This document discusses different network topologies and switching techniques. It begins by defining network topology and describing five common topologies - bus, ring, star, mesh, and hybrid. It then defines what a computer network is and categorizes networks by size into LAN, PAN, MAN and WAN. The document also discusses random access protocols including ALOHA, CSMA and their variations. It compares TCP and UDP protocols. Finally, it discusses circuit switching and its two technologies - space division switching using crossbar switches, and multistage switching.

1. 1) Network Topology :-
The physical arrangement of the computer system or node which is connected to each other via
communication mediu is called topology.
Bus Topology:
Bus topology is a network type in which every
computer and network device is connected to a
single cable. It is bi-directional. It is a multi-point
connection and a non-robust topology because if
the backbone fails the topology crashes. In Bus
Topology, various MAC (Media Access Control)
protocols are followed by LAN ethernet connections
like TDMA, Pure Aloha, CDMA, Slotted Aloha, etc.
Ring Topology:
In this topology, it forms a ring connecting devices with exactly
two neighboring devices.
A number of repeaters are used for Ring topology with a 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 data flows in one direction, i.e.., it is unidirectional, but it can
be made bidirectional by having 2 connections between each
Network Node, it is called Dual Ring Topology. In-Ring Topology, the Token Ring Passing protocol
is used by the workstations to transmit the data.
Star Topology:
In star topology, all the devices are connected to a single hub
through a cable. This hub is the central node and all other nodes
are connected to the central node. The hub can be passive in
nature i.e., not an intelligent hub such as broadcasting devices, at
the same time the hub can be intelligent known as an active hub.
Active hubs have repeaters in them. Coaxial cables or RJ-45
cables are used to connect the computers. In Star Topology, many
popular Ethernet LAN protocols are used as CD(Collision
Detection), CSMA (Carrier Sense Multiple Access), etc.
Mesh Topology:
In a mesh topology, every device is connected to another device via a
particular channel. In Mesh Topology, the protocols used are AHCP (Ad
Hoc Configuration Protocols), DHCP (Dynamic Host Configu.
Hybrid Topology :
This topological technology is the combination of
all the various types of topologies we have
studied above. It is used when the nodes are free
to take any
form. It means these can be individuals such as
Ring or Star topology or can be a combination of
various types of topologies seen above. Each
individual topology uses the protocol that has
been discussed earlier.
Tree Topology :
This topology is the variation of the Star topology. This topology has a hierarchical flow of data. In
Tree Topology, protocols like DHCP and SAC (Standard Automatic Configuration ) are used.
2) What is network and explain
its types:-
A computer network is a group of
computers linked to each other
that enables the computer to
communicate with another
computer and share their
resources, data, and applications.
A computer network can be
categorized by their size. A
computer network is mainly of four types:
● LAN(Local Area Network)
●
● PAN(Personal Area Network)
● MAN(Metropolitan Area Network)
● WAN(Wide Area Network)
LAN(Local Area Network)
● Local Area Network is a group of computers connected to each other in a small area such
as building, office.
● LAN is used for connecting two or more personal computers through a communication
medium such as twisted pair, coaxial cable, etc.
● It is less costly as it is built with inexpensive hardware such as hubs, network adapters,
and ethernet cables.
● The data is transferred at an extremely faster rate in Local Area Network.
● Local Area Network provides higher security.
PAN(Personal Area Network)
● Personal Area Network is a network arranged within an
individual person, typically within a range of 10 meters.
● Personal Area Network is used for connecting the computer
devices of personal use is known as Personal Area Network.
● Personal computer devices that are used to develop the
personal area network are the laptop, mobile phones, media
player and play stations.
MAN(Metropolitan Area Network)
● A metropolitan area network is a network that covers a
larger geographic area by interconnecting a different LAN to form
a larger network.
● Government agencies use MAN to connectReservation.
● It can be used in a college within a to the citizens and
private industries.
● In MAN, various LANs are connected to each other through
a telephone exchange line.
