Understanding Installation Issues
In many cases, the installation team is not the same individual
or group of individuals who set down the initial design or performed the survey.
However, the installation of a WLAN has to be closely tied to the WLAN design
and survey, and therefore the documentation stage of the survey is critical. If
important details are left out, or not explained fully, the installer might make
assumptions, and the resulting WLAN installation might not be what the survey
team or the design engineers had in mind.
The installer must take into account many different concerns,
including overall type of facility (public or private), aesthetics, the physical
security that will be needed, the environmental conditions, the local building
codes, and fire regulations. These considerations are in addition to the general
items such as mounting and connecting the WLAN components to the network.
The actual installation usually falls into two separate
tasks:
These two tasks must be worked on hand in hand, but are often
separated based on the expertise or job functions of the individual. For larger
sites, the tasks are often divided.
Above all, take care to ensure the installation does not alter
the design set down by the site survey team. The site survey step was critical
to finalizing the design of the WLAN, and alterations at this point in the
project need to be discussed with the survey engineer and tested if
necessary.
Facility Construction
The facility construction and its effect on a site survey
and WLAN operation were discussed in detail Chapter 8, "Discovering Site-Specific Requirements."
After the survey has been conducted, the WLAN is designed to deliver the
necessary performance with the facility construction in mind. That process
partially dictates where the access points (APs)
and antennas will be located. In the installation phase, the type of
construction again plays a role in how easy or difficult it is to install a
system.
The difficulty of installation varies widely with the building
type. In most warehouses or manufacturing facilities, mounting is usually
straightforward because the APs and antennas are attached either to the wall or
the ceiling rafters. For facilities with enclosed ceilings, mounting can become
in issue. How much of an issue depends on physical security, aesthetics, and the
type and height of the ceiling. Survey engineers who are familiar with
installation procedures can make the installation process easier by identifying
in their surveys optimal AP locations.
Aesthetics
Many facility managers are extremely concerned about building
aesthetics. To maintain the look and feel of the surroundings, the installer
needs to be creative, but still work within the boundaries of the site survey.
An experienced survey team can make the install easier by testing and
recommending solutions that work well from the aspect of aesthetics. Survey
engineers with minimal experience might overlook this step and leave it up to
the installer to figure a way out of the problem. Therefore, a survey engineer
should be part of an installation team, at least for some short period of time.
This helps the survey engineer understand the potential problems that might
arise during the installation process.
In some cases, even when aesthetics are important, a
wall-mounted AP in plain sight might be acceptable. In Figure 12-1, a nonintrusive AP is mounted to an office
wall. This particular AP uses internal omnidirectional antennas, keeping the
overall look very clean.
Much of the aesthetics are directly related to the AP itself,
as well as the desired antennas. Some APs are just cleaner looking and can fit
well into the environment, whereas others just do not blend well into the
surroundings. Adding external antennas exacerbates the problem with aesthetics.
In some cases, a little logic and imagination need to be used. For example, Figure 12-2 shows one way to use external
patch antennas while still maintaining a clean look. In this case, the AP is
placed next to the picture to just indicate there is an antenna behind the
picture. In most cases, however, the AP would be placed on the backside of the
wall or above the ceiling and the cable run down through the center of the wall,
exiting to the antenna behind the print.
The particular photo shown in Figure 12-2 was taken during a site survey. Testing showed
that the print had no effect on the performance, and the photo was used in the
site survey report to indicate exactly where to place the antenna.
In some cases, antennas cannot be hidden easily, and the
installer will need help to keep the aesthetics clean. Theme parks, for example,
are extremely sensitive about the looks of their environment. In one scenario, a
theme park contained a remote beach with an old aircraft environment. The WLAN
required that a Yagi antenna be installed outdoors to enable communications from
a building on the remote beach. To blend into the environment, the Yagi was
mounted to a mast and then covered with a fake windsock.
Health-care
locations also want to maintain a clean aesthetic. In these cases, you can paint
many of the antennas (using, of course, a nonmetallic paint) to assist in
blending APs into the environment. In one case, the customer even went to the
extent of using patch antennas mounted to the hallway walls and covered the
antennas with vinyl wallpaper that matched the wall covering used in the
hallway.
Appendix C,
"Alternative Antennas," describes a ceiling-tile antenna. This antenna is
attached to the top of a ceiling tile, and therefore is totally hidden from
view. The downside to a ceiling antenna is the need for adaptor cables (and
tying to match to existing ceiling tiles). As an alternative, Figure 12-3 shows a mounting system from Maxrad that
provides a very unique mounting, for both an AP and for antennas. The entire
fixture can be assembled and installed as a complete system. It contains a
2.4-GHz diversity omnidirectional antenna with an outward radiation pattern. In
addition to that, the bracket is designed to hold the AP just high enough above
the ceiling tile to permit an attached 5-GHz dipole or patch antennas to radiate
as well as possible (for being above the ceiling). Of course, the survey
engineer should first test with this type of antenna to ensure accurate
deployment. This is just one reason why it is a great idea for survey engineers
to understand installation issues.
