What does AdhocOfdm look like when it's working?

Live forum: http://rt2x00.serialmonkey.com/viewtopic.php?t=3173

matthew_exon

12-02-2007 18:05:59

I know that this is a frequently asked question, but I've read and re-read the FAQ and the documentation and I still can't figure out the answer...

I have an RT2500 PCI card that I'm using in ad hoc mode, and I would like to use it at 54Mbps. Apparently the command is "iwpriv ra0 set AdhocOfdm=1". I've done that, and it doesn't seem to make any difference

[code1k4yn9jz]# iwconfig ra0
ra0 RT2500 Wireless ESSID:"XXXX"
Mode:Ad-Hoc Frequency=2.422 GHz Bit Rate:11 Mb/s
RTS thr:off Fragment thr:off
Encryption key:XXXX-XXXX-XX Security mode:restricted
Link Quality=60/100 Signal level=-69 dBm Noise level:-217 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0

# iwpriv ra0 set AdhocOfdm=1
# iwconfig ra0
ra0 RT2500 Wireless ESSID:"XXXX"
Mode:Ad-Hoc Frequency=2.422 GHz Bit Rate:11 Mb/s
RTS thr:off Fragment thr:off
Encryption key:XXXX-XXXX-XX Security mode:restricted
Link Quality=60/100 Signal level=-69 dBm Noise level:-217 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0[/code1k4yn9jz]

What am I supposed to be seeing here? iwpriv hasn't given me any output at all. If it hadn't worked, surely iwpriv would print an error? I'd expect it to print [i1k4yn9jz]something[/i1k4yn9jz], such as maybe "yay, that worked, your card is now in OFDM mode" or "boo, that didn't work, you're still working at a measly 11Mbps". There doesn't even seem to be a "iwpriv ra0 get AdhocOfdm" command to confirm the new value. Can someone who's got AdhocOfdm working post what the output looks like, including the "before" and "after" iwconfig output?

The FAQ says 'Some cards support "breaking the rules" though to get the full 54mb/s.' That seems ambiguous to me - it could mean "some wifi cards support breaking the rules, and the rt2500 is one of them", or "some rt2500 cards support breaking the rules, others don't". It probably means the latter, but I find that really weird. Surely this is dictated by the chip, not the board itself? Anyway, how can I find out whether or not my board is supposed to support this? Does anyone have some examples of cards that definitely work and cards that definitely don't work? If it helps, here's my lspci output

[code1k4yn9jz]0000:00:14.0 Network controller: RaLink Ralink RT2500 802.11 Cardbus Reference Card (rev 01)
Subsystem: Belkin: Unknown device 700a
Flags: bus master, slow devsel, latency 32, IRQ 10
Memory at de000000 (32-bit, non-prefetchable) [size=8K]
Capabilities: [40] Power Management version 2[/code1k4yn9jz]

I'm just really confused by all of this. I've been fighting against this for a long time, and by this stage a definitive "no, that can't possibly work" would be totally fine. But I'd really like to know one way or the other, especially since I'm considering playing with the new driver, which would be a waste of time if my card definitely will never, ever work.

Thanks for any help!
Mat

IvD

12-02-2007 18:18:03

The ieee80211 standard dictates the maximum speed for adhoc network is 11Mb/s. The Ralink chipsets (including rt2500) support the adhocofdm feature that will override the rule and allow speeds up to 54Mb/s over the adhoc network. These drivers are not alone in this, as some other chipsets/drivers also have a config option to bypass the rule.

Note that when using this option, it should be enabled on _all_ cards within the network in order to allow the correct speeds. So if you have 2 cards in the network, both cards should be allowed to use 54Mb/s on the network.

matthew_exon

12-02-2007 19:11:08

Maybe I wasn't very clear. I know that the rt2500 chip [i16rurd51]can[/i16rurd51] support AdhocOdfm. But does that mean that any card based on an rt2500 chip [i16rurd51]must[/i16rurd51] support AdhocOdfm? That's what's not clear from the FAQ.

IvD

12-02-2007 22:53:31

Yes, the chipsets are capable of working with 54Mbit in adhoc, only the driver will limit the rates. This means that the adhocofdm option will work for all rt2500 chipsets.

matthew_exon

13-02-2007 06:10:55

Aha, great, thanks for that.

In that case, could I suggest rewording the FAQ slightly to make this more clear? That is, instead of 'Some cards support "breaking the rules" though to get the full 54mb/s', how about 'However, some cards, including all those based on the rt2500 and rt2570 chipsets, support "breaking the rules" to get the full 54mb/s'?

I still have my problem though, which is that it [iocfexs4j]isn't[/iocfexs4j] working for me, or at least it doesn't appear to be working. What can I do next?

IvD

13-02-2007 10:16:24

Like I said, are you sure the other stations within the adhoc network also allow 54mbit/s speeds.

matthew_exon

13-02-2007 12:01:37

There is only one wifi computer here. I'm trying to cut down on the variables, so for the moment I have every other device turned off. I want to first set up the first device and make sure that it's configured properly. Then I'll turn on the second one and try to get that working too. Are you saying that it's impossible to configure just one card existing on its own with no other devices at all to be high speed ad hoc?

My goal was always to get my server and my desktop communicating wirelessly at 54Mbps. I also had a laptop with an 11Mbps PCMCIA card. My plan was to first buy a 54Mbps PCI card for one machine, get that at least talking at 11Mbps, and then buy a second card. I bought a Belkin 54Mbps PCI card and managed to get that much working. Then, the time came to buy a second high-speed card. I bought the exact same Belkin card. When it arrived, it turned out that Belkin were now using Broadcom chipsets. So despite going out of my way to buy a card that would use the same configuration as what I already had, I actually ended up with two completely different cards that require completely different configuration. Which was very irritating.

So I'm doing my best. First I want to get the original RT2500 configured correctly to run an ad-hoc network on its own at 54Mbps. Then I will move on to the far harder task, which is getting the Broadcom card to work, which will probably require ndiswrapper and other horribleness. Because that's likely to be so hard (it's proven very hard in the past), I want to make sure that the "easy" RT2500 card is correctly set up before I start playing with the harder card.

wolleric

08-11-2007 14:19:45

So is this topic completely dead? I'm experiencing exactly the same issue. So far the RT2500 is the only Wifi device.
Can I ignore the displayed bitrate if there is no cell connected? I'm using rt2500 CVS from yesterday and a 2.6.24-rc1 kernel.

matthew_exon

08-11-2007 15:08:38

As far as I'm concerned, the topic is moot since my server died a couple of months ago and I now only have one machine, the speed of the wifi network is kinda irrelevant -(

I'm still interested in a definitive answer, though.

Spy84464

10-11-2007 10:25:23

As far as I know, there is no guarantee that different devices (using different chipset) will work together at adhoc ofdm rates since it's not standard.