2.1 Networks including the internet

Main Content

Purpose and benefits of networks

A network is a group of connected devices that can communicate and share resources. These devices can include computers, printers, servers, phones, and other hardware. The main purpose of a network is to let devices work together instead of working alone.

In a network, users can share files, use the same printer, access the same internet connection, and communicate more easily. For example, in a school network, many computers can use one printer, one file server, and one internet connection. This saves money and makes work easier.

Networks also make it easier to manage data. Files can be stored in one place so that users can find the latest version. Backups can also be done centrally, which means important data is less likely to be lost. In larger organisations, a network manager can control who is allowed to access certain files or websites.

However, networks also have drawbacks. They can be expensive to set up because cabling, switches, and servers cost money. They also need maintenance. If an important device fails, many users may be affected. Security is also more difficult, because malware or hackers can spread through a network if protection is weak.

LAN and WAN

A LAN stands for Local Area Network. It covers a small geographical area, such as one room, one building, one school, or one office. In a LAN, the hardware is usually owned by the organisation or person using it. A LAN is often fast because the distance between devices is short.

A school computer room is a good example of a LAN. All the computers, printers, switches, and cables are in one place and are owned by the school. A LAN often uses copper cables, fibre-optic cables, or wireless connections such as WiFi.

A WAN stands for Wide Area Network. It covers a much larger geographical area. It may connect devices or smaller networks across towns, cities, or even countries. A WAN is often made by joining together several LANs.

The best example of a WAN is the internet. In a WAN, not all the hardware is owned by one person or organisation. Some of the connections may use communication companies’ equipment, such as telephone lines, fibre links, or mobile networks.

A LAN is usually cheaper, faster, and easier to control than a WAN. A WAN is useful when people in different places need to stay connected, but it is usually more complex and may depend on outside providers.

Client-server model

In a client-server network, some computers are called servers and other computers are called clients. The server is a powerful computer that provides services. The clients request those services.

For example, a file server stores files. A print server manages printing. A web server stores web pages. A client computer sends a request, the server processes it, and then sends back the result.

This model gives central control. Security settings, software updates, backups, and user accounts can all be managed in one place. This makes client-server networks good for schools, offices, and other large organisations.

The drawbacks are that servers are expensive and need specialist maintenance. Also, if the server fails, many users may lose access to services.

A client-server model should be used when central control, reliability, and security are important.

Peer-to-peer model

In a peer-to-peer network, all computers have equal status. There is no central server controlling the network. Each computer can share files or resources directly with the others.

This type of network is simpler and cheaper to set up. It is often used in homes or small offices where only a few devices need to share files or printers.

The problem is that there is no central management. Each user is responsible for their own files, backups, and security. This can lead to weaker security and poor organisation. It also becomes less efficient as the network gets larger.

A peer-to-peer model is best for small networks where low cost and simple setup matter more than central control.

Thin-client and thick-client

A thin client depends heavily on a server. Most of the processing and storage happen on the server, not on the client device itself. A thin client usually needs a constant network connection to work properly.

Examples include cloud-based office software, remote desktop systems, and point-of-sale systems connected to a central server. Thin clients are useful when an organisation wants central control and cheaper client devices.

The weakness of a thin client is that it depends on the network and server. If the connection is lost, the user may not be able to continue working.

A thick client does most of its processing on its own device. It can usually work even without a network connection. Installed software such as Microsoft Word on a laptop is a thick-client example.

Thick clients give better performance and allow offline use, but they usually need more powerful hardware and may be harder to manage across many devices.

So, the key difference is this: a thin client relies on the server, while a thick client relies mainly on itself.

Bus topology

In a bus topology, all devices are connected to one main cable called the bus. This cable has a terminator at each end. The terminators stop signals from bouncing back along the cable and causing errors.

When a device sends data, the signal travels along the whole cable. Every device can see the data, but only the device with the correct address accepts it. The others ignore it.

This topology is simple and cheap because it needs less cable. However, it is slow when many devices are trying to send data. Collisions can happen because many devices share the same communication line. Also, if the main cable breaks, the whole network can stop working.

