Page 140 - DCAP406_DCAP_207_Computer Networks

Professiona University Unit 9: Network Layer

Unit 9: Network Layer Notes

CONTENTS
Objectives
Introduction

9.1 Network Layer Design Issues
9.2 Routing
9.2.1 Routing Table

9.3 Routing Protocols
9.4 Internetworking
9.5 Summary
9.6 Keywords
9.7 Review Questions

9.8 Further Readings

Objectives

After studying this unit, you will be able to:

Discuss Network layer design issues along with connection oriented and connectionless
services
Describe various concepts of routing algorithm with comprehensions of adoptive and
non-adoptive algorithms

Understand the routing protocols for internal and external networks

Introduction

The network layer deals with forwarding packets from the source node to the destination node
using different routes. Hence, the network layer transports traffic between devices that are not
locally attached. In doing so, it controls the operation of the subnet, which involves routing of
the packets from the source to destination. Routes are based on static or dynamic routing tables.
The destination IP address is checked for packet received on a router interface. If the packet is not
addressed for the router where it is received, the router will look up the destination network
address in the routing table so that it may be routed accordingly. Therefore, the network layer
must know about the topology of the communication subnet and choose appropriate paths
through it. The routes are chosen in such a manner so that the network layer avoids overloading
some of the communication lines while leaving others idle. The routing algorithm is part of the
network layer. The routing algorithm enables the network layer to decide to which output line
an incoming packet should be forwarded. Routing algorithms provides correctness, simplicity,
robustness, stability, fairness and optimality. All these functions of network layer differ from
the data link layer whose objective is to transmit the bits from one end of a wire to the other end.
The Network layer is the lowest layer that deals with end-to-end transmission.

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