When planning a wireless LAN installation, be sure to carefully assess and
resolve risks. Otherwise unforeseen implications, such as RF interference, poor
performance, and security holes will wreak havoc. By handling risks during the
early phases of the deployment, you’ll significantly increase the success of
a wireless LAN.
Common risks to consider
With a firm understanding of requirements, consider the following
elements when evaluating and resolving risks for deploying wireless LANs:
- RF interference. Devices such as 2.4 GHz cordless phones, microwave
ovens, and neighboring wireless LANs, can cause damaging RF
interference that impedes the performance of a wireless LAN. To minimize
the risk of RF interference, perform a RF site survey to detect the presence
of interference, and define countermeasures before installing the access points.The problem with RF interference is that it’s not always controllable.
For example, you may deploy an 802.11b wireless LAN in an office complex,
then three months later the company next door installs a wireless LAN set
to the same channels. This results in both wireless LANs interfering with
each other.A possible solution to minimize this risk is to utilize directive antennas
that ensure transmit and receive power of the your wireless LAN falls only
within your facility. This would limit the impact of the interfering wireless
LAN. Of course you could also specify the use of 802.11a, which offers more
flexibility in choosing channels that don’t conflict with others. - Interoperability issues. The lack of interoperability among 802.11
FHSS, 802.11b DSSS, and 802.11a OFDM causes problems in some cases. Even though
these standard are all 802.11, they don’t interoperate with each other. With
so many standards, you run the risk of not allowing some users on the wireless
LAN.Consider a company that installs 802.11a access points throughout the facility
today. This provides interoperability with 802.11a users, but precludes
the operation of 802.11b-equipped user devices. Until multimode
radio NICs are commonplace, you’ll need to carefully consider the impacts
of choosing the specific wireless LAN standard. - Security holes. The potential for an unauthorized person accessing
corporate information is a significant threat for wireless LANs. An eavesdropper
can use a wireless LAN analyzer, such as Wildpacket’s Airopeek or Sniffer
Technology’s Sniffer
Wireless to passively receive and view contents of 802.11 frames. Of course
this could disclose credit card numbers, passwords, and other sensitive information.Avoid security risks by carefully assessing the vulnerabilities of a wireless
LAN, and define effective security mechanisms based on the value of information
you need to protect. In some cases, you may simply need firewall protection.
Other applications may require effective forms of encryption. Of course
802.1X
will also provide added security. - Applications interfaces. In some cases, interfaces with applications
located on various hosts and servers can bring about major problems when using
a wireless LAN. A relatively short loss of connectivity due to RF interference
or poor coverage area causes some applications to produce errors. This occurs
mostly with legacy applications lacking error recovery mechanisms for wireless
systems.For example, a user may be using an inventory application by scanning items
and entering total counts via a keypad on the scanner. If loss of connectivity
occurs after scanning the bar code and before entering the count, the host-based
application could log the use out without completing the inventory transaction.
As a result, the application on the host may record an incorrect or invalid
value for the inventory item.To avoid these types of risks, carefully define the types of applications
the wireless user devices will interface with. If needed, incorporate solutions
such as wireless middleware to provide adequate handle recovery mechanisms
related to wireless LANs. -
Unclear requirements. If you deploy a wireless LAN without first
clarifying requirements,
then the wireless LAN may not satisfy the needs of the users. In fact poor
requirements are often the reason why information system projects are unsuccessful.
As a result, always define clear requirements before getting to far with
the deployment.For example, you may install 11 Mbps 802.11b today to support needs for
a moderate number of users accessing e-mail and browsing the Web. Ten months
later the organization may increase the density of users or need to utilize
multimedia applications demanding a higher performing solution. The organization
would then be facing a decision to migrate to either 802.11g or 802.11a.If 802.11g products are available, the migration could simply involve firmware
upgrades; however, the total capacity of 802.11g might not be sufficient
to satisfy requirements. 802.11a would provide greater capacity, but would
require changing access point hardware. In this case, the organization should
have initially chosen 802.11a initially. - Product availability. Solid requirements and an effective design
significantly reduce most deployment risks, assuming the design specifies
products that are actually available when you need them. The trouble is that
vendors often miss projected release dates and have limited volumes when the
products are first available.For example, multimode 802.11a/b radio NICs should be available
on the market by the end of 2002. You’re incurring a risk, however, if it’s
crucial that these products available by then. A similar hazard surfaces
if you’re depending on the availability of 802.11g by a specific date to
upgrade existing 802.11b access points to support higher requirements. Of
course the advice here is to not totally rely on projected release dates.
By identifying and solving potential risks, you’ll have a much more successful
wireless LAN deployment. The key is to fully understand wireless requirements
during early stages of the deployment project, identify related risks, and provide
effective solutions.
Jim Geier provides independent consulting
services to companies developing and deploying wireless network solutions.
He is the author of the book, Wireless
LANs (SAMs, 2001), and regularly instructs workshops on wireless LANs.
