About duplex in WAPs

As I can understand, most wireless cards sold today are half duplex.
Is this also correct for Wireless Access Points? I was wandering since
I consider building my own WAP. Are there any solutions where you can
use full duplex on 802.11b?

Thanks.

--
Martin Holt Juliussen

Martin Holt Juliussen <(E-Mail Removed)> writes:

> As I can understand, most wireless cards sold today are half duplex.
> Is this also correct for Wireless Access Points? I was wandering since
> I consider building my own WAP. Are there any solutions where you can
> use full duplex on 802.11b?

I've never tried it but I suppose you could use two pairs of access
points, and make one the "transmit" pair and the other the "receive"
pair ala how a typical E1/T1 works. That is, transmit and receive
are used here to mean the same things they would when talking about
an actual wired circuit wherein one pair of wires is used to receive
data and the other pair of wires is used to transmit data, and each
one gets its own IP address, etc...

Billy Y..

Martin Holt Juliussen <(E-Mail Removed)> wrote:
> As I can understand, most wireless cards sold today are half duplex.
> Is this also correct for Wireless Access Points? I was wandering since
> I consider building my own WAP. Are there any solutions where you can
> use full duplex on 802.11b?

Half-duplex is the only way that is possible, if you use one channel.
The transmitted signal (at the antenna) is around ten billion times stronger
than the recieved signal, and totally swamps it.
Using seperate channels for transmit and recieve, perhaps.

--
http://inquisitor.i.am/ | private.php?do=newpm&u= | Ian Stirling.
---------------------------+-------------------------+--------------------------
What a wonderfull world it is that has girls in it! -- Robert A Heinlein.

802.11 transmission is asynchronous, so within the BSS it's inherently
half-duplex.

The equivalent of adding a second wirepair (10BaseT half-duplex vs.
full-duplex is the closest analogy) would be, as Ian says, to somehow bond
together two channels, one for sending and one for receiving.

I believe this would require massive changes to the 802.11 MAC and PHY.
Concurrent sending and receiving implies two concurrent senders, which the
802.11 state machines and protocols are designed to avoid. Some devices
support a proprietary Turbo mode, which doubles the bitrate by bonding
channels, but I believe ordinary half-duplex operation is used. Plus, I'm
not sure that 802.11 devices have antennas that support concurrent transmit
and receive. Ian?


"Ian Stirling" <(E-Mail Removed)> wrote in message
news:bmhbvu$dga$1$(E-Mail Removed)...
> Martin Holt Juliussen <(E-Mail Removed)> wrote:
> > As I can understand, most wireless cards sold today are half duplex.
> > Is this also correct for Wireless Access Points? I was wandering since
> > I consider building my own WAP. Are there any solutions where you can
> > use full duplex on 802.11b?
>
> Half-duplex is the only way that is possible, if you use one channel.
> The transmitted signal (at the antenna) is around ten billion times
stronger
> than the recieved signal, and totally swamps it.
> Using seperate channels for transmit and recieve, perhaps.
>
> --
> http://inquisitor.i.am/ | private.php?do=newpm&u= | Ian
Stirling.
> ---------------------------+-------------------------+--------------------
------
> What a wonderfull world it is that has girls in it! -- Robert A
Heinlein.

>As I can understand, most wireless cards sold today are half duplex.

As of a few weeks ago no wireless nics on the market were full duplex.
And I don't believe that will change any time soon.

>Is this also correct for Wireless Access Points?

A 5 minute google surch didn't find any AP's that claim to be full
duplex, with the exception of one due out in 2004.

> I was wandering since
>I consider building my own WAP. Are there any solutions where you can
>use full duplex on 802.11b?
>
>Thanks.

------------
When your PC gives a little they give a lot.
http://www.dslreports.com/forum/disco

"Martin Holt Juliussen" <(E-Mail Removed)> wrote in message
news:1066146835.773580@gurney...
> As I can understand, most wireless cards sold today are half duplex.
> Is this also correct for Wireless Access Points? I was wandering since
> I consider building my own WAP. Are there any solutions where you can
> use full duplex on 802.11b?
>
> Thanks.
>
> --
> Martin Holt Juliussen

You could use two radios in an AP, much like current bridge offerings such
as the Western Multiplex Tsunami line does. That's true full duplex in a
point to point situation. Consider that even if you have two radios in your
infrastrusture AP, it would still be shared bandwidth once you add the
second client. A two radio AP would be a nice feature, but wouldn't solve
all wireless "ills".

The full-duplex Tsunami bridges appear to use completely proprietary
protocols. There certainly are ways to do full-duplex wifi, but I doubt if
any are built on 802.11.

