SS 3 First Term

Learning Objectives

• Describe network types and how IP addressing and DNS work.
• Explain network topologies and the devices used in networks.
• Explain protocols and the TCP/IP and HTTP families.
• Describe internet infrastructure and network security.

Network Types, IP Addressing and DNS

A computer network is two or more devices connected to share data and resources. Networks let devices share printers, files, applications and internet access, allow people to communicate and collaborate, and make data available from anywhere, so almost every digital solution is eventually delivered over a network. Networks are described by their scale. A LAN, or Local Area Network, covers one building or small campus and is typically owned by a school, office or home. A MAN, or Metropolitan Area Network, spans a city or town and is used by companies or city authorities. A WAN, or Wide Area Network, spans a country, a continent or the whole world and is provided by telecoms and internet providers. The internet is the largest WAN, a worldwide network of networks joined by routers.

Every device on a network needs a unique address so data can be delivered to the right place, and this is the IP (Internet Protocol) address. Just as a home has a house address, a device has an IP address. Two formats are in use. IPv4 uses 32 bits, written as four numbers separated by dots such as 192.168.1.10, and offers about 4.3 billion addresses. IPv6 uses 128 bits, written in hexadecimal groups separated by colons, for example 2001:db8::1, and offers an astronomically larger number of addresses. An IPv4 address is often split into a network part and a host part so devices on the same local network are grouped. Public IP addresses are visible on the internet, while private addresses such as 192.168.x.x are used inside a home or office network.

People cannot remember long numbers, so the internet uses names such as a school's web address. The Domain Name System (DNS) is the address book of the internet, translating these domain names into the IP addresses that computers use. When a browser is given a name, it asks a DNS server for the matching IP address, the DNS server returns it, and the browser connects to that address to reach the website. The whole translation happens in a fraction of a second and is essential to everyday use of the internet.

Protocols, TCP/IP and HTTP/HTTPS

A protocol is a set of agreed rules that govern how data is transmitted across a network. Protocols guarantee that different devices and programs can understand each other, no matter who made them, rather like the rules of a conversation, who speaks first, how a message is acknowledged and what happens when a message is lost. TCP/IP is the fundamental protocol suite of the internet. IP, the Internet Protocol, handles addressing and routing, moving packets from the source device to the destination across many networks. TCP, the Transmission Control Protocol, breaks the data into packets, sends them, checks that they arrive in order and asks for retransmission of any packet that is lost.

The internet does not send a whole message in one stream. It uses packet switching, splitting data into small packets, each sent independently over whatever route is best, then reassembling them at the destination. Strictly, data is broken up, routers forward each packet toward its destination, TCP reassembles the packets in the correct order and checks for losses, and the receiver acknowledges receipt so lost packets can be sent again. Packet switching is what keeps the internet reliable even when individual paths fail. HTTP, the Hypertext Transfer Protocol, is the protocol that requests and delivers web pages, with the browser issuing an HTTP request and the server responding with the page data. HTTPS is HTTP secured with TLS/SSL encryption, so data exchanged between browser and server is scrambled and unreadable to anyone who intercepts it.

For any site that handles personal data, such as school portals or payment pages, HTTPS is essential. Other protocols fill specific jobs. FTP moves files between computers over a network, SMTP sends outgoing email, POP and IMAP receive email, and DHCP assigns IP addresses to devices automatically. Each protocol has one clear job, and together they make the internet work smoothly. Scenario question, a student opens the school portal at home on her phone, a LAN connects her phone to the internet, DNS resolves the address, HTTPS encrypts the connection, and TCP reassembles the packets that the routers delivered.

Internet Infrastructure and Network Security

The internet looks simple from a browser, but it is built from many physical parts, fibre-optic and copper cables, underground and undersea, that carry most data; routers and switches that direct data between networks; servers and data centres that store websites and services and respond to requests; and network interface cards in every connected device. Logically, the internet connects networks in a hierarchy, home and office networks join local internet service providers, which connect through regional networks to large backbone providers. Because data can take many paths, the internet keeps working even if one path fails. In the client-server model, a client such as a browser requests a service, and a server such as a web server provides it, which is the model behind most of the web and the model used for building websites.

Networks face serious threats, including interception, where a third party reads data as it travels; phishing, which tricks users into revealing passwords or personal data; malware and viruses that infect devices; ransomware that locks files and demands payment; and denial-of-service attacks that overwhelm a server with traffic. Essential safeguards are encryption through HTTPS and VPNs, firewalls that filter traffic in and out of a network, strong passwords and multi-factor authentication, regular software updates and antivirus protection, and backups plus access controls for stored data. These measures serve the security triad of confidentiality, keeping data private, integrity, keeping data unchanged, and availability, keeping services up. When a network is secure, all three hold. Scenario work traces a secure payment over HTTPS, naming the encryption on the network, the firewall on the server and the strong login, each protecting a different part of the journey.

Transmission media means the paths over which data travels.

Network Topologies and Devices Review

A network topology is the physical or logical layout of how devices are connected. Common topologies include the bus, star and ring arrangements, each with different strengths in cost, speed and fault tolerance.

Four devices appear regularly in a working network. A router connects different networks and chooses the best path for data travelling between them. A switch connects devices within the same network and delivers data to the right device on that network.

A modem converts digital signals to analogue signals and back, allowing a home or office network to use telephone, fibre or cable lines. A wireless access point allows devices such as phones and laptops to join the network without cables. In the Creative Brains Academy laboratory, computers link to a switch, the switch connects to a router, and the router reaches the wider internet.

Topologies describe how nodes are arranged in a network.

Routers move data between different networks.

Switches deliver data within one network.

Modems and wireless access points connect the network to the outside world.