● The most widely used protocols in MAN are RS-232, Frame Relay, ATM, ISDN, OC-3, ADSL,
etc.
● It has a higher range than Local Area Network(LAN).
Uses Of Metropolitan Area Network:
● MAN is used in communication between the banks in a city.
● It can be used in an Airline city.
● It can also be used for communication in the military.
●
WAN(Wide Area Network)
● A Wide Area Network is a network that extends over a large
geographical area such as states or countries.
● A Wide Area Network is quite bigger network than the LAN.
● A Wide Area Network is not limited to a single location, but it spans over a large
geographical area through a telephone line, fibre optic cable or satellite links.
● The internet is one of the biggest WAN in the world.
● A Wide Area Network is widely used in the field of Business, government, and education.
3) What is random access protocol and explain its types with
advantages and dis- advantages :-
Random Access Protocol: In this, all stations have same
superiority that is no station has more priority than another
station. Any station can send data depending on medium’s
state( idle or busy). It has two features:
1. There is no fixed time for sending data
2. There is no fixed sequence of stations sending data
The Random access protocols are further subdivided as:
(a) ALOHA – It was designed for wireless LAN but is also applicable for shared medium. In this,
multiple stations can transmit data at the same time and can hence lead to collision and data
being garbled.
● Pure Aloha:
When a station sends data it waits for an acknowledgement. If the acknowledgement
doesn’t come within the allotted time then the station waits for a random amount of time
called back-off time (Tb) and re-sends the data. Since different stations wait for different
amount of time, the probability of further collision decreases.
● Slotted Aloha:
It is similar to pure aloha, except that we divide time into slots and sending of data is
allowed only at the beginning of these slots. If a station misses out the allowed time, it
must wait for the next slot. This reduces the probability of collision.
Algorithm Advantage Disadvantage
IALOHA Easy to use Collision becomes greater when the number of tags in
the interrogation zone of the reader is becoming larger
Slotted ALOHA Collision interval reduced to half and
throughput doubled compared to Aloha
Fail to work when the number of transponders in the
systems becomes larger
Frame slotted
ALOHA
Can be improved to increase throughput
and reduce collision
Number of tags is always unknown to the reader
Dynamic frame
slotted aloha
Numbers of tags can to be identified Estimation of the number of tags algorithm is not
standardized
(b) CSMA – Carrier Sense Multiple Access ensures fewer collisions as the station is required to
first sense the medium (for idle or busy) before transmitting data. If it is idle then it sends data,
otherwise it waits till the channel becomes idle. However there is still chance of collision in CSMA
due to propagation delay. For example, if station A wants to send data, it will first sense the
medium.If it finds the channel idle, it will start sending data. However, by the time the first bit of
data is transmitted (delayed due to propagation delay) from station A, if station B requests to send
data and senses the medium it will also find it idle and will also send data. This will result in
collision of data from station A and B.
CSMA access modes-
● 1-persistent: The node senses the channel, if idle it sends the data, otherwise it
continuously keeps on checking the medium for being idle and transmits
unconditionally(with 1 probability) as soon as the channel gets idle.
● Non-Persistent: The node senses the channel, if idle it sends the data, otherwise it checks
the medium after a random amount of time (not continuously) and transmits when found
idle.
● P-persistent: The node senses the medium, if idle it sends the data with p probability. If
the data is not transmitted ((1-p) probability) then it waits for some time and checks the
medium again, now if it is found idle then it send with p probability. This repeat continues
until the frame is sent. It is used in Wifi and packet radio systems.
● O-persistent: Superiority of nodes is decided beforehand and transmission occurs in that
order. If the medium is idle, node waits for its time slot to send data.
● (c) CSMA/CD – Carrier sense multiple access with collision detection. Stations can
terminate transmission of data if collision is detected.
CSMA (cont.)
Advantages:
Less collisions probabilities compared to ALOHA.
Transmission on demand only.
