So here I am typing on a mobile handheld more powerful then my first computer 20 years ago and thinking. “We sure do take advantage of our technology and how many actually stop to understand how it works?” Again I’ll be generalizing but if you need more leave a comment for further topics.

Really as I press a key it connects a switch that sends off an electrical signal to tiny piece of sand. Ok its a very sophisticated silicon chip but in essence that alone is prolly deeper then some have gone. I know my mother would never get that far.

The processor then does some magic in storing the keystroke in a buffer and echos the typed character out to the screen. Did I forget to mention the character isn’t actually stored as we see it? The switch is an electric signal of on and off the computer sees as zeros and ones. This set of numbers represents the character from the ascii table my computers happens to have set as its code page. This gets really deep if you dig into unicode but in not going there today.

Instead I was thinking of texting on mobiles and the message magically appears on a friends mobile. This process is just as forgotten as the unicode table is for my mother.

So what happens when I hit send? Well really the whole thing started off when you turned your phone on. The first thing the radio does is send a signal out on all the bands it knows of. The phone announces “Here I am!” And hopefully a cell tower picks it up and passes the message to a base station.

The station then says “I hears you and these are all the cell towers around you. Send me your info”
The cell sends its identification and this is verified thru the network with the carrier that you get the bill from.

Now let’s actually send a sentence of data. If its short it will actually fit in one data packet. The packet is an envelop with the address of the destination and source. It has error checking added in and away it goes.

Now for longer stuff like this post it will be broken up into many many packets and each one will be enumerated (given a number). They race through the network and do not have to follow the same path. One packer goes from cell tower 1 to base station 1 to switch 1 to data line 1 to router 1 to any number of routers to a destination. There are almost endless paths and we could add in microwave towers, optical switches, satellites and all kinds of crazy stuff.

Since we are transmitting through the air a lot can happen. We can bounce signal’s off walls, off clouds, cars, trains, airplanes and even dust. Packets get corrupted on the way and the computers need to know how to reassemble the information. That’s where the enumeration and error checking comes in. It is best I’d the error can be corrected and you’d be surprised at some of the routines that can be used to do this. Usually the destination will ask to retransmit at least one packet and that one piece gets sent

Other radio signals also get in the way. We actually share the same bandwidth with tens of thousands of people every second. The carrier will set up several channels in the band and they are time division up to send and receive at certain intervals. At any time you could be switching channels slowing down or speeding up your signal to be synchronized in the air.

Now since we are mobile add in the complexity of moving between cell towers and adding different paths. Doppler effects and general relativity adjustments for satellite communications it is a wonder anything gets communicated at all.