Data link layer

Question

What do u mean by there is no contention in a coma/ CD network. Why csma/ cd is not suitable for a high propagation delay network?

Comments

CSMA/CD is a contention base protocol.

Our goal is to handle collisions in a contention base protocol. CSMA/CD listen while talking and in that way it detect collisions.

you can read about it more here

http://www.erg.abdn.ac.uk/users/gorry/eg3567/lan-pages/csma-cd.html

Its not suitable for high propagation delay networks (like satellite) because when the distance between communicating channels is high enough then collisions can't be detected.

Answer 1

CSMA/CD or Carrier-sense multiple access with collision detection  is a contention based multiple access protocol .

Contention period in CDMA/CD  is defined as 2xt_p  where t_p =propagation time

In CSMA/CD sending station must listen the channel for collision while it is transmitting the frame. Infact the sender has to listen to the channel for atleast 2t_p time to assure that it has successfully capture the channel.

Hence the transmission time >= 2*t_p

Now for high propagation delay network,  t_p value must be huge.. Hence transmission time will be greater

For given bit rate , increase in transmission time causes the need of longer frames..

So to sum it up , CSMA/CD is not suited for  high propagation delay network due to :

• need to longer frames           // inefficient
• signal attenuation