Network Communication Models ---- Kumari-NetworkAdmin

Network Communication Models ---- Kumari-NetworkAdmin

How network communications works
OSI / ISO Model
TCP / IP Model

OSI / ISO Model
The OSI model, created in 1984 by ISO, is a reference framework that explains the process of transmitting data between computers. It is divided into seven layers that work together to carry out specialised network functions, allowing for a more systematic approach to networking.
The OSI model consists of seven abstraction layers arranged in a top-down order:

1. Physical Layer
2. Data Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer

Physical Layer – BITS
The physical layer 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 0’s and 1’s and send them to the Data Link layer.

Functions of Physical Layer
1. Bit synchronization
2. Bit transmission rate control
3. Physical topologies
4. Transmission mode such as Simplex, half-duplex, full-duplex
Data Link Layer (DLL) - 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 the DLL to transmit it to the Host using its MAC address.

The packet received from the Network layer is further divided into frames depending on the frame size of the NIC(Network Interface Card).

DLL also encapsulates Sender and Receiver’s MAC address in the header.

Functions of Data Link Layer
1. Framing
2. Physical addressing (MAC Address)
3. Error control
4. Flow Control
5. Access control
Network Layer – PACKETS & Routing

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 Network Layer
1. Routing
2. Logical Addressing.
Transport Layer – SEGMENTS

The data in the transport layer is referred to as Segments.

The transport layer 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.

It also adds Source and Destination port numbers in its header and forwards the segmented data.

Functions of Transport Layer
1. Segmentation and Reassembly
2. Service Point Addressing or Port Addressing
Session Layer – SESSIONS & CHECKPOINTS

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

This layer allows a process to add checkpoints that are considered synchronization points in the data.

These synchronization points help to identify the error so that the data is re-synchronized properly.

Functions of Session Layer
1. Session establishment
2. Session maintenance
3. Session termination
4. Synchronization

Presentation Layer – DATA & ENCRYPTION

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.

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.

Application Layer – Desktop Application

Application layer 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.

Example: Applications – Browsers, Skype Messenger, E-Mail Services, Directory Services etc.

Functions of the Application Layer
1. Handling of Applications.
2. Produce data to be transferred
3. Handling of Application Services

TCP / IP Model
The main work of TCP/IP models 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.


Layers of TCP/IP Model
1. Network Access Layer
2. Internet Layer(IP)
3. Transport Layer(TCP/UDP)
4. Application Layer