Organization of the Network layer

There are two possible internal organizations of the network layer: datagram and virtual circuits.

Datagram Organization

The datagram organization has been very popular in computer networks. Datagram-based network layers include IPv4 and IPv6 in the global Internet, CLNP defined by the ISO, IPX defined by Novell or XNS defined by Xerox.

This organization is connectionless and hence each packet contains:

• The network layer address of the destination host.
• The network layer address of the sender.
• The information to be sent.

To understand the datagram organization, let’s consider the slides below. A network layer address represented by a letter, has been assigned to each host and router. Host A wishes to send some information to host J.

Forwarding Tables

Routers use hop-by-hop forwarding in the datagram organization. This means that when a router receives a packet that is not destined to itself, it looks up the destination address of the packet in its forwarding table.

A forwarding table is a data structure that maps each destination address to the device. Then, a packet must be forwarded for it to reach its final destination.

forwarding tables must ...