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WLAN Driver

RTIP-32 Reference Manual

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WLAN Driver

The WLAN Driver enables RTIP-32 applications to use wireless LANs using the 802.11b protocol. Currently, the driver supports the Prism 802.11b chipset used by Symbol, Intersil, and Agere devices for PCMCIA and CompactFlash cards. To higher protocol levels, wireless LAN interfaces behave just like Ethernet.

The WLAN Driver is an optional add-on for RTIP-32 and must be purchased in addition to RTIP-32 to be available. Applications requiring the WLAN Driver must include header file Wlanapi.h and link library Wlan.lib. The WLAN Driver API is documented in the RTIP-32 Reference Manual.

The WLAN driver has separate xn_bind... functions for PCI and for PCMCIA/CompactFlash devices. For PCI cards, use xn_bind_prism. There is no need to manually configure IRQs or I/O addresses since the PCI BIOS will have assigned suitable values.

For PCMCIA/CompactFlash devices, use xn_bind_prism_pcmcia. Before xn_interface_open_config is called, RTPCInit must also be called. The WLAN driver does not support hot plugging, so a removeable WLAN card should be inserted before xn_interface_open_config is called. The WLAN driver does not handle PCMCIA events, so RTPCInit's parameters IRQ and Handler can be set to -1 and NULL, respectively.

After xn_interface_open or xn_interface_open_config is called, the WLAN interface must be configured using function xn_wlan_setup. Options include Ad-Hoc or Infrastructure mode and the use of encryption.

In Infrastructure mode (also called BSS, Basic Service Set), the interface will only connect to Access Points. An Access Point is a special communication device which will route packets between a wireless LAN and an Ethernet LAN. One Access Point can usually serve several stations (a device with a 802.11 interface). While an Access Point must be configured for a specific radio channel, stations connecting to it can usually sense which channel to use.

In Ad-Hoc mode (also called IBSS, Independent Basic Service Set), the interface will only connect to other stations to form a 2-node peer-to-peer network. The radio channel to be used must be manually configured to identical values on both stations. Even if no encryption is used, both stations must use identical SSIDs (Service Set Identifier, network name) to successfully connect.

The 802.11 standard defines optional data encryption (WEP, Wireless Encryption Protocol) with 64-bit or 128-bit keys (which, however, only have a real length or 40 and 104 bits, respectively). Some devices can store up to 4 such keys, which is not supported by this WLAN driver. Nevertheless, the encryption protocol requires the specification of a key index. The same key index must be specified in xn_wlan_setup as used by the Access Point or peer station. Of course, the key length and the key itself must also match.

The 802.11 standard also defines an optional mechanism for authentication called Shared Key. Systems not using Shared Key authentication are called Open Systems. Unfortunately, the Shared Key authentication allows intruders to detect a key of an active connection and is therefore not recommended for security reasons.

Further details about configuring a WLAN interface are given in section xn_wlan_setup.

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