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networks to exist in the same place without interfering with one another. When you create a network,
you must select a channel to use.
Since the available unlicensed spectrum varies from one country to another, the number of available
channels also varies.
7.11.2 Additional Wireless Terms
The following table describes some wireless network terms and acronyms used in the VMG's Web
Configurator.
Table 29 Additional Wireless Terms
TERM
RTS/CTS Threshold
Preamble
Authentication
Fragmentation
Threshold
7.11.3 Wireless Security Overview
By their nature, radio communications are simple to intercept. For wireless data networks, this means
that anyone within range of a wireless network without security can not only read the data passing over
the airwaves, but also join the network. Once an unauthorized person has access to the network, he or
she can steal information or introduce malware (malicious software) intended to compromise the
network. For these reasons, a variety of security systems have been developed to ensure that only
authorized people can use a wireless data network, or understand the data carried on it.
These security standards do two things. First, they authenticate. This means that only people presenting
the right credentials (often a username and password, or a "key" phrase) can access the network.
Second, they encrypt. This means that the information sent over the air is encoded. Only people with
the code key can understand the information, and only people who have been authenticated are
given the code key.
These security standards vary in effectiveness. Some can be broken, such as the old Wired Equivalent
Protocol (WEP). Using WEP is better than using no security at all, but it will not keep a determined
attacker out. Other security standards are secure in themselves but can be broken if a user does not use
them properly. For example, the WPA-PSK security standard is very secure if you use a long key which is
difficult for an attacker's software to guess - for example, a twenty-letter long string of apparently
random numbers and letters - but it is not very secure if you use a short key which is very easy to guess -
for example, a three-letter word from the dictionary.
Chapter 7 Wireless
DESCRIPTION
In a wireless network which covers a large area, wireless devices are sometimes not
aware of each other's presence. This may cause them to send information to the AP at
the same time and result in information colliding and not getting through.
By setting this value lower than the default value, the wireless devices must sometimes get
permission to send information to the VMG. The lower the value, the more often the
devices must get permission.
If this value is greater than the fragmentation threshold value (see below), then wireless
devices never have to get permission to send information to the VMG.
A preamble affects the timing in your wireless network. There are two preamble modes:
long and short. If a device uses a different preamble mode than the VMG does, it cannot
communicate with the VMG.
The process of verifying whether a wireless device is allowed to use the wireless network.
A small fragmentation threshold is recommended for busy networks, while a larger
threshold provides faster performance if the network is not very busy.
VMG8825-B Series User's Guide
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