Sony PSP duplex

All 802.11b is full duplex.

That's incorrect.  All 802.11 (a/b/g) is HALF duplex.

How do I decide who is correct?

Hold on, I'll illicit some support.  :)

Think of a radio walkie talkie with the Push to Talk button (or a CB Radio) - you can talk OR listen - not both (like a cell phone).

I'll back you up pseudocyber, as far as I have ever read I have never seen anything to the contrary. However my word likely isn't enough so:

"802.11b is a half duplex protocol – it can send OR revive, but not both at the same time. "
from: http://www.homenethelp.com/802.11b/index.asp

Whoops, guess I should refresh before posting  :-)  Still I agree 100%
--Rob

Google, it's a wonderful thing for concensus research ... ;)  Thanks RobWill. :)

It's half as pseudo mentioned. Here's a forum link discussing why:
http://www.cwnp.com/phpBB2/viewtopic.php?t=368&

Here's another link also:
http://www.homenethelp.com/802.11b/index.asp

Very valid points... it would be a hell of a lot more overhead to have it operate at full duplex, plus there wouldn't be the same pauses in need to signal, which would cause more interference issues than we already get in the 2.4 GHz range.

"Sorry - Ellicit some support, not Illicit :)"

I thought that was the reason for the smiley in the first place.


Speaking of typos, it's great that two of you can quote the same one:

""802.11b is a half duplex protocol – it can send OR revive, but not both at the same time. "
from: http://www.homenethelp.com/802.11b/index.asp"

unless revive means something I haven't come across before.

"Google, it's a wonderful thing for concensus research ... "

provided you know how to use it. I tried for two days to fund the answer to this question and all I got were ads for duplex printers.

However, it also turned up a number of WAPs which claim to be full duplex. Is that useless if no cards can take advantage of it?

What about this device?

http://www.datahunter.com/oem.html

WAPs can be full duplex on their ETHERNET connection, but to my knowledge, not the wireless - or at least AND be compliant to the 802.11 spec.

"Full Duplex – 9600 to 115 kbps Asynchronous"

That's very confusing.  I suppose it's talking about the WIRED side.  However, "Asynchronous" means NOT synchronous.  

Google's Web Definition of "Asynchronous":  A type of two-way communication that occurs with a time delay, allowing participants to respond at their own convenience. Literally not synchronous, in other words, not at the same time.

Plus, I think that chipset is made to build into something else - is this what you're looking for?  A Full Duplex capable 802.11 device?  As I said, to my knowledge, that would by definition be out of specification with the IEEE 802.11 specification.

Another way to think of Wi-Fi is as what Nextel wishes it was. :-)

No, I'm not looking for a chipset, just an answer to the question, and i wasn't sure if this type of product implied a different answer than was being given.

I'm perfectly willing to believe that a published spec like this one may have an error in it; I just need to be sure it's not showing us a situation where wireless can be full-duplex.

Recall that this relates to the PSP, a specific piece of hardware. So are we sure that Sony did not do anything clever with their cards in ad hoc mode whereby the signals or frequencies or whatever are split in some way that are still 802.11b but are also full duplex?

The walkie talkie example has the sender explicitly giving up control of the channel to allow the other guy to talk. What happens in a multi player game where both players are sitting on a button?

Wireless radios (WAP and client) both have to "explicitly give up control of the channel" as well.  This is part of the large protocol overhead of 802.11.  If both players want to transmit at the same time, they will roll the dice (generate a random number) to see which one gets to transmit first.  It's more complicated than that, but that's essentially how they resolve the issue.

Download the 802.11 spec:  http://grouper.ieee.org/groups/802/11/

Not saying some company like Sony might have done something proprietary.  But if it's 802.11 compliant, then its half duplex.

Errrmmmm.. 802.11b & g are half-duplex.  It all has to do with communicating over a single channel within the approved 802.11 operating range:  the 11 slightly overlapping channels which really only result in channels 1, 6 & 11 being able to be run side by side and not step on each other.

The real issue of Half-duplex wireless is the inability to TX & RX at the same time - it doesn't work in a single channel environment and takes us back to the problem with HUBs in a wired network environment.  In wireless, the transmission medium is shared and there is no way to control communication links (the way switches do) and allow for simultaneous TX/RX over the medium - trying to run it Full-Duplex over a shared medium will result in horrible performance due to packet collisions & retransmissions...

If you send on 1 or 6 or 11 and receive on one of the others, that's not going to be full-duplex? Or are you saying the channels are so close to each other that for all practical purposes they are the same channel and the interference will happen often enough to make it worthless?

Sending/receiving over multiple channels is the basis for MIMO and the Super-G specs.  It doesn't go Full-duplex, but is half-duplex over multiple channels, resulting in increased capacity through running 2 or 3 simultaneous load-balanced Wireless connections, or spreading out the "shared medium" hurt over 2 or 3 channels.  Still not Full duplex, for full-duplex you have to have:
 - Dedicated listening channel  
 - Dedicated transmit channel,  with no medium contention...

From a signaling perspective, the channels assigned to 802.11b & g communications start at 2.412GHz with 5MHz spacing between channels:
Channel    GHz
1             2.412
2             2.417
3             2.422
4             2.427
..             ...

The signal "bleed" on the 2.4GHz spectrum is about +/- .015Ghz (or 15MHz), so to get "clean" communications between AP and client, it's generally accepted that you set your gear to either channel 1, 6 or 11.

Aside from my experience, I forgot to add citiation of my assistance source:  http://www.wi-fiplanet.com/tutorials/article.php/972261

Regarding channels, normally, the AP will advertise the channel its using in the SSID - so receiving clients, who want to talk to it, will tune to the correct channel.

Have we beat the duplex horse to death?

WI FI works like a hub (not a switch),so it can be said to be a half duplex device.

It uses collision avoidence.