Guide to Networking Concepts and Protocols in 6 Units

Points Covered
UNIT 1:
1. The Internet Architecture
2. Networking Devices
3. OSI Model
4. TCP/IP Model
5. Topologies
6. Types of Networks with diagrams.
7.
UNIT 2:
1. X.25
2. Frame Relay
3. FDDI
4. Token Ring
5. Bluetooth
6. RFID
7. Asynchronous Transfer Mode (ATM)
UNIT 3:
1. Data Link Layer
2. Error Control
3. Flow Control
4. Types of services provided to the network layer
UNIT 4:
1. Classful IP Addressing
2. Difference between IPV4 and IPV6
3. Piggybacking
4. Methods to improve QoS
5. Subnet, subnet mask, Private IP, Public IP and NAT
6. Congestion Control and how it works in TCP
7. TCP and UDP
8. Explain TCP with its header format
9. Socket
UNIT 5:
1. Application Layer
2. DNS
3. SMTP
4. POP3

5. HTTP
6. URL
7. FTP
8. Basic functions of e-mail system
9. HTTP,FTP Difference
UNIT 6:
1. Network Security Goals
2. Public key Encryption/Decryption
3. Public and Private key Encryption
4. What is a firewall? Mention the types of firewalls
5. Steps followed in creating digital signature
6. Differentiate between digital signature and digital certificate
UNIT 01
1.The Internet Architecture
⇒
● The Internet is called the network of networks.
● It is a global communication system that links together thousands of
individual networks.
● In other words, the internet is a collection of interlinked computer
networks, connected by copper wires, fiber-optic cables, wireless
connections, etc. As a result, a computer can virtually connect to other
computers in any network.
● These connections allow users to interchange messages, to communicate
in real time (getting instant messages and responses), to share data and
programs and to access limitless information.
Process
TCP/IP provides end to end transmission, i.e., each and every node on one
network has the ability to communicate with any other node on the network.
Layers of Internet Architecture
Internet architecture consists of three layers −

Application Protocol:Third layer in internet architecture is the application layer
which has different protocols on which the internet services are built. Some of the
examples of internet services include email (SMTP facilitates email feature), file
transfer (FTP facilitates file transfer feature), etc.
TCP:TCP stands for "Transmission Control Protocol". It provides end to end
transmission of data, i.e., from source to destination. It is a very complex protocol
as it supports recovery of lost packets.
IP:In order to communicate, we need our data to be encapsulated as Internet
Protocol (IP) packets. These IP packets travel across a number of hosts in a
network through routing to reach the destination. However IP does not support
error detection and error recovery, and is incapable of detecting loss of packets.
2.Networking Devices
Hub : A hub is a physical layer networking device which is used to
Connect multiple devices in a network. They are generally used to connect computers in
a LAN.
Switch : A switch is a data link layer networking device which connects devices in a
network and uses packet switching to send and receive data over the network.
Router : A router is a device that connects two or more packet-switched networks or
sub networks.
Gateway : Connects two networks with different transmission protocols together.
LAN : A local area network (LAN) is a collection of devices connected together in one
physical location, such as a building, office, or home. Or Connects computer and
hardware.

Bridge : It combines two LANs to form an extended LAN. Bridges are used to divide
large busy networks into multiple smaller and interconnected networks to improve
performance.
Modem : Modem stands for Modulation Demodulation. A modem converts the digital
data signals into analogue data signals. Modem enables computers to send or receive
data over the telephone.
ADSL : Stands for Asymmetric digital subscriber line which facilitates fast transmission
of data.
3.OSI Model
⇒
● OSI stands for Open Systems Interconnection.
● It is a 7 layer architecture with each layer having specific functionality to perform.
● All these 7 layers work collaboratively to transmit the data from one person to
another across the globe.
Layer 1: Physical Layer (Bits)
● The lowest layer of the OSI reference model is the physical layer.
● It is responsible for the actual physical connection between the devices.
● The physical layer contains information in the form of bits. I
● t is responsible for transmitting individual bits from one node to the next.
● When receiving data, this layer will get the signal received and convert it into 0s
and 1s and send them to the Data Link layer, which will put the frame back
together.

The functions of the physical layer are as follows:
● Bit synchronization
● Bit rate control
● Physical topologies
● Transmission mode
Layer 2: Data Link Layer (Frames)
● The data link layer is responsible for the node-to-node delivery of the message.
● The main function of this layer is to make sure data transfer is error-free from
one node to another, over the physical layer.
● When a packet arrives in a network, it is the responsibility of DLL to transmit it to
the Host using its MAC address.
● Data Link Layer is divided into two sublayers:
-Logical Link Control (LLC)
-Media Access Control (MAC)
The functions of the Data Link layer are :
● Framing : It provides a way for a sender to transmit a set of bits that are
meaningful to the receiver.
● Physical addressing : After creating frames, the Data link layer adds physical
addresses (MAC address) of the sender and/or receiver in the header of each
frame.
● Error control : Data link layer provides the mechanism of error control in which it
detects and retransmits damaged or lost frames.
● Flow Control : The data rate must be constant on both sides else the data may
get corrupted thus, flow control coordinates the amount of data that can be sent
before receiving acknowledgement.
● Access control : When a single communication channel is shared by multiple
devices, the MAC sub-layer of the data link layer helps to determine which device
has control over the channel at a given time.
Layer 3: Network Layer (Packets)
● The network layer works for the transmission of data from one host to the other
located in different networks.
● It also takes care of packet routing i.e. selection of the shortest path to transmit
the packet, from the number of routes available.
● The sender & receiver’s IP addresses are placed in the header by the network
layer.

