HP Vm200 User Manual

Chapter 5: Wireless configuration
5
Wireless configuration
Contents
Wireless coverage......................................................................................................... 5-2
Factors limiting wireless coverage...................................................................... 5-2
Configuring overlapping wireless cells............................................................... 5-3
802.11n best...

Wireless configuration
Wireless coverage
5-2
Wireless coverage
As a starting point for planning your network, you can assume that when operating at high 
power, the V-M200 radio provides a wireless networking area (also called a wireless cell) of 
up to 300 feet (100 meters) in diameter. Before creating a permanent installation, you should 
always perform a site survey to determine the optimal settings and location for the V-M200.
The following sections provide information on wireless coverage. A tool...

Wireless configuration
Wireless coverage
5-3
Configuring overlapping wireless cells
When the radio is operating in the 2.4 GHz band, overlapping wireless cells occur when two 
or more APs are within transmission range of each other. This may be under your control, 
(for example, when you use several cells to cover a large location), or out of your control (for 
example, when your neighbors set up their own wireless networks). In either case, the 
problems you face are similar.
NoteOverlapping channels do...

Wireless configuration
Wireless coverage
5-4
The solution to this problem is to set the two networks to different channels with as great a 
separation as possible in their operating frequencies. This reduces crosstalk and enables 
client stations connected to each V-M200 to transmit at the same time. 
Selecting channels
For optimal performance when operating in the 2.4 GHz band, select an operating frequency 
that is different by at least 25 MHz from the frequency used by other wireless APs that 
operate...

Wireless configuration
Wireless coverage
5-5
Sample channel selections
For example, when operating in 802.11b mode, the V-M200 supports the following 
14 channels in the 2.4 GHz band. 
However, the number of channels available for use in a particular country are determined by 
the regulations defined by the local governing body. The following table shows the number of 
channels that are available in North America and Europe. 
Since the minimum recommended separation between overlapping channels is 25 MHz...

Wireless configuration
Wireless coverage
5-6
In North America, you can reduce transmission delays by using different operating 
frequencies as shown in the following figure.
Alternatively, you can stagger cells to reduce overlap and increase channel separation as 
shown in the following figure. 
Cell 1
Channel = 1Cell 2
Channel = 6Cell 3
Channel = 11
AP AP AP
Cell 1
Channel = 1Cell 2
Channel = 6Cell 3
Channel = 11Cell 4
Channel 1
AP AP AP AP 

Wireless configuration
802.11n best practices
5-7
This strategy can be expanded to cover an even larger area using three channels as shown in 
the following figure.
802.11n best practices
This section provides recommendations on how to best use 802.11n wireless technology, 
especially when legacy (a/b/g) clients must also be supported. 
Supporting legacy wireless clients
The 802.11n standard is very similar to the 802.11g standard, in that both provide mechanisms 
to support older wireless standards. In...

Wireless configuration
802.11n best practices
5-8
If protection is not used, 802.11b clients may transmit a frame while an 802.11g frame is 
already being sent. This leads to a collision and both devices need to re-transmit. If there are 
enough devices in the network, the collision rate will grow exponentially and prevent any 
useful throughput from the wireless network.
802.11n clients face the same problem as described for 802.11g clients. Legacy a/b/g clients 
cannot detect the High Throughput (HT)...

Wireless configuration
802.11n best practices
5-9
NoteNote that some people may refer to this mode as Greenfield, which is not correct. Greenfield 
is an 802.11n-specific preamble. The V-M200 does not support this preamble and therefore 
does not support Greenfield mode.
The Pure-N modes can be used when there is no legacy wireless traffic present in or around 
the premises on the channels that will be used. All client devices must support 802.11n. 
802.11n/a, 802.11n/b/g
These modes are referred to as...

Wireless configuration
Radio configuration
5-10
When Auto 20/40 MHz is selected, the V-M200 radio uses a 40 MHz channel width. However, 
both 20 and 40 MHz clients can associate. The channel selected on the radio page is the 
primary channel and the secondary (or extension) channel is located adjacent to it. The 
secondary channel is either above or below depending on which channel was selected as the 
primary. In the 5 GHz band, the channels are paired: 36 and 40 are always used together, 44 
and 48 are...