which Wifi cards can be used for a WAP?

[Brian Reichert]

I'm looking at the impressive list of wireless network cards supported
by FreeBSD here:

http://www.freebsd.org/releases/5.3R/hardware-i386.html#WLAN

But, I have the specific interest of building an 802.11g WAP. I
seem to recall lore that not all Wifi cards could be used this way
(something about needing to be able to run in ad-hoc mode, or some
such.)

Is my memory faulty, or can any old 802.11g Wifi card be pressed
into service? I'm specifically looking into various PCI-based
cards, if that affects anyone's advice...

(If someone can recomment a better forum for the question; I'll
accept advice on that matter, too. :)

Of course, any specific advice about good antenna, good driver/throughput,
etc, would also be accepted gleefully...

[Brian Reichert]

Post by Brian Reichert
I'm looking at the impressive list of wireless network cards supported
http://www.freebsd.org/releases/5.3R/hardware-i386.html#WLAN
But, I have the specific interest of building an 802.11g WAP. I
seem to recall lore that not all Wifi cards could be used this way
(something about needing to be able to run in ad-hoc mode, or some
such.)

The ath(4) manpage speaks of a 'hostap' mode, but the manpage
confuses me.

First, it says:

The driver may also be configured to operate in hostap mode. In
this mode a host may function as an access point (base station).

Then:

Access points are different than operating in IBSS mode. They
operate in BSS mode.

So, I'm confused, which mode does a WAP need to be in, 'BSS' or
'hostap'?

Quickie research on this 'hostap' mode (which I'd never heard of
until I began this research) seems to be what I need, but the
verbiage in the ath(4) manpage is throwing me...

Anyway, a survey of the manpages for various WiFi drivers supporting
'hostap' mode seems to sum up as such:

wi(4)
Cards based on the Intersil PRISM chips, but I don't think
any of them support 802.11g.

at(4)
I guess everything listed here, with a URL to an up-to-date list:

<http://customerproducts.atheros.com/customerproducts>

In case anyone's following the same rabbit trail I am, on that
search page, if I select:

WLAN Product: PCI

I get a huge list of PCI cards, and which 802.11 bands they
support. (The search page won't let me exclude those cards that
don't support 802.11g, but that subset it tiny.)

That narrows my search, at this time, to 17 PCI cards supporting
802.11g. I'm currently assuming that anything on this list is
indeed supported by FreeBSD's ath(4) driver.

Please feel free to disabuse me of that notion...

[Brian Reichert]

Post by Brian Reichert
<http://customerproducts.atheros.com/customerproducts>

In perusing many of these cards specs, I see many of them offer a
'turbo mode' of 108 Mbps.

- Is this something magically supported by the hardware? By that,
I mean: if I use a compatible WiFi card in a laptop, they'll just
negotiate the higher rate, and as such the kernel driver has no
impact?

- I'm seeing 'turbo 802.11g' vs. 'Super G'. I haven't found any
thing that tells me if these are synonyms, or if they are
incompatable unofficial extansions of a spec. Does anyone here
know?

[Joerg Sonnenberger]

Post by Brian Reichert
In perusing many of these cards specs, I see many of them offer a
'turbo mode' of 108 Mbps.

That's a vendor-specific mode. I strongly advice you _against_ using it,
it's using at least one additional channel and only adds speed for very
short distances. If you follow the common recommendation of leaving one
channel before and after the active channel, you end up using at least
5 channels for turbo mode compared to three for normal, it's not worth
the trouble.

Joerg

[Brian Reichert]

Post by Joerg Sonnenberger
That's a vendor-specific mode. I strongly advice you _against_ using it,
it's using at least one additional channel and only adds speed for very
short distances. If you follow the common recommendation of leaving one
channel before and after the active channel, you end up using at least
5 channels for turbo mode compared to three for normal, it's not worth
the trouble.

Ok, cool; thanks...

Post by Joerg Sonnenberger
Joerg

[Sam Leffler]

Post by Joerg Sonnenberger

Post by Brian Reichert
In perusing many of these cards specs, I see many of them offer a
'turbo mode' of 108 Mbps.

