Telecommunication in ancient Greece

The Greek historian Polybius (c. 200 – c. 118 BC) documented two methods for communication at a distance -- telecommunication.

The first was an analog hydraulic system. The terminals consisted of identical vessels filled with water. The sender signaled the receiver with a torch when he was ready to transmit and they both let water out of their vessels until the end of transmission torch was raised. If the amount of water drained from both vessels was the same, the height of the water in the receiver designated the message.

This method was imprecise and could only transmit one of a number of pre-defined messages. The second, digital method could transmit any written message. It used a 5-bit representation of characters to send messages using torches. Messages were transmitted one character at a time by raising torches in two of five positions.

The operators had identical tablets showing the letters and the torch positions (1-5) designated the column and row of the letter being sent. If this tablet were used:

the message 22, 51, 13, 13, 45 would spell out ΗΕΛΛΩ.

Note that messages could be encrypted by changing the tablets.

(If you find this interesting, check out Claude Chappe's French telecommunication system).

iPad WiFi is poor

My wife just got an iPad – the first tablet in our house.  It was not easy to get it away from her, but last night I managed to take the iPad to bed.  I was expecting an insanely great experience, but my first impression was that network access was slow and flaky.

To test my impression, I compared it to a Dell Precision laptop.  First, I pinged UCLA, a nearby university, 100 times using both the laptop and the iPad.  The average ping time for iPad was 63.7 milliseconds, over twice that of the Dell, and the standard deviation four times as great.  No wonder it seemed flaky.

	Dell	iPad
Minimum	18	22.7
Maximum	120	231.9
Mean	30.2	63.7
Standard deviation	14.9	64.8

Next I tested file transfer times (Mb/s), and the laptop was faster:

	Dell	iPad
Upload	6.29	1.77
Download	1.83	.17

That was no surprise given the variability in ping times. It doesn't look like I'll be making a lot of Skype calls or watching movies in bed.

My bedroom is at the back of the house, so I checked the signal strength. As shown below, it dropped to around -65 db as I walked from the office, where the WiFi access point is located, to the bedroom.



The laptop is not perfect in the bedroom -- it does better when it is near the access point, but its radio is clearly more sensitive than that of the iPad. iPad Wifi is more like that of a netbook than a laptop.

Notes:
I measured iPad ping time using Typhuun System Scope Lite, the transfer rate using Speedtest.net and the signal strength with Metageek Inssider.

A reader pointed out that the results were affected by my pinging UCLA, which introduced Internet and server variability into the test. I repeated the test, pinging a machine within my house and found the following:

Dell: minimum 1, maximum 90, mean 5.96, standard deviation 12.6 with zero dropped packets (1 sec timeout)
iPad: minimum 5.04, maximum 202.02, mean 18.56, standard deviation 32.49 with 8 dropped packets (1 sec timeout)

Not surprisingly, the iPad remains relatively poor.

Intel Light Peak -- goodbye USB?

We have seen many examples of early prototypes of devices that eventually became main stream. Intel hopes to replace your USB cable with an optical link they are calling "Light Peak."

Here you see a demonstration of a laptop streaming two simultaneous HDTV programs to a television set. The black box between the laptop and display will eventually disappear, leaving a USB replacement.

Today's USB 2.0 connections have a speed of 480 Mbps, while Light Peak connections will begin at 10 Gbps in both directions. With mass production and engineering refinement, speeds would increase well beyond that. This is a common pattern -- one technology approaches its limit, and is then leapfrogged by a new technology.

This also seems to happening as electronic flash storage replaces rotating magnetic disk drives. Many portable devices already use electronic storage, and flash is beginning to be used in laptops and servers. (I've ordered my next laptop with flash storage).

If Light Peak succeeds (and it may not), it will dramatically alter the speed relationships between input/output and storage devices and memory, resulting in significant system redesign.

Can you think of other instances in which a new information technology has replaced an older one? What did we use for storage before hard drives?

164 terabit per second communication

We discuss exponential improvements in electronic, storage and communication technology and backbone networks.

The first NSFNet backbone links had a speed of 64 kilobits per second. Today, links with speeds of 10 gigabits per second are common. That is considerable improvement, but researchers have recently achieved 164 terabits per second over a distance of 2,500 kilometers, an indication that we will one day see much faster backbone links.

The researchers reported using "164 wavelength-division multiplexed channels modulated at 100 Gbps in the effort." In plain English, what is that saying?

How many times faster is 164 terabits per second than 10 gigabits per second? How many times faster is 10 gigabits per second than 64 kilobits per second?

Undersea cables

We discuss backbone connectivity, including udersea cables. The first undersea cable carried telegraph traffic between New York and London in 1858.



Today, undersea cables have a combined capacity of over 7 terabits per second, as shown in this map:



The map also shows the site of a recent cable cut off the Egyptian coast. The cut was attributed to a ship dragging its anchor, and repairs are underway, but some wonder if it may have been cut intentionally.

Undersea cables are high-capacity components of a rapidly growing global nervous system. (You might think of the connected people and computers as being like neurons). You can read the story of the construction of the FLAG cable in an epic article from Wired Magazine entitled Mother Earth Mother Board.

You can get an idea of the history and importance of undersea cables in Arthur C. Clarke's "How the World was One" or check this Web site on the history of Atlantic and other cables.

Satellite links also carry intercontinental traffic -- how does their speed, capacity, latency, and ease of deployment compare with undersea cables?