Tuesday, March 29, 2016

WiFi and Basic Needs

This illustration says it all.

It might be stretching things a bit, but it does indicate how staying connected seems to have becomesome sort of a desperate, visceral need. We now choose hotels and eateries based on their ability to provide reliable bandwidth as much as the quality of accomodation or food. There is now a joke going around that, even at home, the best way to have a family get-together is to switch off the wireless router!

In an earlier post, I had figured that all WiFi devices talk to each other in the 2.4 GHz frequency, and that as per international protocols this band is divided into 79 channels (each 1 MHz wide) which the devices can change up to 1600 times per second, just to keep a data connection going.

I still have no idea how the scientists managed to create anything that sends out 1,000,000,000 vibrations per second, let alone how they go about slicing it like a cake and passing it around with all the icing and toppings intact.

Perhaps it is easier to understand things that are happening at an individual device level. Here are two parameters from my WiFi analyser:

The first screenshot shows that the signal strength ranges from -100 dBm (decibel milliwatts) to -40 dBm. The key unit here is that of power - Watts. It takes a thousandth (1/1000) of a Watt to send out signal equal to 0 dB.

The negative sign comes from the log scale. To quote WirelessAnnonymous:
Under a log 10 scale, a value of -2 represents 10 to the -2 power, which equals 0.01. Likewise, a negative dBm means that you're applying a negative exponent in your power calculations; 0 dBm equals 1 mW of power, so -10 dBm equates to 0.1 mW, -20 dBm equates to 0.01 mW, and so forth. It's a lot easier, and more useful in some calculations, to describe a weak signal as -100 dBm as opposed to 0.0000000001 mW.
The following shot illustrates how the signal strengh drops the further you move away from a router. The closest ones are sending out signals stronger than -50dBm while the farthest ones have the green bands diminishing into the -90 dBm range.

Then you have the next most important thing: the media access control (MAC) address.

When you have millions of data signals riding piggypack on radio waves, it is necessary to ensure that they reach the right destinations. For this, each WiFi device comes with a unique MAC address and they all use the address resolution protocol (ARP) to avoid cross-talk. If we compare the whole set up to city traffic, MAC represents the final destinations (a mall, home or fuel station). Vehicles (data packets) traveling along the roads (the internet protocol/IP) are capable of reaching anywhere but get an entry only to those places which have a matching MAC address.

This brings us to the next basic need - how do we stay safe from the carjackers, and hackers hiding in the dark streets?


* Reading signal strength -- http://www.tomshardware.com/forum/9782-43-read-signal-strength
* How to Geek - MAC Address - http://www.howtogeek.com/169540/what-exactly-is-a-mac-address-used-for/
* Ask Leo: IP address vs. MAC address -- https://askleo.com/whats_the_difference_between_a_mac_address_and_an_ip_address/

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