That's a vendor-specific mode. I strongly advice you _against_ using it,
it's using at least one additional channel and only adds speed for very
short distances. If you follow the common recommendation of leaving one
channel before and after the active channel, you end up using at least
5 channels for turbo mode compared to three for normal, it's not worth
the trouble.

This is misleading. First turbo mode can only be used in the 2.4G band
on channel 6 and does not impact operation on channels 1 and 11. Any
channels in between already suffer from normal (i.e. non-turbo) use
because the channel spread in the 2.4 band means traffic is visible if
you use the in-between channels. Further, turbo mode (as part of
SuperG) requires that the AP detect non-turbo capable stations and
disable turbo use when such stations are present.

As to whether or not to use it; I said in another note that it's really
most useful in the 5Ghz band where there's more available spectrum and
channel spread eliminates any possible interference.

Sam

[Sam Leffler]

Post by Sam Leffler

Post by Joerg Sonnenberger

Post by Brian Reichert
In perusing many of these cards specs, I see many of them offer a
'turbo mode' of 108 Mbps.

That's a vendor-specific mode. I strongly advice you _against_ using it,
it's using at least one additional channel and only adds speed for very
short distances. If you follow the common recommendation of leaving one
channel before and after the active channel, you end up using at least
5 channels for turbo mode compared to three for normal, it's not worth
the trouble.

This is misleading. First turbo mode can only be used in the 2.4G band
on channel 6 and does not impact operation on channels 1 and 11. Any
channels in between already suffer from normal (i.e. non-turbo) use
because the channel spread in the 2.4 band means traffic is visible if
you use the in-between channels. Further, turbo mode (as part of
SuperG) requires that the AP detect non-turbo capable stations and
disable turbo use when such stations are present.

I was wrong; turbo mode requires a 40Mhz wide band so when operating on
channel 6 it'll splatter 1 and 11. Regardless, compliant AP's are
supposed to monitor the air and drop out of turbo if non-turbo traffic
is detected. This is part of the Dynamic Turbo component of SuperG and
happens transparently to SuperG stations.

Sam

[Sam Leffler]

Post by Brian Reichert

Post by Brian Reichert
<http://customerproducts.atheros.com/customerproducts>

In perusing many of these cards specs, I see many of them offer a
'turbo mode' of 108 Mbps.
- Is this something magically supported by the hardware? By that,
I mean: if I use a compatible WiFi card in a laptop, they'll just
negotiate the higher rate, and as such the kernel driver has no
impact?

Turbo mode is an Atheros-specific thing that bonds two channels to
double the effective bandwidth. I know of no other vendor that
implements it. There are various techniques for increasing the
effective bandwidth of an 802.11 medium; none are standardized (yet).

Post by Brian Reichert
- I'm seeing 'turbo 802.11g' vs. 'Super G'. I haven't found any
thing that tells me if these are synonyms, or if they are
incompatable unofficial extansions of a spec. Does anyone here
know?

SuperG is a label for a number of different features that are
implemented as Atheros-specific protocol extensions. Other vendors can
implement most of them (Atheros has released the details of these
extensions) but it's unlikely you'll find many vendors picking them up.
I have code that implements most of SuperG (only compression is
missing) but haven't committed any of these yet (not sure when I'll do
this and/or if all warrant going in FreeBSD).

Turbo 11g is the use of Atheros Turbo mode in the 2.4GHz band. This is
only possible on channel 6 as you need to bond two channels and is
permitted only when non-Turbo-capable stations are detected.
Consequently it's really only useful in the 2.4 band in a private
environment. OTOH you can operate in 11a (5GHz) with more freedom and
SuperG can easily get you transfer rates upwards of 60 Mb/s.

Sam

[Brian Reichert]

Post by Brian Reichert
<http://customerproducts.atheros.com/customerproducts>

Another feature of some cards that I haven't found a clear picture
of:

Some cards have an antenna built right onto the card, and others
seem to come with a remote antenna that hangs off of a six-foot (or
so) cable.

