The Need For Layered Architecture :

- Layered architecture in computer networks refers to dividing a network’s

functioning into different layers, each responsible for a certain communication
component. The major goal of this layered architecture is to separate the complex
network communication process into manageable, smaller activities that can be
better developed.
- Every network consists of a specific number of functions, layers, and tasks to
perform. Layered Architecture in a computer network is defined as a model where
a whole network process is divided into various smaller sub-tasks. These divided
sub-tasks are then assigned to a specific layer to perform only the dedicated tasks.
A single layer performs only a specific type of task. To run the application and
provide all types of services to clients a lower layer adds its services to the higher
layer present above it. Therefore layered architecture provides interactions
between the sub-systems. If any type of modification is done in one layer it does
not affect the next layer.

As shown in the above diagram, there are five different layers. Therefore, it is a five-
layered architecture. Each layer performs a dedicated task. The lower-level data for
example from layer 1 data is transferred to layer 2. Below all the layers Physical Medium is
present. The physical medium is responsible for the actual communication to take place.
For the transfer of data and communication layered architecture provides simple
interface.

B.C.A TY Notes By - Sandeep Chavan

Elements of Layered Architecture
There are three different types of elements of a layered architecture. They are described
below:
 Service: Service is defined as a set of functions and tasks being provided by a lower
layer to a higher layer. Each layer performs a different type of task. Therefore, actions
provided by each layer are different.
 Protocol: Protocol is defined as a set rule used by the layer for exchanging and
transmission of data with its peer entities. These rules can consists details regarding a
type of content and their order passed from one layer to another.
 Interface: Interface is defined as a channel that allows to transmit the messages from
one layer to the another.

B.C.A TY Notes By - Sandeep Chavan

OSI Reference Model :

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

Data Flow In OSI Model

- When we transfer information from one device to another, it travels through 7

layers of OSI model. First data travels down through 7 layers from the sender’s end
and then climbs back 7 layers on the receiver’s end.

B.C.A TY Notes By - Sandeep Chavan

Data flows through the OSI model in a step-by-step process:

Application Layer: Applications create the data.

Presentation Layer: Data is formatted and encrypted.

Session Layer: Connections are established and managed.

Transport Layer: Data is broken into segments for reliable delivery.

Network Layer : Segments are packaged into packets and routed.

Data Link Layer: Packets are framed and sent to the next device.

Physical Layer: Frames are converted into bits and transmitted physically.

Each layer adds specific information to ensure the data reaches its destination correctly,
and these steps are reversed upon arrival.

The OSI model consists of seven abstraction layers arranged in a top-down order:

Physical Layer – Layer 1

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. It 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.

Data Link Layer (DLL) – Layer 2

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.
Functions of the Data Link Layer
 Framing: Framing is a function of the data link layer. It provides a way for a sender to
transmit a set of bits that are meaningful to the receiver.
 Error Control: The 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 an acknowledgment.

B.C.A TY Notes By - Sandeep Chavan

Network Layer – Layer 3
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.
Functions of the Network Layer
 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: To identify each device inter-network 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.

Transport Layer – Layer 4

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 acknowledgment of the successful data transmission and re-transmits the data if an
error is found.
Services Provided by Transport Layer
 Connection-Oriented Service
 Connectionless Service

Session Layer – Layer 5

This layer is responsible for the establishment of connection, maintenance of sessions,
and authentication, and also ensures security.

Presentation Layer – Layer 6

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.
Functions of the Presentation Layer
 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 cipher text 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.

Application Layer – Layer 7

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 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.

B.C.A TY Notes By - Sandeep Chavan

TCP/IP Reference Model :

- TCP/IP stands for Transmission Control Protocol/Internet Protocol, which are the core
protocols of the Internet. This model defines how data is transmitted over networks,
ensuring reliable communication between devices.
- It consists of four layers: the Link Layer, the Internet Layer, the Transport Layer, and the
Application Layer. Each layer has specific functions that help manage different aspects of
network communication, making it essential for understanding and working with modern
networks.
- TCP/IP was designed and developed by the Department of Defense (DoD) in the 1960s
and is based on standard protocols. The TCP/IP model is a concise version of the OSI
model. It contains four layers, unlike the seven layers in the OSI model.