The functions of the Network layer are :
● Routing: The network layer protocols determine which route is suitable from
source to destination. This function of the network layer is known as routing.
● Logical Addressing: In order to identify each device on internetwork uniquely, the
network layer defines an addressing scheme. The sender & receiver’s IP
addresses are placed in the header by the network layer. Such an address
distinguishes each device uniquely and universally.
Layer 4 : Transport Layer (TPDU)
● The transport layer provides services to the application layer and takes services
from the network layer.
● The data in the transport layer is referred to as Segments. It is responsible for the
End to End Delivery of the complete message.
● The transport layer also provides the acknowledgement of the successful data
transmission and re-transmits the data if an error is found.
The functions of the transport layer are as follows:
● Segmentation and Reassembly: This layer accepts the message from the
(session) layer, and breaks the message into smaller units. Each of the segments
produced has a header associated with it. The transport layer at the destination
station reassembles the message.
● Service Point Addressing: In order to deliver the message to the correct process,
the transport layer header includes a type of address called service point address
or port address. Thus by specifying this address, the transport layer makes sure
that the message is delivered to the correct process.
Layer 5 : Session Layer (SPDU)
● This layer is responsible for the establishment of connection, maintenance of
sessions, authentication, and also ensures security.
●
The functions of the session layer are :
● Session establishment, maintenance, and termination: The layer allows the two
processes to establish, use and terminate a connection.

● Synchronization: This layer allows a process to add checkpoints which are
considered synchronization points into the data. These synchronization points
help to identify the error so that the data is re-synchronized properly, and ends of
the messages are not cut prematurely and data loss is avoided.
● Dialog Controller: The session layer allows two systems to start communication
with each other in half-duplex or full-duplex.
Layer 6 : Presentation Layer (PPDU)
● The presentation layer is also called the Translation layer.
● The data from the application layer is extracted here and manipulated as per the
required format to transmit over the network.
The functions of the presentation layer are :
● Translation: For example, ASCII to EBCDIC.
● Encryption/ Decryption: Data encryption translates the data into another form or
code. The encrypted data is known as the ciphertext and the decrypted data is
known as plain text. A key value is used for encrypting as well as decrypting
data.
● Compression: Reduces the number of bits that need to be transmitted on the
network.
Layer 7 : Application Layer (APDU)
● At the very top of the OSI Reference Model stack of layers, we find the
Application layer which is implemented by the network applications.
● These applications produce the data, which has to be transferred over the
network.
● This layer also serves as a window for the application services to access the
network and for displaying the received information to the user.
● Example: Application – Browsers, Skype Messenger, etc.
The functions of the Application layer are :
● Network Virtual Terminal
● FTAM-File transfer access and management
● Mail Services
● Directory Services

4.TCP/IP Model
⇒
Layer 1 : Network Access Layer

This layer corresponds to the combination of Data Link Layer and Physical Layer of the
OSI model. It looks out for hardware addressing and the protocols present in this layer
allows for the physical transmission of data.
Layer 2 : Internet Layer
This layer parallels the functions of OSI’s Network layer. It defines the protocols which
are responsible for logical transmission of data over the entire network.
The main protocol residing at this layer are:
1.IP
2.ICMP( Internet Control Message Protocol)
3.ARP(Address Resolution Protocol)
Layer 3 : Transport Layer
The transport layer is responsible for error-free, end-to-end delivery of data from the
source host to the destination host.
The two main protocols present in this layer are :
1.TCP
2.UDP
Layer 4 : Application Layer
This layer performs the functions of the top three layers of the OSI model: Application,
Presentation and Session Layer. It is responsible for node-to-node communication and
controls user-interface specifications. Some of the protocols present in this layer are:
HTTP, HTTPS, FTP, TFTP, Telnet, SSH, SMTP, SNMP, NTP, DNS, DHCP, NFS, X
Window, LPD.
TCP/IP OSI
TCP refers to the Transmission Control
Protocol.
OSI refers to Open Systems
Interconnection.
TCP/IP has 4 layers. OSI has 7 layers.
TCP/IP is more reliable OSI is less reliable
TCP/IP does not have very strict
boundaries.
OSI has strict boundaries
TCP/IP follow a horizontal approach. OSI follows a vertical approach.
TCP/IP uses both the session and
presentation layer in the application layer
itself.
OSI uses different session and
presentation layers.

TCP/IP developed protocols then model. OSI developed the model then protocol.
Transport layer in TCP/IP does not
provide assurance delivery of packets.
In the OSI model, the transport layer
provides assurance delivery of packets.
TCP/IP model network layer only provides
connectionless services.
Connection less and connection oriented
both services are provided by network
layer in OSI model.
Protocols cannot be replaced easily in the
TCP/IP model.
While in the OSI model, Protocols are
better covered and are easy to replace
with the change in technology.
5.Topologies
⇒ Topology is the layout of computer networks. It shows how devices and cables are
connected to each other.
● Bus Topology:
-The bus topology is designed in such a way that all the stations are connected
through a single cable known as a backbone cable.
-Data is transmitted in a single route, from one point to the other.
Advantages:
-Low cost cable
-Moderate data speeds
-Familiar Technology
Disadvantages:
-Difficult Troubleshooting
-Reconfiguration difficult: Adding new devices to the network would slow down
the network.
● Ring Topology:
-Ring topology is like a bus topology, but with connected ends.
-The last computer is connected to the first, thus forming a ring shape.
-The data flows in one direction, i.e., it is unidirectional.
-The data in a ring topology flow in a clockwise direction.
-The most common access method of the ring topology is token passing.
Token passing: It is a network access method in which a token is passed
from one node to another node.
Token: It is a frame that circulates around the network.
Working of Token passing:

● A token moves around the network, and it is passed from computer to
computer until it reaches the destination.
● The sender modifies the token by putting the address along with the data.
● The data is passed from one device to another device until the destination
address matches. Once the token is received by the destination device,
then it sends the acknowledgement to the sender.
● In a ring topology, a token is used as a carrier.
Advantages:
-Network Management
-Cost
-Product availability
Disadvantages:
-Difficult troubleshooting
-Reconfiguration difficult
● Star Topology
-Star topology is an arrangement of the network in which every node is
connected to the central hub, switch or a central computer.
-Hubs or Switches are mainly used as connection devices in a physical star
topology.
-Star topology is the most popular topology in network implementation.
Advantages:
-Efficient troubleshooting
-Network Control
-Limited Failure
-Familiar technology
Disadvantages:
-A Central point of failure
-Cable
● Tree Topology
-Tree topology combines the characteristics of bus topology and star topology.
-A tree topology is a type of structure in which all the computers are connected
with each other in hierarchical fashion.

