When Rebooting is Not an Option
Larry Rudolph is sitting in the back seat of a cab on his way to Carnegie Mellon University in Pittsburgh when the driver suddenly stops the vehicle and says: “Excuse me, I need to reboot my taxi.” The driver shuts off the car, counts until ten, and then turns it back on. The digital speedometer, which had been reading zero despite the car’s movement, is now working again. Rudolph says it was the first time he saw someone reboot a car. It was strange-but it worked.
Rebooting has become routine for many computer users. They know that when their PCs crash or a piece of software doesn’t work, the technical support person’s first question is usually, “Have you tried rebooting your system?” Indeed, restarting a machine-be it a car or a computer-can many times fix the problem. But according to Rudolph, a principal researcher at MIT’s Computer Science and Artificial Intelligence Laboratory, we are moving toward a day when all sorts of electronic equipment-computers, PDAs, cell phones, TV sets, MP3 players, perhaps even the kitchen’s microwave-will be exchanging data and trying to make our lives easier and more comfortable. And in this emerging technoscape of pervasive computing, the “turn off, turn on” solution will be of no help.
In this world of autonomous interacting machines, Rudolph says it is easy to envision a nightmare scenario in which a small failure starts a chain reaction, the result being a whole menagerie of devices ringing and beeping and generally misbehaving. With so many elements talking to each other-and no central server to control them-it will be hopeless to find which is the malfunctioning one when a major failure breaks out. Rudolph says humans are relatively good at tracking down errors. The problem is that today’s equipment doesn’t give us any clue of where the problem might be. But this situation would change completely if electronic devices began to carry special systems capable of detecting anomalous behavior-and pointing out this information to the user.
Rudolph is leading a team of researchers to create such failure-detecting systems and test them in a pervasive computing environment. The work is part of project Oxygen, a five-year, multimillion-dollar partnership between the lab and six major corporations. Since the components of Oxygen are being built from scratch, now is the time to think about methods to overcome systemic failures Rudolph says. He spoke with Technology Review editorial intern Erico Guizzo.
TR: Why is rebooting becoming less practical?
RUDOLPH: The classic answer when something goes wrong is to reset or reboot and start it again. This solution has worked so far. But very soon it’s not going to work for, say, devices in our houses. It won’t be clear what to reboot. The vision of Oxygen is that there’s no PC that is the center, there’s no central server to which everything is connected. In a house, the main computer may be in the study, while all the other devices may be in the living room, the dining room, and the kitchen. Everything is spread around and soon they will start talking to each other. There will be times when you touch something in one room and it adversely affects something in another room.
TR: And then the on-off switch is of no help?
RUDOLPH: That’s right. Imagine that a battery runs low, causing some unusual behavior, which, through a series of unexpected events causes some other part of the system to fail-the telephone doesn’t stop ringing, for example. But since the system is no longer in one place, how do we find the root cause? Or, if we don’t care about the cause, how does one stop the telephone from ringing? We can reboot the telephone, but if that doesn’t solve the problem, then what? Also, future robust computer systems will likely be “fault tolerant” so that if one computer fails, the computation will automatically continue on some other computer. In that case, shutting down the main computer may not stop the phone from ringing. Should you reboot the living room? Or maybe the house? And if that doesn’t work, should you try rebooting the whole neighborhood?
TR: What is the solution?
RUDOLPH: Before pervasive computing, I had been working on parallel processing, where it is well known that the debugging is a nightmare. In a parallel computing system you have to handle ten, twenty, a hundred, a thousand, ten thousand processors. But those processors are all the same. In pervasive computing, on the other hand, we’re talking about lots and lots of pieces that are all different-different technologies, different generations, different software. How do I debug that? IBM has been pushing something they call autonomic computing-techniques to do self-reflection, self-healing, and other things with beautiful names. The computer automatically finds what’s wrong and fixes it. I think we’re really far from that. But the one thing we do know is that when something was working and it suddenly stopped working, it’s because something has changed. So our systems should at least give the human a chance to find out the problem. It is easier to tell what has recently changed than to decide if that change is right or wrong.
TR: Can you make a machine send the user a message saying it’s going to fail?
RUDOLPH: Things change all the time and mostly it is normal behavior. We are trying to develop systems that can figure out typical patterns of behavior for individual system components and communication links. These systems can learn the common patterns in communication connections, and the typical patterns of input and output values of certain processes.
TR: Can you give an example of this?
RUDOLPH: Suppose my computer music system starts having annoying pauses. It might be due to a network congestion problem because I started up a Web browser. Or, if I’m listening to a CD, it might be due to a scratch on the disc. In the first case, the system will notice a change in the communication rates, whereas in the second case it might notice a change in the values of the audio stream itself. So in the first case-starting up a browser-the system may recognize that this is typical behavior and the user should just wait for the connection to get better. But if the cause is a scratch, then the user should be told to examine the disc and the CD player. The user has a hope-sometimes a very slim hope-to know where to look for the problem.
TR: Does the fact that devices are going wireless makes things more difficult?
RUDOLPH: Yes. Imagine a television set that can answer my telephone. I’m watching TV and the telephone rings. I answer the call using the TV, which activates my TiVo digital video recorder. Suppose that suddenly the TV starts ringing without stop, and I want to disconnect the telephone from the TV. How do I do that? If I’m lucky, there’s a plug on the telephone outlet in the wall going into the TV. So I could just disconnect that plug. Very soon, though, we’re not going to have wires anymore. The communication will all be wireless-802.11, Bluetooth, whatever. I might have to stand in front of an annoying, ringing TV fumbling with buttons trying to disconnect the telephone.
TR: Why didn’t engineers think about failure-detecting systems before?
RUDOLPH: Before the Internet, people built systems that were very well engineered-the telephone network, for example. AT&T understood its behavior-and owned the whole system. Then things like the Internet came around. Now no one owns the whole thing-it’s too big, it’s too distributed. We are no longer able to engineer the whole world. We can’t rebuild the Internet. What’s great about the Oxygen experience is that we’re building new systems, so we can try to do something right from the start without the pressure on having to follow release dates. Universities have time to do something right.
TR: That’s why MIT is doing this kind of development work, instead of the companies that will sell the products?
RUDOLPH: That’s right. Academia has an important role here in that we are helping to figure out how to build systems defensively. Nokia is a partner of Oxygen. Nokia cares a lot about security and privacy. But how much is Nokia willing to spend on research on security and privacy when it knows that teenage girls dominate the cell phone market, and they are not worried about privacy and security; they care about color and style and games and other features. So if Nokia is going to spend a lot of research money on security and privacy and some other company spends their research money on the finicky tastes of teenagers, Nokia is going to lose market share. On the other hand, if MIT, Stanford, Boston University, or any university can develop a solid system with security and privacy and make it public, it would be much easier for Nokia to incorporate that technology.
TR: What have you done so far?
RUDOLPH: We’re just starting. We talked about the example of a telephone talking to a TV. But how grandma can use this system? When there’s no wire, how does grandma know that the phone is talking to the computer? And how does she stop it? Does she find the IP address of the telephone and delete it? No, she’s not going to do that. One possible solution: you hold up a handheld device with a camera and have it view the room. Whenever it sees devices it can figure out what they are, so it knows, for instance, that it is pointing at a TV, or a telephone. Then it consults a database and concludes, “that telephone is talking to that TV.” So now we can give feedback to grandma, probably visually. You can use the image of the room and overlay a blue line connecting the telephone and the TV. And then touching the screen you can choose to break that connection.
TR: How do you plan to simulate failures in the systems you are developing?
RUDOLPH: We don’t have to. They just happen!
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