- The main work of TCP/IP is to transfer the data of a computer from one device to
another. The main condition of this process is to make data reliable and accurate so that
the receiver will receive the same information which is sent by the sender. To ensure that,
each message reaches its final destination accurately, the TCP/IP model divides its data
into packets and combines them at the other end, which helps in maintaining the accuracy
of the data while transferring from one end to another end.

How Does the TCP/IP Model Work?

Whenever we want to send something over the internet using the TCP/IP Model, the
TCP/IP Model divides the data into packets at the sender’s end and the same packets have
to be recombined at the receiver’s end to form the same data, and this thing happens to
maintain the accuracy of the data. TCP/IP model divides the data into a 4-layer procedure,
where the data first go into this layer in one order and again in reverse order to get
organized in the same way at the receiver’s end.
Layers of TCP/IP Model
 Application Layer
 Transport Layer(TCP/UDP)
 Network/Internet Layer(IP)
 Network Access Layer

The diagrammatic comparison of the TCP/IP and OSI model is as follows:

B.C.A TY Notes By - Sandeep Chavan

1. Network Access Layer - This layer is the lowest layer in the TCP/IP model. It is compared
with the combination of the data link layer and the physical layer of the OSI Model. They
are similar but not identical. This layer is the group of communication protocols that acts
as a link to which the host is connected physically. It is mainly concerned with the physical
transmission of the data.

The protocols used in this layer are: ETHERNET, Token Ring etc

2. Internet Layer - The Internet layer is compared to the network layer of the OSI model.
The main responsibility of the network layer is to transport data packets from the source
to the destination host across the entire network. The transmission done by the internet
layer is less reliable.

The main protocols used in this layer are:

IP - It is the primary protocol in the internet layer. It stands for Internet Protocol. It is
responsible for the transmission of data packets from the source to the destination host. It
is implemented in two versions, IPv4 and IPv6.

ARP - It stands for Address Resolution Protocol. Its main responsibility is to find the
physical address of the host using the internet address or IP address.

B.C.A TY Notes By - Sandeep Chavan

3. Transport Layer - The transport layer is responsible for the end-to-end communication
and delivery of the non-erroneous data. It provides services that include connection-
oriented communication, flow control, reliability, multiplexing. This layer is similar to the
transport layer of the OSI model.

The main protocols of this layer are:

 TCP - It stands for Transmission Control Protocol. It is a connection-oriented
protocol and provides reliable communication and error-free delivery of data from
the source to the destination host. It is optimized for accurate delivery than timely
delivery. It is used by many internet applications including World Wide
Web(WWW), email.

 UDP - It stands for User Diagram Protocol. It provides simple, cost-effective but
unreliable service. It prioritizes speed over the accuracy of delivery.

4. Application Layer - It is the topmost layer of the TCP/IP model. Its functions are similar
to the combination of the application layer, session layer, and presentation layer. It is
responsible for user interface specifications. It contains communication protocols used in
the process to process communication across an Internet protocol computer network.

Some of the protocols used in this layer are:

HTTP - It stands for Hypertext Transfer Protocol. It is the foundation of data

communication for the World Wide Web. The hypertext includes hyperlinks to other
resources that can be accessed easily by the user.

SMTP - It stands for Simple Mail Transfer Protocol. It is used for sending and receiving
electronic mails.

FTP - It stands for File Transfer Protocol. It is a standard communication protocol used for
transferring files from one computer to another over a network.

B.C.A TY Notes By - Sandeep Chavan

Ethernet Technology :

- Ethernet is a wired technology that allows devices to connect and communicate with
each other on a local area network (LAN) or wide area network (WAN). It's the most
popular LAN technology in use today, and is known for its reliability, security, and
ease of installation.
- Ethernet was developed in the early 1980s and was the first high-speed LAN
technology. It started out using coaxial cable, but has since progressed to using
twisted pair copper wiring and fiber-optic wiring.
- Ethernet is the most widely used LAN technology and is defined under IEEE
standards 802.3. The reason behind its wide usability is that Ethernet is easy to
understand, implement, and maintain, and allows low-cost network
implementation. Also, Ethernet offers flexibility in terms of the topologies that are
allowed. Ethernet generally uses a bus topology. Ethernet operates in two layers of
the OSI model, the physical layer and the data link layer.
- Standard Ethernet can transmit data at up to 10 Mbps, while Fast Ethernet can
transmit at up to 100 Mbps.
- Ethernet is more secure than wireless technology because devices must be
connected using physical cables. This makes it harder for outsiders to access
network data or hijack bandwidth.