-There is only one path between two nodes for the data transmission. Thus, it
forms a parent-child hierarchy.
Advantages:
-Support for broadband Transmission
-EasilyExpandable
-Easily Manageable
-Error detection
Disadvantages:
-Difficult troubleshooting
-High cost
-Reconfiguration difficult
● Mesh Topology
-Mesh technology is an arrangement of the network in which computers are
interconnected with each other through various redundant connections.
-There are multiple paths from one computer to another computer.
-The Internet is an example of the mesh topology.
Advantages:
-Fast communication
-Easier Reconfiguration
Disadvantages:
-Cost
-Management
-Reduces Efficiency
● Hybrid Topology
-The combination of various different topologies is known as Hybrid topology.
A Hybrid topology is a connection between different links and nodes to transfer
the data.
Advantages:
-Scalable: Size of the network can be easily expanded
-Flexible
-Effective
Disadvantages:
-Complex design

- Costly Hub
6.Types of Networks with diagrams.
Personal Area Network
⇒A personal area network, or PAN, is a computer network organized around an
individual person within a single building. This could be inside a small office or
residence. A typical PAN would include one or more computers, telephones, peripheral
devices, video game consoles and other personal entertainment devices.
Local Area Network
A local area network, or LAN, consists of a computer network at a single site, typically
an individual office building. A LAN is very useful for sharing resources, such as data
storage and printers. LANs can be built with relatively inexpensive hardware, such as
hubs, network adapters and Ethernet cables.
Metropolitan Area Network
A metropolitan area network, or MAN, consists of a computer network across an entire
city, college campus or small region. A MAN is larger than a LAN, which is typically
limited to a single building or site. Depending on the configuration, this type of network
can cover an area from several miles to tens of miles
Wide Area Network
A wide area network, or WAN, occupies a very large area, such as an entire country or
the entire world. A WAN can contain multiple smaller networks, such as LANs or MANs.
The Internet is the best-known example of a public WAN.

UNIT 02
1.X.25
⇒
-X.25 is a standard suite of protocols used for packet switching across computer
networks.
-It usually allows various logical channels to make use of the same physical line.
-X.25 basically encompasses or suits the lower three layers of the Open System
Interconnection (OSI) reference model for networking. These three protocol layers are :
● Physical Layer 1: This layer provides various communication lines that
transmit or transfer some electrical signals. X.21 implementer is usually
required for linking.
● Frame Layer (Data Link Layer) : It provides a communication link and
transmission that is error-free among any two physically connected nodes
or X.25 nodes.
● Packet Layer : Packet layer is also known as Network Layer protocol of
X.25. This layer also defines and explains the format of data packets and
also the procedures for control and transmission of data frames.
Benefits or advantages of X.25
➨It is reliable protocol as it uses error control and retransmission of bad packets.
➨It has faster response times.
➨It does not have blocking except when network storage is flooded completely.
➨It handles both high speed and low speed data requirements.
➨The network is highly available due to use of distributed routing.
➨It uses addressing capabilities.
➨It can be statistically multiplexed.
Drawbacks or disadvantages of X.25
➨It offers low data rate which is about 64 Kbbps.
➨It utilizes flow control and error control at data link and network layer. This
results into larger overhead and consecutively slows down the transmissions.
➨Queuing delays
➨Small packet size
➨No QoS guarantees
➨Used for data only

2.Frame Relay:
● ⇒Frame Relay is a packet switched communication service from LANs
(Local Area Network) to backbone networks and WANs. It operates at two
layers: physical layer and data link layer.
● Frame relay is a fast packet technology based on X.25. Data is
transmitted by encapsulating them in multiple sized frames. The protocol
does not attempt to correct errors and so it is faster. Error correction is
handled by the endpoints, which are responsible for retransmission of
dropped frames.
● Frame Relay Devices are
-DTE − Data Terminal Equipment
-DCTE: − Data Circuit Terminating Equipment
3.FDDI
● FDDI (Fiber Distributed Data Interface) is a network standard that uses
fiber optic connections in a local area network (LAN) that can extend in
range up to 200 kilometers (124 miles).
● The FDDI protocol is based on the token ring protocol. A FDDI LAN can
support thousands of users.
Features
● FDDI uses optical fiber as its physical medium.
● It operates in the physical and medium access control (MAC layer) of the
Open Systems Interconnection (OSI) network model.
● It provides a high data rate of 100 Mbps and can support thousands of
users.
● It is used in LANs up to 200 kilometers for long distance voice and
multimedia communication.
● It uses a ring based token passing mechanism and is derived from IEEE
802.4 token bus standard.
● It contains two token rings, a primary ring for data and token transmission
and a secondary ring that provides backup if the primary ring fails.
● FDDI technology can also be used as a backbone for a wide area network
(WAN).

