This is a very dense topic; there's just so much here. Try searching (Ctrl+f) if you want to find something specific. Information on everything here is probably not complete.

Defining a network

A connection between two or more computer systems which are capable of sharing hardware and software resources; this connection may be wired or wireless.


A network that covers a wide area (Wide Area Network). These are used when computers situated far away from each other need to connect to each other. A connected number of LANs can form a WAN.

A WAN consists of two kinds of systems: end systems and intermediate systems. An end system is a computer that does not extend the network (the network "ends" at that computer). An intermediate system can extend the network to other computers.



A LAN is akin to a small, private network. Hence the name, Local Area Network. It will usually contain a number of systems connected to hubs or switches. Routers and/or modems allow LANs to connect to WANs.



This is simply a wireless LAN. Signals are provided using radio or infrared waves. Generally works over smaller distances, up to about 100m.

Comparing the sizes of different kinds of networks

Wide Area Network 100km to 1000km
Metropolitan Area Network 1km to 100km
Local Area Network 10m to 1000m
Personal Area Network 1m to 10m


This term is used to describes a number of interconnected networks (internetwork, shortened to internet).


Ways to create a network.


Computers are connected to a centralized server. The computer from which connection requests are made is the client, the computer that receives these requests is the server. A few more things to note:

Peer to Peer

Each computer in a peer to peer network is called a node. These nodes are all connected to each other (hence the name). It is decentralized.

Advantages of either model

P2P Client-Server
Less congestion Better security
Parts of a file may be downloaded from different nodes Better protection from malware, since files are stored in one (central) location
Files available from multiple hosts

Client types

Thin clients

A thin client needs to be connected to a more powerful machine for it to be able to process data. It has little horsepower on its own and thus can do little on its own. This can be both hardware (i.e. a POS terminal) and software (i.e. a web browser).


Advantages Disadvantages
Less costly to scale (since low-cost devices can be used) High reliance on a centralized server (if it goes down, a thin client isn't very useful)
Data/software updates from a central source (greater control over the client) More expensive initially, to set up
Better protection against malware (the server can handle this instead of the client)

Thick clients

This kind of client can work online or offline; it doesn't have a high reliance on a server. This can also be hardware (i.e. regular ol' computer) or software (i.e. text editors).


Advantages Disadvantages
Offline data processing Less secure (security depends on the client)
More control/autonomy given to the client Data/software updates are handled individually
Less reliance on a server Worse data integrity relative to other similar devices

Comparing the two (in terms of software)

Thin client (software) Thick client (software)
Constant reliance on server Less reliance on server (can work reasonable well without a network connection)
Few hardware resources required (less memory, storage, processing power, etc.) Heavy reliance on local resources
Reliance on a stable network connection Better tolerance of slow networks
Data is stored remotely Data is stored locally

Network infrastructure




Requirements to establish a network

5 things are required for a network:

Modes of transmission

  1. Simplex

    Data goes one way only (i.e. data transmission from a keybord to CPU, data being sent from a computer, radio/television stations)

  2. Half-Duplex

    Data goes two ways, but not at the same time (i.e. walkie-talkies)

  3. Full-Duplex / Duplex

    Data goes two ways, at the same time (i.e. broadband connection on a phone line, telephones)

Types of messages

  1. Unicast message

    A message is sent from one point to another (1:1) (think of text messaging).

  2. Multicast

    A message is sent to a specified group of devices (think of group messaging or email lists).

  3. Broadcast

    A message is sent to anyone and everyone. If you want to receive it, you can.

Network topologies

Point-to-point connection

This topology connects one computer directly to another. Messages are sent as unicast messages. Simplex and duplex transmission may be supported. Difficult to scale

Bus topology

Computers are connected to a central link. There are no direct connections to any computers here. Messages need to be broadcast, even if they are intended for a specific system.

These are easy to scale, and is not reliant on the status/situation of any individual node (i.e. if a node dies, the network still works). However, if the main cable dies, then the network goes down. It suffers from bottlenecking and lacks security since packets pass through multiple nodes.

Transmitting packets in a bus topology

Each node looks at the packet and detemines whether or not the recipient of the packet corresponds to the address of the node. If it matches, it's not sent forward. The opposite is also true.

Terminators exist at each end of the central cable. If nobody receives the packet, it is terminated here.

Mesh topology

Each system is individually connected to every other system in the network. Messages have the leverage of being one of unicast, multicast or broadcast. Duplex transmission works here.

A lot of cabling is needed, however, which proves costly and makes maintenance difficult. Conversely, identifying faults in the network is relatively easy, broken links do not affect the rest of the network, and scaling the network is somewhat easier.

Star topology

Each system is connected to a central server (think client-server model). Duplex transmission works here, and messages may be unicast, multicast or broadcast. The central device may be a hub or switch. This is the most common way of setting up a network.

If an end system fails, then the rest of the network can function normally. Security is also better, since packets are received by a specified computer. However, if the central server fails, then the entire network goes down. Installation costs - intially - are high.

Hybrid topology

A combination of two or more topologies. These can offer great control over the network, but are complex to install, configure and maintain.

Transmission media


Twisted-pair cables

This kind of cable has the lowest data transfer rate and suffers from external interference (i.e. E.M. radiation). It is affordable, however. These can be purchased as unshielded cables (as the name implies) or shielded (which contains a thin layer of metal foil to reduce external interference).

Coaxial cables

These cost more than twisted-pair cables, but have better transfer rates and are less susceptible to external interference. These have about 80 times the transmission capacity of twisted-pair cables. Generally not used for long-distance telephone cabling.

