2.2 Chipset Compatibility

While there are many vendors selling Wi-Fi hardware, the radio chipsets come from a relatively small set of manufacturers. With a few exceptions, radio chipset support under Linux is quite good, and getting better.

Before getting into the nuts and bolts of radio chipsets, there is one online resource that you absolutely need. Jean Tourrilhes at Hewlett Packard is the author of the Linux Wireless Tools (covered later in this chapter). He also maintains an extensive web page that includes the Wireless LAN How-To. The page is located at http://www.hpl.hp.com/personal/Jean_Tourrilhes/index.html. For information regarding a specific radio chipset and driver support in Linux, look on the Devices & Drivers page: http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Linux.Wireless.drivers.html. The page is updated frequently and has extensive information on many esoteric wireless devices and drivers.

2.2.1 Common Chipsets

Although there are probably less than 50 manufacturers of Wi-Fi radio chipsets, this book simply does not have the space to cover each of these manufacturers in detail. We cover the five most popular manufacturers and their chipsets, which, in reality, produce 80% of all 802.11 hardware.

2.2.1.1 Intersil Prism II

Before it became a part of Intersil, a company called Harris developed the Prism I reference standard for 802.11, based on an AMD AM930 processor core . This chipset is 802.11 only, so we won't cover any details of driver support, but they are available on Jean Tourrilhes' web site, listed in the previous section.

At one point, Prism II has been the most widely available and popular 802.11b radio chipset. Intersil licensed the chipset and reference designs for Prism II to a large number of vendors. A partial list of vendors using Prism II radios in their access points, PCMCIA cards, PCI cards, USB adapters, and Compact Flash (CF) cards includes:

• Compaq

• Nokia

• Proxim

• D-Link

• Linksys

• Netgear

• SMC

• Senao/Engenius

Nearly all of these vendors have products using other radio chipsets. Unfortunately, many products have kept the same name and sometimes even the same part number, while changing the underlying radio chipset. A good case in point: the D-Link DWL-650. This radio card initially shipped with a Prism II chipset and was very popular, because it worked in a Linux box. However, D-Link changed chipsets when it released the DWL-650 Version 2, choosing an ADMtek chipset. It is very difficult to tell from the packaging which version of the DWL-650 you are purchasing.

Although you have a very good chance of finding an 802.11b radio card that uses a Prism II chipset, there is no guarantee that the chipset is inside your card. This applies to every other card manufacturer as well. Once you've decided on a radio card, research online to make sure you know which chipset it uses.

Several manufacturers licensed the Prism II reference design from Intersil and based their products around this design. These manufacturers include Lucent, Symbol, and Aironet/Cisco. However, the radios designed by these manufacturers use different firmware and are not compatible with Prism II drivers, although some cards may appear to work: the driver will load, but the card may function only partially or not at all.

2.2.1.2 Lucent WaveLan/Orinoco

The original Lucent WaveLan radios developed at AT&T (before Lucent was spun off as a separate company) were 900 MHz radios, later followed by 2.4 GHz radios in the Industrial, Scientific, and Medical (ISM) band . These cards used an Ethernet MAC chip onboard, rather than a MAC chip that met standard 802.11 specifications.

The history of WaveLan is of name changes, mergers, and acquisitions. Lucent released a newer version of the card, the WaveLan IEEE, which met the 802.11 specifications, and then later upgraded the card to support 802.11b (based on the Prism II reference design, discussed previously). Not too long afterward, the WaveLan brand was renamed to Orinoco. Lucent then spun off this part of its company into a separate company named Agere. Another Lucent spin-off called Avaya also sells radio cards using the Orinoco chipset. Most recently the end unit sales of Orinoco have been acquired by Proxim, while Agere still manufactures the radio chipsets.

Lucent/Agere was one of the few vendors not only to manufacture the radio chipset, but to sell end- user equipment in the form of radio cards and access points.