Disadvantages:
x Unknown delay when more nodes are connected.
x Collisions still occur.
x Network with heavy traffic may not benefit with CSMA
(d) CSMA/CA – Carrier sense multiple access with collision avoidance. The process of collisions
detection involves sender receiving acknowledgement signals. If there is just one signal(its own)
then the data is successfully sent but if there are two signals(its own and the one with which it
has collided) then it means a collision has occurred. To distinguish between these two cases,
collision must have a lot of impact on received signal. However it is not so in wired networks, so
CSMA/CA is used in this case.
CSMA/CA avoids collision by:
1. Interframe space – Station waits for medium to become idle and if found idle it does not
immediately send data (to avoid collision due to propagation delay) rather it waits for a
period of time called Interframe space or IFS. After this time it again checks the medium
for being idle. The IFS duration depends on the priority of station.
2. Contention Window – It is the amount of time divided into slots. If the sender is ready to
send data, it chooses a random number of slots as wait time which doubles every time
medium is not found idle. If the medium is found busy it does not restart the entire
process, rather it restarts the timer when the channel is found idle again.
3. Acknowledgement – The sender re-transmits the data if acknowledgement is not received
before time-out.
TCP UDP
Full form It stands for Transmission Control Protocol. It stands for User Datagram Protocol.
Type of
connection
It is a connection-oriented protocol, which
means that the connection needs to be
established before the data is transmitted over
the network.
It is a connectionless protocol, which
means that it sends the data without
checking whether the system is ready to
receive or not.
Reliable TCP is a reliable protocol as it provides
assurance for the delivery of data packets.
UDP is an unreliable protocol as it does
not take the guarantee for the delivery of
packets.
Speed TCP is slower than UDP as it performs error
checking, flow control, and provides assurance
for the delivery of
UDP is faster than TCP as it does not
guarantee the delivery of data packets.
Header size The size of TCP is 20 bytes. The size of the UDP is 8 bytes.
Acknowledgm
ent
TCP uses the three-way-handshake concept. In
this concept, if the sender receives the ACK,
then the sender will send the data. TCP also has
the ability to resend the lost data.
UDP does not wait for any
acknowledgment; it just sends the data.
Flow control
mechanism
It follows the flow control mechanism in which
too many packets cannot be sent to the receiver
at the same time.
This protocol follows no such mechanism.
Error
checking
TCP performs error checking by using a
checksum. When the data is corrected, then the
data is retransmitted to the receiver.
It does not perform any error checking,
and also does not resend the lost data
packets.
Applications This protocol is mainly used where a secure
and reliable communication process is
required, like military services, web browsing,
and e-mail.
This protocol is used where fast
communication is required and does not
care about the reliability like VoIP, game
streaming, video and music streaming,
etc.
BASIS FOR
COMPARISON
GUIDED MEDIA UNGUIDED MEDIA
Basic The signal requires a physical path for
transmission.
The signal is broadcasted through air
or sometimes water.
Alternative
name
It is called wired communication or
bounded transmission media.
It is called wireless communication or
unbounded transmission media.
Direction It provides direction to signal for traveling. It does not provide any direction.
Types Twisted pair cable, coaxial cable and fiber
optic cable.
Radio wave, microwave and infrared.
Flow Control Error Control
It is a method used to maintain proper transmission of
the data from sender to the receiver.
It is used to ensure that error- free data is delivered from
sender to receiver.
Feedback-based flow control and rate-based flow
control are the various approaches used to achieve
Flow control.
Many methods can be used here like Cyclic Reduction
Check, Parity Checking, checksum.
It avoids overrunning and prevents data loss. It detects and corrects errors that might have occurred
in transmission.
Examples are Stop and Wait and Sliding Window. Examples are Stop-and-Wait ARQ, Go-Back-N ARQ,
Selective-Repeat ARQ.
