BL4S200 User’s Manual
138
6. U
SING
THE
W
I
-F
I
F
EATURES
Chapter 6 discusses using the TCP/IP Wi-Fi features on the
BL5S220 board. This networking feature is
not
available on
other BL4S200 models, which have other network interfaces.
6.1 Introduction to Wi-Fi
Wi-Fi, a popular name for 802.11b/g, refers to the underlying technology for wireless local
area networks (WLAN) based on the IEEE 802.11 suite of specifications conforming to
standards defined by IEEE. IEEE 802.11b describes the media access and link layer control
for a 2.4 GHz implementation, which can communicate at a top bit-rate of 11 Mbits/s. Other
standards describe a faster implementation (54 Mbits/s) in the 2.4 GHz band (802.11g).
The adoption of 802.11 has been fast because it's easy to use and the performance is com-
parable to wire-based LANs. Things look pretty much like a wireless LAN.
Wi-Fi (802.11b/g) is the most common and cost-effective implementation currently avail-
able. This is the implementation that is used with the BL5S220. A variety of Wi-Fi hard-
ware exists, from wireless access points (WAPs), various Wi-Fi access devices with PCI,
PCMCIA, CompactFlash, USB and SD/MMC interfaces, and Wi-Fi devices such as Web-
based cameras and print servers.
802.11b/g can operate in one of two modes—in a managed-access mode (BSS), called an
infrastructure mode, or an unmanaged mode (IBSS), called the ad-hoc mode. The 802.11
standard describes the details of how devices access each other in either of these modes.
6.1.1 Infrastructure Mode
The infrastructure mode requires an access point to manage devices that want to communi-
cate with each other. An access point is identified with a channel and service set identifier
(SSID) that it uses to communicate. Typically, an access point also acts as a gateway to a
wired network, either an Ethernet or WAN (DSL/cable modem). Most access points can
also act as a DHCP server, and provide IP, DNS, and gateway functions.
When a device wants to join an access point, it will typically scan each channel and look
for a desired SSID for the access point. An empty-string SSID (" ") will associate the
device with the first SSID that matches its capabilities.
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