In addition to the Lucent, Agere, and Avaya brands, which use the Orinoco chipset, the Apple AirPort line of products is based on the WaveLan IEEE chipset but is not compatible with Linux drivers for Orinoco. Other vendors that sell radios using the Orinoco chipset include Enterasys, Elsa, Buffalo, HP, IBM, Dell, Sony, and Compaq. Again, many of these vendors also produce radios using chipsets from other manufacturers.

2.2.1.3 Aironet/Cisco

The original Aironet radios were similar to the original Lucent WaveLan: they started at 900 MHz and then moved to 2.4 GHz. Again, they were not initially compatible with the 802.11 standard. Aironet produced the 4500 (802.11) and 4800 (802.11b) series of radios, based on the Harris Prism chipset, but with proprietary firmware.

The story of Aironet is also one of acquisition: Cisco purchased Aironet in March of 2000. Prior to the purchase, Aironet had released the 4800B family of radio cards, including ISA, PCI, and PCMCIA versions, based on the Intersil Prism II chipset. These radios were renamed as the Cisco 340 series of cards. Cisco has since released the 350 series of radio cards that feature 100 mW of transmit power (as opposed to the 30 mW offered by the majority of radios). The 350 family also includes a MiniPCI form factor radio card.

The majority of consumer Wi-Fi radio cards have radios that feature 30 mW of transmit power. Notable exceptions to this are the Cisco 350 cards, the Senao/EnGenius 100 and 200 mW cards, similar 100/200 mW cards from Zcomax, and a few models from D-Link.

2.2.1.4 Symbol

Symbol developed frequency- hopping radios in the 2.4 GHz band called Spectrum24. In a slight twist, Symbol made sure its products were 802.11-compliant from the beginning. Symbol came somewhat late to the 802.11b market, but it released a new line called Spectrum24 High-Rate. Again, these cards are based on the Intersil Prism II chipset with custom firmware. Both 3Com and Intel sell OEM versions of these cards.

Symbol sells mostly PCMCIA cards but also offers a PCI card. Symbol main strength is integrated products ”it offers PDAs with built-in wireless and barcode readers for industrial, medical, and manufacturing applications. Symbol also has one of the few CF implementations of 802.11b. Versions of these cards are also available and sold as an OEM package by Socket Communications.

2.2.1.5 Atmel

Atmel was the first to market a USB 802.11b chipset. However, that chipset did not include a radio, so various radios can be used with this chipset, including the Intersil Prism II radios. Linksys and D-Link both sell USB radio adapters based on the Intersil chipset. SMC and 3Com both sell PCMCIA cards using the Atmel chipset.

2.2.1.6 Atheros

Atheros is unique in that its chipsets are not based on the Intersil Prism II reference designs. It was the first to market 802.11a chipsets. For quite some time, any 802.11a radios available for purchase were built using the Atheros chipset. Atheros has since introduced dual-mode 802.11a/b radios with its ar5211 chipset and tri-mode a/b/g radios using their ar5212 chipset.

Proxim, SMC, Linksys, and D-Link all sell 802.11a, as well as dual- and tri-mode radio products using the Atheros chipset. The primary form factors are PCMCIA and MiniPCI. Linksys and D-Link both sell PCI dual- and tri-mode radios; however, they consist of a PCI card with a MiniPCI radio onboard.

2.2.1.7 Broadcom

Broadcom has both 802.11b and 802.11g radio chipsets. It has completely ignored the Linux community despite the many references to Linux on its web pages. No Linux drivers are available for Broadcom radio cards as of this writing. Cards based on the Broadcom 802.11b chipset include the Dell TrueMobile 1180 and the Linksys WMP11 (previous versions of this card used the Intersil Prism II chipset). Cards based on the Broadcom 802.11g chipset include the Linksys WPC54G and WMP54G.

Linux, Driver Support, and the GPL

There are a few fronts on which the proprietary approach of a few hardware vendors clashes with the spirit of the Linux community.

Companies that manufacture many of the unsupported Wi-Fi cards refuse to divulge enough information on their radios and firmware for the open source community to effectively build drivers.

