ZyXEL Communications VANTAGE CNM 2.0 -, Руководство пользователя

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Vantage CNM 2.0 User’s Guide
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Appendix H
Wireless LAN and IEEE 802.11
A wireless LAN (WLAN) provides a flexible data communications system that you can use to
access various services (navigating the Internet, E-mail, printer services, etc.) without the use
of a cabled connection. In effect a wireless LAN environment provides you the freedom to
stay connected to the network while roaming around in the coverage area.
Benefits of a Wireless LAN
Wireless LAN offers the following benefits:
It provides you with access to network services in areas otherwise hard or expensive to wire,
such as historical buildings, buildings with asbestos materials and classrooms.
It provides health care workers like doctors and nurses access to a complete patient’s profile
on a handheld or notebook computer upon entering a patient’s room.
It allows flexible workgroups a lower total cost of ownership for workspaces that are
frequently reconfigured.
It allows conference room users access to the network as they move from meeting to meeting,
getting up-to-date access to information and the ability to communicate decisions while “on
the go”.
It provides campus-wide networking mobility, allowing enterprises the roaming capability to
set up easy-to-use wireless networks that cover the entire campus transparently.
IEEE 802.11
The 1997 completion of the IEEE 802.11 standard for wireless LANs (WLANs) was a first
important step in the evolutionary development of wireless networking technologies. The
standard was developed to maximize inter operability between differing brands of wireless
LANs as well as to introduce a variety of performance improvements and benefits.
The IEEE 802.11 specifies three different transmission methods for the PHY, the layer
responsible for transferring data between nodes. Two of the methods use spread spectrum RF
signals, Direct Sequence Spread Spectrum (DSSS) and Frequency-Hopping Spread Spectrum
(FHSS), in the 2.4 to 2.4825 GHz unlicensed ISM (Industrial, Scientific and Medical) band.
The third method is infrared technology, using very high frequencies, just below visible light
in the electromagnetic spectrum to carry data.