3.1a: Network Types & Performance
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
Wide Area Network
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.
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.
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.
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.
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.
What is a network topology?
Network topology refers to layout of computer systems on a local network.
Devices in a network topology diagram are often called 'nodes'. Two types of typology are star and mesh.
Each computer system is connected to a central device, usually a hub or switch.
How it works:
Each computer system is connected to the central hub or switch and transfers its data packets there.
The hub or switch looks at the destination address and transfers the packets directly to the intended computer.
A star topology has improved security because data packets are sent directly to and from the hub / switch in the centre and not necessarily all devices like in a bus or ring topology.
New systems can be attached directly to the central system so the network doesn't need to be shut down. System failures of attached computers won't usually cause complete network failure.
Transfer speeds are generally fast in a star topology as there are minimal network collisions.
Extra hardware (the hub or switch) is required to be purchased, installed and maintained.
If the central system (the hub or switch) fails then the whole network will be unusable until the error is fixed.
In a full mesh network, each computer system is connected to every other computer system.
There is also a partial mesh network where only some nodes (e.g. a printer) are connected to every other node.
How it works:
Data packets are transferred to the destination address along the quickest path, travelling from node to node.
If a pathway is broken, there are many alternative paths that the packets can take.
If one cable or system fails then data packets can take an alternative route and still reach the destination address.
Because of the large possible number of systems and connections, a mesh topology can usually withstand large amounts of data traffic.
New systems can be added to the network without disrupting the entire topology.
Because of the possibly large amount of cables required (especially in a full mesh topology) this network layout can be expensive to install and maintain.
Redundant cabling should be avoided - this is when cables are connected between systems that won't ever need to communicate.
There are several different factors that can affect the performance (speed) of a network, such as:
The bandwidth available*
Interference (e.g. thick walls)
Applications being used
Number of users at the same time
Distance to travel / signal strength
Server / CPU Performance
Number of data collisions
Amount of data to transfer
* Bandwidth is the maximum amount of data that can be sent across a network at once.
3.1a - Network Types & Performance:
1a. Describe the difference 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.
3. Draw and label diagrams of client-server, peer-to-peer, star and mesh networks. 
4. An office currently uses a star topology but is considering changing to a mesh topology. Describe two advantages and two disadvantages of both topologies. 
5. State five factors that could affect the performance of a network.