1.3.1 Computer Networks
In this lesson, you will learn about Local Area Networks (LANs) and Wide Area Networks (WANs), including their characteristics, advantages and disadvantages. You will also explore the main factors that can affect network performance, including bandwidth, number of users, transmission media, latency and error rate.
Computer Networks
A computer network is a group of computers and other devices that are connected so that they can communicate and share data and resources.
Networks can allow users to share files, printers, internet connections and other services. The two main types of network are Local Area Networks (LANs) and Wide Area Networks (WANs).
LAN (Local Area Network)
A Local Area Network (LAN) connects computers and other devices within a relatively small geographical area, such as a home, school, office or single organisation site.
The network hardware used within a LAN is usually owned and maintained by the person or organisation that operates the network. A LAN may use both wired connections, such as Ethernet cables, and wireless connections, such as Wi-Fi.
Devices on a LAN can communicate with one another and share resources such as files, printers, servers and an internet connection.
LANs are useful because devices within one site can communicate and share resources efficiently. However, the network still needs to be installed, managed and secured, and failures in important network hardware can interrupt access to shared resources.
| Advantages | Disadvantages |
|---|---|
| Fast communication between devices on the same local network. | Limited to a relatively small geographical area. |
| Resources such as files, printers and internet access can be shared. | Network hardware must be installed, maintained and secured. |
| Local control makes access and security easier to manage. | Failure of important hardware can interrupt access to shared resources. |
| Usually cheaper to set up and manage than a WAN. | Unauthorised users or compromised devices can create security risks. |
WAN (Wide Area Network)
A Wide Area Network (WAN) connects computers or LANs across a large geographical area. A WAN may connect different sites within a city, across a country or even around the world.
Unlike a LAN, the organisation using a WAN does not usually own all of the communication infrastructure between its different locations. Connections are often provided or leased from telecommunications companies or other service providers.
For example, a company with offices in different cities could use a WAN to connect the LAN at each office so that employees can access shared systems and data. The internet can be considered the largest WAN, connecting networks across the world.
| Advantages | Disadvantages |
|---|---|
| Connects users and networks across large geographical areas. | Can be more expensive to operate than a LAN. |
| Allows different sites to share data and central services. | Performance may be slower because data often travels further and through more network infrastructure. |
| Supports communication and collaboration between distant locations. | Often depends on external telecommunications or service providers. |
| Allows central systems and data to be accessed from different locations. | Security can be more complex to manage across multiple locations. |
Factors Affecting Network Performance
Network performance describes how effectively data can be transmitted through a network and therefore how quickly users can access network services and resources.
Performance can be affected by several factors, including bandwidth, the number of users and devices, the transmission media being used, latency and the rate of transmission errors.
Bandwidth
Bandwidth is the amount of data that can be transmitted across a network in a given amount of time. It is usually measured in bits per second (bps) or units such as megabits per second (Mbps).
A network with greater bandwidth can transmit more data in the same amount of time. Bandwidth describes capacity, rather than the delay experienced by an individual piece of data. This is particularly important when large amounts of data are being transferred, such as when streaming video or downloading large files.
The available bandwidth depends partly on the network equipment and transmission media being used.
Number of Users and Devices
The available bandwidth on a network is shared by the users and devices that are actively sending or receiving data.
As more users send and receive data at the same time, there may be less bandwidth available to each user or device. This can cause network congestion, where data takes longer to be transmitted.
The type of activity also matters. For example, streaming high-resolution video usually requires much more bandwidth than sending a short text message or opening a simple webpage. A small number of users carrying out bandwidth-intensive activities can therefore affect performance significantly.
Transmission Media
Transmission media is the method used to carry data from one device to another. Data may be transmitted using wired media, such as copper or fibre-optic cables, or wirelessly using technologies such as Wi-Fi.
Different transmission media have different bandwidths and levels of reliability. For example, a wired Ethernet connection may provide a faster and more stable connection than a weak Wi-Fi connection, while fibre-optic cables can carry large amounts of data over long distances.
Wireless connections are convenient because devices can connect without physical cables, but their performance can be affected by distance, obstacles and interference. These factors can also increase the chance of transmission errors, meaning some data may need to be sent again. The transmission medium therefore affects both the speed and reliability of data transmission.
Network Latency
Latency is the delay between data being sent from one device and arriving at another. It is usually measured in milliseconds (ms).
A network can have high bandwidth but still feel slow to respond if its latency is high. This is especially noticeable in real-time activities such as video calls and online gaming, where delays can cause lag.
Latency can increase when data has to travel a long distance, pass through many intermediate network devices, or when the network is congested.
High bandwidth and low latency are both desirable, but they describe different aspects of network performance.
Error Rate
Data transmitted across a network can sometimes be received incorrectly. Error rate describes how often data is received incorrectly during transmission. Transmission errors can occur because of factors such as interference, weak wireless signals or problems while data is being transmitted. When an error is detected, the affected data may need to be sent again. This is called retransmission.
A network with a high error rate therefore wastes some of its available bandwidth retransmitting data, which can reduce overall network performance. For example, a device with a weak Wi-Fi signal may repeatedly fail to receive some data correctly. If those parts have to be sent again, transferring the complete file takes longer.
These factors can interact with one another. For example, a network with limited bandwidth may perform adequately with a few users but become congested when many users begin streaming or transferring large files at the same time.