.
o The middle core is responsible for the data transferring whereas the copper mesh
prevents from the EMI(Electromagnetic interference).
o Common applications of coaxial cable are Cable TV networks and traditional
Ethernet LANs.
Coaxial Cable Standards
 Coaxial cables are categorized by their Radio Government (RG) ratings.
 Each RG number denotes a unique set of physical specifications, including the
wire gauge of the inner conductor, the thickness and type of the inner insulator,
the construction of the shield, and the size and type of the outer casing.
 Each cable defined by an RG rating is adapted for a specialized function.

Types of Coaxial cable :

1. Baseband transmission: It is defined as the process of transmitting a single
signal at high speed.
2. Broadband transmission: It is defined as the process of transmitting multiple
signals simultaneously.
Advantages :
o The data can be transmitted at high speed.
o It has better shielding as compared to twisted pair cable.
o It provides higher bandwidth.
Disadvantages :
o It is more expensive as compared to twisted pair cable.
o If any fault occurs in the cable causes the failure in the entire network.

FIBRE OPTIC CABLE

o Fibre optic cable is a cable that uses electrical signals for communication.
o Fibre optic is a cable that holds the optical fibres coated in plastic that are used to
send the data by pulses of light.
o The plastic coating protects the optical fibres from heat, cold, electromagnetic
interference from other types of wiring.
o Fibre optics provide faster data transmission than copper wires.

Basic elements of Fibre optic cable:

o Core: The optical fibre consists of a narrow strand of glass or plastic known as a
core. A core is a light transmission area of the fibre. The more the area of the
core, the more light will be transmitted into the fibre.
o 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 fibre.
o Jacket: The protective coating consisting of plastic is known as a jacket. The
main purpose of a jacket is to preserve the fibre strength, absorb shock and extra
 fibre protection.

Advantages:
o Greater Bandwidth
o Less signal attenuation
o Immunity to electromagnetic interference
o Resistance to corrosive materials
o Light weight
o Greater immunity to tapping

Disadvantages :
o Requires Expertise for Installation and maintenance
o Unidirectional light propagation.
o Higher Cost.

Propagation Modes of Fibre Optics

 Current technology supports two modes (multimode and single mode) for
propagating light along optical channels, each requiring fiber with different
physical characteristics.
 Multimode can be implemented in two forms: step-index or graded-index.

Multimode Propagation
 Multimode is so named because multiple beams from a light source move through
the core in different paths.
  How these beams move within the cable depends on the structure of the core.

Single-Mode Propagation

 Single-mode uses step-index fiber and a highly focused source of light that limits
beams to a small range of angles, all close to the horizontal.
 The single-mode fiber itself is manufactured with a much smaller diameter than
that of multimode fiber, and with substantially lower density (index of refraction).
 The decrease in density results in a critical angle that is close enough to 90° to
make the propagation of beams almost horizontal.
 In this case, propagation of different beams is almost identical, and delays are
negligible. All the beams arrive at the destination “together” and can be
recombined with little distortion to the signal.
UNGUIDED MEDIA
o An unguided transmission transmits the electromagnetic waves without using any
physical medium. Therefore it is also known as wireless transmission.
o In unguided media, air is the media through which the electromagnetic energy
can flow easily.

Unguided transmission is broadly classified into three categories : Radio Waves, Microwaves ,
 Infrared

RADIO WAVES

o Radio waves are the electromagnetic waves that are transmitted in all the
directions of free space.
o Radio waves are omnidirectional, i.e., the signals are propagated in all the
directions.
o The range in frequencies of radio waves is from 3Khz to 1Ghz.
o In the case of radio waves, the sending and receiving antenna are not aligned, i.e.,
the wave sent by the sending antenna can be received by any receiving antenna.
o An example of the radio wave is FM radio.

Applications of Radio waves:

o A Radio wave is useful for multicasting when there is one sender and many
receivers.
o An FM radio, television, cordless phones are examples of a radio wave.

Advantages of Radio waves:

o Radio transmission is mainly used for wide area networks and mobile cellular
phones.
o Radio waves cover a large area, and they can penetrate the walls.
o Radio transmission provides a higher transmission rate.
 MICROWAVES
Microwaves are of two types - Terrestrial microwave & Satellite microwave

Terrestrial Microwave
o Terrestrial Microwave transmission is a technology that transmits the focused
beam of a radio signal from one ground-based microwave transmission antenna to
another.
o Microwaves are the electromagnetic waves having the frequency in the range
from 1GHz to 1000 GHz.
o Microwaves are unidirectional as the sending and receiving antenna is to be
aligned, i.e., the waves sent by the sending antenna are narrowly focused.
o In this case, antennas are mounted on the towers to send a beam to another
antenna which is km away.
o It works on the line of sight transmission, i.e., the antennas mounted on the
towers are at the direct sight of each other.

Characteristics of Terrestrial Microwave:

o Frequency range: The frequency range of terrestrial microwave is from 4-6 GHz
to 21-23 GHz.
o Bandwidth: It supports the bandwidth from 1 to 10 Mbps.
o Short distance: It is inexpensive for short distance.
o Long distance: It is expensive as it requires a higher tower for a longer distance.
o Attenuation: Attenuation means loss of signal. It is affected by environmental
 conditions and antenna size.

Advantages of Terrestrial Microwave:

o Microwave transmission is cheaper than using cables.
o It is free from land acquisition as it does not require any land for the installation
of cables.
o Microwave transmission provides an easy communication in terrains as the
installation of cable in terrain is quite a difficult task.
o Communication over oceans can be achieved by using microwave transmission.

Disadvantages of Terrestrial Microwave:

o Eavesdropping.
o Out of phase signal
o Susceptible to weather condition
o Bandwidth limited

Satellite Microwave
o A satellite is a physical object that revolves around the earth at a known height.
o Satellite communication is more reliable nowadays as it offers more flexibility
than cable and fibre optic systems.
o We can communicate with any point on the globe by using satellite
communication.
o The satellite accepts the signal that is transmitted from the earth station, and it
amplifies the signal. The amplified signal is retransmitted to another earth station.
Advantages of Satellite Microwave:
o The coverage area of a satellite microwave is more than the terrestrial microwave.
o The transmission cost of the satellite is independent of the distance from the
centre of the coverage area.
o Satellite communication is used in mobile and wireless
communication applications.
o It is easy to install.
o It is used in a wide variety of applications such as weather forecasting, radio/TV
signal broadcasting, mobile communication, etc.

Disadvantages of Satellite Microwave:

o Satellite designing and development requires more time and higher cost.
o The Satellite needs to be monitored and controlled on regular periods so that it
remains in orbit.
o The life of the satellite is about 12-15 years. Due to this reason, another launch of
the satellite has to be planned before it becomes non-functional.

INFRARED WAVES
o An infrared transmission is a wireless technology used for communication over
short ranges.
o The frequency of the infrared in the range from 300 GHz to 400 THz.
 o It is used for short-range communication such as data transfer between two cell
phones, TV remote operation, data transfer between a computer and cell phone
and devices that resides in the same closed area.

Characteristics of Infrared:
o It supports high bandwidth, and hence the data rate will be very high.
o Infrared waves cannot penetrate the walls. Therefore, the infrared communication
in one room cannot be interrupted by the nearby rooms.
o An infrared communication provides better security with minimum interference.
o Infrared communication is unreliable outside the building because the sun rays
will interfere with the infrared waves.