Networks Unit 3

Networks

A network is a number of computer systems connected together

Advantages

Advantages

Share Software

Share data

Share peripherals (printers)

Centralised backup

Easy to monitor network activity

Access data from any computer

Network requirements and connectivity

Disadvantages

Security problems - files sent between computers could spread a virus

A network manager may need to be employed which is expensive

If the server is down, all workstations on the network are affected

Hackers can gain access to files quicker

Initial cost of servers is also expensive

Connectivity

Connectivity is the process of connecting the parts of a network to allow the data to transfer

Without connectivity, data could not be easily exchanged between computers without the use of removable storage

Wired connections use a wired connection protocol e.g cable using ethernet

Wireless does not use cabling but requires both the transmitting and receiving machine to have wireless network adaptor cards

Wireless is generally slower in terms of bit rate although the advantage of greater freedom can offset this

Lan and wan

A LAN is a network in which the computer systems are all located relatively close to each other, for example, in the same building or on the same site, such as a school.

A WAN is a network in which the computers systems are all located distantly from each other, for example, in different buildings all over the country or in different countries. The Internet is an example of a WAN. Many LANs could be linked using a WAN.

Bus

The computers (nodes) are connected to a single cable on which data can be sent, called the bus.

The bus has terminators on each end, which are needed to close each end of the cable.

The bus carries data packets along the cable.

As the packets arrive at each computer system, it checks the destination address contained in the packet to see if it matches its own.

If the address does not match, the computer system ignores the packet. If the address of the computer system matches that contained in the packet, it processes the data.

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Network Topologies

A network topology is the layout of computer systems on a network. There are a number of different network topologies. Some common network topologies include: Bus, Ring, Star and Mesh.

Advantages

Easy to add more computer systems to the network without disrupting the network

Quick and easy to set up – well suited for temporary networks

Cost-effective as less cabling is needed

Disadvantages

It is difficult to troubleshoot the bus if there’s a fault

Limited cable length and number of stations – performance degrades as additional computers are added

If there is a problem with the main cable or connection, the entire network goes down

Low security – all computers on the bus can see all data transmissions

Data collisions are more likely, which causes the network to slow down. A collision is when two computers try to send a packet at the same time

Proper termination is required

Ring

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Each node connects to exactly two other nodes, providing a single pathway for signals through each node.

Advantages

The transmission of data is simple as packets travel in one direction only, so no collisions

Data is quickly transferred without a bottleneck – consistent data transfer speeds

Adding additional nodes has very little impact on bandwidth

Disadvantages

If any of the computer systems fail, the ring is broken and data cannot be transmitted efficiently

a problem with the main cable or connection and the entire network goes down

It is difficult to troubleshoot the ring


Because nodes are wired together, to add another you must shut down the network

Star

Where one or more central switch, hub or computer acts as a central conduit to transmit messages


Advantages

Good performance/fast network speed

Easy to set up

Easy to add more computer systems

Disadvantages

Expensive to install as more cable is required

Extra hardware required, such as a hub

Minimal network collisions

failure of workstations will have no
effect on the network

Better security

Sending data over a Star network

Computer A adds computer D’s address to packet

Computer A sends packet to switch

Switch looks at address on packet

Switch compares to stored list of addresses on network

Switch forwards packet to computer D’s address

Mesh

Each node relays data for the mesh network. All mesh nodes cooperate in the distribution of data in the network.

This is very reliable as it can 'self-heal' by reconfiguring around broken paths. This network is complex, expensive and difficult to set up. A large part of the network may be redundant