a switch is a switch is a switch

Switching and the corresponding devices are most fundamental for today’s networking. Switches are those little boxes at home (or not so little boxes in the data centers), where You plug Your network cables in and out. Yes, earlier on there were other things called HUBs, Bridges, Token-Rings, but they are all are past and forgotten like the Neanderthals. The switches however have remained and still play an important role in nearly every network.

The reason for this success is, that the switches do separate and structure networks in a very effective way. They are stupid enough to be fast and have enough intelligence to know, who is located where. If You plug in the cable coming from your brand-new IP-TV into the switch, your switch will learn the unique name of the new device nearly immediately. From now on the switch knows the name of the device connected via that cable and port. This enables it to send addressed data packets directly to the correct recipient rather than broadcasting them into all directions.

Today’s switches, especially the ones used in professional environments, can do much more and much more sophisticated things. But the basic principle for the success is still the same. Communication needs clear and unique addresses and the switch is the unit on the lowest level distributing the „mail“ very quickly and in a reliable way just like a good old postman does. He knows all the names and addresses and puts the letters into the correct mailbox (though I have to admit that this capability has been lost to some extent, since the post service has been privatized, at least in Germany).

There is one fundamental problem with switches, when networks are growing larger. Once you have more than one switch and more than one link between them, there may be more than one way to the same destination. This is a serious problem, because every switch has to communicate the addresses, which it knows, to all the other switches, so that the messages can find their way to the correct destination. This may result in a scenario, where packets could move in a circle. This is bad enough, if it happens with real-life post items like letter, postcards and packets. But it’s even worse with electronic packets, because they are not material but copied at each instance. So packets running in a circle will be copied and multiplied again and again, until an electronic storm arises and makes the network crash. Not a theoretical problem, this really happens sometimes, even today, when some ultra-modern device forgets the basics.

This phenomenon is the reason, why the internet does not so much have a father, but rather a mother. The first practically working solution to the problem was invented by a woman: Radia Perlman. Her Spanning-Tree-Protocol (STP) is at the heart of nearly every modern network and one of the main preconditions for building world-wide communication structures like the internet. Read her story and be amazed, how fascinating technical history and the process of innovation can be.  I find one sentence from her most remarkable for every engineer (but not only for engineers): „I invented the technology just by being very clearheaded and really understanding things.“ Indeed, that’s what it takes.

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