Fibre optic cables

Most commonly used to send data over long distances, since they offer the best transfer rates, have great signal strength and are least affected by external interference. These have about 26,000 times the transmission capacity of twisted-pair cables. They cost much, however, and are not as easy to maintain as other types of cables. Data is transmitted in the form of light.

  1. Single-core (or single-mode): uses a single light source to transmit data, which results in less reflection as the light travels through the cable. It allows for a better transmission rate and distance.
  2. Multi-core (or multi-mode): uses multiple light sources, resulting in more reflection. They work better over shorter distances.


Twisted-pair Coaxial Fibre optic
Cost lowest higher highest
Bandwidth lowest higher highest
Attenuation (reduction of signal strength) at high frequencies highest higher lowest
Susceptibility to interference highest higher lowest
Need for repeaters (hardware that boosts signal strength ("repeats" it)) highest higher lowest

Factors that cause poor performance of cables

Susceptibility to interferance & extent of attenuation at high frequencies.

Wireless data transmission

Data transmission through electromagnetic radiation (radio/microwave/infrared).

A few things to note:

  1. Penetration

    This refers to the ability of EM radiation to pass through different media (i.e. walls). Radio waves have the best penetration power, followed by microwaves and then infrared.

  2. Attenuation

    This refers to the deterioration of signal strength (i.e. reduction in amplitude). Infrared has the highest attenuation of the three waves, since it can be affected by rain or walls.

    High attenuation can be advantageous however. In the case of infrared waves, it proves superior for indoor use. Its low attenuation means any emitted infrared signals have a low chance of interfering with each other.

  3. Bandwidth

    A measure of the amount of data that can be transmitted per second.

Wired vs. wireless



WiFi and Bluetooth

Both offer wireless communication between devices are use electromagnetic radiation for this purpose.


79 channels (or different frequencies) are available for connection. When a device is paired, it will use one of these 79 channels (randomly). If a channel is in use, another will be selected. This technology is known as spread spectrum frequency hopping.


This also makes use of spread spectrum frequency hopping technology. It is better suited for full-scale networks since it offers better data trasnfer rates, range and security as compared to bluetooth. The internet can be accessed through WiFi by a WAP (Wireless Access Point) up to 100m away.


Geostationary Earth Orbit (GEO) satellites

These are located at the highest altitude as compared to the rest of the satellites mentioned in this document. They are used to provide long-distance telephone and computer network communication. Only three are needed for global coverage. The word "Geostationary" refers to the fact that the satellite remains in the same place relative to the earth during orbit (i.e. it orbits at the same speed as the earth spins).

Medium Earth Orbit (MEO) satellites

These are a bit closer to the earth. They are used for GPS. 10 are needed for global coverage.

Lower Earth Orbit (LEO) satellites

Closest to the earth, and are generally used to supplement mobile phone networks. 50 are required for global coverage, but several hundred are currently in orbit.

Other information

Satellites can act as a part of a network, and can connected directly to other ground-based parts of a network. It does come with its own problems - namely delays, due to the distance, and difficulty when it comes to maintenance.

Hardware definitions

  1. Hub

    A hub is a non-intelligent device that forwards any data packets (or simply "packets") it receives to all connected computers.

    Hubs lack security and are wasteful of bandwidth. They can be wired or wireless.

    They are generally not used nowadays.

  2. Switch

    A switch is an intelligent device that forwards any received data packets to a specific computer (i.e. a hub that does not automatically forward anything it receives to all computers in a network).

    They offer better security, and are more resourceful of bandwidth.

    Each device a network will have a MAC (Media Access Control) address. It uniquely identifies it. A switch will use these addresses to determine who is sending the packet and who is receiving it.

    These can be wired or wireless.

  3. Repeater

    A repeater aims to undo any loss of signal strength (attenuation). They essentially amplify both analogue (i.e. received from copper cables) and digital signals (i.e. received from fibre optic cables).

    They can be used when sending data over long distances, or to simply provide better coverage for wireless networks (think of WiFi repeaters).

  4. Bridge

    A bridge will interconnect LANs. These LANs must use the same protocol (i.e. they must be wired or wireless only, not both). These can be wired or wireless.

  5. Router

    A router determines a route for packets to travel from one network to another (i.e. from a LAN to a WAN). Routers do not require a homogenous protocol between networks; it can translate protocols as needed, to allow for communication.

    Routers can:

    • restrict broadcasts to within a LAN
    • act as a gateway (more on this below)
    • translate protocols (to allow them to communicate with each other)
    • transfer data between networks
    • determine efficient routes for data to travel to its destination
  6. Gateway

    A gateway is essentially an access point to another network (think of the gate to your home, or door to your flat). They can be used to connect dissimilar LANs, and may translate protocols as needed. They can act as routers, firewalls and servers. Wired and wireless versions exist.

  7. Modem

    This is essentially an ADC (modulator) and a DAC (demodulator) in one device. The name is derived from the words "modulator" and "demodulator".

    Wireless modems also exist.

  8. Network Interface Card (NIC)

    This is needed to allow a device to connect to a network. Generally part of device hardware and contains the MAC address of the device.

  9. Wireless Network Interface Card (WNIC)

    The same as an NIC, but wireless. They use an antenna to communicate with networks (through microwaves (not the kitchen appliance)). They can plug into the USB port of a computer, or can be integrated in the main board.

By every stretch of the imagination, the amount of content here is a bit much.

This article was written on 29/09/2023. If you have any thoughts, feel free to send me an email with them. Have a nice day!