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logical bus topology

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by nt259

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shared bus, 10Mbps
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A B C D
10Mbps 10Mbps 10Mbps 10Mbps

A logical bus topology with station B transmitting a frame to station D.

1) Data is framed by the data link layer & handed over to the NIC at the physical layer. Assuming it's OK for the station to transmit, what is the job of the NIC when it's transmitting >

2) How does a signal travel in a logical bus topology ?

3) All stations constantly "listen" for a signal. This is called "Carrier Sensing" What is a NIC supposed to do when it senses a signal on the wire? Differentiate the actions taken by Station D & station A & C.

4) Let's say that station C has something to transmit simultaneously with station B but B has already begun transmitting. The first step for sharing the medium is for a station to "listen". What is purpose of listening first? When you listen and somebody else is transmitting, what do you do ?

5) Let's say that both B & C had listened and nobody was transmitting and had simultaneously begun to transmit. What is this condition called ? How is it resolved? Why wouldn't this problem ever happen on a Token Ring network? How does Ehternet switching avoid this problem ?

2 replies

by cg it

lol what your asking questions from the CCNA exam?
over view of questions 1 though 4
ethernet has to wait intil the wire is free which is why the approximate bandwidth utilization is about 37% to 40% of total bandwidth whereas with token ring, machines on the LAN pass a token around and whoever has it can transmit. Effective utilization hovers around 75% of total bandwidth.

for question # 5 collisions occur if 2 machines on the same LAN transmit at the same time of which both stop, drop the packet[s] it was going to send, wait for random period of time and then start the whole listening/transmiting dance again.

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