Bus topology is suitable only in simple, small, low-cost situations. It is not a good choice for modern large networks.

Star topology

In a star topology, every device connects to a central device, usually a switch. When one device sends data, it first goes to the switch. The switch then sends it to the correct destination.

This makes the network more reliable. If one cable fails, only one device is affected, not the whole network. It is also easier to add or remove devices.

The main weakness is that the central switch is a single point of failure. If the switch fails, the whole network is affected.

A star topology is the most common choice for schools, offices, and homes because it is reliable and easy to manage.

Mesh topology

In a mesh topology, devices are connected to many or all of the other devices. In a full mesh, every device has a direct link to every other device.

This gives very high reliability. If one path fails, data can travel along a different path. That is why mesh topologies are useful in systems where reliability is very important.

The drawback is cost and complexity. A full mesh needs a lot of cables and connections. It is hard to expand and expensive to maintain.

Mesh is a good choice when fault tolerance is more important than cost.

How packets move in different topologies

A packet is a small piece of data sent across a network.

In a bus topology, a packet travels along the shared main cable. Every device receives the signal, checks the address, and only the correct device accepts it.

In a star topology, the sending device sends the packet to the central switch. The switch checks where the packet should go and forwards it only to the correct device.

In a mesh topology, the packet may travel along one of several possible routes. If one route is unavailable, another route can be used. This is why mesh networks are so reliable.

In a hybrid topology, packet movement depends on the topologies being combined. For example, data might move through a star section and then across a mesh section.

Choosing the right model or topology

When deciding which model or topology to use, think about cost, size, reliability, security, and ease of management.

A client-server network is best when many users need central control and shared services. A peer-to-peer network is best when the network is small and simple.

A star topology is best for most modern LANs because it is reliable and easy to expand. A bus topology is only suitable in very simple and cheap systems. A mesh topology is best for important systems where downtime must be avoided. A hybrid topology is best for large and complex organisations.

Cloud computing

Cloud computing means using software, services, or storage on remote servers through the internet instead of keeping everything on your own computer.

For example, when you store files on Google Drive or use an online document editor, you are using cloud computing. The data or software is stored somewhere else, often in a data centre, and you access it over a network.

Cloud computing has many benefits. You can access files from different places and different devices. It is easier to share files and work together with others. Updates and maintenance are often handled by the provider. Storage or services can also be increased easily when needed.

There are also drawbacks. A reliable internet connection is needed. There may be ongoing subscription costs. Users may have less control over their data and software. There are also privacy and security concerns because data is stored on someone else’s servers.

Public cloud and private cloud

A public cloud is owned and managed by a third-party company. Its services are shared between different users or organisations. It is usually cheaper because the provider shares the costs across many customers.

A private cloud is used by one organisation only. It may be managed by the organisation itself. It gives more control and can offer stronger security, but it is more expensive.

A public cloud is a good choice when low cost and easy access matter most. A private cloud is better when an organisation needs greater control, privacy, or custom security settings.

Wired and wireless networks

A wired network uses physical cables to connect devices. A wireless network uses signals through the air.

Wired networks are usually faster, more stable, and more secure. They are less affected by interference. This makes them suitable for desktop computers, servers, and situations where strong performance is needed.

Wireless networks are easier to install and allow users to move around. They are useful for laptops, tablets, and phones. However, wireless signals can be affected by walls, distance, and interference. Wireless networks are also usually less secure than wired networks because signals travel through the air.

So, the choice depends on the situation. Wired is better for speed and reliability. Wireless is better for mobility and convenience.

Hardware used to support a LAN

Router

A router connects one network to another. A common example is a home router, which connects a LAN to the internet.

Routers read the IP address in a packet and decide the best path for that packet to take. If a packet must travel across several networks, it may pass through several routers. Each move from one router to another is called a hop.

A router can also help assign IP addresses inside a network and may include other features such as wireless access, firewall protection, and switch functions.