4.Token Ring
● A token-ring network is a local area network (LAN) topology that sends data in
one direction throughout a specified number of locations by using a token.
● The token is the symbol of authority for control of the transmission line.
Ring Latency –
The time taken by a single bit to travel around the ring is known as ring latency.
RL = d/v + N*b (b-bit delay, d-propagation delay, v-velocity, n-no. Of stations in
ring)
5.Bluetooth
● It is a Wireless Personal Area Network (WPAN) technology and is used for
exchanging data over smaller distances.
● A bluetooth LAN is an ad-hoc network , which means that the network, if formed
instantly, the devices then find each other and form a network called Piconet.
● A Bluetooth network is called a piconet and a collection of interconnected
piconets is called scatternet.
● Piconet can have max eighth stations (connect upto 8 devices)
Architecture of Bluetooth :

6.RFID
● Radio Frequency Identification (RFID) refers to a wireless system comprising two
components: tags and readers.
● The reader is a device that has one or more antennas that emit radio waves and
receive signals back from the RFID tag.
● Tags- which use radio waves to communicate their identity & other information to
nearby readers, can be possible or active.
There are two types of RFID :
Passive RFID –
In this device, RF tags are not attached by a power supply and passive RF tags stored
their power. When it is emitted from active antennas, the RF tag are used specific
frequencies like 125-134MHZ as low frequency, 13.56MHZ as a high frequency and 856
MHZ to 960MHZ as ultra-high frequency.
Active RFID –
In this device, RF tags are attached by a power supply that emits a signal and there is
an antenna which receives the data.
Features of RFID :
● An RFID tag consists of two-part which is an microcircuit and an antenna.
● This tag is covered by protective material which acts as a shield against the outer
environment effect.
● This tag may be active or passive in which we mainly and widely used passive
RFID.

Application of RFID :
● It is utilized in tracking shipping containers, trucks and railroad cars.
● It is used in Asset tracking.
● It is utilized in credit-card shaped for access application.
● It is used in Personnel tracking.
● Controlling access to restricted areas.
● It uses ID badging.
● Supply chain management.
● Counterfeit prevention (e.g., in the pharmaceutical industry).
Advantages of RFID :
● It provides data access and real-time information without taking too much time.
● RFID tags follow the instruction and store a large amount of information.
● The RFID system is non-line of sight nature of the technology.
● It improves the Efficiency, traceability of production.
● In RFID hundreds of tags read in a short time.
Disadvantages of RFID :
● It takes longer to program RFID Devices.
● RFID is intercepted easily even if it is Encrypted.
● In an RFID system, there are two or three layers of ordinary household foil to
dam the radio wave.
● There is privacy concern about RFID devices; anybody can access information
about anything.
● Active RFID can be costlier due to the battery.
7.Asynchronous Transfer Mode (ATM):
● It is an International Telecommunication Union- Telecommunications Standards
Section (ITU-T) efficient for call relay and it transmits all information including

multiple service types such as data, video, or voice which is conveyed in small
fixed-size packets called cells.
● Cells are transmitted asynchronously and the network is connection-oriented.
Benefits of ATM:
● Dynamic bandwidth for bursty traffic meeting application needs and delivering a
high utilization of networking resources; most applications are or can be viewed
as inherently bursty.
● Can handle mixed network traffic very efficiently.
UNIT 03
1.Data Link Layer
⇒Takes the bits from the physical layer and encapsulates them into frames. Frame
Management is what the data link layer does.
Packets : A small segment of a layer message
Frames : Frame is a data that is transmitted between network points as a unit complete
with addressing & necessary protocol control information.
Functions of data link layer
• Providing a well-designed service interface to the network layer.
• Dealing with Transmission errors.
• Regulating the flow of data so that slow receivers are not swamped by fast senders.

2.Error Control
⇒Error control in the data link layer is the process of detecting and correcting data
frames that have been corrupted or lost during transmission.
Types of Error Control
a.Error Detection : Errors may occur due to noise or any other impairments during
transmission from transmitter to the receiver, in a communication system. It is a class of
technique for detecting garbled i.e. unclear and distorted data or messages.
Techniques:
1)Parity Check:
● The parity check is done by adding an extra bit, called parity bit to the data to
make a number of 1s either even in case of even parity or odd in case of odd
parity.
● While creating a frame, the sender counts the number of 1s in it and adds the
parity bit in the following way
○ In case of even parity: If a number of 1s is even then parity bit value is 0. If
the number of 1s is odd then parity bit value is 1.
○ In case of odd parity: If a number of 1s is odd then parity bit value is 0. If a
number of 1s is even then parity bit value is 1.
● On receiving a frame, the receiver counts the number of 1s in it. In case of even
parity check, if the count of 1s is even, the frame is accepted, otherwise, it is
rejected. A similar rule is adopted for odd parity checks.
2)Checksum:
● Data is divided into fixed sized frames or segments.
● The sender adds the segments using 1’s complement arithmetic to get the sum.
It then complements the sum to get the checksum and sends it along with the
data frames.
● The receiver adds the incoming segments along with the checksum using 1’s
complement arithmetic to get the sum and then complements it.
● If the result is zero, the received frames are accepted; otherwise, they are
discarded.
3)Cyclic Redundancy Check (CRC):
● Cyclic Redundancy Check (CRC) involves binary division of the data bits being
sent by a predetermined divisor agreed upon by the communicating system. The
divisor is generated using polynomials.

○ Here, the sender performs binary division of the data segment by the
divisor. It then appends the remainder called CRC bits to the end of the
data segment. This makes the resulting data unit exactly divisible by the
divisor.
○ The receiver divides the incoming data unit by the divisor. If there is no
remainder, the data unit is assumed to be correct and is accepted.
Otherwise, it is understood that the data is corrupted and is therefore
rejected.
b.Error Correction : It simply means reconstruction and rehabilitation of original data
that is error-free. But the error correction method is very costly and is very hard.
Techniques
Backward Error Correction (Retransmission) − If the receiver detects an error in the
incoming frame, it requests the sender to retransmit the frame. It is a relatively simple
technique. But it can be efficiently used only where retransmitting is not expensive as in
fiber optics and the time for retransmission is low relative to the requirements of the
application.
Forward Error Correction − If the receiver detects some error in the incoming frame, it
executes error-correcting code that generates the actual frame. This saves bandwidth
required for retransmission. It is inevitable in real-time systems. However, if there are
too many errors, the frames need to be retransmitted.
The four main error correction codes are:
● Hamming Codes
● Binary Convolution Code
● Reed – Solomon Code
● Low-Density Parity-Check Code

