May 17, 2014 ~ Network Services

Saturday, May 17, 2014

Current Configuration and Baselines

By Unknown11:48 PMNetwork + Chapter 6No comments

Current Configuration and Baselines Of particular value when you are upgrading a network or installing new hardware or software are the server and client configuration documents. If these have been properly maintained, they include information about the current hardware configuration (including I/O address, IRQ, DMA, and memory address),...

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Error Messages and Log Files

By Unknown11:46 PMNetwork + Chapter 6No comments

Error Messages and Log Files A careful perusal of error messages and log files can give you a good sense of the health of a network. This is important because you may not want to add a new network device to a network that is experiencing problems. Log files record every...

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Environmental Issues

By Unknown11:41 PMNetwork + Chapter 6No comments

Environmental Issues Environmental conditions, as they relate to installing or upgrading a network and its components, are important. Just like human beings, computers require a proper environment in order to function correctly. If the environment is harsh, the device...

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Environmental Issues
Environmental conditions, as they relate to installing or upgrading a network and its components, are important. Just like human beings, computers require a proper environment in order to function correctly. If the environment is harsh, the device will not function at peak efficiency. Surprisingly, environmental conditions and their consequences may be the most overlooked topic in the entire industry of networking. Often problems that seem to appear out of nowhere and appear to make no sense are caused by environmental conditions. Let’s examine the frequently elusive challenges that we all face at one time or another:

Power problems
ESD problems
EMI problems
RFI problems
Climate problems

Power Problems

Alternating current (AC), which is “food” to PCs and other network devices, is normally 110 volts and changes polarity 60 times a second (or 60 Hertz). These values are referred to as line

voltage. Any deviation from these values can create problems for a PC or other network device. Power problems fall into three categories:

Overage
Underage
Quality

Power Overage Problems

During a power overage, too much power is coming into the computer. Power overage can take two forms:

A power spike occurs when the power level rises above normal levels and then drops back to normal in less than one second.
A power surge occurs when the power level rises above normal levels and stays there for

more than one or two seconds.

FIGURE 6 . 1 Comparing a power spike and a power surge

Typically, power surges last longer than a second or two, and they may last for several minutes.

For this reason, surges are usually more damaging than spikes (although a very large spike can damage a computer’s power supply just as much as a surge). Figure 6.1 shows the difference

between a spike and a surge. Two types of devices are used to protect computers and other network devices from power

overage problems:

Surge protectors
Line conditioners

A surge protector contains a special electronic circuit that monitors the incoming voltage level and trips a circuit breaker when the overvoltage reaches a certain level (called the overvoltage threshold). The problem with surge protectors is that the threshold is set too high to be safe. By the time the circuit breaker trips, some overvoltage has gotten to the power supply of the computer, possibly damaging it. Nor does a surge protector protect against power surges and spikes that are lower than the threshold. For the most part, a surge protector is better than nothing, but not by much. It is really only a multiple-outlet strip and should not be considered

anything more.

TIP:

Surge protectors with a very low overvoltage threshold cost upward of $50. They sacrifice themselves in the event of any significant overvoltage but are smart enough not to trip for just a small amount over the standard power levels. Additionally, most of these protectors contain electronic circuits that can “shave off” any overvoltage and ensure that the powered devices receive only

the voltage they need.

Line conditioners are a much better choice for protecting against surges and spikes. Line conditioners use several electronic methods to “clean” all power coming into them. The best models

can be prohibitively expensive, but there is a way to get a kind of “natural” line conditioner. An Uninterruptible Power Supply (UPS) uses a battery and power inverter to run the computer

equipment that plugs into it. A battery charger continuously charges the battery. The battery charger is the only thing that runs off line voltage. The computer itself runs off steady voltage

supplied by the UPS. When power problems occur, the battery charger stops operating and the equipment continues to run off the battery. The power coming from the UPS is always a continuous

110 volts, 60 Hertz. Because the AC power from the wall never crosses over the battery charger to run the computer components, it’s considered a “natural” line conditioner. As you

will see, the UPS is the solution for a number of power problems.

Power Underage Problems

Power underages occur when power levels drop below the standard, and they are almost as common as power overages. There are three types of power underages:

A sag is an inverted spike. Sags occur when power levels drop below normal and rise back to normal within a brief period of time (usually less than one second). It is doubtful that you would be aware of sags (you might see a light flicker off and then on), although your computer might reboot.
A brownout, on the other hand, occurs when power drops below normal levels for several seconds or longer. In other words, a brownout is an inverted surge. The lights in the room will dim for a short period of time and then come back to full brightness.

