3.3a - Network Characteristics
What is a network?
A network is more than one computer system connected together allowing for communication and sharing of resources.
Networks can be split into different types, usually categorised by their geographical distance apart and the area that they serve.
Local Area Network
A local area network (LAN) has computer systems situated geographically close together, usually within the same building or small site, like a school or office.
The network infrastructure of a LAN (such as servers and routers) is usually owned and managed by the network owner.
Wide Area Network
A wide area network (WAN) has computer systems situated geographically distant to each other, possibly across a country or even across the world.
WANs often use third party communication channels, such as connections by internet services providers like BT or Virgin Media.
Other network types do exist, such as a Metropolitan Area Network (MAN) for computer systems connected across a town or city or a Personal Area Network (PAN) for devices connected and used by an individual.
Advantages and Disadvantages of using a Network
There are many benefits but also some drawbacks to using a network compared to having an unconnected ('standalone') computer:
Advantages of Networks
Easily share files, software and hardware between computers.
Disadvantages of Networks
There is an initial cost because network devices like routers are required. Larger companies will need to buy and maintain a server.
Log in from any connected computer and access your data and files.
A network manager / administrator might need to be employed to maintain the network.
An administrator can monitor network activity and control security settings.
Data from computers on the network can be automatically backed up on central storage.
Security breaches are more likely and malware, such as worms, can spread quickly across the network.
If the web server fails, all connected computers won't be able to access files or log on.
Client-Server and Peer-to-Peer Networks
Clients make requests to a server, the server manages that request and responds. For example, if the user (client) makes a request to access www.bbc.co.uk to a web server.
Large services like Amazon and Google will need very powerful servers to handle millions of requests a second.
The client is completely dependent on the server to provide and manage the information. The server controls network security, backups and can be upgraded to manage higher demand.
The network can be controlled centrally from the server to easily backup data and update software.
Hardware, software and resources can be shared across the network, such as printers, applications and data files.
The network allows for improved scalability, meaning more clients can be easily added to the central server.
Large amounts of traffic congestion will cause the network to slow down.
If a fault occurs with the server then the whole network will fail.
IT technicians may be required to manage and maintain the network.
Malware, such as viruses, can spread quickly across the network.
Client-Side & Server-Side Processing
Processing data when using a web application can be performed by the client (client-side) or by sending/receiving data with the server (server-side).
Server-side processing is reserved for more important tasks such as processing user input, interacting with databases and structuring web applications. It is also used to further validate data as client-side processing can be modified or even disabled on the browser so further checks are used to prevent malicious code, such as an SQL injection from being used.
For peer-to-peer networks, data is shared directly between systems without requiring a central server. Each computer is equally responsible for providing data.
Peer to peer is optimal for sharing files that can then be downloaded.
Without a dedicated server there is no central device to manage security or backups. Backups must be performed on each individual system.
Computer performance will decrease with more devices connected to the network, especially if other machines are slow.
This is a simpler network than client-server to set up as no server is required.
Clients are not dependent on a server.
Perfect for quickly sharing files between systems, such as downloading media files.
When sending data across a network, files are broken down into smaller parts called data packets.
Whole files are too large to transfer as one unit so data packets allow data to be transferred across a network quickly.
Each packet of data is redirected by routers across networks until it arrives at its destination. Data packets may split up and use alternative routes to reach the destination address.
When all the packets have arrived at the destination address the data is reassembled back into the original file.
Contents of a Data Packet:
The data itself
A checksum - this is a calculation on the data to see if any errors or corruption have occurred during transmission.
Packet Switching vs Circuit Switching
The key difference is that a circuit-switched network sends data along the same route. A packet-switched network sends data packets along different routes.
With a packet-switched network the data is split into packets.
The data packets are transmitted over a network and may take different routes to its destination.
When all the packets have arrived the data is reassembled.
The Internet is an example of a packet-switching network.
Advantages of Packet Switching:
Transmission is more secure as it is harder for a hacker to intercept complete data because it can take different routes.
If a network device fails the data packets can take an alternative route.
Data packets can be sent efficiently and individually across less busy routes.
Disadvantages of Packet Switching:
Reassembling the data takes longer because packets may arrive out of order.
It is less reliable than circuit switching as some data packets may not reach the destination (this is called packet loss).
When data is transmitted over a circuit-switched network all of the data takes the same route to the destination address in one continuous stream.
The data is quickly reassembled at the destination because it is already in the correct order.
The old telephone system is an example of a circuit-switched network.
Advantages of Circuit Switching:
Reassembling the data is quick because the packets arrive in the order that they were sent.
It is more reliable than packet-switching because data is sent in one continuous stream.
The transmission is fast and should encounter fewer errors - once the connection has been securely established.
Disadvantages of Circuit Switching:
Less secure as hackers could intercept the data and more easily access the data as it all takes the same route.
Establishing a connection takes time to set up.
If any device fails on the route then the whole connection breaks and data transfer will be incomplete.
3.3a - Network Characteristics:
1a. Describe two differences between a LAN and WAN. 
1b. Give an example of how a LAN and a WAN could each be used. 
2a. Describe how peer-to-peer networks and client-server networks function.
2b. Give one use for both types of network.
2c. Describe the difference between client-side and server-side processing and give an example of when each would be used. 
3a. Describe how packet switching works. 
3b. Describe the advantages of packet switching. 
3c. Describe the disadvantages of packet switching. 
4a. Describe how circuit switching works. 
4b. Describe the advantages of circuit switching. 
4c. Describe the disadvantages of circuit switching. 
5a. Draw and label diagrams of client-server and peer-to-peer networks. 
5b. Draw diagrams of packet switching and circuit switching.