ethernet , jam signal

Question

Consider two nodes A and B on the same Ethernet segment, and suppose the propagation delay between the two nodes is 300 bit times. Suppose at time both nodes A and B begin to transmit a frame. Assume both nodes transmit a 60 bit jam signal after detecting a collision. For 10^7 bits per set Ethernet, find the time at which both nodes A and B sense an idle channel? [in microseconds]( Marks: 0.00 )

1.   22.5 micro sec
2.   27.5 micro sec
3.   72.5 micro sec
4.   66 micro sec

Comments

Yeah answer should be 66 micro sec bcz 60 ms to detect the collision and 6 ms of PD of jam signal. So in total 66 ms.

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an you please explain your answer?

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i think it goes like that....

given 10^7 bits per second so 1 s=10^7 bits

distance between A and B is 300 bits => 300bits=300/10^7=>30 micro s and like that jam signal 6us

at t=0 both A and B send data

t=30us both realised collision happned

after realisation of collision both send jam signal

t=36us both both A nd B completed to send jam signal

at t=36+30=66us B's last bit reaches to A now the channel is totally free.

Answer 1

Given BW = 10⁷ bit/sec which means

1sec ------- 10⁷ bit

1bit --------- 10^-7 sec

It is given "the propagation delay between the two nodes is 300 bit times"

PD = Propogation delay

PD = 300 * 10^-7 sec

PD = 30 micro sec.

Now, Collision Occur between 0* PD to 1* PD

And, Collision Detected between 0*PD to 2*PD

Suppose in worst case stations detected collision in 2PD = 2*30 msec = 60 msec.

And after detecting the collision both stations send 60 bit jam signal, in terms of time it is equal to 60 * 10^-7 sec = 6 micro sec.

Total time = 60 micro sec + 6 micro sec = 66 micro sec.

And after all these both stations sense the channel is idle at 66 micro sec.

Comments

@ Shubhanshu 

why have we ignored the transmission delay for jamming signal??? please

Answer 2

This can be solution.

Comments

a and b two collision is occur then they send jamming signal to each other after that at what time a and b finish the transmission of packet ?