Computer Networks Ethernet

Question

what is the mean of this equation in Ethernet  ?
Transmission Time >= 2*Propagation Time

Comments

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I think this Page help u-

Ethernet used CSMA/CD for access Control .

here Tt-Transmission time,Tp=Propagation time

So,

Transmission Time >= 2*Propagation Time

Answer 1

Propagation time is the amount of time it takes for one particular signal to get from one point to another. Transmission time is time gap between two successive transmission

suppose u want  to send data from point A to B then amount of time required for it is equal to propagation time .

as soon as receiver receives data , it will send u an acknowledgement . acknowledgement will take time = atleast that of propagation time . after getting ack A will send next packet to B . therefore A has to wait MINIMUM of 2*propagation time before it sends next data item ,

therefore PROPAGATION TIME>= TRANSMISSION TIME

Answer 2

Ethernet uses CSMA/CD and in CSMA/CD ,in worst case maximum time to reach the frame bit to other end is Tp and then Tp time is required to get back the collision signal to node again.So it takes one RTT and at that time node still should be sending the data,then only it can be sure that the collision signal it received,belonged to its frame.And it have to retransmit the packet again.

So Transmission Time >= 2* Propogation Time

In this case sender is sending the data until collision signal is reached back to sender,so it can be make sure whether its packet got involved in collision or not (including worst case too).

Comments

Thanks

I think it is used for acquire the channel by a single host in came/cd