IPV4 IPV6
1 The length of ipv4 is 32 bit The length of ipv6 is bit
2 In Ipv4 arround 4 billion unique IP addresses can be
generated
In IP seeks around 340 trillion unique IP addresses
can be generated
3 the range of IPV 4 address is to 255 the range of IPV 6 address is to FFFF (65535)
4 Ex: 192:255:108:253 Ex: 2001:DB02:2002:1800:445:CFA:4587:25F
5 It consists of 4 octets , each has 8 bits It consists of 8 octets each 16 bits
6 Ipv4 is a numeric address separated by dot Ipv6 is an alphanumeric address separated by colon
7 Ipv4 has total five classes Ipv6 has no classes
What is smtp ? Describe how it works ?
SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in sending and receiving e-mail.
However, since it is limited in its ability to queue messages at the receiving end, it is usually used
with one of two other protocols, POP3 (Post Office Protocol) or IMAP (Internet Message Access
Protocol), that let the user save messages in a server mailbox and download them periodically
from the server. In other words, users typically use a program that uses SMTP for sending e-mail
and either POP3 or IMAP for receiving e-mail. → How SMTP works: SMTP works as a three-step
process, using a client/server model. First, an e-mail server uses SMTP to send a message from
an e-mail client, such as Outlook or Gmail, to an e-mail server. Second, the e-mail server uses
SMTP as a relay service to send the e-mail to the receiving e-mail server. Third, the receiving
server uses an e-mail client to download incoming mail via IMAP and place it in the inbox of the
recipient.
Switching techniques
In large networks, there can be multiple paths from sender to receiver. The switching technique will
decide the best route for data transmission.->Switching technique is used to connect the systems for
making one-to-one communication.
Classification Of Switching Techniques
Circuit Switching
● Circuit switching is a switching technique that
establishes a dedicated path between sender and
receiver. —1>In the Circuit Switching Technique, once
the connection is established then the dedicated path
will remain to exist until the connection is
terminated.—2>Circuit switching in a network
operates in a similar way as the telephone works.—
3>A complete end-to-end path must exist before the
communication takes place.—4>In case of circuit switching technique, when any user wants to
send the data, voice, video, a request signal is sent to the receiver then the receiver sends back
the acknowledgment to ensure the availability of the dedicated path. After receiving the
acknowledgment, dedicated path transfers the data.—5>Circuit switching is used in public
telephone network. It is used for voice transmission.—6>Fixed data can be transferred at a time
in circuit switching technology.
Communication through circuit switching has 3 phases
● Circuit establishment
● Data transfer
● Circuit Disconnect
Circuit Switching can use either of the two
technologies:
Space Division Switches:
● Space Division Switching is a circuit
switching technology in which a single transmission path is accomplished in a switch by using a
physically separate set of crosspoints.
● Space Division Switching can be achieved by using crossbar switch. A crossbar switch is a
metallic crosspoint or semiconductor gate that can be enabled or disabled by a control unit.
● The Crossbar switch is made by using the semiconductor. For example, Xilinx crossbar switch
using FPGAs.
● Space Division Switching has high speed, high capacity, and nonblocking switches.
Space Division Switches can be categorized in two ways:

2. ● Crossbar Switch
● Multistage Switch
Crossbar Switch
The Crossbar switch is a switch that has n input lines and n output lines. The crossbar switch has n2
intersection points known as crosspoints.
Disadvantage of Crossbar switch:
The number of crosspoints increases as the number of stations is increased. Therefore, it becomes very
expensive for a large switch. The solution to this is to use a multistage switch.
Multistage Switch
● Multistage Switch is made by splitting the crossbar switch into the smaller units and then
interconnecting them.
● It reduces the number of crosspoints.
● If one path fails, then there will be an availability of another path.
Advantages Of Circuit Switching:
● In the case of Circuit Switching technique, the communication channel is dedicated.
● It has fixed bandwidth.
Disadvantages Of Circuit Switching:
● Once the dedicated path is established, the only delay occurs in the speed of data transmission.
● It takes a long time to establish a connection approx 10 seconds during which no data can be
transmitted.
● It is more expensive than other switching techniques as a dedicated path is required for each
connection.
