1.3 - Computer networks, connections and protocols

• Computer network


  Two or more computers or devices that are linked together, either using cables or wirelessly, so they can communicate and share resources
• Devices that may be connected to a network

  • Computers
  • Printers
  • Smartphones
  • Tablets
  • Gaming consoles
  • Fitness trackers
  • Smart watches
  • Internet-connected home appliances
• Advantages of computer networks

  • Ability for computers to share hardware resources such as printers and internet connections
  • Ability to exchange data between computers without needing to use physical media
  • Network users can communicate easily using email or video calls
  • Allows central management and control of computers in larger organisations
• Disadvantages of computer networks

  • Additional hardware needed to set up a network can be expensive
  • If one machine gets infected with malware it can quickly spread to other machines
  • Possibility of hackers targeting the network to gain access to several computers
• Local area network (LAN)

  The type of network found in homes, schools and single-site companies and organisations, covering a small geographic area
• Wide area network (WAN)


  The type of network used by large organisations with offices in different locations, covering a wide geographic area and linking together the LANs for each site
• The internet is essentially a huge, worldwide WAN
• Bandwidth


  How much data can be transmitted over a network in a given period of time, usually measured in bits (or megabits) per second
• Factors affecting network performance

  • Bandwidth capacity
  • Number of users
  • Transmission media
  • Error rate
• Client-server network


  A network with two types of computers: servers that provide services, and clients that request those services
• Advantages of client-server networks

  • Activities can be managed and controlled centrally
  • Users' files can be stored on the server
  • Software and security updates can be managed centrally
• Disadvantages of client-server networks

  • If the server becomes unavailable, users cannot access their files
  • Servers can become overwhelmed by too many requests
  • Server hardware is typically more expensive
• Peer-to-peer (P2P) network


  A network where all computers have equal status and are connected directly, without a central server
• Advantages of peer-to-peer networks

  • Easy to set up as they do not require expensive or dedicated hardware
  • More robust as there is no single point of failure
• Disadvantages of peer-to-peer networks

  • No central management or maintenance
  • No centralised backup of files
  • Possibility of files becoming out-of-date
  • Devices going offline when being accessed
• Network interface controller/card (NIC)


  Hardware that allows a device to connect to a network, either through an ethernet port or a wireless radio transmitter/receiver
• Media Access Control (MAC) address


  A unique identifier used when transmitting data around a network
• Copper wire


  Standard network cables consisting of twisted pairs of copper wires, transmitting data as electrical signals at bandwidths of 100 Mb to 1 Gb per second
• Fibre-optic cable


  Cables made up of thin glass strands that transmit data as pulses of light, not suffering from electromagnetic interference
• Transmission media


  Data is transferred between devices either through cables (wired) or by radio waves (wireless)
• Copper wire


  • Standard network cables consist of eight individual copper wires that are arranged in pairs
  • Each pair of cables is twisted together to reduce interference from other signals and therefore improve transmission
• Data transmission through copper wire

  • Data is transmitted as electrical signals
  • There are different ratings that indicate how quickly the cable can reliably transmit data and over what range
  • The bandwidth is generally between 100 Mb and 1 Gb per second, for a distance of up to about 100 metres
• Wired LAN connection


  Most PCs have built-in wired LAN port and so connecting computers using copper wire can be a cost-effective option if the bandwidth is adequate
• Fibre-optic cable


  • Made up of many thin glass strands (or fibres), which transmit data as pulses of light
  • Do not suffer from electromagnetic interference
  • Do not break easily as they are strong, flexible and do not corrode
• Fibre-optic cable performance


  • Have a very high bandwidth of up to 100 Tb per second
  • Capable of transmitting data over distances of 100 kilometres or more
  • Often used to connect WANs across large geographic areas
• Radio waves


  • Wireless networking technologies, such as Wi-Fi and Bluetooth, use radio waves to connect devices
  • Radio waves form part of the electromagnetic spectrum and their use is strictly controlled by governments
  • The most commonly used frequencies for data transmission are 2.4 GHz and 5 GHz
• Radio wave performance