"Kevin Webb" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> "Martin Holt Juliussen" <(E-Mail Removed)> wrote in message
> news:1066146835.773580@gurney...
> > As I can understand, most wireless cards sold today are half duplex.
> > Is this also correct for Wireless Access Points? I was wandering since
> > I consider building my own WAP. Are there any solutions where you can
> > use full duplex on 802.11b?
> >
> > Thanks.
> >
> > --
> > Martin Holt Juliussen
>
> You could use two radios in an AP, much like current bridge offerings such
> as the Western Multiplex Tsunami line does. That's true full duplex in a
> point to point situation. Consider that even if you have two radios in
your
> infrastrusture AP, it would still be shared bandwidth once you add the
> second client. A two radio AP would be a nice feature, but wouldn't solve
> all wireless "ills".
>
>

gary <(E-Mail Removed)> wrote:
> 802.11 transmission is asynchronous, so within the BSS it's inherently
> half-duplex.
>
> The equivalent of adding a second wirepair (10BaseT half-duplex vs.
> full-duplex is the closest analogy) would be, as Ian says, to somehow bond
> together two channels, one for sending and one for receiving.
>
> I believe this would require massive changes to the 802.11 MAC and PHY.
> Concurrent sending and receiving implies two concurrent senders, which the
> 802.11 state machines and protocols are designed to avoid. Some devices
> support a proprietary Turbo mode, which doubles the bitrate by bonding
> channels, but I believe ordinary half-duplex operation is used. Plus, I'm
> not sure that 802.11 devices have antennas that support concurrent transmit
> and receive. Ian?

I'm almost totally sure that most don't.
There may be the odd one.
I'm doubtfull that a station transmitting on full power at
an adjacent channel on an antenna 15cm away won't interfere with
recieving a client 100m away, with a signal a million times weaker.
It could be done with current hardware, but it'd require two access
points/trancievers per node, and routing setup appropriately.

For example with a laptop, a couple of USB wireless lan cards seperated
by a bit, two accesspoints and static routes setup between them
so that the traffic flows in one direction only.


--
http://inquisitor.i.am/ | private.php?do=newpm&u= | Ian Stirling.
---------------------------+-------------------------+--------------------------
My inner child can beat up your inner child. - Alex Greenbank

"Ian Stirling" <(E-Mail Removed)> wrote in message
news:bmik45$16d$1$(E-Mail Removed)...
> gary <(E-Mail Removed)> wrote:

<snip...>

>> Plus, I'm
> > not sure that 802.11 devices have antennas that support concurrent
transmit
> > and receive. Ian?
>
> I'm almost totally sure that most don't.
> There may be the odd one.
> I'm doubtfull that a station transmitting on full power at
> an adjacent channel on an antenna 15cm away won't interfere with
> recieving a client 100m away, with a signal a million times weaker.
> It could be done with current hardware, but it'd require two access
> points/trancievers per node, and routing setup appropriately.

Don't forget that "adjacent channel" here means 25 Mhz away.

>
> For example with a laptop, a couple of USB wireless lan cards seperated
> by a bit, two accesspoints and static routes setup between them
> so that the traffic flows in one direction only.

Could you explain in more detail how you would use static routes?

My first guess was you either push duplex "down" into 802.11 MAC, which I
claim is prohibitively expensive and error-prone (but watch, someone will
prove it's already been done - and I'd actually like to know if so), or you
push it "up" into a virtual driver sitting on top of two BSS's (could be two
cards in a laptop, or an AP that supports multiple concurrent BSS'es) that
exports a bidirectional interface above and uses the BSS'es below
unidirectionally.

This last is certainly doable, although I don't know if any performance gain
is worth sacrificing 1/3 of the available bandwidth for 802.11b/g. It goes
without saying that all devices in the net would have to have the same
proprietary mods for this to work. Also, to make it work on an AP or router,
you'd have to have a way to modify runtime on the device (load/configure
driver binary, understand internal driver interfaces, etc.). Is there any
off-the-shelf home/SOHO equipment that lets you do this?

>
>
> --
> http://inquisitor.i.am/ | private.php?do=newpm&u= | Ian
Stirling.
> ---------------------------+-------------------------+--------------------
------
> My inner child can beat up your inner child. - Alex
Greenbank

"AJ" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
>
> >As I can understand, most wireless cards sold today are half duplex.
>
> As of a few weeks ago no wireless nics on the market were full duplex.
> And I don't believe that will change any time soon.
>
> >Is this also correct for Wireless Access Points?
>
> A 5 minute google surch didn't find any AP's that claim to be full
> duplex, with the exception of one due out in 2004.

Could you send me a URL for this one?

>
> > I was wandering since
> >I consider building my own WAP. Are there any solutions where you can
> >use full duplex on 802.11b?
> >
> >Thanks.
>
> ------------
> When your PC gives a little they give a lot.
> http://www.dslreports.com/forum/disco