In a previous tutorial,
we discussed the steps for deploying a wireless LAN, which includes requirements
gathering, design, installation, testing, and planning for operational
support. What we’ll do now is focus on the important steps of installing
the distribution
system and access points.
Careful Planning
As with any other project, the planning of a WLAN installation involves establishing
a schedule and assigning resources. For example, you may need two installers
working over a period of six weeks to install 150 access points and only one
installer for a couple days for a smaller network with five access points.
You’ll also need to accomplish some up front coordination to ensure that the
installation is completed on schedule. The access points will tie back to switches
via Ethernet; therefore, you need to communicate with the people responsible
for supporting the existing Ethernet systems if they already exist. Each access
point requires a 10Mbps or 100Mbps Ethernet connection, depending on the design
of the WLAN. In addition, it will likely be safer and optimum in terms of performance
to separate the access points from the rest of the corporate network via a router
or virtual LAN(VLAN)
for effective integration into the existing system.
When considering the installation schedule, think about the time of installation.
The best approach is to install access points and the distribution system during
operational downtimes. For example, don’t attempt going full speed ahead with
an installation in retail stores in November or December because of the holiday-related
activities. Also avoid installations in office complexes during the daytime
when there are lots of people milling around.
In larger facilities, you’ll likely come across locked doors leading to locations
where you need to install access points or cabling. As a result, coordinate
access to these locked rooms before getting too far along. It’s best to actually
have a phone number (preferably a cell phone) of someone who can get you into
rooms at the last minute if necessary.
Identify Locations for Access Points
The installation locations of access points have significant impact on performance.
So, you want to be sure to do this right by performing a radio frequency (RF)
site survey before installing the access points. The site survey will spot potential
sources of RF interference and provide a basis for determining the most effective
installation locations for access points. You can refer to a previous tutorial
and related case studies discussing site surveys I performed for the Miami International
Airport and Naval Post Graduate
School for details on performing RF site surveys for WLANs.
When deciding where to place an access point, bear in mind coverage and performance
requirements. You shouldn’t over do it when meeting these requirements because
of possibly of running out of access point channels. Also take into account
the maximum cable length limitations (100 meters) for the cable running from
the Ethernet switch to the access point. If a 100 meter cable won’t reach your
preferred access point location, then think about moving the access point or
possibly using a WLAN bridge
For best signal propagation results, mount the access points as high as possible.
Keep in mind, though, that you might need to service the access point from time-to-time
by using an ordinary ladder.
Electricity is something else you should consider when identifying a location
for the access point. Focus on using power-over-Ethernet
(PoE)
the Category 5
you’ll probably need an electrician to hard wire the access point to a source
of electricity.
This is an obvious step that many would consider trivial; however, keep in
mind that the installation of WLANs is somewhat different than wired counterparts.
For example, you’ll need radio-based test equipment that is able to receive
and analyze RF signals. You could use devices such as AirMagnet
or Yellow
Jacket, which are able to analyze WLAN signals when performing the RF site
survey and testing the final installation. Of course other more common tools
such as a ladder, mounting brackets, wire crimpers and a hammer are also necessary
as well.
Install the distribution system
The distribution system includes Ethernet switches and possibly routers along
with Category 5 twisted pair cabling that runs to each access point. Be sure
to label all cables according to company specifications or methods that you
define. The main idea is to identify each end of the cable by some number scheme
that lets you know which access point you’re dealing with when connecting the
wire to a patch panel and rewiring or troubleshooting the system in the future.
Some companies require that the Ethernet cabling be installed within a metal
conduit, which provides some additional fire safety. As a result, determine
whether the conduit is required in order to properly install (and quote) the
system. You certainly don’t want to discover the need for a conduit during the
final testing — they you might have to start from scratch.
Configure and Install Access Points
In most cases, especially when you have multiple access points, you won’t be
able to meet requirements and the design using the default access point settings.
For example, you’ll need to set the access points within close proximity to
each other to different radio channels
in order to minimize inter-access point interference. In addition, set transmit
power, encryption, authentication, request-to-send
/ clear-to-send and fragmentation
to proper values.
Besides the 802.11 settings, you need to configure the Internet protocol (IP)
address to comply with an effective IP address plan. Be sure to do this before
mounting the access point to avoid difficulties in finalizing the installation.
I know of several companies who learned this the hard way by installing a large
number of access points only later to find that all access points are set to
the same, default IP address. This causes conflicts when trying to configure
the access point over the Port 80 Web interface from a convenient, centralized
location from the wired-side of the network. There only resolution was to go
to each access point and set the IP address via a laptop and serial cable attached
to the access point’s console port, a rather time consuming task.
In office facilities, install the access points above the drop down ceilings.
You can simply remove the ceiling tile and place a wooden shelf over the top
of the ceiling struts to act as a platform for the access point to reside. The
antenna can remain above the ceiling tile for most situations. In fact, it’s
often best to conceal the access point as much as possible to improve security.
In some facilities, you may need to mount the access point on a shelf or post.
Just keep the access point beyond easy reach of people to minimize the possibility
of tampering.
Antennas
certainly impact the propagation of radio waves, and improper orientation can
change signal coverage to something different than what was determined during
the RF site survey. In most cases, you need to point the antenna vertical to
the ground to maximize range (assuming the more common omni-directional antennas).
Test the Installation
Don’t take it for granted that your coverage and wiring is okay. Test it using
tools such as AirMagnet or Yellow Jacket by ensuring that signal strength is
high enough in all areas where users will roam. In addition, make certain that
performance meets requirements while utilizing client devices that actual users
will operate. If coverage is not up to par, then you may need to move some access
points or install additional ones.
Accomplish the tests during times when there are typical users in the facility.
I’ve seen significant impacts on propagation from groups of people getting in
between the client device and the access point. For example, hospitals get much
less coverage within patient rooms when full of doctors and nurses. As a result,
run these tests under the worst situations.
Document the final installation
After completing the installation, don’t forget to carefully document what
was done. Documentation should include a diagram depicting the location of installed
access points and applicable configuration settings. You’ll certainly need this
documentation in order to physically find the access points in the future, assuming
you were really good at concealing them. In addition, the configuration information
will be necessary in order to monitor, troubleshoot and upgrade the WLAN.
Jim Geier provides independent consulting services to companies
developing and deploying wireless network solutions. He is the author of the
book, Wireless LANs.
Join Jim for discussions as he answers questions in the 802.11 Planet Forums.