How it works

- Ethernet uses a protocol, or set of rules, to define how devices format and transmit
data. Data is broken into packets, and each packet is transmitted using the
CSMA/CD algorithm. This algorithm detects collisions and ensures that packets
arrive at their destination without colliding with other packets.

B.C.A TY Notes By - Sandeep Chavan

 - There are different types of Ethernet networks that are used to connect devices
and transfer data. Let’s discuss them in simple terms:

1. Fast Ethernet: This type of Ethernet network uses cables called twisted pair or CAT5. It
can transfer data at a speed of around 100 Mbps (megabits per second). Fast Ethernet
uses both fiber optic and twisted pair cables to enable communication.
2. Gigabit Ethernet: This is an upgrade from Fast Ethernet and is more common
nowadays. It can transfer data at a speed of 1000 Mbps or 1 Gbps (gigabit per second).
Gigabit Ethernet also uses fiber optic and twisted pair cables for communication. It often
uses advanced cables like CAT5e, which can transfer data at a speed of 10 Gbps.
3. 10-Gigabit Ethernet: This is an advanced and high-speed network that can transmit data
at a speed of 10 gigabits per second. It uses special cables like CAT6a or CAT7 twisted-pair
cables and fiber optic cables. With the help of fiber optic cables, this network can cover
longer distances, up to around 10,000 meters.
4. Switch Ethernet: This type of network involves using switches or hubs to improve
network performance. Each workstation in this network has its own dedicated connection,
which improves the speed and efficiency of data transfer. Switch Ethernet supports a wide
range of speeds, from 10 Mbps to 10 Gbps, depending on the version of Ethernet being
used.

In summary, Fast Ethernet is the basic version with a speed of 100 Mbps, Gigabit Ethernet
is faster with a speed of 1 Gbps, 10-Gigabit Ethernet is even faster with a speed of 10
Gbps, and Switch Ethernet uses switches or hubs to enhance network performance.

Advantages
- Cost-effective: Ethernet is affordable to install.
- High speed: Ethernet provides fast data transmission.
- Secure: Ethernet provides a secure channel for data transmission.

Disadvantages

- Collisions: When two devices try to transmit at the same time, their packets collide
and are lost, which can decrease network performance.
- Scalability: As the number of devices on an Ethernet network increases, the
likelihood of collisions increases, which can eventually make the network
unusable.
- Security: Because Ethernet uses a shared medium, any device on the network can
listen in on other devices' traffic.
- Complex and costly wiring: Wiring up an Ethernet network can be complex and
costly.

B.C.A TY Notes By - Sandeep Chavan

CSMA/CD :

- Carrier sense multiple access with collision detection (CSMA/CD) is a network

protocol used in Ethernet networks to manage collisions. It's a medium access
control (MAC) method that uses carrier sensing and collision detection to prevent
multiple devices from sending data at the same time over the same Ethernet wire.
- CSMA/CD is a modification of pure carrier-sense multiple access (CSMA). It was most
commonly used in early Ethernet technology for local area networking. However, the
growing popularity of Ethernet switches in the 1990s made CSMA/CD less common
and important.

How Does CSMA/CD Work ?

 Step 1: Check if the sender is ready to transmit data packets.
 Step 2: Check if the transmission link is idle.
The sender has to keep on checking if the transmission link/medium is idle. For this, it
continuously senses transmissions from other nodes. The sender sends dummy data
on the link. If it does not receive any collision signal, this means the link is idle at the
moment. If it senses that the carrier is free and there are no collisions, it sends the
data. Otherwise, it refrains from sending data.
 Step 3: Transmit the data & check for collisions.
The sender transmits its data on the link. CSMA/CD does not use an ‘acknowledgment’
system. It checks for successful and unsuccessful transmissions through collision
signals. During transmission, if a collision signal is received by the node, transmission is
stopped. The station then transmits a jam signal onto the link and waits for random
time intervals before it resends the frame. After some random time, it again attempts
to transfer the data and repeats the above process.
 Step 4: If no collision was detected in propagation, the sender completes its frame
transmission and resets the counters.

