Answer / shahin

CSMA/CD (Carrier Sense Multiple Access/Collision
Detection)is media-access mechanism is what keeps networks
running.

If two or more computers transmit data at the same time, we
get data collision. And thus, no data is sent or received.

We have CSMA/CD for both preventing and controlling collisions.

Suppose 4 system connected as on bus topology or connected
on a Hub.

As we know, in Hub one collision domain & one broadcast
domain. More simply, Hub port just copied data wat it
received & paste it on the rest of the port apart from dat
port from where hub received this data.

So how its detects collision...

Before sending any data, Ethernet NIC first test the voltage
of the line. If its normal, i mean voltage level on line its
start sending data. (Specific voltage level value i didn't
remember).

If two NIC test this voltage level at the same time & they
found its normal for start sending data. When they send
data, data will collide somewhere in the line. Hence data
lose occur & delay in communication.

When NIC detects collision, they wait for random period of
time. (Time i didn't remember). After certain time period
they test the line again & if they found normal. they will
start sending data.

Note: CSMA/CD is not used on Full Duplex Ethernet networks.


3rd Question:

As far my knowledge, there is no such specific command for
this. But we can make any full duplex line in to half duplex
also.

Router(config)#interface fastethernet 0/0
Router(config-if)#duplex ?
auto Enable AUTO duplex configuration
full Force full duplex operation
half Force half-duplex operation



Buddy, i can say this much about it. Hope it may help u
little bit..!!!

Thankx for nice question.

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