● It is inefficient to use because once the path is established and no data is transferred, then the
capacity of the path is wasted.
● In this case, the connection is dedicated therefore no other data can be transferred even if the
channel is free.
Message Switching
● Message Switching is a switching technique in which a message is transferred as a complete
unit and routed through intermediate nodes at which it is stored and forwarded.
● In Message Switching technique, there is no establishment of a dedicated path between the
sender and receiver.
● The destination address is appended to the message. Message Switching provides a dynamic
routing as the message is routed through the intermediate nodes based on the information
available in the message.
● Message switches are programmed in such a way so that they can provide the most efficient
routes.
● Each and every node stores the entire message and then forward it to the next node. This type
of network is known as store and forward network.
● Message switching treats each message as an independent entity.
Advantages Of Message Switching
● Data channels are shared
among the communicating devices
that improve the efficiency of using
available bandwidth.
● Traffic congestion can be
reduced because the message is temporarily stored in the nodes.
● Message priority can be used to manage the network.
● The size of the message which is sent over the network can be varied. Therefore, it supports the
data of unlimited size.
Disadvantages Of Message Switching
● The message switches must be equipped with sufficient storage to enable them to store the
messages until the message is forwarded.
● The Long delay can occur due to the storing and forwarding facility provided by the message
switching technique.
Packet Switching
● The packet switching is a switching technique in which the message is sent in one go, but it is
divided into smaller pieces, and they are sent individually.
● The message splits into smaller pieces known as packets and packets are given a unique
number to identify their order at the receiving end.
● Every packet contains some information in its headers such as source address, destination
address and sequence number.
● Packets will travel across the network, taking the shortest path as possible.
● All the packets are reassembled at the receiving end in correct order.
● If any packet is missing or corrupted, then the message will be sent to resend the message.
● If the correct order of the packets is reached, then the acknowledgment message will be sent.
Approaches Of Packet Switching:
There are two approaches to Packet Switching:
Datagram Packet switching:
● It is a packet switching technology in which
packet is known as a datagram, is considered as an independent entity. Each packet contains
the information about the destination and switch uses this information to forward the packet to
the correct destination.
● The packets are reassembled at the receiving end in correct order.
● In Datagram Packet Switching technique, the path is not fixed.
● Intermediate nodes take the routing decisions to forward the packets.
● Datagram Packet Switching is also known as connectionless switching.
Virtual Circuit Switching
● Virtual Circuit Switching is also known as connection-oriented switching.
● In the case of Virtual circuit switching, a preplanned route is established before the messages
are sent.
● Call request and call accept packets are used to establish the connection between sender and
receiver.
● In this case, the path is fixed for the duration of a logical connection.
Let's understand the concept of virtual circuit switching through a diagram:
In the above diagram, A and B are the sender and
receiver respectively. 1 and 2 are the nodes.
● Call request and call accept packets are used to
establish a connection between the sender and
receiver.
● When a route is established, data will be
transferred.
● After transmission of data, an acknowledgment
signal is sent by the receiver that the message has
been received.
● If the user wants to terminate the connection, a
clear signal is sent for the termination.
What is HTTP? Describe different kinds of http request?
The Hypertext Transfer Protocol (HTTP) is the foundation of the World Wide Web, and is used to load
web pages using hypertext links. HTTP is an application layer protocol designed to transfer information
between networked devices and runs on top of other layers of the network protocol stack. A typical flow
over HTTP involves a client machine making a request to a server, which then sends a response
message.
HTTP (Hypertext Transfer Protocol) specifies a collection of request methods to specify what
action is to be performed on a particular resource. The most commonly used HTTP request
methods are GET, POST, PUT, PATCH, and DELETE. These are equivalent to the CRUD operations
(create, read, update, and delete).
GET: GET request is used to read/retrieve data from a web server. GET returns an HTTP status
code of 200 (OK) if the data is successfully retrieved from the server.
POST: POST request is used to send data (file, form data, etc.) to the server. On successful
creation, it returns an HTTP status code of 201.
