Frequently Asked Questions

1.	Is network management the same as network control?
2.	Why the toaster?

Answers

1.

Gulliver's Travels can be interpreted at several levels: it is both a fascinating book for children and a biting political satire ("my principal Design was to Inform, and not to amuse thee," said Jonathan Swift). [5] Similarly there at least two levels of answer about the distinction between management and control of devices or networks. First there is a clear distinction: Management is carried out by an operator sitting at a management station. He or she enters commands to reconfigure equipment and those commands are carried out. Control, by contrast, is carried out autonomously by the network, without operator intervention in response to some external stimulus. For example, a link fails and the network automatically reconfigures equipment to route around it. I pick up my telephone and dial a number in Vancouver. The network detects this without operator intervention and reconfigures equipment to route my call. There is, however, a deeper level at which these operations are similar, if not identical. Both can be thought of as a stimulus (which could be an operator command) causing changes to the device.

2.

There is a classical joke comparing "real" engineers with object-oriented computer architects with which you are probably familiar. In case you are not, with acknowledgements to the anonymous author, here goes. Once upon a time a king decided to test his two chief advisors. He showed them a toaster and asked them to design an embedded computer for it. The first advisor, an engineer, replied, "Using a four-bit microcontroller, I would write a program that reads the darkness knob and quantises its position from snow white to coal black. The program would use that level as the index to a table of timer values. It would turn on the heating elements and start the timer with the initial value selected from the table. At the end of the time delay, it would turn off the heat and pop up the toast . Come back next week, and I'll show you a working prototype." The second advisor, a computer specialist with object-oriented design training, immediately recognised the danger of such short-sighted thinking. He said, "Toasters don't just turn bread into toast; they are also used to warm frozen waffles . What you see before you is really a breakfast food cooker. As your subjects become more sophisticated, they will demand more functionality. They will need a breakfast food cooker that can also cook sausages, fry bacon, and scramble eggs. A toaster that only makes toast will soon be obsolete. If we don't look to the future, we will have to redesign the toaster completely in just a few years . "With this in mind, let's formulate a more intelligent solution to the problem. First, create a class of breakfast foods . Specialise this class into subclasses: grains, pork, and poultry. The specialisation process should be repeated with grains divided into toast, muffins, pancakes and waffles; pork divided into sausage and bacon; and poultry divided into scrambled eggs, hard-boiled eggs, poached eggs, fried eggs and various omelette classes. "The ham and cheese omelette class is worth special attention because it must inherit characteristics from the pork, dairy , and poultry classes. Thus, we see that the problem cannot be properly solved without multiple inheritance. At run time, the program must create the proper object and send a message to it that says, 'Cook yourself.' The semantics of this message depend, of course, on the kind of object, so they have a different meaning to a piece of toast than to scrambled eggs. "Reviewing the process so far, we see that the analysis phase has revealed that the primary requirement is to cook any kind of breakfast food. In the design phase, we have discovered some derived requirements. Specifically, we need an object-oriented language with multiple inheritance. Of course, users don't want the eggs to get cold while the bacon is frying, so concurrent processing is required, too. "Don't forget the user interface. The lever that lowers the food lacks versatility, and the darkness knob is confusing. Users won't buy the product unless it has a user -friendly graphical interface. When the breakfast cooker is plugged in, users should see the company logo appear on the screen, and when they click on it, the message 'Booting Linux 2.8' appears (Linux 2.8 should be available by the time the product gets to the market). Users can use a menu to select the foods they want to cook. "Having made the wise decision of specifying the software first in the design phase, all that remains is to pick an adequate hardware platform for the implementation phase. A 1.2-GHz processor with 128 MB of memory, a 30-GB hard disk and a colour VGA monitor should be sufficient. If you select a multitasking, object-oriented language that supports multiple inheritance and has a built-in GUI, writing the program will be a snap. (Imagine the difficulty we would have had if we had foolishly allowed a hardware-first design strategy to lock us into a four-bit microcontroller!)" The king had the computer specialist beheaded, and they all lived happily ever after. I hope that, as you travel through this book, savouring its object-oriented flavour, you will keep your head.

^[5] It is also the source of the Endianness problems which have plagued computing, but that piece of programming trivia is irrelevant here.