A blackout is a total loss of power for several seconds, several minutes, or several hours.

Any one of these problems will cause your computers and other network devices to malfunction. Figure 6.2 contrasts these power problems.

To ward off power underage problems, you need only one device: a UPS, which allows network devices to continue to function even in the complete absence of power. Some are intelligent and can shut down your computer in the case of a blackout.

FIGURE 6 . 2 Comparing power underage problems

Power Quality Problems

Power quality problems generally indicate that stray frequencies have entered the power supply through the power cord. Stray frequencies can cause strange problems (such as intermittent

reboots or hangs) and can damage a device’s power supply. You can detect problems in power quality only with an oscilloscope. If you’re having power quality problems, you need either a

UPS or a line conditioner.

Electrostatic Discharge (ESD) Problems

ESD occurs when two items with dissimilar static electrical charges are brought together. Nature doesn’t like things to be unequal, so static electrical charges will “jump” from the item with more electrons. This jump is seen as an electrical spark and thus is called an electrostatic discharge. ESD can damage electronic components because the several thousand electrons moving through delicate circuit junctions of silicon chips render the chips useless.

Static can be damaging to equipment and uncomfortable for users at the same time. For example, one worker had the habit of walking around the office without shoes. Walking across a nylon carpet in cotton socks created an immense static charge. When he got within 15 centimeters (not a typo) of the keyboard, the static charge jumped from his fingers to the keyboard. This not only caused him considerable pain, but it also burned out one of the horizontal scan rows on the keyboard, destroying it forever. Fortunately, the computer was properly grounded; otherwise, much more damage could have been done.

TIP:

Properly grounding equipment can prevent static, as can maintaining room humidity in the 40–60 percent range.

Electromagnetic Interference (EMI) Problems
EMI occurs when magnetic fields intersect network or computer cables, causing interference in the cables. Motors and transformers, which are ubiquitous in an office (in air conditioners, heaters,
and so on), are a typical source of EMI. A common mistake is to run network cable through an elevator shaft or through a ceiling that hides a bank of transformers in fluorescent lights.
Finding the source of EMI can be a challenge. The best approach is to follow a cable with an inexpensive compass, noting strong, odd needle movement. When you find the source of the EMI, you can protect the cable against it by either replacing the cable with a shielded cable (or fiber-optic cable, which is immune to both EMI and RFI) or by moving the cable far away from the source of the EMI.

Radio Frequency Interference (RFI) Problems
RFI occurs when radio signals interfere with the normal operation of electronic circuits (computers in particular). Everyday sources of RFI include television and radio transmitters, which by nature create a specific radio frequency as part of the transmission process. Other sources are two-way radios and cellular phones.
The only way to protect against both EMI and RFI is to use shielded network cables. Shielded cable, as used in shielded twisted-pair (STP) and coaxial cable, can reduce the effects of RFI.
You could also use fiber-optic cable, which is immune to EMI and RFI, throughout your entire network, although this option can get a little pricey.

Real World Scenario
“Let’s Be Careful Out There!”

In one of the strangest cases of RFI I have ever seen, a server was resetting almost every night, right about 3 AM, while doing a tape backup. Changing the tape drive, the power supply, and other components were of no avail. The log files showed that the tape drive was operating normally and that the server would simply go down and restart, returning to normal operation. Frustrated with dead ends, an engineer was on-site at 3 AM to observe the failure. He noticed that a police patrol car was parked nearby, radioing in status reports. Separated only by a wall, the server didn’t have a chance with 25 watts of VHF radio signal being transmitted from only a few meters away. The radio signal was resetting the server, and once the policeman was done filing reports, the RFI was gone and the server restarted.

Climate Problems
Network devices (including computers and servers) are very sensitive to temperature extremes and can fail prematurely if subjected to them. The environment for network devices should be
roughly the same as that for human beings. Keep the temperature consistently at 70 degrees Fahrenheit, and keep the relative humidity between 40 and 60 percent. Maintaining consistent
temperature and humidity can be a challenge because every computer constantly generates heat. Larger companies usually place network equipment in a special room that is climate controlled.

TIP:
Even if your company can’t provide a climate-controlled server room, you can do at least one thing to avoid climate problems: never put servers in a network closet without ventilation. It is better to put servers out in the open, locked to a desk, than to lock them up in an unventilated closet. Also, never put an electronic
device of any kind directly in front of a heat source, such as a space
heater. This can cause the components to fail prematurely because excessive heat can damage electronic components.

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Saturday, May 17, 2014

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