3.Flow Control
⇒ Is a technique that allows two stations working at different speeds to communicate
with each other.
Two Types of flow control are:
Feedback-based flow control
⇒ The receiver sends back information to the sender about its current situation of
handling data, and gives the sender permission to send more data or reduce data flow.
Rate-based flow control
⇒ The protocol has a built in mechanism that limits the rate at which sender may
transmit data without feedback from the receiver.
4.Types of services provided to the network layer
⇒
a)Unacknowledged Connectionless Services
● No logical connection is established beforehand or released afterward.
● If a frame is lost due to noise on the line, no attempt is made to detect the loss
or recover from it in the data link layer.
● This class of service is appropriate when the error rate is very low so that
recovery is left to higher layers.
b)Acknowledged Connectionless Services
● No logical connections used,
● Each frame sent is individually acknowledged. Sender knows whether a frame
has arrived
● correctly. If it has not arrived within a specified time interval, it can be sent again.
● This service is useful over unreliable channels, such as wireless systems.
c)Acknowledged Connection-Oriented Service
When connection-oriented service is used, transfers go through three distinct phases.
Connection is established, one or more frames are actually transmitted and then
connection is released, freeing up the variables, buffers, and other resources used to
maintain the connection.
5.Framing
⇒ Framing is a point to point connection between two devices that consists of a wire in
which data is transmitted as a stream of bits.
Framing Methods in detail

a)Byte Count
-It uses a field in the header to specify the number of bytes in the frame.
-Once the header information is being received it will be used to determine the end of
the frame.
b)Flag Bytes with Byte stuffing Framing
-This method gets around the boundary detection of the frame by having each
appended by the frame start and frame end special bytes.
-If they are the same they are called Flag Bytes.
c)Flag Bits with Bit Stuffing Framing
-This method achieves the same thing as Byte stuffing methods by using Bits(1) instead
of Bytes (8 Bits)
-It was developed for High-level Data Link Control (HDLC) Protocol.
UNIT 04
1.Classful IP Addressing
The 32 bit IP address is divided into five subclasses. These are:
Class A
Class B
Class C
Class D
Class E
Each of these classes has a valid range of IP addresses. Classes D and E are reserved
for multicast and experimental purposes respectively. The order of bits in the first octet
determines the classes of IP addresses.
IPv4 address is divided into two parts:
-Network ID
-Host ID
The class of IP address is used to determine the bits used for network ID and host ID
and the number of total networks and hosts possible in that particular class. Each ISP or
network administrator assigns an IP address to each device that is connected to its
network.

Class A:
IP addresses belonging to class A are assigned to the networks that contain a large
number of hosts.
-The network ID is 8 bits long.
-The host ID is 24 bits long.
Class B:
IP addresses belonging to class B are assigned to the networks that range from
medium-sized to large-sized networks.
Class C:
IP addresses belonging to class C are assigned to small-sized networks.
Class D:
IP addresses belonging to class D are reserved for multicasting. The higher order bits of
the first octet of IP addresses belonging to class D are always set to 1110. The
remaining bits are for the address that interested hosts recognize.
Class E:
IP addresses belonging to class E are reserved for experimental and research
purposes. IP addresses of class E ranges from 240.0.0.0 – 255.255.255.254. This class
doesn’t have any sub-net mask. The higher order bits of first octet of class E are always
set to 1111.

2.Difference between IPV4 and IPV6
● IPv4 is a 32-Bit IP address whereas IPv6 is a 128-Bit IP address.
● IPv4 is a numeric addressing method whereas IPv6 is an alphanumeric
addressing method.
● IPv4 binary bits are separated by a dot(.) whereas IPv6 binary bits are separated
by a colon(:).
● IPv4 offers 12 header fields whereas IPv6 offers 8 header fields.
● IPv4 supports broadcast whereas IPv6 doesn’t support broadcast.
● IPv4 has checksum fields while IPv6 doesn’t have checksum fields
● When we compare IPv4 and IPv6, IPv4 supports VLSM (Variable Length Subnet
Mask) whereas IPv6 doesn’t support VLSM.
● IPv4 uses ARP (Address Resolution Protocol) to map to MAC addresses
whereas IPv6 uses NDP (Neighbor Discovery Protocol) to map to MAC
addresses.
3.Piggybacking
⇒ This technique in which the outgoing acknowledgement is delayed temporarily is
called piggybacking.
Advantages of piggybacking :
● The major advantage of piggybacking is the better use of available channel
bandwidth. This happens because an acknowledgement frame needs not to be
sent separately.

● Usage cost reduction
● Improves latency of data transfer
Disadvantages of piggybacking :
● The disadvantage of piggybacking is the additional complexity.
● If the data link layer waits long before transmitting the acknowledgement (block
the ACK for some time), the frame will rebroadcast.
4.Methods to improve QoS
a)Scheduling: Packets from different flows arrives at a switch or router for processing
a.1)FIFO
In first-in, first-out (FIFO) queuing, packets wait in a buffer (queue) until the node (router
or switch) is ready to process them. If the average arrival rate is higher than the average
processing rate, the queue will fill up and new packets will be discarded.
a.2)Priority Queue
In priority queuing, packets are first assigned to a priority class. Each priority class has
its own queue. The packets in the highest-priority queue are processed first. Packets in
the lowest- priority queue are processed last.
a.3)Weighted Fair Queuing

b)Traffic Shaping
Traffic shaping is a mechanism to control the amount and the rate of the traffic sent to
the network. Two techniques can shape traffic: leaky bucket and token bucket.
b.1)Leaky Bucket
-A leaky bucket algorithm shapes bursty traffic into fixed-rate traffic by averaging the
data rate. It may drop the packets if the bucket is full.
-A simple leaky bucket algorithm can be implemented using FIFO queue. A FIFO queue
holds the packets. If the traffic consists of fixed-size packets (e.g., cells in ATM
networks), the process removes a fixed number of packets from the queue at each tick
of the clock. If the traffic consists of variable-length packets, the fixed output rate must
be based on the number of bytes or bits.
b.2)Token-Bucket
-The token bucket allows bursty traffic at a regulated maximum rate.