PUT: A PUT request is used to modify the data on the server. It replaces the entire content at a
particular location with data that is passed in the body payload. If there are no resources that
match the request, it will generate one.
PATCH: PATCH is similar to PUT request, but the only difference is, it modifies a part of the data.
It will only replace the content that you want to update.
DELETE: A DELETE request is used to delete the data on the server at a specified location.
Why analog-to-analog modulation technique is required?
It is required because the sender’s signal is of low pass and can be of the same range. For example,
each radio station has a low pass signal, which may be of the same range. Different stations signal
to avoid intermixing; each low pass signal must be shifted to a diverse range on the frequency band.
Analog-to-analog conversion can be accomplished in three ways:
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)
1. Amplitude Modulation:
In AM transmission, the carrier signal is modulated so that its amplitude varies with the changing
amplitudes of the modulating signal. The frequency and phase of the carrier remain the same.
Only the amplitude changes to follow variations in the information. The following figure shows
how this concept works. The modulating signal is the envelope of the carrier.
AM is normally implemented by
using a simple multiplier
because the amplitude of the
carrier signal needs to be
changed according to the
amplitude of the modulating
signal.
2. Frequency Modulation
In FM transmission, the
frequency of the carrier signal is
modulated to follow the
changing voltage level (amplitude) of the modulating signal. The peak amplitude and phase of the
carrier signal remain constant, but as the amplitude of the information signal changes, the
frequency of the carrier changes correspondingly.
The following figure shows the relationships of the modulating signal, the carrier signal, and the
resultant FM signal. FM is normally implemented by using a voltage-controlled oscillator as with
FSK. The frequency of the oscillator changes according to the input voltage which is the
amplitude of the modulating signal.
FM Bandwidth
The actual bandwidth is difficult to determine exactly, but it can be shown empirically that it is
several times that of the analog signal or 2(1 + β)B where β is a factor depends on modulation
technique with a common value of 4.
3. Phase Modulation:
In PM transmission, the phase of the
carrier signal is modulated to follow the
changing voltage level (amplitude) of the
modulating signal. The peak amplitude
and frequency of the carrier signal
remain constant, but as the amplitude of
the information signal changes, the
phase of the carrier changes
correspondingly. It is proved
mathematically that PM is the same as
FM with one difference.
In FM, the instantaneous change in the carrier frequency is proportional to the amplitude of the
modulating signal; in PM the instantaneous change in the carrier frequency is proportional to the
derivative of the amplitude of the modulating signal. The following figure shows the relationships
of the modulating signal, the carrier signal,
and the resultant PM signal.
Explain Digital to analog
conversion ? describe its
types ?
Digital to Analog Conversion
Digital Signal – A digital signal is a signal that represents data as a sequence of discrete values;
at any given time it can only take on one of a finite number of values.
Analog Signal – An analog signal is any continuous signal for which the time varying feature of
the signal is a representation of some other time varying quantity i.e., analogous to another time
varying signal.
The following techniques can be used for
Digital to Analog Conversion:
1. Amplitude Shift keying – Amplitude Shift
Keying is a technique in which carrier signal is
analog and data to be modulated is digital. The
amplitude of analog carrier signal is modified to
reflect binary data.
The binary signal when modulated gives a zero
value when the binary data represents 0 while
gives the carrier output when data is 1. The
frequency and phase of the carrier signal
remain constant.
Advantages of amplitude shift Keying –
● It can be used to transmit digital data over
optical fiber.
● The receiver and transmitter have a simple
design which also makes it comparatively
inexpensive.
● It uses lesser bandwidth as compared to FSK thus it offers high bandwidth efficiency.
Disadvantages of amplitude shift Keying –
● It is susceptible to noise interference and entire transmissions could be lost due to
this.
● It has lower power efficiency.
2. Frequency Shift keying – In this modulation the frequency of analog carrier signal is modified to
reflect binary data.
