Challenges Unique to WLAN
Management
WLANs present several unique management challenges. Many relate
to the physical aspects of the wireless environment, whereas some are the result
of the dynamic nature of the wireless network and its
mobile users and devices. Knowledge of these challenges will help ensure that
you do not overlook these areas in framing your management strategy for the
enterprise-class WLAN. Some of the most commonly experienced problems and
challenges you will face include the following:
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The dynamic nature of the transparent medium
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The mobility of endpoints
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The persistence of endpoints
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The nature of mobile endpoints
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Wireless security management
These challenges are fundamental in nature and simply
characteristic of the wireless environment. None is insurmountable, and
examining each in turn can assist in addressing them in your management
strategy.
Dynamic Nature of the Transport
Medium
Wired networks are deterministic in nature. That is, they
function on a predictable basis with very little outside influence on their
operation. Wireless LANs, on the other hand, can be considered statistical or probabilistic in nature. As
mentioned in the introduction to this chapter, the wireless LAN will function
differently depending upon the number of users associated to a particular access
point, the amount of traffic generated by those users and devices, and outside
interference, either from nearby but external networks or from factors such as
the physical environment.
Most enterprise-class WLANs are made up of several access
points providing large areas of coverage in one or more buildings. However, the
dynamic nature of the transport medium, the RF spectrum upon which 802.11 WLANs
are based, means that one cell will by its very nature have different
characteristics from another cell. This can even be the case in the same
building. The cell's size and shape are dependent not only on the transmission
power of the access point but also on such effects as the composition of walls
and floors, the location of physical obstacles such as furniture, the existence
of other nearby devices using similar radio frequencies, and so on.
A carefully designed WLAN is capable of withstanding the vast
majority of these effects. However, the fact remains that a wireless LAN's
behavior is isolated in both time and space. Appreciation of this fact prepares
the network manager to face these challenges and to ensure that the tools he or
she puts in place can help identify unique radio-based problems, often before
they negatively impact the end users.
Mobility of Endpoints
WLANs enable and promote mobility. Thus, at any point in time,
a mobile device could be at any
location on the network. Mobile devices, such as laptops,
PDAs, or even wireless-equipped vehicles or manufacturing equipment, can roam
from access point to access point. In a wired environment, the network manager
(or network management toolset) knows and can predict where a particular
endpoint is. In the vast majority of cases, endpoints are
literally "wired" to a jack and, in turn, a switched port on your networking
infrastructure. That is not so in the wireless LAN. Devices
move about the building, campus, or factory floor. Without specific tools or
reports, it is often difficult, or even impossible, to identify a wireless
device's location. Indeed, they will often change IP addresses on a daily basis,
sometimes more often. Layer 3 (inter-subnet) roaming results in the client being
assigned a new IP address.
Intermittent Connectivity of Mobile Endpoints
Most wired networks are a collection of physically static
devices that present a degree of "persistence" in their connectivity. That is,
they usually remain online and connected for long periods of time, if not
indefinitely.
In the wireless space, especially with the introduction of
PDAs, Application-Specific Devices (ASD) such as bar-code scanners, wireless
voice handsets, and smart phones, wireless-enabled devices come online and go
offline on an irregular, unpredictable basis. Of course, that is not to say that
all mobile devices are going offline all the time, but rather the nature of many
mobile devices (such as PDAs) is such that a system cannot automatically assume
they are online at a particular time.
Management tools and strategies that rely upon persistence of
connectivitythe ability to reliably contact, ping, identify, or locate end
deviceswill not handle such an environment well. A toolset that automatically
generates reports and alerts on hosts or devices that it can no longer contact
might generate many false-positive alerts or alarms, for example. Management
tools that rely upon agents (or specific management software) might create
erroneous alerts if they cannot consistently contact these devices on a
predictable basis.
Diverse Nature of Wireless
Endpoints
Remember that access points are not the only wireless devices
on your network. Each client device is also fitted with a radio and an antenna.
So not only does your WLAN present you with the challenge of dealing with many
(sometimes hundreds or thousands) access points, but each client device also
needs to be dealt with.
Typically, an enterprise-class WLAN will standardize upon the
infrastructure required for the WLAN; that is, the design will detail what
specific products are used, how the infrastructure devices are configured, and
so on. Such standardization is quite often not the case when it comes to client devices. There are often many different makes and models of laptops
or mobile devices within the company. Even laptops that come with embedded
wireless adaptors and that are manufactured by the same vendor will sometimes
have different radio interfaces. It is not uncommon for an enterprise to have a
mixture of different makes of laptops, different platforms (for example, Windows
2000, Windows XP, Linux, and MacOS), different client adaptors, and differing
versions of firmware and client software. Contrast this with the wired network,
where the vast majority of devices are easy to install; that is, you literally
plug them into the network and they work. You do not have to worry about whether
the wireless network adaptors have the latest firmware, whether the correct
software application and version have been installed, or whether the
configuration of the software is completed and appropriate profiles have been created.
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