|
8.11
|
|
Network Power Supply Issues: Surge Suppressors and
Uninterruptible Power Supply (UPS) Functions
|
|
|
|
|
8.11.1
|
Surge suppressors: networking device locations
|
|
|
Surge
suppressors are usually mounted on a wall power socket, to which a
networking device is connected. This type of surge suppressor has circuitry
that is designed to prevent surges and spikes from damaging the networking
device. A device called a metal oxide varistor (MOV) is most often
used as this type of surge suppressor. An MOV protects the networking
devices by redirecting excess voltages, that occur during spikes and
surges, to a ground. Simply put, a varistor is a device that is capable of
absorbing very large currents without damage. An MOV can hold voltage
surges on a 120 V circuit to a level of approximately 330 V.
Unfortunately, an MOV
may not be an effective means of protecting the networking device that is
attached to it. This is because the ground also serves as the common
reference point for data signals going into and out of the computer.
Dumping excess voltages into the power line near the computer can create
problems. While this type of voltage diversion can avoid damage to the
power supply, it can still result in garbled data.
When surge suppressors
that are located in close proximity to networking devices divert large
voltages onto the common ground, this can create a large voltage
differential between network devices. As a result, these devices can
experience loss of data, or in some instances damaged circuits.
You should also be
aware that this type of surge suppressor has a limited lifetime, dependent,
in part, on heat and usage. For all of these reasons, this type of surge
suppressor would not be the best choice for your network.
|
|
|
|
8.11
|
Network Power Supply Issues: Surge Suppressors and
Uninterruptible Power Supply (UPS) Functions
|
|
|
|
8.11.2
|
Surge suppressors: for power panel locations
|
|
In
order to avoid problems associated with surges, what you could do, instead
of installing individual surge suppressors at each work station, is to use
a commercial quality surge suppressor. These should be located at each
power distribution panel, rather than in close proximity to the networking
devices. By placing a commercial grade surge suppressor near the power
panel, the impact on the network, of voltage surges and spikes diverted to
ground, can be reduced.
|
|
|
8.11
|
Network Power Supply Issues: Surge Suppressors and
Uninterruptible Power Supply (UPS) Functions
|
|
|
|
8.11.3
|
UPS: for certain LAN devices
|
|
The
problem of sags and brownouts can best be addressed by the use of uninterruptible
power supplies (UPS). The extent to which UPS must be provided for a
LAN depends on factors such as the budget, the types of services the LAN
provides, the frequency of regional power outages, and the typical length
and duration of power outages, when they do occur. At a minimum, every
network file server should have a source of backup power. If power wiring
hubs are required, then they must also be supported with backup power.
Finally, in extended star topology networks, where internetworking devices
such as bridges and routers are used, power backup must be provided to
them, as well, in order to avoid failures in the system. Where possible,
power backup should also be provided for all work areas. As every network
administrator knows, it does little good to have an operational server and
wiring system, if they cannot ensure that computers will not go down before
users can save their spreadsheets and word processing files.
|
|
|
8.11
|
Network Power Supply Issues: Surge Suppressors and
Uninterruptible Power Supply (UPS) Functions
|
|
|
|
8.11.4
|
UPS: for certain electrical problems
|
|
Sags
and brownouts are usually power outages that are of a relatively short
duration, and are caused by something, such as a lightning strike. This
creates a power overload, and trips a circuit breaker. Because circuit
breakers are designed to automatically reset, they can work from the
surrounding power grid to where the source of a short is located in order
to re-establish power. This usually occurs within seconds or minutes.
Longer power outages
can occur, however, when an event, such as a severe storm or flood, causes
physical disruption of the power transmission system. Unlike shorter power
outages, this type of disruption in service is usually dependent on service
crews for repair.