-In this , as packets come each receives a token from the bucket which helps to send
the packet to the network. If it does not have a token it cannot be sent and if the tokens
are over the sending is stopped as it limits the upload of packets.
c)Resource Reservation
A flow of data needs resources such as a buffer, bandwidth, CPU time, and so on. The
quality of service is improved if these resources are reserved.
d)Admission Control
Admission control refers to the mechanism used by a router, or a switch, to accept or
reject a flow based on predefined parameters called flow specifications.Before a router
accepts a flow for processing, it checks the flow specifications to see if its capacity (in
terms of bandwidth, buffer size, CPU speed, etc.) and its previous commitments to other
flows can handle the new flow.
5.Subnet, subnet mask, Private IP, Public IP and NAT
a)Subnet : When a bigger network is divided into smaller networks, to maintain security,
then that is known as Subnetting. So, maintenance is easier for smaller networks.
b)Subnet mask : A subnet mask is a 32 bits address used to distinguish between a
network address and a host address in IP address. A subnet mask identifies which part
of an IP address is the network address and the host address.

c) Private and public IP
PRIVATE IP ADDRESS PUBLIC IP ADDRESS
The scope of Private IP is local. The scope of Public IP is global.
It is used to communicate within the
network.
It is used to communicate outside the
network.
Private IP addresses of the systems
connected in a network differ in a uniform
manner.
Public IP may differ in a uniform or
non-uniform manner.
It works only on LAN. It is used to get internet service.
It is used to load the network operating
system.
It is controlled by ISP.
Private IP can be known by entering
“ipconfig” on the command prompt.
Public IP can be known by searching
“what is my ip” on google.
Private IP uses numeric code that is not
unique and can be used again
Public IP uses a numeric code that is
unique and cannot be used by other
Private IP addresses require NAT to
communicate with devices
Public IP does not require a network
translation
Private IP addresses are secure Public IP address has no security and is
subjected to attack
Example: 192.168.1.10 Example: 17.5.7.8

6.Congestion Control and how it works in TCP
⇒Congestion Control is a mechanism that controls the entry of data packets into the
network, enabling a better use of a shared network infrastructure and avoiding
congestive collapse.
TCP uses a congestion window in the sender side to do congestion avoidance. The
congestion window indicates the maximum amount of data that can be sent out on a
connection without being acknowledged. TCP detects congestion when it fails to receive
an acknowledgement for a packet within the estimated timeout.
Open Loop Congestion Control
Open loop congestion control policies are applied to prevent congestion before it
happens. The congestion control is handled either by the source or the destination.
Closed Loop Congestion Control
Closed loop congestion control techniques are used to treat or alleviate congestion after
it happens.

8.Explain TCP with its header format
TCP header structure
TCP wraps each data packet with a header containing 10 mandatory fields totaling 20
bytes (or octets). Each header holds information about the connection and the current
data being sent.
The 10 TCP header fields are as follows:
● Source port – The sending device’s port.
● Destination port – The receiving device’s port.
● Sequence number – A device initiating a TCP connection must choose a random
initial sequence number, which is then increment according to the number of
transmitted bytes.
● Acknowledgment number – The receiving device maintains an acknowledgment
number starting with zero. It increments this number according to the number of
bytes received.
● TCP data offset – This specifies the size of the TCP header, expressed in 32-bit
words. One word represents four bytes.
● Reserved data – The reserved field is always set to zero.
● Control flags – TCP uses nine control flags to manage data flow in specific
situations, such as the initiating of a reset.
● Window size TCP checksum – The sender generates a checksum and transmits
it in every packet header. The receiving device can use the checksum to check
for errors in the received header and payload.
● Urgent pointer – If the URG control flag is set, this value indicates an offset from
the sequence number, indicating the last urgent data byte.
● mTCP optional data – These are optional fields for setting maximum segment
sizes, selective acknowledgments and enabling window scaling for more efficient
use of high-bandwidth networks.
9.Socket
⇒A socket is one endpoint of a two-way communication link between two programs
running on the network.
Types of Sockets :
There are two types of Sockets: the datagram socket and the stream socket.

Datagram Socket :
This is a type of network which has connectionless points for sending and receiving
packets. It is similar to a mailbox. The letters (data) posted into the box are collected
and delivered (transmitted) to a letterbox (receiving socket).
Stream Socket:
In Computer operating systems, a stream socket is a type of interprocess
communications socket or network socket which provides a connection-oriented,
sequenced, and unique flow of data without record boundaries with well defined
mechanisms for creating and destroying connections and for detecting errors. It is
similar to a phone. A connection is established between the phones (two ends) and a
conversation (transfer of data) takes place.
UNIT 05
1.Application layer
● The application layer is closest to the end user.
● Network applications enable users to send and receive data with ease.
● The application layer acts as an interface between the applications and the
underlying network.
● Application layer protocols help exchange data between programs running on the
source and destination hosts.

● The TCP/IP application layer performs the functions of the upper three layers of
the OSI model.
● Common application layer protocols include: HTTP, FTP, TFTP, DNS.
2.DNS
● DNS stands for Domain Name System.
● DNS is a directory service that provides a mapping between the name of a host
on the network and its numerical address.
● DNS is required for the functioning of the internet.
● DNS has some protocol that allows the client & servers to communicate with
each other.
Working of DNS
1. The client requests for the IP address of a particular domain name to the DNS
resolver.
2. The resolver requests to the root DNS server.
3. The root DNS server then forwards the query to the Top-level DNS server.
4. The top-level domain server has all the information about the authoritative DNS
servers.
5. The authoritative server then returns the IP address corresponding to the
requested domain name to the resolver.
6. The resolver then returns the IP address to the host.
3.SMTP
● SMTP stands for Simple Mail Transfer Protocol
● SMTP is the standard protocol for email services on a TCP/IP network
● SMTP is an application layer protocol that enables the transmission and delivery
of email over the internet.

