computer science yr 11 revision

computer science yr 11 revision

1. circuit switching

   • a path across the network is established.
   • that path is locked and remains open for the duration of the communication.
   • advantages
     • data arrives in the order it was sent
       • data arrives at a constant speed
     • can start reading transmissions as soon as first bit arrives, as data arrives sequently
   • disadvantages
     • only one transmission at a time along each channel - clogs the channel
   • pathfinding

2. packet switching

   • the data is split into lots of small chunks called packets
   • each one is sent independently, likely using different paths
   • the packets are re-assembled at the other side
   • advantages
     • multiple transmissions can happen simultaneously
     • large transmissions don't clog the network
   • disadvantages
     • lag is needed to allow several packets to arrive before reading as the first packet sent may not be first packet recieved

3. TCP/IP

   • TCP/IP stack
     • Application layer
       • provides application services to users and programs
       • transport layer
         • handles data - consistency functions(error checking)
         • network layer
           • provides network addressing and routing (IP address)
           • Data link
             • prepares and corrects data to be passed to the physical layer
             • physical layer
               • transmits and recieved bits. the physical layer is the transciever that drives the signals on to the network.

4. IP addresses and DNS

   • IP(internet protocol) address are the unique identifiers assigned to computers on a TCP/IP network(including the internet)
     • It is usually written in the form of 4 8-bit denary numbers seperated by dots(e.g. 143.45.120.201
   • DNS
     • Domain Name system is a system to store domain name (bbc.co.uk or google.com) and look up their IP address.
     • when you type a web address into a browser, your ISP(internet service provider) sends the domain name to its DNS server, which returns the IP address
   • it has 3 ranges of IP address that reserve internal network: 10.0.0.0 - 2.55.255.255 , 172.16.0.0-172.31.255.255 and 192.168.0.0 - 192.168.255.255
   • IPv4
     • there are more that 4.2 billion devices on the internet, sot here are't enough IP addresses to assign one to each device
   • IPv6
     • while IPv4 is still the main system used on the internet, there is a newer version called IPv6
     • Ipv6 use a 128 bit address
     • this is 100+ addresses for every atom on the surface of the earth.