Ethernet

Ethernet is a standard used in wired LANs. It controls how devices send data through the network. Ethernet defines things like wiring, transmission rules, and frame structure.

Data in Ethernet is sent in frames. A frame contains information such as the source MAC address, destination MAC address, the data itself, and an error-checking part called the Frame Check Sequence (FCS).

Ethernet is important because it gives rules that allow devices from different manufacturers to communicate correctly on the same network.

CSMA/CD and collisions

In some shared network systems, especially bus topology, two devices may try to send data at the same time. This causes a collision.

CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection.

This works in steps:

1. A device listens to check whether the communication channel is free.
2. If the channel is busy, the device waits.
3. If the channel is free, the device sends its data.
4. If two devices send at the same time, a collision happens.
5. The devices detect the collision.
6. A jamming signal is sent.
7. Both devices stop transmitting.
8. Each waits for a random time, then tries again.

This method reduces the chance of repeated collisions and helps shared networks work more efficiently.

Bit rate and broadband speed

Bit rate is the amount of data sent each second. A higher bit rate usually gives better quality sound or video, but it needs more bandwidth.

A lower bit rate uses less data, but quality may drop. The picture may look blurry or blocky, and sound quality may be lower.

Broadband speed affects how well streaming works. High-speed broadband can support higher bit rates, smoother playback, and better quality. Slow broadband may cause buffering, pauses, and reduced quality.

So, bit rate affects quality, and broadband speed affects whether that quality can be delivered properly.

The internet and the World Wide Web

The internet is a global network of networks. It is the physical and logical system that allows computers and other devices around the world to communicate.

The World Wide Web or WWW is one service that uses the internet. It is a collection of web pages and websites that are accessed using a web browser.

So, the internet is the system of connections, while the web is one thing that runs on top of it. The web uses the internet, but the internet is not the same as the web.

Hardware used to support the internet

Public and private IP addresses

A public IP address is visible on the internet and can be reached from outside the local network. Devices or services that need to be accessed over the internet, such as web servers, often use public IP addresses.

A private IP address is used inside a local network. It is not directly reachable from the public internet. This improves security because internal devices are hidden from direct outside access.

So, public IP addresses allow direct internet communication, while private IP addresses are mainly for internal use and help protect devices.

URL and DNS

A URL or Uniform Resource Locator is the address used to locate a resource on the web. A URL tells the browser where to find a page or file.

A URL often includes:

• the protocol, such as http or https
• the domain name, such as example.com
• the path to the resource, such as /images/logo.png

When a user types a URL into a browser, the browser needs to find the IP address of the web server. This is the job of the DNS, which stands for Domain Name System or Domain Name Service.

The DNS matches human-readable domain names to IP addresses.

The basic process is:

1. The user types a URL into the browser.
2. The browser checks whether it already knows the IP address.
3. If not, it asks a DNS server.
4. The DNS server finds the matching IP address, or asks higher-level DNS servers if needed.
5. The IP address is returned to the browser.
6. The browser sends a request to the web server at that IP address.
7. The web server sends back the webpage data.
8. The browser displays the page.

Without DNS, people would have to remember long numerical IP addresses for every website.

Key Terms

Network — a group of connected devices that can communicate and share resources.

LAN — a local area network covering a small area, such as one building.

WAN — a wide area network covering a large area and often made from several LANs.

Client — a computer that requests services from a server.

Server — a computer that provides services or resources to clients.

Peer-to-peer — a network model where all computers have equal status and there is no central server.

Thin client — a device or program that depends on a server for most of its work.

Thick client — a device or program that does most of its own processing.

Topology — the physical layout of a network.

Bus topology — all devices share one main cable.

Star topology — all devices connect to a central switch.

Mesh topology — devices are connected by multiple paths.

Hybrid topology — a combination of different topologies.

Packet — a small piece of data sent across a network.

Cloud computing — using storage, software, or services on remote servers through the internet.

Public cloud — cloud services provided by a third party and shared by many users.

Private cloud — cloud services used by one organisation only.

