The Network Layer

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Brian Bramer,
School of Computing and Mathematical Sciences,
De Montfort University, Leicester


Introduction

The Network Layer manages the virtual link between two host computers. This determines the interface between the hosts and the IMP (ie splits data into packets, routes them over the virtual line, corrects for lost packets, reassembles packets back into messages). Layers 1 (physical), 2 (data link) and 3 (network) are usually called the communications subnet (or just subnet) separating the pure communications aspects of the network looked after by the IMPs from the application layers looked after by the hosts.

The design issues of layer 3 are:

  1. subnet-host interface
     
  2. routing of packets
     
  3. resolving of congestion and deadlocks

Contents

  1. Packet switching networks
    1. Packet size
    2. Packet switching services
  2. Internal structure of the subnet
    1. Comparison of datagrams and virtual circuits
  3. Routing
    1. Routing algorithms
  4. CCITT recommendation X25 for packet switching networks