Bandwidth Assumptions For Wi-Fi; Overcoming Physical Impediments - Black Box SmartPath LWN602A User Manual

Chapter 2: Preparing for a WAN Deployment
• Client Software
- Depending on the deployment, users can use built-in Microsoft
(supplicants).
- For better services and troubleshooting, consider a third-party supplicant such as Juniper Networks

2.2.5 Bandwidth Assumptions for Wi-Fi

People frequently talk about how much coverage an access point provides; however, it is capacity—not coverage—that typically
constrains an access point in an enterprise environment. The challenge is not how far the RF signal can travel (coverage), but how
to deliver enough bandwidth to meet the demands of business applications (capacity). In other words, you might be able to cover
an office of 50 people with one access point, but if all 50 people choose to access it at the same time, it might become overload-
ed. Indeed, if you use the formulas provided in this paper, you should find the saturation of access points on your campus to be
more than sufficient. Enterprise users are accustomed to speedy switched networks and expect similar performance from their
wireless LAN connections. This is why documenting the size and type of applications that will rely on your WLAN is so critical to
your planning. In short, if you plan for optimal capacity, complete coverage will follow automatically.
In general, the way to increase capacity is to add more access poisnts (within reason) and tune down the radio power to avoid
interference. One reason for deploying a high-capacity network is to create a WLAN for voice and data applications. In such a
WLAN, everyone has a VoIP handset running wirelessly all the time.
In general, the following table shows the standard densities for office deployments:
Office Requirements
Coverage (low capacity)
Standard office deployment
Standard office deployment with voice
NOTE: Data rate is not the same as TCP throughput. Because of various headers, inter-frame gaps, and session creation, real TCP
throughput usually does not exceed 22 Mbps at data rates of 54 Mbps.

2.2.6 Overcoming Physical Impediments

Not every potential deployment is a standard business campus. The following scenarios are a few that merit special consideration.
• Open Space
Open spaces, such as a large foyer or an outdoor area, are very easy to cover with Wi-Fi because there are few impediments to
propagation and fewer opportunities for multipath interference. In such spaces, Wi-Fi signals can propagate many hundreds of
feet. This is good if you want to provide coverage for just a few users.
You will run into challenges if there are many users and high-capacity service goals. In these situations, it is important to tune
down the RF to a minimal level. The SmartPath APs do this on their own automatically. Another trick is to take advantage of
obstacles that block Wi-Fi. Look for trees or walls and put neighboring access points on either side of them. Doing so limits the
interference of the two access points and allows for the installation of more access points with less interference.
• Warehouse and Retail
Warehouse and retail environments present many challenges. One of the largest challenges is that RF characteristics often
change because of varying inventory levels and, in the case of retail, seasonal displays (such as tinsel or a stack of soda cans on
an end cap). Additionally, metal shelves and high ceilings can be challenges to propagation. To resolve with these issues, it is
wise to put at least one access point per aisle to ensure coverage for that aisle. This usually requires a higher density of access
points than would otherwise be required.
Page 18
Table 2-1. Standard densities for office deployments.
Expected Data Rate
with 802.11g Clients 20 MHz
12 to 24 Mbps -39 Mbps
36 Mbps -104 Mbps
54 Mbps -130 to -144 Mbps
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Windows , Linux and/or Macintosh
® ® ®
Expected Data Rate
with 802.11n Clients
40 MHz
-81 Mbps
-216 Mbps
-270 to -300 Mbps
client software
®
Odyssey Client.
®
Access Point Density)
1 access point per 8000 square feet
1 access point per 5000 square feet
1 access point per 2000 to 3000 square feet