Docs Linux Wlan FAQ 2

2. General information

An introduction to the 802.11 Wireless Local Area Networks (LAN) standard and the Linux-WLAN project

2.1 What is the Linux WLAN project, anyway?

The goal of the Linux WLAN project is to develop a complete, standards based, wireless LAN system using the GNU/Linux operating system. What differentiates this project from the Linux wireless extensions and other Linux wireless projects is that we’re basing everything on the recently approved IEEE 802.11 standard.

The WLAN packageĀ  can be obtained from http://www.linux-wlan.org and contains a device driver and support utility for GNU/Linux supporting the Intersil reference design PRISM Direct Sequence Spread Spectrum (DSSS) Wireless LAN (WLAN) Adapters (PRISM cards for short). This design uses the PCMCIA interface and form factor.

The PRISM card is an IEEE 802.11 compliant 2.4 GHz DSSS WLAN network interface card that uses the Intersil PRISM chipset for its radio functions and the AMD PCNet-Mobile chip (AM79C930) for its Media Access Controller (MAC) function.

2.2 Why would I want a wireless LAN?

A wireless LAN (WLAN) is a flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN. Often the use of cables is impractical if not impossible, in which case WLANs have proven their effectiveness: very portable, no need to wire every workstation and every room, entire networks can be easily moved without the requirement to additional wiring, cable drops or reconfiguration of the network. Different LANs at distant locations can be connected (bridged). For instance, to connect 2 offices across the street. Not to mention the fact it will make the geek in you go nuts.

2.3 What is the best WLAN card?

Who are we to judge? It depens on your needs (performance, coverage, reliability, infrastucture) and – of course – your budget. No single vendor can provide all of the products and services to meet every mobile computing need.

We do have a list of vendors that sell cards that fall under the umbrella of the IEEE 802.11 standard and have proven to work with the Linux WLAN drivers:

Zoom Telephonics
Intalk/Nokia
Samsung (Korea)
DDBTEL (Taiwan)
GemTek (Taiwan)
MELCO (Japan)
Bay Networks

It is also worth mentioning that there exist other fine fully 802.11 compliant cards which have Linux drivers as for instance:

Wavelan IEEE — http://www.fasta.fh-dortmund.de/users/andy/wvlan/
Aironet Arlan — http://www.cs.ubc.ca/spider/jennings/
Webgeat Aviator2.4 — http://www.cse.ogi.edu/~omega/wireless/aviator/
Raytheon Raylink — http://world.std.com/~corey/raylink.html
others

2.4 What cards are supported and which aren’t?

The following vendors are selling hardware using a similar design as the Intersil PRISM card. The following vendors have proven to have compatible hardware:

Zoom Telephonics
Intalk/Nokia
Samsung (Korea)
DDBTEL (Taiwan)
GemTek (Taiwan)
MELCO (Japan)
Bay Networks
If you have a card that is not supported by the Linux WLAN project, then you might want to check the Linux Wireless LAN HOWTO ( http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/ ), where you can find a list of other known Linux WLAN drivers.

2.5 What is IEEE 802.11?

IEEE 802.11 specifies a wireless LAN standard developed by the IEEE (Institute of Electrical and Electronic Engineering) committee. The 802.11 working group took on the task of developing a global standard for radio equipment and networks operating in the 2.4GHz unlicensed frequency band for data rates of 1 and 2Mbps. The standard does not specify technology or implementation but simply specifications for the physical layer and Media Access Control (MAC) layer. The standard allows for manufacturers of wireless LAN radio equipment to build interoperable network equipment.

The IEEE 802.11 standard defines the protocol for two types of networks: (1) ad-hoc and (2) infrastructure networks. A simple network where communication is established between multiple stations in a given coverage area without the use of an access point or server is refereed to as an ad-hoc network. In order for all stations to have fair access to the wireless media, the standard specifies the rules that each station must observe so that they all have fair access to the wireless media.

To ensure that throughput is maximized for all of the users, it also provides methods for arbitrating requests to use the media. The infrastucture network uses an access point that controls the allocation of transmit time for all stations and allows mobile stations to roam from cell to cell. The access point is used to handle traffic from the mobile radio to the wired or wireless backbone of the infrastructure network. This arrangement ensures proper handling of the data traffic. The access point routes data between the stations and other wireless stations or to and from the network server.

A complete overview of the IEEE 802.11 standard is beyond the scope of this FAQ, so point your browser to http://grouper.ieee.org/groups/802/11/ for all specification details about the physical layer (PHY) and medium access control layer (MAC). Required material for those who want to help out with the development of the Linux WLAN drivers and a typical monday-morning headache is guaranteed: you just can’t miss it.

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