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Learning by Doing: CISCO Certified Network ... - SCN Research

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only one port at a time. The hub allows port one “x” seconds to transmit (but it doesn’t<br />

send a notification to port 1 that it is their turn) then changes to port two if no information<br />

is transmitted. It allows port one to finish then changes to port two. It will allow port<br />

two “x” seconds to transmit and then it will change to port three if no information is<br />

transmitted. The process is repeated on port three, then four, then five and then to all the<br />

ports one at a time. But, as we have said, hubs are not intelligent. Once the hub finds<br />

information being transmitted over a port it does not go to the next port it starts back over<br />

at the first port. Therefore you want your more important devices on the first ports.<br />

In our diagram let’s look at an example for workstation “A” to send information<br />

to workstation “D.” The information from workstation “A” enters the hub on port 1. The<br />

hub then makes duplicate copies of that information and sends it to each port (active or<br />

not). In this case workstations “B,” “C,” and “D” will receive the copies. The<br />

to:00-00-00-00-00-04<br />

from: 00-00-00-00-00-01<br />

1 3 5 7<br />

Workstation Workstation Workstation Workstation<br />

“A” “B” “C” “D”<br />

mac: 00-00-00-00-00-01 00-00-00-00-00-04<br />

Figure 2—Workstation A sends a request to workstation D.<br />

to:00-00-00-00-00-04<br />

from: 00-00-00-00-00-01<br />

1 3 5 7<br />

Workstation Workstation Workstation Workstation<br />

“A” “B” “C” “D”<br />

mac: 00-00-00-00-00-01 00-00-00-00-00-04<br />

Figure 3—The information is duplicated and sent to every node attached to the hub.<br />

82

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