Cace Technologies AirPcap Wireless Capture Adapters Benutzerhandbuch
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AirPcap User’s Guide
A Brief Introduction to 802.11
Terminology
The terms Wireless LAN or WLAN are used to indicate a wireless local
area network, e.g. a network between two or more “stations” that uses
radio frequencies instead of wires for the communication.
area network, e.g. a network between two or more “stations” that uses
radio frequencies instead of wires for the communication.
All components that can “connect” to a WLAN are referred to as stations.
Stations fall into one of two categories: access points or wireless clients.
Stations fall into one of two categories: access points or wireless clients.
Access points transmit and receive information to/from stations using
radio frequencies. As we shall see later, the particular choice of a radio
frequency determines a wireless “channel.” An access point usually acts as
a “gateway” between a wired network and a wireless network.
radio frequencies. As we shall see later, the particular choice of a radio
frequency determines a wireless “channel.” An access point usually acts as
a “gateway” between a wired network and a wireless network.
Wireless clients can be mobile devices such as laptops, personal digital
assistants (PDAs), IP phones or fixed devices such as desktops and
workstations that are equipped with a wireless network interface card.
assistants (PDAs), IP phones or fixed devices such as desktops and
workstations that are equipped with a wireless network interface card.
In some configurations, wireless devices can communicate directly with
each other, without the intermediation of an access point. This kind of
network configuration is called peer-to-peer or ad-hoc.
each other, without the intermediation of an access point. This kind of
network configuration is called peer-to-peer or ad-hoc.
A Basic Service Set (BSS) is the basic building block of a WLAN. The
“coverage” of one access point is called a BSS. The access point acts as
the master to control the stations within that BSS. A BSS can be thought
of as the wireless version of an IP subnet. Every BSS has an id called the
BSSID
“coverage” of one access point is called a BSS. The access point acts as
the master to control the stations within that BSS. A BSS can be thought
of as the wireless version of an IP subnet. Every BSS has an id called the
BSSID
, which is the MAC address of the access point servicing the BSS,
and a text identifier called the SSID.
802.11 Standards
802.11
is a standard that defines the physical layer and the data-link layer
for communication among wireless devices. The original 802.11
specification was ratified in 1997, uses the 2.4 GHz frequency band, and
allows transmission rates of 1 or 2 Mbps.
802.11a
specification was ratified in 1997, uses the 2.4 GHz frequency band, and
allows transmission rates of 1 or 2 Mbps.
802.11a
, ratified in 1999, is an extension of 802.11 that operates at 5 GHz.
It supports 8 additional transmission rates: 6, 9, 12, 18, 24, 36, 48 and 54
Mbps.
802.11b
Mbps.
802.11b
, ratified in 1999, is an extension of 802.11 that uses the same 2.4
GHz frequency band, and supports two additional transmission rates: 5.5
and 11 Mbps.
802.11g
and 11 Mbps.
802.11g
, ratified in 2003, is backward compatible with 802.11b, and
supports the same additional transmission rates found in 802.11a: 6, 9, 12,