A Network is a number of computer systems connected together.

Unit 3 - Network

Advantages

Share peripherals such as printers.

Share Software

Share data/files.

Easier for internal communication/ can send email

Centralised backup

Easier to monitor network activity

Centralised maintenance (manage the network from one location)

Can access data from any computer

Disadvantages

Bus

The computers 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.

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

image

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.

Transmission of data

Ring

image

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

Star

image

advantages and disadvantages

Good performance/fast network speed

Easy to set up

Easy to add more computer systems

without taking the network down

failure of workstations will have no

effect on the network

Minimal network collisions

Better security

Expensive to install as more cable is required

Extra hardware required, such as a hub

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

image

Circuit swtiching - old method of transferring data, very slow. Direct

if the server gets hacked all computers are at risk and hackers can access the data easier

Disadvantages

Data collisions are common

Disadvantages

If the cable fails or a computer fails the whole server falls down

If you want to add another computer to the network you have to completely redo and take apart the old network

click to edit

Packet switching- new method of transferring data. It splits the data into packets before transmission, packets are then sent in order but might arrive out of order. Each packet can take a different route to its destination, data is then reassembled at the destination.

Data packets contents

length is the number of bits in the packet

packet ID is needed so that afterwards the data from multiple packets can be arranged into the correct order.

Source address is the IP address of the device that sent the data.

Destination address is the IP of the device that should receive the data.

Protocol is an indication of which protocol (HTTP, FTP, SMTP, etc.) has been used to form the packet.

Data is the reason a packet is being sent in the first place. Eventually, all packet components are discarded except for the data itself.

Checksum is a technique that verifies that the data was sent matches the data was recieved.