Switch — a device that forwards data only to the correct destination on a LAN.

NIC — a network interface card for wired network access.

WNIC — a wireless network interface card for wireless access.

WAP — a wireless access point that lets wireless devices join a network.

Bridge — a device that connects two network segments.

Repeater — a device that strengthens and retransmits signals.

Router — a device that connects networks and forwards packets using IP addresses.

Ethernet — a standard for wired LAN communication.

Collision — when two devices send data at the same time on the same channel.

CSMA/CD — a method for detecting and dealing with collisions on shared media.

Bit streaming — continuous sending of data so it can be played or used straight away.

Bit rate — the amount of data sent each second.

Broadband speed — the speed of an internet connection.

Internet — the global network of networks.

WWW — the collection of websites and web pages accessed through the internet.

Modem — a device that converts signals for internet communication.

PSTN — the public switched telephone network, the traditional telephone system.

Dedicated line — a permanent high-speed connection between two points.

IP address — a unique address that identifies a device on a network.

IPv4 — a 32-bit IP address written in four denary blocks.

IPv6 — a 128-bit IP address written in eight hexadecimal blocks.

Subnetting — dividing a network into smaller sub-networks.

Public IP address — an IP address visible on the internet.

Private IP address — an IP address used only inside a local network.

Static IP address — an IP address that stays the same.

Dynamic IP address — an IP address that can change and is assigned automatically.

URL — the web address of a resource.

DNS — the system that changes domain names into IP addresses.

Exam-Style Questions & Answers

Question 1 [4]

Explain the difference between a LAN and a WAN.

Model Answer:

1. A LAN covers a small geographical area such as one building, school, or office, while a WAN covers a much larger area such as a city, country, or the whole world.
2. In a LAN, the hardware is usually owned by the person or organisation using it, but in a WAN some of the communication links may be owned by outside companies.
3. A LAN is usually faster and easier to manage because the devices are close together, while a WAN is more complex because it connects networks over long distances.
4. A good example of a LAN is a school network, while a good example of a WAN is the internet, which connects many LANs together.

Question 2 [4]

Describe the client-server model of networking.

Model Answer:

1. In a client-server network, the server is a powerful computer that provides services such as file storage, printing, email, or web access.
2. The client is the computer that sends a request to the server when it needs a service or resource.
3. The server processes the request and sends back the required data or service, for example sending a file or loading a webpage.
4. This model is useful because management, security, and backups can be controlled centrally, although it can be expensive and the server can become a single point of failure.

Question 3 [4]

Describe how CSMA/CD works on a shared network.

Model Answer:

1. A device first listens to the communication channel to check whether it is free before sending any data.
2. If the channel is busy, the device waits, but if the channel is free, it starts transmitting its data.
3. If two devices transmit at the same time, a collision happens, and the devices detect that the data has clashed.
4. They send a jamming signal, stop transmitting, wait for a random amount of time, and then try to send the data again.

Question 4 [4]

Explain the difference between real-time streaming and on-demand streaming.

Model Answer:

1. Real-time streaming means the user watches or listens as the event is happening, while on-demand streaming means the user chooses content that was already stored earlier.
2. Real-time streaming is used for things like live sports, video calls, or live news, while on-demand streaming is used for platforms such as film or video services.
3. Real-time streaming needs a very steady connection and low delay because the content must arrive quickly, while on-demand streaming can cope better with small delays by using buffering.
4. On-demand streaming usually gives more playback control, such as pause or rewind, while real-time streaming often gives fewer control options during the live event.

Question 5 [4]

Explain how a URL and DNS are used to locate a webpage on the World Wide Web.

Model Answer:

1. The user enters a URL into the browser, and the URL contains the address of the resource the user wants to access.
2. The browser takes the domain name from the URL and checks whether it already knows the matching IP address.
3. If it does not know the IP address, it sends the domain name to a DNS server, which looks up the correct IP address for that domain.
4. The DNS returns the IP address, and the browser uses it to contact the web server, which then sends back the webpage for display.