Physical Security
The physical security of an AP is sometimes based on the old
adage "out of sight, out of mind." In some situations, APs placed above ceiling
tiles seem to meet this level of "security." In environments with heavy public
traffic but inconstant monitoring, such as a school or other public building,
however, this practice is not adequate. Although one would hope that students
and others would not be prone to mischief, you must plan for just such
mischief.
The mounting of the antenna must be such that it is secure and
cannot be removed easily. However, the real security threat is the AP itself.
Securely mounting the AP and the radios modules within the AP is critical.
Some devices, such as the Cisco Aironet 1200, provide a
security slot that enables you to attach a Kensington-type locking cable
(identical to the ones used for securing laptops). Some APs also offer unique
mounting brackets that enable you to use a small padlock (see Figure 12-4).
At times you might need to provide a totally secure box for the
AP (which is often the case when APs are mounted for public access and you do
not have a secure location in which to mount the AP). Various boxes are
available to enclose an AP. These can be as simple as a small plastic lock box
available at any electrical-supply outlet or even some home-improvement stores.
Plastic can be drilled easily (for cable entry) and, in some cases, the antenna
might even work well through the plastic (but this should be tested as part of
the site survey).
Environment
A few APs can handle outdoor or harsh environmental
conditions (for example, the Intermec WA21 or Cisco Aironet 1300, shown in Figure 12-5), but the vast majority of APs
available today are not up to such tasks. If you plan to place an AP in an
outdoor area such as an open-air patio for public access or a beach house where
salt spray and humidity are very common, you typically need some type of extra
enclosure.
Several different enclosures are on the market today. They vary
in size, features, and material. Some might offer heating and cooling systems,
contain a power supply, or have AC line voltage fed into them. Others rely on
Power over Ethernet (PoE), as do the enclosures
available from TerraWave shown in Figure
12-6. When specifying enclosures, look for features such as these:
-
NEMA ratings. Some enclosures are intended for indoor use to
provide a degree of protection against dust, falling dirt, and dripping
noncorrosive liquids; others are intended for outdoor installation.
-
A opening large enough to facilitate component installation and
maintenance.
-
A method for direct mounting or optional external mounting
feet.
-
A seamless one-piece gasket to provide oil-tight and dust-tight
seal.
-
A lockable door.
-
Dual antenna connections for external diversity
antennas.
In many cases, these environmental enclosures are used for
more than just environmental protection. For example, in many cases you can
physically secure the AP by using the lockable door.
Building Codes
Building codes vary widely from location to location. This can
be a problem for a company that is trying to standardize on an implementation
for multiple sites located in different municipalities. There are different
regulations regarding cable usage, fire ratings, accessibility to plenum areas,
and so on. Although this section touches on a few of the issues, this is a topic
that is beyond the scope of this book. Consult local authorities or use local
contractors to guarantee that the installation meets the local regulations.
The National Electric Code (NEC)
defines a plenum space as a compartment or chamber where one or more air ducts
are connected and form part of the air distribution system used for ventilation
into locations where people reside.
The space above acoustic ceiling tiles can be classified as
plenum if the space extends beyond a single room. Typically, this space is
common to the majority of the building (or at least to a particular floor). This
type of construction is common. The reason for rating this as a plenum area is
that in the case of fire, any smoke or fumes in the plenum area can travel
through the air ventilation and into other inhabited areas. Therefore, equipment
placed in the plenum must meet certain requirements for fire and smoke. If the
walls extend above the ceiling tile and seal off the space, the area above the
ceiling might be exempt from the plenum rating.
To meet the requirements of the NEC, you
must use cables rated for plenum spaces (labeled as Communication Plenum Cable, or CPM). Similarly, any
equipmentincluding APs, antennas, and antenna cablesinstalled above the ceiling
must meet the plenum ratings.
Although the NEC defines the plenum ratings, and most cities
use these same ratings, some localities have defined their own local codes. This
is something that the installer must research before installing any equipment
into a plenum area.
Another regulation in some localities concerns certification of
the individuals accessing the plenum areas. Some regulations specify that any
person accessing a plenum area must hold a valid heating, air conditioning, and ventilation
certification (HVAC). This regulation might impact well beyond the
installation portion of a WLAN project. If an HVAC contractor is used for the
installation (installing the APs and running cables), what happens if an AP
fails sometime down the road and needs to be replaced? If such a regulation
applies in this locality, it is illegal for an IT person (unless HVAC certified)
to access the AP above the ceiling.
One company had a custom AP enclosure made to meet this HVAC
certification requirement, as well as any plenum requirements. Figure 12-7 shows the enclosure, which once installed is
totally isolated from the plenum air space and opens from the user side of the
ceiling. This permits anyone (with keys to the boxes) to access the AP for
installation and maintenance. The box itself had to be installed by an HVAC
contractor, but once installed and wired, the IT staff could handle all the
necessary maintenance.
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