What Is the Network Layer? Definition and Practical Applications

The network layer, one of seven layers that make up the larger communication process across the internet, is of utmost importance in computer networking as it provides logical addressing, routing, and forwarding capabilities. It ensures efficient and reliable transmission of data packets across interconnected networks, supports the dynamic routing of networks, works to establish secure communications, and enables global connectivity. Its processes are critical for modern computer networks' proper functioning and performance.

What is the network layer?

The network layer is a critical component of the networking architecture that operates at the third layer of the Open Systems Interconnection (OSI) model. It serves as an intermediary between the data link layer (Layer 2) and the transport layer (Layer 4) in the OSI model. Its primary purpose is to provide logical addressing, routing, and forwarding of data packets across networks.

At its core, the network layer establishes and maintains end-to-end communication between devices that connect to disparate networks. It accomplishes this by assigning unique addresses to each device, known as logical addresses. One widely used logical addressing scheme on the internet is internet protocol (IP) addressing.

The network layer encapsulates the data received from the transport layer into smaller units called packets. In addition to the data they carry, these packets include information such as the source and destination IP addresses, packet sequencing information, and error-checking codes.

OSI model

The OSI or Open Systems Interconnection model contains seven layers, each with a distinct set of duties for the communication system. Each layer interacts with the various layers above and below to facilitate smooth communication and data transmission. The OSI is the overall framework that outlines these responsibilities and functions. The seven layers of the model are as follows:

1. Physical layer

2. Data link layer

3. Network layer

4. Transport layer

5. Session layer

6. Presentation layer

7. Application layer 

Overall, these seven layers act together to facilitate data transfer from device to device effectively.

Network layer vs. internet layer

It is sometimes easy to confuse the network layer and internet layer and use the terms interchangeably, but they differ depending on which communication model is in context. The network layer refers to the third layer of the OSI model, which handles logical addressing and routing. It focuses on delivering data packets from the source to the destination across multiple networks.

The internet layer, meanwhile, specifically refers to the network layer in the TCP/IP protocol suite (another reference model of how the internet works). It is responsible for accepting and routing IP packets. Like the network layer, the internet layer in TCP/IP also plays a fundamental role in enabling global internetworking by connecting diverse networks into a unified inter-network, such as the internet.

Both of these layers serve the same purpose for the most part, but the network layer is present in the OSI model, while the internet layer is part of the TCP/IP model.

What does the network layer do?

The network layer performs several essential functions in a networking system, including addressing, routing, fragmentation and reassembly, quality of service, and error handling. Take a look at each in more detail:

• Addressing: The network layer assigns unique addresses to devices on a network, such as IP addresses. These addresses help identify the source and destination of data packets.

• Routing: It determines the optimal path for data packets to reach their destination across multiple networks. This involves analyzing routing tables, considering network conditions, and making forwarding decisions.

• Fragmentation and reassembly: When data packets are too large to fit into the maximum transmission unit (MTU) of a network, the network layer fragments them into smaller units at the source and reassembles them at the destination.

• Quality of service (QoS): The network layer can prioritize certain types of traffic, ensuring that critical data, such as real-time traffic, receive preferential treatment in terms of bandwidth and latency.

• Error handling: It can identify and amend errors in data packets through error detection and correction mechanisms.

What is a packet?

A packet is a unit of data that’s transmitted across a network. The packet consists of a header, a payload, and a trailer. The header contains control information, such as source and destination addresses, identifying value, and error-checking codes. Inside the payload is the real data being transmitted. The trailer contains information to inform the recipient device when it reaches the end of the packet.

Why is the network layer important?

The network layer plays a crucial role in the overall functioning of a computer network. A few reasons why it is important include:

• Addressing and routing: The network layer enables logical addressing, which allows devices to be uniquely identified on a network. It also determines the most efficient route for data packets to reach their destination, considering factors such as network congestion, reliability, and performance.

• Interconnectivity: The network layer facilitates the interconnection of different networks, enabling seamless communication and data transfer between devices and networks that may employ different underlying technologies.

• End-to-end delivery: The network layer ensures reliable end-to-end delivery of data packets across multiple networks. It handles packet fragmentation and reassembly, error detection and correction, and congestion control mechanisms to optimize data transmission.

• Network security: The network layer contributes to network security by implementing features such as virtual private networks (VPNs). These measures help protect data confidentiality, integrity, and availability during transmission.

Careers that use network layers and how to get started

Various careers utilize and reference the network layer and the broader OSI model when dealing with the internet and determining the requirements to connect multiple systems. These careers all relate to network communications and computer networking and involve handling how computers and various systems communicate with each other. Popular jobs in computer networking that involve the network layer and the OSI model include:

• Computer technician

• Computer engineer

• Network administrator

• Network analyst

• Database administrator

• Network engineer

• Network security analyst

• Computer systems analyst

Read more: What Are Computer Information Systems? Definition, Degree, and Careers

How to enter into a networking career

To prepare for one of these roles in computer networking, ensure you have the proper education. Most professionals in these careers have at least a bachelor’s degree in a related discipline, such as IT or network operations and security. Completing a degree in one of these fields exposes you to important topics related to these jobs, such as networks and security, programming, cybersecurity, and various fundamentals of information technology. 

If your goal is to pursue more advanced or senior roles within the field of computer networking, a master’s degree in a related subject is an option for you as well. You can also prepare for your career outside of formal education by earning relevant certifications. These credentials show potential employers that you have the skills you’ll need to perform in a computer networking role effectively. They also allow you to build experience with the necessary tools and systems professionals use. Some certifications to consider include: 

• CompTIA Network+: This certification verifies that you have a solid background in various networking concepts and network security.

• CCNA Certification: This credential from Cisco helps you build knowledge in networking fundamentals, network security, and IP protocols.

• ITIL 4 Foundation: With this certification from Axelos, get an introduction to key IT and digital service delivery concepts.

Read more: 6 Network Certifications for Your IT Career in 2024

Build your computer networking skills with Coursera

The network layer is an integral part of the OSI model, assuring the efficient and secure transmission of data across computer networks. Without the routing technology at the network layer level, the internet would not be possible. Now that most organizations are using computer networking to transmit data, you’ll find many opportunities for a career in this field.

If you’d like to learn more about the network layer or other areas of computer networking, completing a course and receiving a relevant certificate is a great place to start. On Coursera, you can enroll in some of the top courses in the world. Check out The Bits and Bytes of Computer Networking, offered by Google. This course is perfect for beginners with limited prior experience looking for a strong introduction to computer networking basics. It’s entirely online for your convenience and takes approximately 25 hours to complete.

If you want to explore related topics through an in-depth course, consider enrolling in Packet Switching Networks and Algorithms from the University of Colorado. This course, which features flexible deadlines, is estimated to take 17 hours to complete. Once you complete it, you’ll receive a shareable certificate.