A network is formed when two or more computers are connected together.
When computers are networked, it allows them to share data and resources. For example: data such as an email can be passed between different computers on a network, or a printer can be accessed by many by multiple computers without a direct connection.
There are many different types of networks, all of which serve different purposes.
The terms Local Area Network (LAN) and Wide Area Network WAN refer to the physical area a network covers.
A Local Area Network (LAN) covers a small geographical area such as a building. All the hardware that makes up the LAN is privately owned, e.g. the company using the LAN owns the LAN.
Examples of LANs include:
LANs can include wired and wireless devices.
A Wide Area Network (WAN) connects LANs and computers over large geographical locations. WANs are owned by companies and access is rented or leased to its users (think about how people must pay for internet access).
Examples:
WANs connect devices and LANs using ethernet, fibre, satellite and phonelines.
There are two models of how computers share resources on a network: Client-server and Peer-to-peer.
Most of the time this comes down to whether you want to use a server.
A server is a computer which provides resources for other computers. Sometimes servers have to be very powerful and sometimes they may look no different from a regular desktop computer. Additionally, the server can occasionally provide more than one type of resource.
Client-server Networks are managed by servers.The server provides services to other computers on the network – this could be file management, access to printers, user access security. Schools use a client-server model: school servers store our files, manage us logging into computers, manage update and back-up and printing.
Benefits
Drawbacks
On a peer to peer network, all the computers are equal (no singular computer is more important than the rest). There is no server, so all computers share files and resources between themselves. Most home networks are Peer to Peer.
Benefits
Drawbacks
To connect computers together, you need specialised hardware. The most common hardware devices are:
A Network Interface Card (NIC) is hardware built into computers and allows them to connect to a network.In the past NICs were not built in and were optional expansion cards.
NICs can be wireless (to connect via WiFi) or wired (to connect via ethernet). NICs can be rated for different speeds, for example: a Ethernet NIC could be capable of different maximum speeds: 10 MB/s 100 MB/s , 1 GB/s, 10 GB/s , etc.
A network switch is used to connect devices together and it is often described as the central networking device. Devices are connected to a switch using Ethernet Cables. When a device sends data to another device, the data is received by the Switch and then directs that data to the device it is meant to.
Switched make use of MAC addresses to direct network traffic.
Most run at 100MB/s (Megabit / second) or 1GB/s (Gigabit / second)
Routers sit between two different networks and allow communication between them. Most often routers connect a LAN (Local Area Network) to the Internet (an example of a Wide Area Network)
Routers make use of IP Addresses to route data between networks.
Routers are a crucial internet device and transfer data packets between different privately owned networks that make up the internet
Wireless Access Points (WAP) allow devices to wirelessly connect to a network via WiFi. WAPs connect directly into a switch, and many can be powered directly over PoE (Power over Ethernet).
All the ways we can connect computer together can be categorised as Wired or Wireless
When picking or comparing connectivity methods we need to consider: Speed / Bandwidth, Range, Latency
Wired connections make use of cables and there are two main types: Copper Cables and Fibre-optic Cables.
Copper cables are the most common type of cable. Pulses of electricity are used to transmit data (as 1s and 0s).
The most common copper cable used in networking is the CAT 5 / CAT 6 cable, which is often simply referred to as an Ethernet Cable. Copper cabling is most commonly used due to being inexpensive and having a wide compatability.
Fibre-optic cables are becoming more common, especially in WANs. They use pulses of light to transmit data.
They provide greater bandwidth, range and latency than copper cables, but are generally too expensive to be used on LANs.
Over the past 10 years Internet Service Providers (ISPs) have been upgrading their networks replacing copper cabling for fibre-optic cabling to provide higher performance broadband.
There are two approaches:
Fibre to the property is more expensive and is more likely to be used by business.
Microwaves and Radio waves are used to transmit binary data. The binary data is represented by pulses of electromagnetic frequency.
WiFi and Bluetooth are the most common protocols for transmitting data wirelessly, however newer protocols have appeared in recent times such as Thread and Zigbee which have become popular in low power home automation. These protocols set the rules for how data is sent and received by devices.
The main benefit of using wireless connections is the convinenece of not having to be tethered by a cable.
While wireless connections are convienent there are many limitations:
WLANs make use of Wireless Access Points (WAP) – these are devices which allow wireless devices to join a LAN using WiFi.
At home your WAP is integrated into a multi-function devices commonly referred to as the "router”.
In commercial settings a WAP is a separate device. In larger buildings a network may have many WAPs in order to provide wider wireless network coverage.
While WiFi and Bluetooth are the most widely known forms of Wireless Connections, there are a range of other technologies we use in our daily lives.
Topologies refer to how networks are physically set-up (how they are all connected with wires or wirelessly).
There are many topologies, many of which that are no longer used. We are going to cover 3 main ones covered by the different Computer Science specifications.
On a star topology network all devices are connected to a central switch. A common misconception is that computer connect directly to a server, however servers connect to the switch just like every other device on the network.
Computers can be connected via wires or wirelessly (when using a WAP).
Benefits
Drawbacks
On a mesh networks computers connect to each other without a switch, often making multiple connections to different computers.
Sometimes all devices on the network will be connected to every other device (full mesh) and other times they connect through each other (partial mesh - shown above).
Benefits
Drawbacks
On a bus network all computers are connected to a single cable and at the end of the bus network cable is a terminator – this stops the signal on the cable being reflected back. This is an old topology which is no longer used – it has many disadvantages compared to modern topologies.
Benefits
Drawbacks
Protocols are a set of rules for how computers communicate.
They stipulate:
Without protocols computers could receive data but wouldn't know what to do with it. If all computers follow the protocols communication should work with few issues.
There are thousands of protocols which manage different types of digital communication between devices, however the commonly used ones are:
Network communication is very complicated. To simplify things we break down different parts of the communication into four layers.
A single protocol must only work at a single layer and each one manages a different part of communication and thus groups similar protocols together.
We call the layered system the TCP/IP Stack.
We need a way of identifying computers so data can be directed to the right one, and when that computer responds it knows where the data came from.
Every packet contains a destination and source address.
There’s two ways of identifying a computer on a network:
When sending data between computers on a LAN we use MAC Addresses. Every Network Interface Card (NIC) has a hard coded unique MAC address.
This address is a 48bit or 64bit binary number, but it is shown in a more human-friendly hexadecimal number.
A device with more than one method of connecting to a network will have multiple unique MAC addresses (one for each connection method).
If there is a situation where two devices had the same MAC address, it would cause a wide range of network errors.
IP Addresses are needed for communication between different networks. The internet and home networks are based on the IP protocol.
They are either 32bits (IPv4) or 128bits (IPv6) wide. We display IPv4 using denary numbers to make them more user friendly:
IPv4: 51.114.200.99
They can be dynamic or static:
We mainly use IPv4 addresses, but we have run out of useable addresses.
We have managed by using dynamic addresses and only assigning IP addresses when a device connects to the internet.
Eventually, to continue adding devices to the internet, we will have to (slowly) continue transitioning over to IPv6.
We should never run out of IPv6 addresses: there are enough to give every grain of sand on Earth an address and still have plenty left over!
Many of the files we send over a network are far too big to be sent in one go. Instead, we break them down into smaller manageable units called packets.
When receiving, for example a website, the website will be able up of thousands of individual packets
Each packet contains additional information to support the data being received and reassembled in the correct order.
This data is stored in the header
When sending packets over a network, or the internet, a series of steps take place. The below example using a webpage outlines the steps.