How is data transmitted?

[imported_goku]

I mean you need a minimum of about 4 wires for data to be transmitted, correct? (assuming 2 of the wires is powering the device) You have one wire for upload and one for download, now this can apply to practically anydevice. So I was wondering though, how does it *actually* get transmitted? This is assuming it's transmitting binary. Are pulses in the wire detected as 0s and 1s? Does it have to do with waves? How does this work?

 

[PsYcHoCoW]

various protocols work in different ways...

Some protocols (synchronous) use a clock line and a data line. Data is read on the falling or rising edge of the clock pulse.

Some other protocols (asynchronous) use just a data line. Beginning with a start code, the sender keeps outputting bits, and "keeps" each bit for a set time. The receiver can read the data line at regular intervals of time, knowing that a new data bit is out at these intervals of time. Bitrate can be determined by a handshake or a setting...



Hope this answers your question.

 

[BrownTown]

also, there is nothing saying you need 4 wires, 2 are sufficient in many cases. for example telephones only have 2 wires. You can always just embed a DC signal along with the information, that will allow you to transmit power and data over the same lines.

 

[insename2]

Originally posted by: BrownTown
also, there is nothing saying you need 4 wires, 2 are sufficient in many cases. for example telephones only have 2 wires. You can always just embed a DC signal along with the information, that will allow you to transmit power and data over the same lines.

doesn't coaxial only have 1?

 

[PottedMeat]

Originally posted by: insename2

Originally posted by: BrownTown
also, there is nothing saying you need 4 wires, 2 are sufficient in many cases. for example telephones only have 2 wires. You can always just embed a DC signal along with the information, that will allow you to transmit power and data over the same lines.

doesn't coaxial only have 1?

coax has 2 - the center conductor and the braid/shield

ex. satellite receivers communicate/power through a single coax line to the LNB on the dish

 

[BrownTown]

theoretically speaking you could probably just use one wire and a really high voltage and reference it to the earth ground. But then again you can jsut use no wires and too. Or use fiber optics, you only really need one cable there too.

 

[Born2bwire]

Originally posted by: BrownTown
theoretically speaking you could probably just use one wire and a really high voltage and reference it to the earth ground.

That's how they did telegraph.

And to head off any question about the coax, the data in coax and in many other high speed protocals (i.e. wifi, wimax) is modulated and phase shifted into the appropriate carrier signal. The bandwidth of the signal is split up into multiple carriers of smaller bandwidths. Wimax has something like 256 carriers and Wifi 64 carriers. Each carrier has a specific amplitude and phase at its frequency. Depending on how many unique amplitude and phase states that we say we can have, we can represent an entire bitstream in one pulse. For example, one type of modulation that Wimax can use is 64 QAM (quadrature amplitude modulation) which can represent 64 possible combinations of amplitude and phase and as such represent any 6 bits. But the exact technique we use is dependent on how strong the signal is. With poorer signal quality, the data is sent at a more robust, albeit one with less throughput, encoding.

So that's how they can transmit data at higher bitrates than the transmission line could support if you just used a square wave.

 

[Peter]

Hey look, I can do it with no wires at all *waves flag*

Data transmission can be done by transmission of waves, matter, or any combination thereof. The possibilities of either are infinite.

 

[interchange]

Originally posted by: Peter
Hey look, I can do it with no wires at all *waves flag*

Data transmission can be done by transmission of waves, matter, or any combination thereof. The possibilities of either are infinite.

Is light a wave or a particle?

There are various "1-wire" buses out there. Usually these are actually two-wires with the second being a ground reference. You wouldn't really want to design a system without a shared ground reference. It would be very lossy. Ideally, you'd have a differential signal with a twisted wire pair. Both wires would theoretically pick up the same interference at each point, so the difference between the two would cancel out the interefernce...all you need is a diff amp to have a very clean signal.