WHAT IS DATA COMMUNICATION ?

• Data communication is the process of transferring data from one place to another or between two locations. 

• It allows electronic and digital data to move between two networks, no matter where the two are located geographically, what the data contains, or what format they are in. 

•  Whenever we talk about communication between two computing devices using a network, five most important aspects come to our mind. These are sender, receiver, communication medium, the message to be communicated, and certain rules called protocols to be followed during communication.

COMPONENTS OF DATA COMMUNICATION

SENDER

• A sender is a computer or any such device which is capable of sending data over a network. It can be a computer, mobile phone, smartwatch, walkie-talkie, video recording device, etc.

RECIEVER

• A receiver is a computer or any such device which is capable of receiving data from the network.
• It can be any computer, printer, laptop, mobile phone, television, etc. In computer communication, the sender and receiver are known as nodes in a network.

COMMUNICATION MEDIA

• It is the path through which the message travels between source and destination.
• It is also called medium or link which is either wired or wireless. For example, a television cable, telephone cable, Ethernet cable, satellite link, microwaves, etc.

MESSAGE

• It is the data or information that needs to be exchanged between the sender and the receiver.
• Messages can be in the form of text, number, image, audio, video, multimedia, etc.

PROTOCOL

• It is a set of rules that need to be followed by the communicating parties in order to have successful and reliable data communication.

TCP/IP MODEL

• The TCP/IP model is a fundamental framework for computer networking. It 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.
• TCP/IP model was developed alongside the creation of the ARPANET, which later became the foundation of the modern internet. 

NETWORK ACCESS LAYER

• The Network Access Layer represents a collection of applications that require network communication.
• This layer is responsible for generating data and initiating connection requests.
• It operates on behalf of the sender to manage data transmission, while the Network Access layer on the receiver’s end processes and manages incoming data.

NETWORK/INTERNET LAYER

• It defines the protocols which are responsible for the logical transmission of data over the entire network.
• The main protocols residing at this layer are IP, ICMP, and ARP.
•  The Internet Layer is responsible for routing packets of data from one device to another across a network.

TRANSPORT LAYER

• The TCP/IP transport layer protocols exchange data receipt acknowledgments and retransmit missing packets to ensure that packets arrive in order and without error. 

• Transmission Control Protocol (TCP) and User Datagram Protocol are transport layer protocols at this level (UDP).

APPLICATION LAYER

• The Application Layer in the TCP/IP model combines the functions of three layers from the OSI model: Application, Presentation, and Session layers. 
• It is responsible for end-to-end communication and error-free delivery of data.
• It shields the upper-layer applications from the complexities of data.
•  The three main protocols present in this layer are HTTP, SSH, and NTP.

OSI MODEL

• The Open Systems Interconnection (OSI) model describes seven layers that computer systems use to communicate over a network.
• . It was the first standard model for network communications, adopted by all major computer and telecommunication companies in
  the early 1980s.
• This layered approach makes it easier for different devices and technologies to work together.
• The OSI Model consists of 7 layers and each layer has specific functions and responsibilities. 

HOW OSI MODEL WORKS ?

PHYSICAL LAYER

• The lowest layer of the OSI reference model is the Physical Layer. It is responsible for the actual physical connection between the devices. 
• Physical Layer 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.
• Common physical layer devices are Hub, Repeaters, Modems and Cables.

DATA LINK LAYER

• 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 . Packet in the Data Link layer is referred to as Frame. 

NETWORK LAYER

• 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.
• Network layer is implemented by networking devices such as routers and switches.

TRANSPORT LAYER

• 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. 

SESSION LAYER

• Session Layer in the OSI Model is responsible for the establishment of connections, management of connections, terminations of sessions between two devices.
•  It also provides authentication and security.

PRESENTATION LAYER

• 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.
• Protocols used in the Presentation Layer are JPEG, MPEG, GIF, TLS/SSL, etc.

APPLICATION LAYER

• At the very top of the OSI Reference Model stack of layers, we find the Application layer which is implemented by the network applications.
• This layer also serves as a window for the application services to access the network and for displaying the received information to the user.
• Protocols used in the Application layer are SMTP, FTP, DNS, etc.