What is a network protocol?

A network protocol is a set of rules that govern how data is exchanged between the devices in a network. Network protocols enable communication between devices that are located in different parts of the world. Consequently, they are critical in today's digital communications.

The Open Systems Interface (OSI) paradigm defined by International Standards Organization (ISO) is the most widely used mechanism for establishing communication between two open systems.

OSI model

The OSI model is not a network architecture because it does not identify the exact services and protocols for each layer. It simply defines the input and output data for each layer, indicating what it should do. The layers must be implemented by network architects based on their requirements and available resources.

The OSI model is made up of seven layers. They are as follows:

  1. Physical layer (L1): It is the first layer that is in charge of physically connecting two systems that need to communicate. It deals with transmission of raw data through physical transmission medium. It manages the physical connection of the network interface card to the network, including cabling, cable terminators, topography, power levels, etc.
  2. Data link layer (L2): It is the firmware layer that uses MAC address or hardware address available in the Network Interface Card to identify the destination. It accepts datagrams from the network layer and turns them into frames through fragmentation. Broken, misplaced, or duplicate frames can cause problems.
  3. Network layer (L3): It is in charge of data routing, switching, and managing the workstations. It uses IP address for uniquely identifying the devices in the network.
  4. Transport layer (L4): It accepts data as a stream of bytes from the higher layer and performs segmentation. It performs in-order end-to-end delivery of messages using port number and sequence number. It performs flow control and error control.
  5. Session layer (L5): This layer creates session among two workstations for data sharing.
  6. Presentation layer (L6): This layer focuses on the correct representation of data, i.e., information syntax and semantics. It is in charge of converting data into network standards and file-level security.
  7. Application layer (L7): It is the topmost layer of the protocol stack. It contains user applications such as Telnet, Email, web application, file transfer application and so forth.
7 layers of ISO/OSI model
OSI model

The seven layers of the OSI model are separated into upper and lower categories. The upper layers are 7, 6, and 5, and the lower layers are 4, 3, 2, and 1. The upper levels are concerned with application difficulties, while the lower layers are concerned with data transit.

Network protocols separate the communication process into discrete activities at every tier of the OSI model. One or more network protocols are used at each layer of communication exchange.

The descriptions of how network protocols work at each tier of the OSI model are as follows:

Layer 7: Application layer network protocols

  • Offers typical services like virtual terminals, file transfers, and email.
Layer 6: Presentation layer network protocols
  • Hides data format inconsistencies between desperate systems
  • Encrypts and decrypts data, and compresses and decompresses it
Layer 5: Session layer network protocols
  • Maintains a log of all user sessions and conversations
  • Establishes and ends user sessions
Layer 4: Transport layer network protocols
  • Oversees the delivery of messages in networks from the beginning to the end
  • Uses error recovery and flow control mechanisms to ensure that packets are delivered in the correct order
Layer 3: Network layer network protocols
  • Route packets depending on network device addresses that are unique
  • Controls network flow and congestion to prevent network resources from being depleted
Layer 2: Data link layer network protocols
  • Responsible for framing.
  • Performs error detection and correction.
Layer 1: Physical layer network protocols
  • Device and network media interfaces are included
  • Represents how the raw data is transmitted over the physical transmission media.


Although some claim that the OSI model is no longer relevant and obsolete compared to the Transmission Control Protocol (TCP)/IP network architecture, its structure is still used to frame protocol discussions and compare and contrast different technologies.


Transmission Control Protocol/Internet Protocol (TCP/IP) is a series of layered protocols used for internet communication. The client-server communication mechanism is used in this suite. The client is the computer that submits the request, and the server is the computer that receives the request and sends the appropriate response.

The client is the computer that submits the request, and the server is the computer that receives the request. The request is processed through four layers; these include Application Layer (HTTP), Transport Layer (TCP), Network Layer (IP), and Data Link Layer.

TCP/IP has four layers:

  1. Application layer: Consists of protocols that performs specific functions. For example, HTTP (HyperText Transfer Protocol) is used in web communication, FTP (File Transfer Protocol) enables exchange of files.
  2. Transport layer: Responsible for reliable in-order end-to-end delivery of messages.
  3. Network layer: Internet Protocol (IP) is used to create a connection at the network layer. The protocol assigns an IP address to the systems connected to the internet so that source and destination machines can be easily identified.
  4. Data link layer: The data link layer is responsible for host-to-host delivery of frames.

TCP/IP is used on the Internet.

How network protocols work?

Network protocols break down large-scale activities into smaller, specific functions organized as layers. The term “protocol suite” refers to a collection of network protocols that work together to provide the networking functionalities.

