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.

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.

The diagram above shows how data is sent over the wire as single on pulse or off electrical pulses each one lasting 1 second.