Internet Technologies, Protocols and the World Wide Web

The internet and the World Wide Web are often confused but are not the same. The internet is the physical and logical infrastructure of interconnected networks, while the web is a service running on top of it that delivers pages, images and videos.

Protocols make this possible. TCP/IP is the fundamental protocol suite: IP handles addressing and routing of packets, and TCP breaks data into packets, checks their arrival, and reassembles them in order. HTTP and HTTPS carry web requests and responses, with HTTPS adding encryption.

IP addressing is the postal system of the network. IPv4 uses 32-bit addresses such as 192.168.1.10, while IPv6 uses 128-bit addresses written in hexadecimal, for example 2001:db8::1, to provide far more addresses. DNS converts human-friendly names such as www.school.ng into the IP addresses the network can route to.

The internet is the infrastructure; the web is a service on top of it.

TCP/IP, HTTP and HTTPS are the core internet protocols.

DNS converts human-friendly names into IP addresses.

IPv4 and IPv6 provide unique addresses for every connected device.

Network Security in the Workplace

Network security protects data, devices and services from attack while they are connected to a network. Every organisation, from a bank in Lagos to a school in Abuja, must defend its systems against interception, phishing, malware and denial-of-service attacks.

A firewall is a security device or software that filters traffic entering and leaving a network. It blocks unauthorised access while allowing normal traffic. A VPN (virtual private network) creates an encrypted tunnel, so remote workers can use the company network securely from anywhere.

Encryption scrambles data so only the intended receiver can read it. HTTPS encrypts web traffic, and VPNs encrypt whole connections. Multi-factor authentication and staff training guard against human error, which is often the weakest link in security.

Firewalls filter incoming and outgoing traffic at the network boundary.

VPNs create encrypted tunnels for remote and secure access.

Encryption such as HTTPS protects data in transit.

Multi-factor authentication and training guard against human error.

Meaning and Benefits of Networking

A computer network is two or more computers joined so that they can exchange data and share resources. The joining may be by cable or by radio. What is shared includes data, printers, storage space, software licences and an internet connection.

The benefits are cost, speed and reliability. Sharing one printer instead of buying one per desk saves money. Sharing an internet connection across a laboratory costs less than separate connections. Sharing files removes the need to pass a pen drive around, and central storage allows a backup of every file in one place.

Networking also allows collaboration. Several people can work on the same file at the same time, and a resource such as a database can be used by many departments at once. A network introduces risks, so access is controlled by permissions and passwords.

Classes of Network

A personal area network covers a very small area, usually a few metres, and connects a device such as a phone to a headset. A local area network covers one building or a small group of buildings, such as a school or an office, and it is owned by one organisation.

A metropolitan area network covers a town or a city, joining several local area networks, such as the branches of a bank across a city. A wide area network covers a country or the world and is formed by joining many networks together. A virtual private network gives a user a secure connection to an organisation's own network from anywhere.

The classification is by area, and the area decides the equipment. The larger the area, the more expensive the equipment and the slower the data becomes, because the signal travels further and passes through more devices.

Transmission Media and Modes

The media are guided and unguided. Guided media carry the signal inside a physical path, such as twisted pair copper cable, coaxial cable and fibre optic cable. Unguided media carry the signal through the air, such as radio waves, microwaves and infrared.

Fibre optic cable carries data as light, so it is not affected by electrical interference, it travels much further than copper without loss of strength, and it carries a very large bandwidth. This makes it the preferred medium for long distances and for the backbone of a network.

Twisted pair copper cable is cheap and is used for connections to a desk. Coaxial cable is thicker and is used where interference is a problem, such as the connection between a television set and a dish.

Data travels in two modes. In simplex, data travels in one direction only. In half duplex, data travels in both directions but not at the same time. In full duplex, data travels in both directions at the same time, which is how a telephone conversation works.

Network Devices

A modem converts a signal from the provider into a signal the computer can use, and back again. A network interface card allows a computer to join a network, by cable or by radio. A repeater regenerates a weakened signal so that it can travel further.

A hub is a simple device that repeats an incoming signal to every other port, so every device receives every frame and the network wastes bandwidth. A switch learns the addresses of the devices on each port and forwards each frame only to the port it is meant for. This makes a switch the standard device in a modern local area network.

A router joins two or more different networks and decides the route for the data travelling between them. A bridge joins two networks of the same type. A gateway joins two networks of different types and may translate between their protocols. An access point provides a wireless connection for devices within its range.

A proxy server acts on behalf of the computers on a network, so that one internet connection can be shared and the addresses of the individual computers are not exposed to the internet.

Topologies and Network Design

Topology is the shape in which the devices are connected. In a bus topology all the devices share one central cable. It is cheap and uses little cable, but a break in the main cable stops the whole network.

In a star topology each device has its own cable to a central switch. A break affects only one device, which is why this is the common layout in schools and offices. In a ring topology the devices are joined in a closed loop and the data travels in one direction around the loop, so a break stops the network.

In a mesh topology each device is connected to several others, so there is more than one route for the data. It is the most reliable and the most expensive. A hybrid topology combines more than one shape, such as a star of stars across the floors of a building.

Topology may be physical, showing the actual cables, or logical, showing the path the data takes. The two may differ. A practical design chooses the topology first, then places the devices, then decides on the media and the addressing scheme.

Practical Work

1. Draw a labelled star and mesh network and name each device.
2. Name three network devices and one job of each.
3. Explain what an IP address and a domain name each do.
4. Explain how a firewall protects a network.

Scenario-Based Questions

1. A school is expanding and needs a reliable network for three buildings. Recommend a topology and the devices.
2. Explain why a switch is used instead of a hub in a busy office.
3. Explain why DNS is needed when people use domain names.
4. Explain how a firewall and a strong password work together.