Archived from groups: alt.internet.wireless (
More info?)
"Nice4" <nice4@yahoo.com> wrote in message
news:88a0c64a.0405080855.36fedc44@posting.google.com...
> > You should be able to get up to 4 - 7 megabits/sec for a one-way data
> > transfer on 802.11b. If your ISP is capable of sending data to you at
120
> > kilobytes/sec (960 kilobits/sec), you should be able to move it at 960
> > kilobits/sec through the whole network. (You *do* mean "kilobyte" by
"KB",
> > right?
> >
> > If you get 120 kilobytes/sec wired, 70 kilobytes/sec wireless, maybe you
> > have a TCP/IP tuning issue on the wifi client. If you don't have a big
> > enough receive buffer, or a poorly chosen segment size that causes IP
> > fragmentation, it could affect your throughput quite a bit.
> >
> > Check out:
> >
> >
http://www.dslreports.com/tools
> >
> > Look at the tweak tools. This site also has excellent network
performance
> > test tools, with a list of servers that covers Europe and Latin America.
> >
> Maybe I am even more confuse. KB=KiloByte and I wish you are right,
> but I just can not achieve such result with my 11b. This is my
> impression.
>
> Modem -> wireless router -wireed-> w2k PC and getting 120KB/s
So far so good. You get 120 kilobytes/sec over your modem to a wired PC,
which is 960 kilobits/sec. It sounds like your modem supports 1 megabit/sec.
Is this correct? Is it cable, DSL, fractional T1, something else?
BTW, for comparison, I have a DSL modem that supports 1.5 megabits/sec from
the network. I routinely get 1.2 - 1.3 megabits/sec downloading to my
wireless client.
>
> --usb 11b adapter--+-> wireless 11b on w2k PC and getting 60-70KB/s,
> since wireless is working in HALF-DUPLEX mode plus its overheads,
> therfore the result is more likely 40% lower in overall performace.
We always get balled up over half-duplex. Half-duplex is an issue only if
you are concurrently sending and receiving on the wireless connection. There
is only one antenna (or one pair for diversity), and it is either
transmitting or receiving, not both. So, if you are receiving and sending a
file concurrently, then the maximum throughput is divided between the two
datastreams. A special case is an infrastructure network (a wifi network
that communicates via an access point, rather than directly between hosts).
If a wireless client sends a file to another wireless client via the access
point, then the throughput is cut in half, because the access point has to
receive and then retransmit each wireless data frame. It is as if you were
concurrently sending and receiving the file.
But if you download a file from an internet server via the modem to a single
wireless client, almost all of the data on the wireless network flows to the
client. The only data flowing in the opposite direction are small 802.11
management frames, and TCP/IP connection management packets such as ACK.
Almost all of the maximum theoretical throughput should be occupied by the
data moving to the client.
So, if your modem can supply nearly 1 megabit/sec of data, your 802.11b
network should be able to move it at nearly that rate. In fact, it should be
90% idle at that rate.
>
> Am I right ?. I have tweaked my network with dslreports tools, ensure
> all router and wireless adapter with MTU 1500 (1460 * 32 =46720
> buffer) with cable. There is no re-transmit packet(s) as per tweak
> test shown. Is there any other thing(s) that I have missed here with
> my 11b system ?
Two things I'd look at here.
First, I wonder if the USB connection is contributing to this problem. USB 1
is supposed to provide up to 12 megabits/sec, but if you have several
devices on the bus, you may not have anywhere near that kind of througput.
Also, I'm not entirely sure there aren't performance problems with wifi on
USB, at least with some vendors. USB is notoriously unreliable. Here's a
quote from an Intel white paper on USB-connected ADSL modems:
"Many service providers tried USB products early in their DSL deployment.
Unfortunately, the providers encountered poor data throughput performance
and numerous USB compatibility issues."
Of course, they claim *their* USB modem works great, but it makes the point.
The white paper is at
http://www.intel.com/network/broadband/modems/ADSL_White%20Paper.pdf.
Also, the correct settings for MTU and MSS depend on whether or not your
modem is using PPOE. PPOE is typically required with ADSL, and usually not
used with cable (but might be in some places). I have MTU set to 1492, to
accomodate the 8-byte PPOE header inserted by my wifi router before each
frame is passed to the ADSL modem. I have MSS set to 1452, to leave room for
the 40-byte IP header that will prefix each TCP segment. The receive window
is a multiple of 1452 (MSS size, not MTU size), because it should hold an
integral number of TCP segments. Don't take these numbers as definitive -
optimal settings may vary from country to country and ISP to ISP. You have
to experiment.
You might want to run the TCP analyzer at
http://www.speedguide.net/
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