The output of a frequency shift keying modulated wave is high in frequency for a binary high input
and is low in frequency for a binary low input. The amplitude and phase of the carrier signal
remain constant.
Advantages of frequency shift Keying –
● Frequency shift keying modulated signal can help avoid the
noise problems beset by ASK.
● It has lower chances of an error.
● It provides high signal to noise ratio.
● The transmitter and receiver implementations are simple for
low data rate application.
Disadvantages of frequency shift Keying –
● It uses larger bandwidth as compared to ASK thus it offers less bandwidth efficiency.
● It has lower power efficiency.
3. Phase Shift keying – In this modulation the phase of the analog carrier signal is modified to
reflect binary data.The amplitude and frequency of the carrier signal remains constant.
It is further categorized as follows:
1. Binary Phase Shift Keying (BPSK):
BPSK also known as phase reversal keying or
2PSK is the simplest form of phase shift keying.
The Phase of the carrier wave is changed
according to the two binary inputs. In Binary
Phase shift keying, difference of 180 phase shift
is used between binary 1 and binary 0.
This is regarded as the most robust digital
modulation technique and is used for long
distance wireless communication.
2. Quadrature phase shift keying:
This technique is used to increase the bit rate i.e
we can code two bits onto one single element. It
uses four phases to encode two bits per symbol.
QPSK uses phase shifts of multiples of 90
degrees.
It has double data rate carrying capacity
compare to BPSK as two bits are mapped on
each constellation points.
Advantages of phase shift Keying – → It is a more power efficient modulation technique as
compared to ASK and FSK. → It has lower chances of an error.→ It allows data to be
carried along a communication signal much more efficiently as compared to FSK.
Disadvantages of phase shift Keying – → It offers low bandwidth efficiency. → The detection and
recovery algorithms of binary data is very complex. → It is a non coherent reference signal.
The transmission medium can be defined as a pathway that can transmit information
from a sender to a receiver. Transmission media are located below the physical layer
and are controlled by the physical layer. Transmission media are also called
communication channels.
Transmission media are of two types −
● Guided Transmission Medium
● Unguided Transmission Medium
The following chart
categorizes transmission
media −
Guided
Transmission
Medium
Guided transmission media
are also called bounded media
or wired media. They comprise
cables or wires through which
data is transmitted. They are
called guided since they
provide a physical conduit from the sender device to the receiver device. The signal
traveling through these media are bounded by the physical limits of the medium.
The most popular guided media are −
● Twisted pair cable
● Coaxial cable
● Fiber optics
Twisted-Pair Cable

3. A twisted pair consists of two conductors (normally copper), each
with its own plastic insulation, twisted together, as shown in below
figure.
One of the wires is used to carry signals to the receiver, and the other is used only
as a ground reference. The receiver uses the difference between the two.
In addition to the signal sent by the sender on one of the wires,
interference (noise) and crosstalk may affect both wires and
create unwanted signals.
Unshielded Versus Shielded Twisted-Pair Cable
The most common twisted-pair cable used in communications is
referred to as unshielded twisted-pair (UTP).
IBM has also produced a version of twisted-pair cable for its use
called shielded twisted-pair (STP).
Coaxial cable:-
• A coaxial cable is a type
of shielded and insulated
copper cable that is used in
computer networks and to
deliver cable TV services to
end users.
• The outer conductor acts
as a shield against noise and
crosstalk. The outer
conductor is enclosed and
whole cable is protected by a
plastic cover.
• The distance between
the outer conductor and inner
conductor plus the type of
material used for insulating the inner conductor determine the cable properties.
• The most standard coaxial cable
connector BNC (Bayone – Neill concelman )
connector.
• BNC connector is used to connect to
the end of the cable to a device(Such as TV).
• Used in cable TV networks
• Used in analog telephone networks
• Used in Ethernet LAN.
Fiber optics:
• Optical fiber transmission systems
were introduced in 1970. It offered
greater advantages over copper based
digital transmission systems. • a thin
flexible fiber with a glass core through
which light signals can be sent.
