1.3.3

• computer network


  two or more computer connected together with the ability to transmit data between each other
• protocol definition 


  set of rules that allow two devices to communicate, protocols are standard so that all devices have a designated way of communicating with each other
• examples of protocols 


  TCP

  IP

  UDP

  HTTP

  HTTPS

  FTP

  POP

  IMAP

  SMTP
• TCP


  Transmission control protocol - error free transmission
• IP


  Internet protocol - routes packets across WAN's
• UDP


  User datagram protocol - communication protocol for time sensitive apps, speedier because it does not establish firm connection with destination before sending
• HTTP/S


  Hyper text transmission protocol(secure) - used for web page rendering with the S adding encryption making it more secure
• TCP/IP


  Transmission control protocol/internet protocol - network protocol used in the routing of packets through networks
• POP3


  post office protocol - mailing protocol used for email access removes email from server
• IMAP


  Internet message app protocol - mailing protocol for email access keeps email on main server
• FTP


  File transfer protocol - used for transmission of files over networks
• What is the TCP/IP stack for?

  a stack of networking protocols that work together passing packets during communication
• application layer of TCP/IP


  Based at the top of the stack, specifies what protocol needs to be used in order to relate the application that's being sent e.g POP3, HTTP
• Transport layer of the TCP/IP

  Establishes end to end connection between the source and recipient computer, splits data into packets and labels the packets with their packet number. If any packets get lost the transport layer requests re transmission of these lost packets
• network layer of the TCP/IP stack

  adds the source and destination IP address, routers operate on the network layer and the router is what uses the IP addresses to forward the packets, sockets are used to specify which device the packets must be sent to and the application being used on that device
• link layer of the TCP/IP stack


  this is the connection between the network devices, it adds the MAC address identifying the NIC of the source and destination computers.
• purpose of protocol layering

  divides complex tasks of networking into smaller and simpler tasks
• LAN


  Local area network - spread over a single site
• WAN


  Wide area network - over a larger geographical area and requires extra hardware
• packets are segments of data that contains information so they can be sent over the internet
• packet header


  sender and recipient IP address

  protocol being used

  order of the packets

  time to live / hop limit tells packet when to expire
• packet payload


  raw data to be transmitted
• packet trailer


  checksum - check if errors have occurred during transmission
• DNS


  Domain name system - the system used to name and organize the internet resources

  the DNS translates the domain names into IP address of the website we want to visit
• packet switching


  data is communicated using packets across a network, packets are sent across the most efficient route
• advantages of packet switching

  multiple methods to ensure data arrives intact e.g checksum

  multiple routes can be used between devices so if one breaks another can be used

  packets can be transferred over very large networks

  more affordable and efficient

  no bandwidth wastage
• disadvantages of packet switching

  time is spent deconstructing and reconstructing packets

  must wait for all packets to arrive before data can be received|

  packets can arrive in the wrong order
• what is circuit switching?

  direct link is created between 2 devices, the link is maintained for the duration of the entire conversation, this requires the 2 devices to transfer and receive data at the same rate
• advantages of circuit switching

  data arrives in logical order allowing faster reconstruction

  enables 2 user to hold a call without a delay in speech
• disadvantages of circuit switching

  bandwidth is wasted

  devices must transfer and receive data at the same rate

  using switches means electrical interference could corrupt data

  ties up sections of the network which cannot be used until transmission has been complete
• modem


  transforms digital information from computer into analogue signals that can be transmitted through wires

  also does this the other way around
• router


  routes data between devices on a small network, modem and router are needed to connect the home to the internet
• wired connection - twisted pair cables

  made up of copper wires

  affordable

  low bandwidth

  used for telephone networks
• wired connection - coaxial


  affected by noise

  moderate bandwidth

  more expensive than twisted pair

  used for cable tvs
• wired connection - fiber optic cables

  highest noise immunity

  highest bandwidth

  expensive

  supports long distance connections

  used for transmitting large amounts of data
• NIC


  Network Interface Controller

  allows both wired and wireless communications between computers

  consists of both a physical layer and link layer
• WAP


  Wireless Access Point

  creates wireless local area networks

  connects to a wired router, switch or hub

  projects Wi-Fi signals

  Wi-Fi range is limited and easily interrupted
• hub 


  multiple devices connected to one network

  slower than switches

  easily congested

  purely hardware
• switch


  connects multiple devices to one network

  active device

  inspects transmissions
• Advantages of client to server

  easier to manage file security

  easier to backup shared data

  easier to install software updates