B.C.A TY Notes By - Sandeep Chavan

CSMA/CA :

- Carrier sense multiple access with collision avoidance (CSMA/CA) is a network

protocol that helps avoid collisions when multiple stations send data over a
network. CSMA/CA is especially important for wireless networks, where collision
detection is not possible.
- CSMA is one of the network protocols which works on the principle of ‘carrier sense’.
CSMA is a protocol developed to increase the performance of the network and
reduce the chance of collision in the network.
- If any device wants to send data then the device first senses or listens to the network
medium to check whether the shared network is free or not. If the channel is found
idle then the device will transmit its data.
- This sense reduces the chance of collision in the network but this method is not able
to eliminate the collision.
- Carrier Sense Multiple Access (CSMA) is a protocol that senses or listens to the
medium before any transmission of data in the medium.

How Does CSMA/CA Work?

 When a frame is ready, the transmitting station checks whether the channel is idle or
busy.
 If the channel is busy, the station waits until the channel becomes idle.
 If the channel is idle, the station waits for an Inter-frame gap (IFG) amount of time
and then sends the frame.
 After sending the frame, it sets a timer.
 The station then waits for acknowledgement from the receiver. If it receives the
acknowledgement before expiry of timer, it marks a successful transmission.
 Otherwise, it waits for a back-off time period and restarts the algorithm.

B.C.A TY Notes By - Sandeep Chavan

Wireless LAN:

- A Wireless Local Area Network (WLAN), also known as a Wireless LAN, is a network
comprising two or more computing devices that communicate through radio waves
without the need for physical connections.
- The computer network that are wireless means the computers are not connected
with wires are called wireless network.
- This network help to reduce the cost of the cables. they make use of radio
communication waves are used to connect devices like laptop to internet.
- A Wi-Fi network is a type of WLAN.
- knowningly or unknowningly all of us used the wireless connection, when
connecting the laptop to wifi hotspot.
- The majority of WLANs are established on the IEEE 802.11 standard.

B.C.A TY Notes By - Sandeep Chavan

 - Wireless LANs are further classified into two categories, these are:

1. Ad-hoc Mode Wireless LANs

Ad hoc networks are formed by a group of wireless nodes that establish peer-to-peer
communication. The ad-hoc mode has been designed to allow communication only among
clients within the transmission range, i.e., within the same cell.

- If a client wants to communicate outside the cell, then it’s a must that one of the
cells acts as the gateway and performs routing.

2. Infrastructure Mode Wireless LANs

Mobile devices or client connect to an Access points that in turn connect via a bridge to the
LAN or internet. The client transmits Frames to other clients via the access point. Access
point serve as the intermediary between wireless nodes and the wired backbone. The
utilization of access points allows the proficient transfer of network resources among
wireless nodes.

Advanctages: 1) Mobility 2) sharing 3) Cost 4) More Connection 5) No Signal Jam

Disadvantages: 1) Security 2) Less Speed 3) Less Control

B.C.A TY Notes By - Sandeep Chavan

Bluetooth :

- Bluetooth is a wireless technology that allows to connect and exchange data over a
short distance without the need for cables or wires.
- It is one of the most common wireless connectivity standards in the world.
- Bluetooth uses short range radio frequency to connect devices such as computer
and mobile phones, when they are close to each other.
- Bluetooth is a standard that manufacturers must incorporate into their devices so
they can recognize and interact with other Bluetooth devices. Bluetooth devices
must be paired before they can exchange information, and the pairing process varies
depending on the device.
- Bluetooth uses short - wavelength radio waves with a frequency of around 2.4 to
2.485 gigahertz.
- Bluetooth is convenient, widely supported and consumes relatively low power.
- It can be fairly secure, depending on how it is configured.

Bluetooth is used in many electronic devices including :

1) Personal Electronics: Wireless keyboards, Speaker, mic etc.

2) Consumer Electronics: Cameras, Television and Home Appliances etc.
3) Car Infotainment System: For Streaming music or directions from a phone.

B.C.A TY Notes By - Sandeep Chavan