Communications

Question:  What goes " *squawk* Pieces of seven!  Pieces of seven!"
Answer: A parroty error

The above joke is an old nerds' joke, reproduced here just in case there's a new generation of nerds that hasn't heard it.

The communications between computers, and between computers and other devices are regulated by protocols.  These are an agreed set of messages to be exchanged between the communicating parties, and rules for their use, to ensure that the data is communicated correctly.   There are many kinds of errors that can occur in sending data down wires or over airwaves; the protocols are designed to make sure the data gets there intact.

In typing this blog post, there will be a communications protocol between my keyboard and the PC; between the PC and my router; between the router and the ISP; and so on through every point before it reaches the Goole servers that host it.

There are also other protocols, such as end-to-end protocols, an example of which is one where the Google server lets my PC know that the data has been correctly delivered to the far end.  There is a button labeled "Save" on my screen, and if I press it, once the post has been saved successfully at the other end, I get a little message telling me so.   If the save is unsuccessful, it tells me that too.  That's an end-to-end protocol doing its thing.

The design of protocols has improved a lot over the years, because of their widespread use (especially in the internet), and they don't often fail.  They used to.  Failed protocols cause communications lines to "hang", and the computers end up doing a hi-tech version of:

Computer A "what?"
Computer B "what?"
Computer A "what?"   endlessly.

But, however well-designed a communications protocol you have, and however reliable it is at getting your message across, there is very little that can be done, (outside of the "cloud"), about the "man with a spade" problem:  A guy puts his spade through your cable/fibre optic, and you're stuffed.

The phone line to our house is suspended on telegraph poles that march alongside the street, past a few houses and into the village about a kilometre away.   The next-door-but-one neighbour is a farmer and last Tuesday evening he drove his big, bright yellow JCB into his driveway, snagging the phone line as he went, breaking it.  Normal service was resumed today.

It seems that having discovered a thick wire slumped across the entry to his field, he thought it would come in handy to stop his cows escaping.