● It is created and maintained by the Internet Engineering Task Force(IETF)
● SMTP is generally integrated within an email client app and is composed of 4 key
components
○ Mail User Agent
○ Mail Submission Agent
○ Mail Transfer Agent
○ Mail Delivery Agent
Advantages
● All you have to do is use your credentials and it will work.
● In case of failure, the message will include an explanation about why the email
failed to be delivered.
● It is extremely easy to start using mail for your transactional emails. All you have
to do is exchange ceremonial and you are set to go. Unlike with API, where
coding is required.
Disadvantages
● Some firewalls can block ports commonly used with SMTP.
● Security matters for SMTP are worse.
● Transmission of binary files using SMTP is not possible without converting it into
text files. Use MIME to send mail in another format.
● Its usefulness is limited by its simplicity.
● It is limited to only 7 bit ASCII characters.
● SMTP servers may reject all mail messages beyond some specific length.
4.POP3 (Post Office Protool)
⇒
-The Message Access Agent contains two types of protocols, i.e., POP3 and IMAP.
-It is a type of computer networking and internet standard protocol that extracts and
receives email from a remote mail server for access by the host machine.

Advantages
● Provides easy and fast access to the emails
● There is no limit on the size of the emails which we receive or send
● Requires less server storage space
● Easy to configure and use
Disadvantages
● Email folder which we download can be corrupted
● Transforming mail folder from local machine to another machine can be difficult
● High risk of virus attack
5.HTTP
⇒ The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
collaborative, distributed, hypermedia information systems. It is the data communication
protocol used to establish communication between client and server.
The Basic Characteristics of HTTP (Hyper Text Transfer Protocol):
● It is the protocol that allows web servers and browsers to exchange data over the
web.
● It is a request response protocol.
● It uses the reliable TCP connections by default on TCP port 80.
● It is stateless means each request is considered as the new request. In other
words, the server doesn't recognize the user by default.
The Basic Features of HTTP (Hyper Text Transfer Protocol):
There are three fundamental features that make the HTTP a simple and powerful
protocol used for communication:

● HTTP is media independent: It specifies that any type of media content can be
sent by HTTP as long as both the server and the client can handle the data
content.
● HTTP is connectionless: It is a connectionless approach in which HTTP client
i.e., a browser initiates the HTTP request and after the request is sent the client
disconnects from server and waits for the response.
● HTTP is stateless: The client and server are aware of each other during a current
request only. Afterwards, both of them forget each other. Due to the stateless
nature of protocol, neither the client nor the server can retain the information
about different requests across the web pages.
6.URL (Uniform Resource Locator)
⇒Components of a URL
A URL can have many forms. The most general however follows a three-components
system as proposed below:
● Protocol: HTTP is the protocol here
● Hostname: Name of the machine on which the resource lives.
● File Name: The pathname to the file on the machine.
● Port Number: Port number to which to connect (typically optional).

URL Class
The URL class is the gateway to any of the resources available on the internet. A Class
URL represents a Uniform Resource Locator, which is a pointer to a “resource” on the
World Wide Web.
Constructors of the URL class
● URL(String address) throws MalformedURLException: It creates a URL object
from the specified String.
● URL(String protocol, String host, String file): Creates a URL object from the
specified protocol, host, and file name.
● URL(String protocol, String host, int port, String file): Creates a URL object from
protocol, host, port, and file name.
● URL(URL context, String spec): Creates a URL object by parsing the given spec
in the given context.
● URL(String protocol, String host, int port, String file, URLStreamHandler handler):
● Creates a URL object from the specified protocol, host, port number, file, and
handler.
● URL(URL context, String spec, URLStreamHandler handler):
● Creates a URL by parsing the given spec with the specified handler within a
specified context.
Methods in URL

7.FTP (File Transfer Protocol)

⇒File Transfer Protocol(FTP) is an application layer protocol that moves files between
local and remote file systems. It runs on the top of TCP, like HTTP. To transfer a file, 2
TCP connections are used by FTP in parallel: control connection and data connection.
● What is a control connection?
For sending control information like user identification, password, commands to change
the remote directory, commands to retrieve and store files, etc., FTP makes use of a
control connection. The control connection is initiated on port number 21.
● What is a data connection?
For sending the actual file, FTP makes use of a data connection. A data connection is
initiated on port number 20.
FTP sends the control information out-of-band as it uses a separate control connection.
Some protocols send their request and response header lines and the data in the same
TCP connection.
FTP Commands – Some of the FTP commands are :
USER – This command sends the user identification to the server.
PASS – This command sends the user password to the server.
RMD – This command causes the directory specified in the path name to be removed
as a directory.
MKD – This command causes the directory specified in the pathname to be created as
a directory.
STOR – This command causes the storage of a file into the current directory of the
remote host.
LIST – Sends a request to display the list of all the files present in the directory.
ABOR – This command tells the server to abort the previous FTP service command and
any associated transfer of data.

QUIT – This command terminates a USER and if file transfer is not in progress, the
server closes the control connection.
Advantages of FTP(File Transfer Protocol):-
● Speed is one of the advantages of FTP(File Transfer Protocol).
● File sharing also comes in the category of advantages of FTP in that between
two machines files can be shared on the network.
● Efficiency is more in FTP.
Disadvantages of FTP(File Transfer Protocol):-
● File size limit is the drawback of FTP; only 2 GB size files can be transferred.
● Multiple receivers are not supported by the FTP.
● FTP does not encrypt the data; this is one of the biggest drawbacks of FTP.
● FTP is insecure. We use login IDs and passwords making it secure but they can
be attacked by hackers.
8.Basic functions of e-mail system
● Composition: It refers to the process of creating messages and answers.
Although any text editor can be used for the body of the message, the system
itself can provide assistance with addressing and the numerous header fields
attached to each message. For example, when answering a message, the e-mail
system can extract the originator's address from the incoming email and
automatically insert it into the proper place in the reply.
● Transfer: It refers to moving messages from the originator to the recipient. In
large part, this requires establishing a connection to the destination or some
intermediate machine, outputting the message, and releasing the connection.
The e-mail system should do this automatically, without bothering the user.
● Reporting: It has to do with telling the originator what happened to the message.
Was it delivered? Was it rejected? Was it lost? Numerous applications exist in
which confirmation of delivery is important and may even have legal significance.
Displaying incoming messages is needed so people can read their email.
Sometimes conversion is required or a special viewer must be invoked, for
example, if the message is a PostScript file or digitized voice. Simple
conversions and formatting are sometimes attempted as well.
● Disposition: It is the final step and concerns what the recipient does with the
message after receiving it. Possibilities include throwing it away before reading,
throwing it away after reading, saving it, and so on. It should also be possible to

