WiFi & Performance

Lindal Kidd has an article up titled Ay-yi-yi! WiFi! It is about getting better performance for Second Life. Most of the article is right on. I think she makes a couple of omissions and forgets a point. But, it is an article worthy of some time to read. I’ll try to add some perspective.

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What’s missing is something we geeks tend to gloss over, I suppose we assume most understand a rather esoteric point in our digital age. Bytes, bits, MB’s, and Mb’s… 

To explain, start with: all data is 0’s and 1’s. A single one or zero is a bit. We divide those bits into groups; bytes, words, double words, quad-words, and someday likely octo-words. All that means is we think of a byte as a group or collection of 8 bits, this: 00 00 00 00. A word is two bytes, this: 00 00 00 00 – 00 00 00 00. A double word has twice as many bits as a word and quad words carry this on with twice as many as a double. And logically that continues on.

These bits and words things are ways of THINKING about digital data. It helps us in our thinking but makes little if any difference to your computer.

However, we do need to represent that data in hardware and transmit that data. We build memory chips that are like collections of on-off switches to hold data. We build data-buses that are highways that carry the data to the memory chips, hard drives, video cards and their special video memory, the CPU, and network cards. All these things live on your computer’s motherboard. The motherboard has all the circuity that connects these things and at some level of thinking it is the motherboard’s physical circuitry that makes up the data-bus to move data between the components.

Trends in computer design change. At one time the idea was to move data bits in parallel. So, if we wanted to move a byte (8 bits) we designed 8 parallel circuits. When the computer’s clock ticked we sent a single down each circuit to set its respective memory switche. Now we design computer data-buses to have 64 circuits. The next step up would be 128. The problem becomes the physical space needed for all these circuits.

We have the room to use 64 circuits inside the computer. Once we leave the motherboard all those circuits are a problem. We can’t afford to have 64 Internet connections.

You may remember parallel printer ports and cables. The connectors for those had 50 pins, connection points. The connectors were big and the cables thick. We now use USB and WiFi to connect our printers. We can do this because we are not sending data in parallel, but instead sequentially. The ones and zeros go down a single tube one at a time and need only one circuit. This is serial processing.

You may remember the flat ribbon cables used to connect the hard disk. Again parallel data circuits were being used. Now we use small cables with few wires (circuits).

Customize Manufacturer Flexible Flat Ribbon FFC Cables for Computer


Customize Manufacturer Flexible Flat Ribbon (left) Serial/SATA (right)

What changed? Why go from parallel to serial? If we can move more data down a wire couldn’t we move twice much through 2 wires? Yes, sort of. But, wires/circuits are physical and each wire has a cost for the material to make it. There is also a physical space cost.

When we want to use wireless we have channels, like a circuit, to deal with. We learned how to move data faster in a single physical circuit to save money. We are learning how to move more data through the air where channels are limited and competition for them is fierce.

We have gotten most of the gains in data throughput by increasing the clock speed for data transmission. Each time the clock ticks we can send a bit of data, a one or zero. The change in technology is a better ability to build high frequency conductors and more precisely measure time to keep computers and various devices in sync. The more precise the faster we can go.

If my clocks are accurate to 1/3,000,000 of a second I can move 3,000,000 bits per second and have them all arrive on time and the receiver can get each bit to the right place based on time.

This is an over simplification, but should be good enough for generalities.

Now we are starting to see WiFi routers use multiple channels. The design cycle repeats. Often a channel is used for sending and another for receiving.

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