Wlan; Wlan Infrastructure; Autonomous Access Points - ASCOM VoWiFi System System Description

System Description
Ascom VoWiFi System
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WLAN

A Wireless Local Area Network (WLAN) uses radio frequency (RF) technology to transmit
and receive data over the air. To enable transmission of such different types of
communication as data and voice, it is essential that hardware and software comply to
specified standards. The Institute of Electrical and Electronics Engineers (IEEE) have
established the IEEE 802.11 standard, which is the most used WLAN standard of today. The
original version was released in 1997 and over the years several amendments have been
added, for example, IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, and IEEE 802.11n. Most of
these were merged with the base standard in 2007 except IEEE 802.11n, which is a more
recent amendment.
See section
supported by the Ascom VoWiFi system.
2.1

WLAN Infrastructure

There are two types of WLAN topologies: the Ad-Hoc mode and the Infrastructure Mode. The
Ad-Hoc mode provides peer-to-peer connectivity where two clients communicate directly
with each other via their WLAN cards. The Infrastructure Mode, on the other hand, is used to
incorporate the wireless clients into an existing wired LAN infrastructure.
In the Infrastructure Mode all communication is passed through the Access Points (APs) that
are connected to the wired LAN. A single AP communicating with a number of clients is
called a Basic Service Set (BSS). A number of interconnected APs with the same network
name is called an Extended Service Set.
The AP is basically a radio transmitter/receiver but, depending on hardware and software, it
can be more or less intelligent. An AP that holds information about the mobile clients
authorized to enter the system is called an autonomous AP (or "fat" AP), whereas an AP
that only is responsible for forwarding received data, is called a controller-based AP (or
"thin" AP). While the autonomous APs carry out all wired to wireless packet format
conversion, encryption, QoS application, and RF statistics monitoring, the very thinnest APs
pass all of this to their central controller, and act basically just as a media converter.
2.1.1

Autonomous Access Points

Figure 2. Autonomous APs connected directly to the LAN.
The example in
of a WLAN in Infrastructure Mode. The individual autonomous APs handle all traffic
handling, authentication, RF management, and mobility functions. They are entirely
independent of each other, and have to be configured separately.
7 September 2011 / Ver. G
4.1 Supported Standards
AP AP
2. Figure
figure 2 shows a system with autonomous APs. This is the most basic type
for a description of the 802.11 amendments
LAN
AP
TD 92313EN
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