Also, there are a number of drivers available that are available only in binary form. The company that manufactures the radio chipset releases most of these drivers. The madwifi driver for the Atheros chipsets, developed by Sam Leffler with the cooperation of Atheros, is a good example. The original driver was developed for BSD but wasn't released, because the Atheros hardware does not enforce valid operating modes that comply with FCC regulations.

As a solution, Atheros developed a Hardware Abstraction Layer (HAL), in binary form, that sits between the hardware and the driver and regulates the hardware to meet FCC requirements. Unfortunately, the binary HAL is available only for i386 architecture, and source is not available.

As such, the madwifi driver is viewed in the open source community as a "black sheep" project, and many people refuse to use the driver, because a large portion of it does not have source publicly available. There is a completely open source driver for the Atheros chipsets under development; see Section 2.4.4 later in this chapter.

Finally, there are issues with some vendors that have released products based on Linux and other open source software products. The open source community has made recent discoveries that show that some vendors appear to be violating the GNU General Public License under which the operating system and tools software were published. As of this writing, this is an unresolved matter.

2.2.2 Determining Your Radio Chipset

As previously discussed, determining the chipset your radio uses can be difficult, because many equipment vendors use chipsets from several different manufacturers. An excellent example is Linksys. Its 802.11b PCMCIA cards use the Prism II chipset. However, the Linksys USB 802.11b adapters use the Atmel chipset, while its 802.11g PCMCIA cards use a Broadcom chipset, and its dual-mode 802.11a/802.11g PCMCIA and PCI cards use the Atheros chipset. The bottom line is that you should determine your card chipset type before installing drivers.

To determine the chipset of a radio card, refer to the following methods :

• If your radio card is PCMCIA or Cardbus, and you have the pcmcia-cs package installed, or are using the kernel tree PCMCIA, use the cardctl ident command. This shows vendor identification strings for the cards that are currently inserted in the PCMCIA slots. This works regardless of whether you have a driver loaded for the card. Here is an example output of the command on a system with two Orinoco cards:

   #  cardctl ident  Socket 0:   product info: "Lucent Technologies", "WaveLAN/IEEE", "Version 01.01",      ""   manfid: 0x0156, 0x0002   function: 6 (network) Socket 1:   product info: "Lucent Technologies", "WaveLAN/IEEE", "Version 01.01",      ""   manfid: 0x0156, 0x0002   function: 6 (network) 

  Here is an example output of the command on a system with a single Senao Prism II-based card:

   #  cardctl ident  Socket 0:   product info: "INTERSIL", "HFA384x/IEEE", "Version 01.02", ""   manfid: 0x0156, 0x0002   function: 6 (network) 

• If your radio card is PCI, use the command lspci -v to show the vendor identification string. Bear in mind that this command shows you all of the devices on your PCI bus, so for some systems this may return a list several pages long.

• If your radio card is USB, you can usually find the vendor identification strings for any USB device by using the dmesg command to show output generated during the boot process. You might also find the same information in /var/log/messages .

These commands usually let you know the manufacturer of the chipset. However, some manufacturers have obfuscated their vendor identification strings, so you still may not find a valid chipset ID.

An excellent resource that is published on the pages of the wlan-ng driver is the WLAN Adapter Chipset Directory (http://www.linux-wlan.org/docs/wlan_adapters.html). This is compiled and updated regularly by the maintainers of wlan-ng, AbsoluteValue Systems, Inc.

All radio devices are required to have the FCC ID printed on them. A final option is to get the FCC ID from your radio card and look it up on the FCC web site (http://www.fcc.gov/oet/fccid). Using this web site, the FCC ID NI3-SL-2011CD from the back of a Senao 100 mW 802.11b card returned a single entry for Senao in Taiwan. If you select this entry by choosing the link for Detail, you are again presented with a number of documents provided to the FCC by the manufacturer. In this particular case, select a PDF document titled "Operational Description," which reads:

The SL-2011CD WLAN PC Card utilize the Intersil Prism II Direct Sequence Spread Spectrum Wireless Transceiver chip set.