ZyXEL Communications VMG5313-B10A, Руководство пользователя

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Chapter 7 Wireless
VMG5313-B10A/-B30A Series User’s Guide
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7.10.2 Additional Wireless Terms
The following table describes some wireless network terms and acronyms used in the VMG’s Web
Configurator.
7.10.3 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.
Because of the damage that can be done by a malicious attacker, it’s not just people who have
sensitive information on their network who should use security. Everybody who uses any wireless
network should ensure that effective security is in place.
A good way to come up with effective security keys, passwords and so on is to use obscure
information that you personally will easily remember, and to enter it in a way that appears random
Table 28
Additional Wireless Terms
TERM DESCRIPTION
RTS/CTS Threshold 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.
Preamble 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.
Authentication The process of verifying whether a wireless device is allowed to use the wireless
network.
Fragmentation
Threshold A small fragmentation threshold is recommended for busy networks, while a larger
threshold provides faster performance if the network is not very busy.