Tuesday, November 27, 2001

Packet switching vs. circuit switching (definition) Some readers tell me they don't know what the difference is between packet and circuit switched networks. Here's a quick overview.

Phones work on circuit switched networks. Like in those old black and white movies where the lady operator pulls those cords to complete a phone call, circuit switched networks establish temporary dedicated lines between sender and receiver. Both sender and receiver are guaranteed some level of quality, and the operator controls the service. The pipes are "smart" and can discriminate between calls (long distance, international, local etc.)

The Internet works on packet switched networks. A message is broken into packets, and each packet gets an address of where it should end up. Each packet then makes its way through any number of different nodes, each one sending it one step closer to its destination. Eventually, all the packets end up where they were supposed to be and are reassembled into the original message. Nothing is guaranteed, packets can get lost. The pipes are dumb, all they do is move the packet along, they don't know what's in it, and all packets are equal (this is the "end to end" principle).

Circuit switched networks allow the carrier to control how people use the network. Packet switched networks (currently) allow people to do whatever they want on the ends. Lots of stuff runs over the internet, including web pages, email, IM, streaming video, files etc.

Carriers (phone companies, cable companies etc.) hate packet switching because it does not allow them to control what people do they way circuit switching does. They are trying to come up with a way to make packet switching more like circuit switching, so they can control the network again and veto innovation at the ends.

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