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<DIV><FONT face=Arial size=2>It's easy enough to saturate wired 10Mb ethernet to
about 95% with only one station transmitting. 100Mb ethernet is reasonably
difficult to saturate to more than about 80%</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Collision detection and avoidance is only a problem
with wireless ethernet if there's something to collide with... If you have
one station transmitting, most people wind up with about 6-700KBytes/sec
(6-7Mbits). The signal-noise ratio is much higher over the wired phy
layer, compared to the wireless phy layer, which would easily explain the drop
in efficiency in itself, even without the additional overheads in the 802.11b
MAC layer.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>In any case, 250-300KB/sec is a bit low for a
point-point link. But after re-reading you don't have point-point - you
have an AP. The packets are being transmitted twice! Once from the
original station to the AP, and then from the AP to the receiving station.
Which explains brilliantly why you're only seeing half the total
throughput you expected to see.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Cheers,</FONT></DIV>
<DIV><FONT face=Arial size=2>Ben.</FONT></DIV>
<DIV><BR></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=039404400-17092002>I
don't know about the wireless side, but I can tell you
that Ethernet uses CSMA/CD (Carrier Sense, Multiple Access,
Collision Detection) to modulate the carrier (radio frequency)
.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=039404400-17092002>Only
one device can talk at one time per "Carrier" - thus, on Ethernet if you have
multiple devices (MA) sharing the carrier and create "two way"
communications (ie. pings originating from both ends) - the packets could
collide, a pause will occur and they will retry. (/CD) - slowing down your
data path.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=039404400-17092002></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=039404400-17092002>THEN, also don't forget, that whilst the CARRIER
communicates at "10Mb" - you are encoding with protocols to transport the data
ie. </SPAN></FONT><FONT face=Arial color=#0000ff size=2><SPAN
class=039404400-17092002>802.3 Frame, Ip Protocol, TCP protocol etc. All of
these carry the payload (read: data) that you are sending.
</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=039404400-17092002>I
would also guess that if you are also encrypting you should (theoretically)
have packet "padding" to filling up any partially-filled frames -
so it will also affect the throughput of the of path (not forgetting the
time it takes (latency) to encrypt and decrypt etc)</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=039404400-17092002></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=039404400-17092002>Finally, there is Latency. This is the time it takes
to get from one side of a device to another. For example, in a router you
expect latency, because the router has to strip the Frame (802.11 or 802.3),
investigate the IP Addresses and protocol, make a decision and then forward it
onto the next interface. All of which takes time - thus affecting the
throughput.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=039404400-17092002></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=039404400-17092002>So I
would assume that, like Ethernet, in wireless you wouldn't get actual
11Mbs of data passing over a link, just like you will not get "10Mb" of data
over an Ethernet link. (In fact, I believe that the throughput of Ethernet is
about 3.9Mb)</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=039404400-17092002>I
can't tell you what to expect on a wireless link (I don't have those figures)
- but look for throughput - it is a better representation.</SPAN></FONT></DIV>
<BLOCKQUOTE>
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> Rowan Wainwright-Smith
[mailto:Rowan@teleaudit.com]<BR><B>Sent:</B> Tuesday, 17 September 2002
9:15<BR><B>To:</B> Cameron Donaghey<BR><B>Subject:</B> Re: [MLB-WIRELESS]
Transfer Rates<BR><BR></FONT></DIV>Cameron,<BR><BR>transfer rates are a
little tricky, 'coz there are two ways of measureing
them<BR><BR>1 PURE Bandwidth - how many BITS per
second!<BR>2. Transfer performance (usually measured in BYTES
per second)<BR><BR>The stats you are getting are pretty reasonable, but you
should be able to get about 550(-600)k/sec <BR><BR><BR>these cards are 11
Mbit,<BR><BR>if you work it out, you are getting about 2.5mbit transfer rate
(not counting TCP overheads) Bear in mind that these devices are 11mbit
TOTAL bandwidth, so if you have two PC's communicating, then you can really
only expect up to approx 5Mbit transfer, 3PC's then about 3.5 Mbit & so
on.<BR><BR>Wireless is NOT switched bandwidth like most modern wired
networks, but shared (like running a hub instead of a full
switch)<BR> Personally not sure about what effect using an AP is
having, but this *could* be reasonable!<BR><BR>maybe the rest of the list
can help you more....<BR><BR>well done on getting your WLan up &
running!<BR><BR>Rowan<BR><BR>Cameron Donaghey wrote:<BR>
<BLOCKQUOTE cite=mid:5.1.0.14.2.20020916154805.00b22050@pop-server
type="cite">Hello Everyone,<BR> I have eventually got my wireless up
and running, only on a private level at the moment, and<BR>yet I am not
entirely sure it is running correctly. I have two machines and in each one
I have<BR>a Compaq WL100 card set to infrastructure mode. I also have a
linksys Wap11 access point<BR>which is running as an access point
only.<BR>I have done some testing and I seem to have a max. transfer rate
between the two machines<BR>of about 310kb/s and the machines are only a
meter or so apart. I would have assumed that<BR>being a 11mb/s network
that I would be able to achieve more so around 500-1000kb/s rather<BR>than
the 300kb/s max. I am currently achieving. Both card say they have
"excellent connections"<BR>and at 11mb/s.<BR>My question to you all, is
the transfer speed of about 300kb/s typical for 802.11b or should I
be<BR>able to achieve higher rates of transfer? If I should be able to
achieve more would anyone have<BR>any suggestions towards resolving the
problem?<BR> Thanks very much,<BR> Cameron
Donaghey<BR><BR></BLOCKQUOTE>
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