Various networking or Information Technology organizations establish network protocols based on industry standards.

Various network protocols

Numerous protocols play an important to achieve communication between various devices connected through the network.

The protocols listed below are widely used in network communication.

  • Transmission Control Protocol (TCP)
  • Internet Protocol (IP)
  • User Datagram Protocol (UDP)
  • Post office Protocol (POP)
  • Simple mail transport Protocol (SMTP)
  • File Transfer Protocol (FTP)
  • HyperText Transfer Protocol (HTTP)
  • HyperText Transfer Protocol Secure (HTTPS)
  • ARP: Address Resolution Protocol
  • Telnet

Let us discuss each of them briefly:

  • Transmission Control Protocol (TCP): TCP provides a reliable connection-oriented service. It guarantees in order delivery of messages using sequence number.
  • Internet Protocol (IP): IP was designed to be used as an addressing protocol. IP packets are routed through the nodes of a network until they reach their destination system. TCP/IP is the most extensively used networking protocol.
  • User Datagram Protocol (UDP): It is a transport layer protocol which offers connection less service for real-time applications.
  • Post Office Protocol (POP): The POP3 protocol is used to receive electronic mail.
  • Simple Mail Transport Protocol (SMTP): SMTP stands for Simple Mail Transfer Protocol. It is used to send emails.
  • File Transfer Protocol (FTP): FTP allows users to transfer files from one system to another.
  • HyperText Transfer Protocol (HTTP): HTTP is a protocol that allows two or more systems to exchange web pages. HTTP is a client-server protocol that allows a client system to connect to a server machine and send a request. The server acknowledges the client’s request and sends back the requested resource.
  • HyperText Transfer Protocol Secure (HTTPS):  HTTPS is identical to HTTP, except that it sends data in an encrypted format. Consequently, HTTPS protects data from being interpreted or altered while it is transmitted.
  • Address Resolution Protocol (ARP): ARP helps mapping IP addresses to physical machine addresses (or MAC addresses for ethernet) on a local network. An ARP cache is used to maintain a mapping between IP address and its corresponding MAC address. ARP gives the rules for forming these connections and also assists in converting addresses in both directions.
  • Telnet: Telnet enables a client machine to login to a remote machine and to make use of the resources available on it.

Network protocols not only govern how devices and processes work alone but also how they communicate with one another. The digital world would not exist without network protocols, which constitutes the bedrock of modern communications.

Common Mistakes

There is always a debate about whether to use the TCP/IP paradigm or the OSI model. To avoid confusion, remember the following points:

  • The OSI model should be preferred if appropriate documentation, definition, and modularization are essential.
  • The TCP/IP paradigm should be preferred if the network's implementation, stability, and security are important.

Context and Applications

This topic is significant in the professional exams for graduate and postgraduate courses,

  • Bachelor of Arts Program with Computer Applications
  • Bachelor of Technology in Computer Science and Engineering
  • Bachelor of Science in Computer Science
  • Master of Science in Computer Science
  • Master of Technology in Computer Science and Engineering
  • Mobile Communication Protocols
  • Email Protocols
  • Ad Hoc Network
  • Computer Networks

Practice Problems

Q.1 Any resource can be located on the internet using URL; URL stands for:  

(A) Uniform Resource Locator

(B) Uniform Run Locator

(C) Unique Resource Locator

(D) None of the above

Correct Option: (A)

Explanation:-URL is a unique identifier which is used to locate address on the internet. It is also known as web address.

Q.2 OSI model is a:

(A) Six-Layer Model

(B) Five-Layer Model

(C) Seven-Layer Model

(D) None of the above

Correct Option: (C)

Explanation:-OSI model is known as open system interconnection model. It is a conceptual model used to describe the functions of networking system.

Q.3 OSI paradigm is an abbreviation for:

(A) Open System Interconnection

(B)  One Service Interface

(C) One System Interface

(D) Open Service Interface

Correct Option: (A)

Explanation:-OSI stands for open system interconnection. It is created by ISO that is International Organization for Standardization.

Q.4 ___________ prevents proxy to a system.

(A) Internet Protocol

(B)  Gateway

(C) Firewall

(D) Antivirus

Correct Option: (C)

Explanation:-Firewall is basically a network security device that monitors outgoing and incoming traffic.

Q.5 __________ is the most common internet protocol.




(D) None of the above

Correct Option: (B)

Explanation:-TCP/IP is a set of communication protocols used in computer networks and internet. TCP stands for transmission control protocol and IP is internet protocol.

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