5. Internet and Communications(Networking Terms/Error Detection/Compression)

5. Internet and Communications(Networking Terms/Error Detection/Compression)

1. Compression

   • Used to make files smaller so that the can be transmitted more quickly
   • Lossy
     • Individual file made smaller, not all data stored
     • e.g JPEG, MP3
   • Lossless
     • Individual fie made smaller, all data is stored
     • e.g PNG, GIF
   • Zipped
     • Several files compressed tone file that is easily stored or transmitted (lossless)
     • e.g ZIP, RAR
   • Decision
     • Precise data needed=lossless
     • Lots of files compressed needed=Zipped
     • Precise data not needed= lossy
       • Reduce transmission time
       • Save disk space

2. Networking Terms

   • IP(Internet protocol) address
     • unique number assigned to a device on a network
     • Used to ensure the right data reaches the right device.
     • IP addresses divided into four sections
     • e.g 192.168.0.5
   • MAC(media access control)address
     • unique number i that is hardwired into a device and cannot be changed
     • 12 digit hexadecimal number
     • e.g 53:a0:6f:10:44:bd
   • Packets
     • When data is sent across a network it is broken into smaller chunks called packets
     • Packet header,data, packet trailer
       • header includes source address+destination address
       • header contains identification number, needed to reassemble data once transmission is complete
     • Advantages of packet switching
       • Packets do not need to take the same route around the network
       • packets do not need to arrive in the same order as they left and reassembled by the recipient computer

3. Error detection

   • Data transmitted without any such check is not to reliable
   • Data can be repeatedly sent until a predetermined number of transmissions are identical i.e assumed to be uncorrupt
   • Parity bit
     • parity bit added to a transmitted piece of data. Set to 1= even number of 1's, Set to 0= odd number of 1's
     • Not completely reliable
   • Checksum
     • Assigns more than one bit for the purpose of error detection