Re: How bad are wireless speeds?

On Sat, 16 Jul 2005 17:31:52 -0400, "Suburban" <sub.this@xxxxxxxx>
wrote:

>I just got a di-524 dlink router, certainly not the cream of the crop but if
>it says 54mbs on the box I expect it to work that way. Anyways everything is
>setup in my room I have good connectivety, strong 54mbs connection to the
>wireless router. I have WEP enabled on the router too, but I run some file
>transfer tests.

What are you using for client radios?
How far away from the DI-524 in feet?

>On wired-wired my speeds where 80mbits solid,

How are you measuring this? I suggest you try IPerf:
http://www.noc.ucf.edu/Tools/Iperf/default.htm

>On wireless-wired speeds dropped to 11mbits (this would be 802.11b speeds
>right?) even though my connection was at 54mbs. I understand WEP can reduce
>speeds.. but this much?
>On wireless-wireless it got even worse. 5mbits!!

First a bit of explanation. Under ideal conditions, you'll get and
maintain a 54Mbit/sec association up to about 8ft from the access
point. Put a few reflectors and add some interference from other
radios in the room, and the speed will drop rapidly. I scribbled a
long and detailed explanation on speed adjustments effects yesterday.
The discussion is on diversity reception, but the explanation involves
speed reduction to deal with error rate reduction:
| http://groups-beta.google.com/group/alt.internet.wireless/browse_frm/thread/d107c5d40abf91f8/909627fc64d6ac2d?tvc=1&q=group:alt.internet.wireless+author:jeff+author:liebermann&hl=en#909627fc64d6ac2dt.internet.wireless+author:jeff+author:liebermann&rnum=4&hl=en#6c068f44529dbe2e

The following was stolen from:
| http://www.intel.com/business/bss/infrastructure/wireless/deployment/hotspot.pdf
I don't consider the numbers very accurate and are very optimistic.
If you want speed, you loose range. Period. Incidentally, the above
article is excellent reading on how Wi-Fi really works.

Rate Approximate Max Indoor Range
1 Mbps 350 ft.
2 Mbps 250 ft.
5.5 Mbps 180 ft.
6 Mbps 300 ft.
9 Mbps 250 ft.
11 Mbps 150 ft.
12 Mbps 200 ft.
18 Mbps 170 ft.
24 Mbps 140 ft.
36 Mbps 100 ft.
48 Mbps 95 ft.
54 Mbps 90 ft.

Also, 54MBits/sec is NOT the transfer speed you'll see with a
benchmark program. It's the wireless connection or association speed.
Transfer speed is roughly 33 to 50% of the connection speed. The best
you can do with a TCP file transfer benchmark under Windoze at
54Mbits/sec is about 24Mbits/sec.

This is stolen from an Atheros PDF at:
http://www.atheros.com/pt/athe ros_range_whitepaper.pdf
with some additions and corrections by me.

Non-overlapping Modulation Max Max Max
Channels ------- | Link TCP UDP
| | | | |
802.11b 3 CCK 11 5.9 7.1
802.11g (with
802.11b) 3 OFDM/CCK 54 14.4 19.5
802.11g only 3 OFDM 54 24.4 30.5
802.11g turbo 1 OFDM 108 42.9 54.8
802.11a 13 OFDM 54 24.4 30.5
802.11a turbo 6 OFDM 108 42.9 54.8

Note that if you have 802.11b compatibilty mode enabled, you get to
slow down even more. The receiver has to listen for 802.11b stations
and simply stops everything while this is done. If it finds an
802.11b signal, it deals with it before returning to 802.11g file
transfers. If you even have an 802.11b device anywhere in range, your
802.11g file transfer performance will suffer.

Finally, all the above is between a wired LAN computah, plugged into
the wireless router, to a wireless computah. If you go wireless to
wireless, divide your thruput by at least two. That's because the
access point is simplex and can only transmit or receive one at a
time. The access point is doing a store and forward on each packet
between wireless clients.

I don't wanna speculate on the validity of your benchmark test without
first having a clue as to your setup and testing methodology.


--
Jeff Liebermann jeffl@xxxxxxxxxxxxxxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
.

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