VTU Module-3 | Network Layer

18EC71 | COMPUTER NETWORKS | Module-3 VTU Notes

Network Layer: Introduction

The Network Layer, also known as Layer 3 in the OSI model, plays a crucial role in facilitating communication across a network. Its primary function is to manage the routing and forwarding of data packets, ensuring efficient and reliable transmission between devices.

Network Layer Services: Packetizing, Routing, and Forwarding

Packetizing involves breaking down data into smaller packets for efficient transmission. Routing is the process of determining the optimal path for these packets to reach their destination, while forwarding involves passing the packets along the chosen route.

Other Services

Apart from packetizing, routing, and forwarding, the Network Layer provides additional services such as fragmentation, error handling, and congestion control. These services contribute to the overall robustness and performance of the network.

Packet Switching: Datagram Approach, Virtual Circuit Approach

Packet switching is a fundamental concept in the Network Layer. The datagram approach treats each packet independently, making routing decisions for each packet individually. In contrast, the virtual circuit approach establishes a predefined path for a series of packets, enhancing efficiency at the cost of some flexibility.

IPv4 Addresses: Address Space, Classful Addressing, Classless Addressing

IPv4 addresses uniquely identify devices on a network. The address space includes a range of possible addresses. Classful addressing divides addresses into classes (A, B, C, D, and E), each with a different range size. Classless addressing provides more flexibility by allowing the allocation of any-sized block of addresses to a network.

DHCP (Dynamic Host Configuration Protocol)

DHCP automates the assignment of IP addresses within a network, making it easier to manage and configure devices dynamically.

Network Address Resolution

Network Address Resolution (NAR) translates logical IP addresses into physical MAC addresses, enabling devices to communicate at the link layer.

Forwarding of IP Packets: Based on Destination Address and Label

Forwarding IP packets involves sending them from one network device to another. This can be based on the destination address, where routers make decisions based on the final destination of the packet. Additionally, label-based forwarding involves attaching labels to packets, allowing routers to make forwarding decisions based on these labels.

In summary, the Network Layer is a critical component of network communication, providing services like packetizing, routing, and forwarding. It manages packet switching through datagram and virtual circuit approaches, utilizes IPv4 addresses with classful and classless addressing, employs DHCP for dynamic address allocation, performs Network Address Resolution, and implements forwarding based on both destination address and labels. These functionalities collectively ensure the efficient and reliable transmission of data across networks.