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Part 3: CCNA Training: What is a Network

Posted: October 21st, 2016

HOW DEVICES COMMUNICATE

When I first started in networking the one thing that I could not get my head around was how does one machine communicate with another?, I understood that P.C’s used binary to communicate but what I could not visualise was how a parcel of data was sent from one interface to another in my mind I used to picture a precession of packets on the wire in line one after the other like in the diagram below.

figure-7

Of course I soon realised that this was not possible, we are talking about a single pair of wires to transmit and receive. The wire can only be in a single state at any one time, like a light bulb can be either off or on, but not both on and off together. On = 1, Off = 0.

It then dawned on me that just like Morse code the wire is carrying a single signal at any one time. Therefore the wire is either on or off, the transmitting interface just like a Morse code operator is “tapping” out the signal one bit at a time, albeit very quickly to achieve the high rates of data throughput we have come to expect.
figure-8
The diagram above shows how data is sent over the wire as single on pulse or off electrical pulses each one lasting 1 second.