Network CSMA/CD

Syllabus Detail

  • Similarities and differences of carrier sense multiple access with collision detection (CSMS/CD) and the carrier sense multiple access with collision avoidance (CSMA C/A) network control

Background

  • Networks are a shared system.
  • When there is sharing, there is interaction.
  • Interaction in networking is the sending of information.
  • When this information is sent at the same time, on the same line, by different people it can cause problems.(lets call them collisions of data on the same wired/wireless network)
  • These problems need to be solved by a protocol to prevent these collisions, hence CSMA/CD and CSMA/CA

Similarities

  • Both use a system of sending and receiving data packets (information)
  • Both use Carrier Sensing ie Is there a carrier
  • Both use Multiple Access ie others users around

Differences CSMA/CD

  • CSMA/CD is for wired or ethernet networks.
  • CSMA/CD it provides a listen, then transmit system
  • CSMA/CD, if there is a collision, it waits a random time .5-10 secs, then sends again. 
  • CSMA/CD, each computer waits a different random time, then sends again.
    • Eg 1,  computer 1 in computer lab 1 wants to send data to the internet, eg a google search
    • Eg 1, computer 2 in computer lab 1 also wants to send data to the internet, eg a goodle search
    • Eg1, there could be a collision down the ethernet cable if they both click search at the same time.

Differences CSMA /CA

  • CSMA/CA is for wireless networks.
  • CSMA/CA uses the Wireless Access Point to control who sends and when they are clear to send.
  • Eg 2,  iPad 1 in room 1 wants to send data to the internet, eg a google search
  • Eg 1, iPad 2 in room 1 also wants to send data to the internet, eg a goodle search
  • The WAP will get a ready to send from iPad1 and iPad2 at the same time.
  • The WAP will give the 'clear to send' to iPad1
  • The WAP will then give the 'clear to send' to iPad 2.

 

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