  • The strength of a radio wave decreases as it moves further away from its transmission source
  • Only suitable for relatively short distances of up to 100 metres
  • Subject to interference from other radio signals of the same or similar frequencies
  • Partially blocked by physical objects such as walls
  • Generally have a bandwidth of about 300 Mb per second
• Wireless access point (WAP)


  • A piece of hardware that connects to a network switch and allows Wi-Fi devices to connect to a network
  • Broadcasts a Service Set Identifier (SSID), which is the name for the network
  • Sends the wireless data that it receives on to the main wired network
  • Can be used to extend the range of a wireless network by transmitting or receiving data from other WAPs
• Network switch


  • The piece of hardware that allows multiple devices to connect together to form a wired network
  • Stores the MAC address of every device connected to it in a table
  • When the switch receives a packet of data it looks at the destination address and forwards it on to the intended device
  • It is possible to connect multiple switches together to increase the number of devices on a network
• Router


  • The piece of hardware that connects networks of different types together
  • Most commonly, routers are used to connect a LAN to the internet
  • Inspects the destination IP address of a data packet to determine whether it is located on the local network
  • If it is not, the data packet is passed on to the connected network
  • Collects data about all of the available routes to transmit data and then determines the most appropriate route for each individual data packet
• Home broadband 'routers'


  Often combine the features of a switch, WAP and router in one device, and are referred to as hybrid devices
• Internet


  • A worldwide collection of computer networks that are all linked together as a WAN
  • The set of rules that ensures that devices can work together on the internet is called the Internet Protocol (IP)
  • Every computer using the internet has a unique IP address, which is used to send data from one device to another across the internet
• Websites


  • Hosted on web servers and are accessed via their IP address
  • Addresses like 212.58.244.26 are hard for humans to remember, so we use a Uniform Resource Locator (URL), such as www.mywebsite.co.uk, which includes the domain name
• Domain Name Server (DNS)

  • Keeps a record of the IP address for each web server that is associated with a particular domain name
  • When a user types the URL for a website into a browser, a request is sent to a DNS server to ask for the matching IP address
• Internet hosting


  • Companies that run servers to provide different types of content via the internet, such as file hosting, web hosting, email hosting, video hosting and game servers
  • Often charge a monthly fee to use their facilities, although some content may be accessed for free
• Cloud computing


  • A generic term that refers to storage, services and applications that are accessed via the internet rather than being stored locally
  • Effectively a network of servers, some that store data and others that run applications
  • Users do not actually need to know the geographical location where their data is stored
• Advantages of cloud computing

  • Files and applications can be accessed from anywhere in the world with an internet connection
  • Cloud applications are always the latest, most up-to-date version and users do not have to update anything themselves
  • Reduces the need for network managers and technical support staff
  • The amount of storage space is flexible, and users can buy additional storage when they run out of space
  • All data that is stored in the cloud is regularly backed up and kept secure by the hosting company, and data can be shared easily with colleagues anywhere in the world
• Disadvantages of cloud computing

  • An internet connection is required to access files and services
  • Users have little control over the security of their data and it is possible that data stored in the cloud could be targeted more easily by hackers than data stored locally
  • It can be unclear who legally owns the data that is stored
  • Cloud providers can change their terms and prices with little notice, and ongoing fees may become expensive in the long run
• Web servers and clients

  • Every website is hosted on a web server, which is a dedicated computer on the internet that responds to HTTP and HTTPS requests by returning web pages
  • Client computers request files from a server, and when you visit a website, the browser on your device requests the web pages from a web server and they are downloaded to your device
• Star network topology


  • Each computer or client is connected individually to a central point, usually a switch or hub
  • The most common network layout, and it tends to be fast and reliable because each client has its own connection to the central node
  • Data is only directed to the intended computer, which helps to keep network traffic to a minimum and reduces data collisions
  • The switch can screen data packets, rejecting any that are corrupt, which can increase security on the network
  • Easy to add new devices as they simply need to be connected to the switch
  • If the connection to one device on the network fails, the rest of the network will be unaffected
  • Requires a lot of cabling, which can be expensive
  • If the central server or switch fails then so will the entire network