Apr 20, 2023 Network Layer

Connecting Devices

Networks do not normally operate in isolation.They are connected to one another using connecting devices.

The need To resolve incompatibility issues

between different networks. Approach

Hardware Software

The result is a virtual network

Apr 20, 2023 Network Layer

Connecting Devices Category

Connecting devices can be categorised into: - Networking devices

Repeater Bridge

Internetworking devices Gateway Router

Figure 16.1 Connecting devices

Apr 20, 2023 Network Layer

Repeater

An electronic device that operates only in the physical layer.

Connects two segments of the same LAN. Needed to correct attenuated or corrupted

signals. A repeater receives a signal before it

becomes too weak or corrupted, regenerates the original bit pattern and sends the refreshed signal.

Therefore, it is capable of extending the physical length of a LAN.

Figure 16.2 Repeater

Figure 16.3 Function of a repeater

Apr 20, 2023 Network Layer

Bridge

A computer that has its own processor, memory and two NIC cards to connect to two different portions of a network.

Operates in both physical and data link layers. Physical layer

Regenerates signals received Data link layers

Provides filtering capability that checks the destination address of a frame and decide if the frame should be forwarded or dropped.

If the frame is to be forwarded, the decision must specify the port, based on its table.

Figure 16.5 Bridge

Figure 16.6 Learning bridge

Figure 16.7 Loop problem

Figure 16.8 Prior to spanning tree application

Figure 16.9 Applying spanning tree

Figure 16.10 Forwarding ports and blocking ports

Apr 20, 2023 Network Layer

Router

A host containing: - Software Routing table

that enables it to determine the best path for a transmission

Operates at the physical, data link and network layers.

Connecting two different networks that adopt common transmission protocol.

Apr 20, 2023 Network Layer

Figure 21-11

Routers in an Internet

Apr 20, 2023 Network Layer

Gateway

A powerful computer. Operates at all layers. Connecting two dissimilar networks that

use different transmission protocol. Therefore, it has the ability to translate

between two different protocols

Figure 21-13

A Gateway

Apr 20, 2023 Network Layer

Network Layer

The need for a network layer: - To enable data exchange between

different networks Responsible for host-to-host delivery

and for the routing of packets through the routers of switches

These functions are made achievable via: - Addressing and Routing

Figure 19.1 Internetwork

Figure 19.2 Links in an internetwork

Figure 19.3 Network layer in an internetwork

Apr 20, 2023 Network Layer

Network Layer (Ctd…)

At source Receives data from transport layer, adds

the source universal address and destination universal address and make sure the packet is the correct size for delivery

At router or switch Find the interface from which the packet

must be sent At destination

Verify the destination address

Figure 19.4 Network layer at the source

Figure 19.5 Network layer at a router

Figure 19.6 Network layer at the destination