Linux Unwired [Electronic resources] نسخه متنی

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/indexl.
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.driversl.
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 productsit 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.

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_adaptersl).
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.