Networks

Networks

1. IP Addresses and DNS

   • An IP address is a unique address assigned to every networked computer or computing device
     • E.g 65.123.217.14
   • Domain names
     • A domain name is the text reference to a site so you don't have to remember the whole IP address.
   • DNS stands for Domain Name System
     • The DNS server has a database of domain names and IP addresses so it can translate the domain name into an IP addresses

2. NICs and MAC addresses

   • NIC - network interface card
     • Every device needs one to connect to the Internet
   • MAC address - media access control address
     • A 48 bit address written as 12 hex digits to make it easier to understand
       • You cannot change it

3. LANs and WANs

   • LAN - Local Area Network
     • For networks covering an area of less than 1km
       • E.g. in a school or small company
   • WAN - Wide Area Network
     • For networks covering an area of more than 1km
       • E.g. an international company

4. Data transmission

   • Packet switching
     • Files are broken up into small 'packets' of data
       • They are marked with their origin and destination
       • The packets are sent to their destination along many different routes
         • They are reassembled in the right order when they reach their destination

5. Client server and peer to peer networks

   • Client server
     • Files are stored on a central mainframe called a file server.
       • The computers that use the resources provided by the server are called clients
         • Advantages: if one client-server connection fails the others are not affected, consistent performance even when the network is heavily used
         • Disadvantages: can be expensive to install because of cabling and switch, if the sever or the central switch goes down the whole network is affected
   • Peer to peer
     • Each computer can share files with other computers in the network through the LAN
     • The computers have equal status and the same role in the network
       • Advantages: LANs run faster because packets don't have to travel back to a central server, using fewer cables means it costs less to set up a network

6. Hosting

   • Companies can host your pages on their own servers
     • E.g. hosting files on OneDrive or YouTube
     • Cloud storage
       • Data is stored on offsite web servers
         • You can only access this data on the Internet
           • You don't have to use up your computer's internal storage

7. Network hardware

   • Router
     • routes packets across a WAN, each router in a network acts as a node and packets are passed from router to router to their destination on the Internet
   • Switch
     • Component of a LAN that knows the MAC addresses of each individual device connected locally - forwards inbound packets to the recipient using its MAC address
   • Ethernet
     • A family of protocols used in LANs
       • Nodes should wait until the connection is quiet before transmitting data
       • Two nodes attempting to transmit simultaneously should stop and each wait a random period before reattempting
   • Transmission media
     • Cables used to connect computers together in a network
       • Fibre optic cables transmit data very fast and are not affected by electromagnetic interference
       • Copper cables have an adequate speed, but are easily breakable and are affected by electromagnetic interference

8. Protocols

   • TCP/IP
     • TCP: defines how messages are broken into packets and reassembled at destination IP: identifies location of a device on the Internet and creates a journey for the packets
   • HTTP and HTTPS
     • HTTP: used for accessing and receiving HTML webpages HTTPS: encrypted version
   • FTP (File Transfer Protocol)
     • Used when transferring files between client and server on a network
   • POP (Post Office Protocol)
     • Receives and holds email for a user until they read it
   • IMAP (Internet Messaging Access Protocol)