An uninterruptible
power source is designed to handle only short-duration power outages. If a
LAN requires uninterrupted power, even during power outages that could last
several hours, then a generator would be needed to supplement the backup
provided by a UPS. Can you think of situations where LANs might need the
added backup of a generator?
|
|
|
8.11
|
Network Power Supply Issues: Surge Suppressors and
Uninterruptible Power Supply (UPS) Functions
|
|
|
|
8.11.5
|
UPS: components
|
|
A UPS
consists of batteries, a battery charger, and a power inverter. The
functions of each are as follows:
- inverter - convert low-level direct
current voltage of the batteries into the AC voltage, normally
supplied by the power line, to networking devices
- battery charger - designed to keep the
batteries in peak condition during periods when the power line system
is functioning normally
- batteries - generally, the bigger
the batteries in a UPS, the longer a period of time it will be able to
support networking devices during power outages
|
|
|
8.11
|
Network Power Supply Issues: Surge Suppressors and
Uninterruptible Power Supply (UPS) Functions
|
|
|
|
8.11.6
|
UPS: differences in UPS features
|
|
|
A
number of vendors have developed UPS systems. You will find that they
differ in the following ways: the power storage capacity of the batteries;
the power delivery capability of the inverter; and the operational scheme
(whether they operate continuously, or only when the input voltage reaches
a specific level). Also, the more features a UPS has, the more it costs.
|
|
|
8.11
|
Network Power Supply Issues: Surge Suppressors and
Uninterruptible Power Supply (UPS) Functions
|
|
|
|
8.11.7
|
UPS: description and operation
|
|
|
As a
rule, UPS devices that offer fewer features, and cost less money, are used
as standby power systems only. This means that they monitor power lines.
If, and when, a problem occurs, the UPS switches over to the inverter,
which is powered by its batteries. The time needed for this switch to occur
is called the transfer time. Usually, the transfer time lasts for
only a short time. This does not usually present a problem for most modern
computers, which are designed to coast on their own power supplies for at
least a hundred milliseconds.
UPS devices that offer
more features, and cost more money, typically operate online. This means
that they constantly supply power from inverters, which are powered by
their batteries. While they do this, their batteries continue charging from
the power line. Because their inverters supply freshly generated AC, such
UPS devices have the added benefit of ensuring that no spikes from the
power line reach the networking devices that they serve. If, and when, the
AC power line goes down, however, the UPS batteries will switch, smoothly,
from recharging to providing power to the inverter. Consequently, this type
of UPS effectively reduces the transfer time needed to zero.
Other UPS products fall
into a hybrid category. While they appear to be online systems, they do not
run their inverters all the time. Because of these differences, be sure to
investigate the features of any UPS you plan to incorporate as part of a
LAN installation.
In any event, a good
UPS should be designed to communicate with the file server. This is
important so that the file server can be warned to shut down files when the
UPS battery power nears its end. Additionally, a good UPS reports instances
when the server starts to run on battery power, and supplies this
information to any work stations running on the network, after the power
outage has occurred.
|
|
|
Summary
|
|
|
The
focus of this chapter was network design and documentation. You
learned that:
- Layer 1 components include:
plugs, cable, jacks, and patch panels
- to finish Layer 1 design,
both a logical and a physical topology must be generated
- Layer 2 devices such as
switches reduce congestion and collision domain size
- Layer 3 devices such as
routers are used to build scalable internetworks (larger LANs, WANs,
networks of networks), or to impose logical structure on the network
- databases, and other shared
resources, as well as the LAN's link to WANs and to the Internet
- any time you install cable,
it is important to document what you have done
- a wiring closet is a
specially designed room used for wiring a data or voice network
- backbone cabling consists
of the backbone cabling runs; intermediate and main cross-connects;
mechanical terminations; and patch cords used for backbone-to-backbone
cross-connection
- surge suppressors are an
effective means of addressing the problems of surges and spikes
Now
that you have worked through this chapter, you are ready to begin the
structured cabling project which is covered in the next chapter.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|