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Deploying a Wireless LAN
Deploying a Wireless LAN
Considerations and Questions in Planning a Wireless LAN
Technology Brief � 2007 Research In Motion Limited. All rights reserved.
Deploying a Wireless LAN
Table of Contents
Executive Summary








1
Section One Areas to consider in deploying a WLAN





1

What are the applications that the user needs





1

Coverage









4

WLAN Standards








6

Standalone and Centrally Coordinated Wireless Networks




9

Site Survey









10

Security









11

Putting It All Together for Voice and Data over WLAN





14
Section Two Questions to pose to WLAN Vendors





15

Architecture








15

Standards









15

Access Points








15

WLAN End-user Devices







16

Management








16

Security









16
Glossary











17 Executive Summary
As wireless LANs (WLANs) continue to grow in popularity, particularly in enterprise networks, your enterprise might be considering
deploying a WLAN to leverage the different advantages that come with this type of technology. The ability to do away with massive
amounts of cabling to mobile workplace is a very obvious advantage. There are many more. Mobile, ubiquitous access to enterprise
IT systems throughout the global enterprise yields a more productive and efficient workforce, allowing employees to access
resources without being tethered to a traditionally static wired network connection. WLANs allow workers to access and contribute
information far more quickly than before, boosting the productivity of all workers who depend on that critical information and,
hence, increasing the overall agility of the organization.
For those organizations that are beginning to plan for a WLAN deployment, this paper identifies areas that should to be considered
and helps the planning and requirement definition of deploying a WLAN. Section two of this paper builds upon the considerations
areas and provides a starting point for posing questions to any WLAN equipment and services vendor.

Section One Areas to consider in deploying a WLAN
One of the most important questions to ask yourself, is what is it youre looking for in your WLAN solution that you cant get from
your wired LAN? The feature that makes most people take the wireless plunge is mobility the ability to connect to the network
through the air. What does mobility mean to you and your organization? Does it mean you want to be able to have network
connectivity throughout your offices? Or does it mean you want your remote offices connected, too? If you have a campus, do
you want to be able to connect to the network both inside and outside? If youre a doctor do you want to be able to access your
patients records at the point of care? Do you want to talk on your VoWLAN phone from one end of the building to the other without
dropping your connection, or use your mobile device anywhere from the lobby to the most remote area in the facility? These types of
questions and others on security, management, etc, all need to be explored and identified up front to effectively plan and deploy a
successful WLAN. This first section goes over these considerations that need to be finalized up front.
What are the applications that the user needs
Wireless capacity is a finite, somewhat scarce resource and, therefore, engineering with little planning or not understanding the
true nature of applications, as is often found for wired LANs, is usually not an option for WLANs. A good handle on the applications
and the load they will generate is essential to avoid overestimating the cost of the WLAN (or underestimating the coverage and
capacity) and will result in a more effective and usable experience for all users. Furthermore, because of the shared nature of the
wireless medium, deploying too many access points might simply contribute to polluting the air waves without any tangible
increase in usability.
Key application parameters to consider when planning a WLAN deployment include the application mix, or the relative proportion
of voice and data traffic, the expected traffic demands and the application performance requirements.
These application requirements eventually translate into constraints for the WLAN deployment such as minimum rate and
maximum cell coverage.
1.
Deploying a Wireless LAN
Considerations and Questions in Planning a Wireless LAN
� 2007 Research In Motion Limited. All rights reserved. 2.
Quality of experience
The quality of experience is the overall performance of a system from the point of view of its end users. It is a measure of how the
system enables the users to do what they need to do when they need to do it. The performance metrics and performance targets
used to assess the users quality of experience depend upon the type of application.
Data applications
For data applications, the time elapsed between the moment the user issues a command and the time when the output of the
command is displayed at the users device is a key measure of the perceived quality of the system. Different applications have
varying response time requirements. Interactive applications in which users issue commands and expect immediate results,
typically require end-to-end, round-trip delays of less than 400ms. This may seem like a lot but includes not only the network
propagation, serialization and queuing delays, but also the TCP timeouts and retransmissions, and the processing delays in the
end systems. The wireless link rate has only a limited effect on the response time when small amounts of data are transmitted.
The delay and quality of the connection are the most important factor in providing good quality of experience for applications that
use small transactions.
For applications in which larger amounts of data are transferred (i.e., a few kilobytes) such as email and browser-based applications,
users are usually prepared to tolerate longer delays of the order of a few seconds. Because of the larger amount of data that must
be transferred, the rate of the connection is more important in this case. Link quality remains essential since TCP, the transport
protocol used by a majority of data applications, interprets packet losses as an indication that it should slow down its transmission
rate. Even if the link rate is high, the TCP throughput will not be very high unless the packet loss rate remains low.
Voice
Voice applications are very sensitive to latency or delay, jitter and packet loss. Conversational voice has much more stringent delay
requirements than any other application.
For excellent conversational voice quality of experience, the end-to-end one-way delay should be less than 150 milliseconds.
Beyond this point some users may notice the excessive delay. A number of factors contribute to the one-way delay of VoIP
connections and, therefore, the WLAN can only use a small portion of the total 150 milliseconds delay budget. Significant
contributors to the delay include the packetization delay, the propagation delay, and de-jitter and playout delay. Other delay
contributors include processing delays in the end systems and queuing delays in the network routers and switches. In a typical
Enterprise network, approximately 50 milliseconds of the total 150 millisecond end-to-end delay budget is available to WLAN
networking. The communications delay between a WLAN phone and the AP must be less than 50 millisecond, and the phone must
be able to roam from one AP to another within 50 milliseconds.
Deploying a Wireless LAN
Considerations and Questions in Planning a Wireless LAN
� 2007 Research In Motion Limited. All rights reserved. 3.
Mixed voice and data applications
The traffic streams generated by voice and data applications have very different characteristics and it is even more challenging to
meet the requirements of both types of traffic with one network. Voice traffic is made up of short packets fairly evenly distributed in
time. As long as they do not exhaust the medium capacity, several voice streams can coexist on the WLAN without any noticeable
impact on voice quality.
Data applications, on the other hand, tend to generate bursts of rather large packets. These bursts often involve several kilobytes
of data. Bursty streams can coexist on the same LAN without any significant degradation of data application performance. But in
a wireless network, if no precautions are taken, even a single bursty data stream can temporarily saturate the medium and cause
voice quality impacting delays an