• Fiber optic cable has the ability to transmit signals over much longer distances.
• Optical fiber are immune to interference and cross talk
Advantages of Optical Fiber Cables
Ø
Wider bandwidth and greater information capacity: The light wave occupies the
frequency range between 2×1012 Hz to 37×1012 Hz. This makes the information carrying
capability of fiber optic cables is much higher.
Ø
Immunity to crosstalk: Since fiber optic cables use glass and plastic fibers, which are
non- conductors of electrical current, no magnetic field is present. No magnetic
induction means no crosstalk.
Ø
Immunity to static interference: As optical fiber cables are non-conductors, they are
immune to electromagnetic interference (EMI) caused by lightning, electric motors,
relays, fluorescent lights and other electrical noise sources.
Ø
Environmental immunity: Optical fibers are more immune to environmental extremes.
They can operate over large temperature variations and are also not affected by
corrosive liquids and gases.
Ø
Safety and convenience: As only glass and plastic fibers are present, no electrical
currents or voltages are associated with them. Also they can be used around any volatile
liquids and gasses without worrying about their causing explosions or fires.
What is line coding and characteristics of line coding and types?
A line code is the code used for data transmission of a digital signal over a transmission line. This
process of coding is chosen so as to avoid overlap and distortion of signal such as inter-symbol
interference.
Properties of Line Coding :- Following are the properties of line coding −
● As the coding is done to make more bits transmit on a single signal, the bandwidth
used is much reduced.
● For a given bandwidth, the power is efficiently used.
● The probability of error is much reduced.
● Error detection is done and the bipolar too has a correction capability.
● Power density is much favorable.
● The timing content is adequate.
● Long strings of 1s and 0s is avoided to maintain transparency.
Types of Line Coding
There are 3 types of Line Coding
● Unipolar
● Polar
● Bi-polar
Unipolar Signaling
Unipolar signaling is also called as On-Off Keying or simply OOK.
The presence of pulse represents a 1 and the absence of pulse represents a 0.
There are two variations in Unipolar signaling −
● Non Return to Zero
● NRZ
● NRZ
● Return to Zero
● RZ
● RZ
Unipolar Non-Return to Zero
NRZ
NRZ
In this type of unipolar signaling, a High in data is represented by a positive pulse called as Mark,
which has a duration T0 equal to the symbol bit duration. A Low in data input has no pulse.
The following figure clearly depicts
this.
Unipolar Return to Zero RZ
In this type of unipolar signaling, a
High in data, though represented by a
Mark pulse, its duration T0 is less than
the symbol bit duration. Half of the bit
duration remains high but it
immediately returns to zero and
shows the absence of pulse during the
remaining half of the bit duration.
It is clearly understood with
the help of the following
figure.
Polar Signaling
There are two methods of
Polar Signaling. They
are −
● Polar NRZ
● Polar RZ
Polar NRZ
In this type of Polar
signaling, a High in data is represented
by a positive pulse, while a Low in data
is represented by a negative pulse. The
following figure depicts this well.
Polar RZ
In this type of Polar signaling, a High in
data, though represented by a Mark
pulse, its duration T0 is less than the
symbol bit duration. Half of the bit
duration remains high but it
immediately returns to zero and shows
the absence of pulse during the remaining half of the bit duration.
However, for a Low input, a negative pulse represents the data, and the zero level remains same for
the other half of the bit duration. The following figure depicts this clearly.
Bipolar Signaling
This is an encoding technique which has three voltage levels namely +, - and 0. Such a signal is called
as duo-binary signal.
An example of this type is Alternate Mark Inversion
AMI
AMI. For a 1, the voltage level gets a transition from + to – or from – to +, having alternate 1s to be of
equal polarity. A 0 will have a zero voltage level.
Even in this method, we have two types.
● Bipolar NRZ
● Bipolar RZ
From the models so far discussed, we have
learnt the difference between NRZ and RZ. It
just goes in the same way here too. The
following figure clearly depicts this.