TCP/IP Model: The Network Layer: Introduction

To properly learn something, we have to start at the beginning. We will be learning one concept at a time, process it, and move to the next.

The goal is consistent learning and absorbing information while feeling engaged and not overwhelmed.

I have divided the network layer articles into six parts.

  1. Introduction to Network layer
  2. Addressing in Network layer
  3. Decoupling the Router
  4. Routing and Routing Protocols in Network Layer
  5. Internet Protocol
  6. DHCP and NAT in Network layer

Goal of this article

I will be giving the introduction of the network layer of the TCP/IP Five-layer network model.

The Network Layer

  • The third layer of the TCP/IP Five-layer model is the network layer.
  • The network layer contains information in the form of datagrams.
  • The network layer manages options on host and network addressing, managing sub-networks, and internetworking.
  • The network layer has the responsibility to route the packets from source to destination, mapping different addressing schemes and protocols.
  • The network layer can be decomposed into two interacting parts:

    • Data plane

      • The per-router functions in the network layer that determine how a datagram arriving on one of a router’s input links is forwarded to one of that router’s output links.
      • The IPv4 and IPv6 protocols and addressing.
    • Control plane

      • The network-wide logic that controls how a datagram is routed among routers along an end-to-end path from the source host to the destination host.
      • Routing algorithms and protocols.
    • This distinction between data-plane and control-plane functions in the network layer is an important concept to keep in mind as we learn about the network layer. It will help in structure our thinking about the network layer and reflects a modern view of the network layer’s role in computer networking.

Functions of Network Layer

Devices that work on the network layer mainly focus on routing. Routing may include various tasks aimed to achieve a single goal.

These can be:

  • Addressing devices and networks.
  • Populating routing tables or static routes.
  • Internetworking between two different subnets.
  • Delivering packets to a destination with best efforts.
  • Provides connection-oriented and connection-less mechanisms.
  • Queuing incoming and outgoing data and then forwarding them according to quality of service constraints set for those packets.

Services of Network Layer

  • Guaranteed delivery

    • This service guarantees that a packet sent by a source host will eventually arrive at the destination host.
  • Guaranteed delivery with bounded delay

    • This service not only guarantees delivery of the packet, but delivery within a specified host-to-host delay bound (for example, within 100 msec).
  • In-order packet delivery

    • This service guarantees that packets arrive at the destination in the order that they were sent.
  • Guaranteed minimal bandwidth

    • This network-layer service emulates the behavior of a transmission link of a specified bit rate (for example, 1 Mbps) between sending and receiving hosts.
    • As long as the sending host transmits bits (as part of packets) at a rate below the specified bit rate, then all packets are eventually delivered to the destination host.
  • Security

    • The network layer could encrypt all datagrams at the source and decrypt them at the destination, thereby providing confidentiality to all transport-layer segments.

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