The vendors' arguments for the cable arrangment is that it allows
for a more optimal placement of the antenna, but other lore suggests
that the cable itself introduces loss of signal.

Does anyone have a concrete opinion on this, or can point me in the
right direction for some research?

[Daniel O'Connor]

Post by Brian Reichert
Some cards have an antenna built right onto the card, and others
seem to come with a remote antenna that hangs off of a six-foot (or
so) cable.
The vendors' arguments for the cable arrangment is that it allows
for a more optimal placement of the antenna, but other lore suggests
that the cable itself introduces loss of signal.
Does anyone have a concrete opinion on this, or can point me in the
right direction for some research?

An onboard antenna will suck - if it's a Cardbus card it will be some dinky
PCB dipole with minimal gain (which you can't reorient for your environment).
If it's a PCI/mini-PCI card then it will be inside your PC and suck even more
so they need an external antenna. (And I've never seen a [mini-]PCI wireless
card without an antenna connector).

Lots of cards have a diversity arrangement where they have 2 RF paths, 1 is on
the PCB and the other goes to an external antenna port. If you plug in an
external antenna it will almost certainly get more gain and be used in
preference.

While cable loss can be an important factor it is usually not an issue if you
choose appropriate cabling and antennas. It may be a problem if you need to
do a long run (>20m) but that is pretty rare, and in that case you might want
to consider relocating the box to be closer to the antenna (or using a USB
wireless interface :)

I would guess most vendors reasoning for not putting an external antenna
connector on a card is cost. Most people don't use them on Cardbus interfaces
and they cost a reasonable amount. On my (terribly ancient) DWL-650 card it
has PCB pads for a connector but it isn't used (the shell prevents it) but it
was fairly easy to modify the card to have an external connector. (YMMV,
fire/smoke warning etc)

[Sam Leffler]

Post by Brian Reichert

Post by Brian Reichert
I'm looking at the impressive list of wireless network cards supported
http://www.freebsd.org/releases/5.3R/hardware-i386.html#WLAN
But, I have the specific interest of building an 802.11g WAP. I
seem to recall lore that not all Wifi cards could be used this way
(something about needing to be able to run in ad-hoc mode, or some
such.)

The ath(4) manpage speaks of a 'hostap' mode, but the manpage
confuses me.
The driver may also be configured to operate in hostap mode. In
this mode a host may function as an access point (base station).
Access points are different than operating in IBSS mode. They
operate in BSS mode.
So, I'm confused, which mode does a WAP need to be in, 'BSS' or
'hostap'?

A "Wireless Access Point" is in charge of a "BSS network". The ath
driver does this with a host-based implementation (as opposed to a
device-based/firmware-based implementation). Numerous other devices are
designed to be used tis way too as doing things on the host reduces
vendors cost.

Post by Brian Reichert
Quickie research on this 'hostap' mode (which I'd never heard of
until I began this research) seems to be what I need, but the
verbiage in the ath(4) manpage is throwing me...
Anyway, a survey of the manpages for various WiFi drivers supporting
wi(4)
Cards based on the Intersil PRISM chips, but I don't think
any of them support 802.11g.
at(4)
<http://customerproducts.atheros.com/customerproducts>
In case anyone's following the same rabbit trail I am, on that
WLAN Product: PCI
I get a huge list of PCI cards, and which 802.11 bands they
support. (The search page won't let me exclude those cards that
don't support 802.11g, but that subset it tiny.)
That narrows my search, at this time, to 17 PCI cards supporting
802.11g. I'm currently assuming that anything on this list is
indeed supported by FreeBSD's ath(4) driver.
Please feel free to disabuse me of that notion...

For 5.3 I believe the only cards you can use to create an 11g ap are
those that use the ath driver. However you should beware as the 5.3 ath
support is significantly out of date wrt the code in current. I would
not suggest using 5.3 to build an 11g ap; only current.

Sam