Monday, May 06, 2013

The Internet -- super fast, but simple; the brain, slower, but complex

Round trip packet time
Which is greater -- the round trip travel time for a data packet sent over the Internet from my home in Los Angeles, California to La Universidad de Magallanes (UM) in Punta Arenas, Chile or the time is takes me to see, recognize and pick up a pen?

This sounds suspiciously like one of those counter-intuitive questions a professor might ask to get a classes' attention, so let me end the suspense. It turns out that both take around the same time, 1/4 second. Let’s see how I reached that conclusion, starting with seeing and picking up a pen.

For that time estimate, we turn to brain science. Luckily, my favorite science podcast, Radiolab, recently broadcast a program on speed, which included a two-minute segment on the communication steps involved in seeing and picking up a pen. Stop and listen to the excerpt -- it enumerates the time spent traversing communication links between your eye and brain, between different regions within your brain, and finally to the top of your brain where the commands to pick up the pen are issued. The entire sequence takes about 1/4 second.

Seeing a pen and picking it up
That is not a great surprise -- picking up a pen seems really fast and automatic. But, what about the round trip time for a packet routed from my home in West Los Angeles to UM? I measured that time using Ping, a simple utility program that sends a packet to a remote host and measures the time it takes for it to get there and an acknowledgement to come back.

As shown here, Ping sent four packets to Punta Arenas. The fastest round trip was 233 milliseconds, the slowest 282 and the average of the four was 259 milliseconds -- just over 1/4 second.
I checked the question answering server at Wolframalpha and learned that the great-circle distance from Los Angeles to Punta Arenas is 6,644 miles. That says our average data packet traveled around 53,000 miles per second -- 28 percent of the speed of light!

Listening to the Radiolab clip, I counted ten communication hops in picking up the pen -- the first from the eye to the middle of the brain, the second from the middle to the back and so forth. Those hops are between clusters of neurons and the information travels along axons.

In the Internet, data packets hop from one router to the next. Routers are special-purpose computers that are programmed to forward packets from one network to another and they communicate either wirelessly or over some sort of cable. In the case of my test, the first hop was wireless -- from my laptop to my home WiFi access point. The second hop was from my home network to my Internet service provider's network over a copper cable. From there the links were all over fiber optic cables, some buried under ground, others under the sea, until they reached the destination computer at UM. The acknowledgement packets traversed a similar path in the opposite direction. Using a program called Traceroute, I counted hops through 18 routers between my house and UM.

Since the distances inside the brain are small, it seems that complex, time consuming processing is taking place in the neurons at each location and the signals between them travel relatively slowly. Contrast that with the Internet, where the communication links are fast, but the processing by each router is simple. It takes a router very little time to forward a packet to the next router along the path to Punta Arenas.
I don't know about you, but I find the speed of the Internet mind blowing but understandable and the complex processing needed to pick up that pen awe inspiring. One day, brain science will reduce both to just being mind blowing.

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