retrieve and reread saved messages, forward them, or process them in other
ways.
9.Difference between HTTP and FTP
HTTP FTP
It stands for HyperText Transfer Protocol. It stands for File Transfer Protocol
It is the set of rules that how web pages
are transferred on different computers
over the internet.
It is the set of rules that permit the
downloading and uploading of files on the
computer over the internet.
It only supports the data connection. It supports both data connection and
control connection
The URL using the HTTP protocol will
start with HTTP.
The URL using the FTP will start with
FTP.
It does not require authentication. It requires authentication.
It is efficient in transferring small files. It is efficient in transferring large files.
It is a stateless protocol. It is not a stateless protocol and it
maintains states.
It uses a one way communication system. It uses a two way communication system.
HTTP is faster. FTP is slower as compared to HTTP.
UNIT 06
1.Network Security Goals

Network security entails protecting the usability, reliability, integrity, and safety of
network and data. Effective network security defeats a variety of threats from entering or
spreading on a network.
Goals
● Confidentiality − The function of confidentiality is to protect precious business
data from unauthorized persons. Confidentiality part of network security makes
sure that the data is available only to the intended and authorized persons.
● Integrity − This goal means maintaining and assuring the accuracy and
consistency of data. The function of integrity is to make sure that the data is
reliable and is not changed by unauthorized persons.
● Availability − The function of availability in Network Security is to make sure that
the data, network resources/services are continuously available to the legitimate
users, whenever they require it.
2.Public key Encryption/Decryption
⇒ Public-key cryptography, or asymmetric cryptography, is an encryption scheme that
uses two mathematically related, but not identical, keys - a public key and a private key.
Unlike symmetric key algorithms that rely on one key to both encrypt and decrypt, each
key performs a unique function.
A Public key encryption has following key ingredients:
a) Plaintext: This is a readable message or data that is feed into the algorithm as input.
b) Encryption Algorithm: The encryption algorithm performs various transformations on
the plain text.
c) Public and Private Keys: This is a pair of keys that has been selected so that if one is
used for encryption then the other is used for decryption.
d) Ciphertext: This is the scrambled message produced as output. It depends on the
key and the energy algorithm used for a given message two different keys will produce
two different ciphertext.
e) Decryption Algorithm: This algorithm accepts the ciphertext and the matching key to
produce original plaintext.

Advantages
● No need to exchange the keys
● Another key cannot be derived from one key
● The confidentiality of the message can be ensured by using the public key
cryptography
● It is possible to establish authentication of the sender by using public key
cryptography
● It is possible to ensure the confidentiality and authentication of the message at
the same time
● It is possible to use public key cryptography for session key exchange
Working Principle of Public Key Encryption
Data confidentiality is about protecting data against unintentional, unlawful, or
unauthorized access, disclosure, or theft.
Data integrity is a concept and process that ensures the accuracy, completeness,
consistency, and validity of an organization's data.
Authentication is the process of determining whether someone or something is, in fact,
who or what it says it is.
Nonrepudiation provides proof of the origin, authenticity and integrity of data. It
provides assurance to the sender that its message was delivered, as well as proof of
the sender's identity to the recipient.
Characteristics of Public Encryption key:
Public key Encryption is important because it is infeasible to determine the decryption
key given only the knowledge of the cryptographic algorithm and encryption key.
Either of the two keys (Public and Private key) can be used for encryption with another
key used for decryption.
Due to Public key cryptosystem, public keys can be freely shared, allowing users an
easy and convenient method for encrypting content and verifying digital signatures, and
private keys can be kept secret, ensuring only the owners of the private keys can
decrypt content and create digital signatures.

4.Public and Private key Encryption

5. What is a firewall? Mention the types of firewalls
⇒Network Firewalls are the devices that are used to prevent private networks from
unauthorized access. A Firewall is a security solution for the computers or devices that
are connected to a network, they can be either in form of hardware as well as in form of
software. It monitors and controls the incoming and outgoing traffic.
eight types of firewalls:
● Packet-filtering firewalls
● Circuit-level gateways
● Stateful inspection firewalls
● Application-level gateways (a.k.a. proxy firewalls)
● Next-gen firewalls
● Software firewalls
● Hardware firewalls
● Cloud firewalls
Advantages of Firewall:
● Blocks infected files
● Stop unwanted visitors
● Prevents Email spamming
● Stops Spyware
Limitations:
● Internal loose ends
● Infected Files
● Effective Cost
● User Restriction
● System Performance

6.The steps followed in creating digital signature are :
Message digest is computed by applying hash function on the message and then
message digest is encrypted using the private key of the sender to form the
digital signature. (digital signature = encryption (private key of sender, message
digest) and message digest = message digest algorithm(message)).
Digital signature is then transmitted with the message.(message + digital
signature is transmitted)
Receiver decrypts the digital signature using the public key of sender.(This
assures authenticity, as only sender has his private key so only sender can
encrypt using his private key which can thus be decrypted by sender’s public
key).
The receiver now has the message digest.
The receiver can compute the message digest from the message (actual
message is sent with the digital signature).
The message digest computed by receiver and the message digest (got by
decryption on digital signature) need to be same for ensuring integrity.

7.Differentiate between digital signature and digital certificate

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