Half/Full Duplex question

I'm using IBM Thinkpad T40 with Intel Pro wireless LAN 2100 3B
mini card and a Linksys WRT54G wireless router. The best transfer
rate I can get is 5.5 Mbps which is half duplex. How can I make use
of the full bandwidth of 11 Mbps for 802.11b? What do I have to
do as far as device driver, firmware, configuration is concern to be
networked using full duplex?
Any suggestions would be greatly appreciated.

Robert

Robert wrote:
> I'm using IBM Thinkpad T40 with Intel Pro wireless LAN 2100 3B
> mini card and a Linksys WRT54G wireless router. The best transfer
> rate I can get is 5.5 Mbps which is half duplex. How can I make use
> of the full bandwidth of 11 Mbps for 802.11b? What do I have to
> do as far as device driver, firmware, configuration is concern to be
> networked using full duplex?
> Any suggestions would be greatly appreciated.
>
> Robert
>
>

802.11b is always HDX. If you are getting a STR of 5.5 Mb/s you are
doing better than most.
--
Cheers, Bob

"Robert" <(E-Mail Removed)> wrote in message
news:lqkVd.139148$(E-Mail Removed) m...
> I'm using IBM Thinkpad T40 with Intel Pro wireless LAN 2100 3B
> mini card and a Linksys WRT54G wireless router. The best transfer
> rate I can get is 5.5 Mbps which is half duplex. How can I make
use
> of the full bandwidth of 11 Mbps for 802.11b? What do I have to
> do as far as device driver, firmware, configuration is concern to be
> networked using full duplex?
> Any suggestions would be greatly appreciated.
>
> Robert

Half duplex is all there is in wireless (over the air).
5.5mbs throughput is normal for an 802.11b device.
The other 5.5 is overhead (protocol, security etc.)

Thanks for the replies. Does that mean if I switch to 802.11g
I can only get at most 27 Mbps or does 802.11g uses full duplex?



"Robert" <(E-Mail Removed)> wrote in message
news:lqkVd.139148$(E-Mail Removed) m...
> I'm using IBM Thinkpad T40 with Intel Pro wireless LAN 2100 3B
> mini card and a Linksys WRT54G wireless router. The best transfer
> rate I can get is 5.5 Mbps which is half duplex. How can I make use
> of the full bandwidth of 11 Mbps for 802.11b? What do I have to
> do as far as device driver, firmware, configuration is concern to be
> networked using full duplex?
> Any suggestions would be greatly appreciated.
>
> Robert
>

"Robert" <(E-Mail Removed)> wrote in message
newsXnVd.124089$(E-Mail Removed) m...
> Thanks for the replies. Does that mean if I switch to 802.11g
> I can only get at most 27 Mbps or does 802.11g uses full duplex?
>
all the 802.11 protocols use the same wireless channel for traffic in both
directions - so from that perspective wifi is half duplex.

but - it isnt that you get 50% of the bandwidth because the protocol is half
duplex, but that there is a lot of overhead for things like encapsulation
and gaps between packets.

interference, signal levels vs local noise, reflections and other usage
specific issues can have a big impact on useful throughput as well. and both
protocols drop to lower data rates as conditions degrade.....

so with 802.11g you will get something on the order of 25 Mbps total (under
good conditions, if you are lucky).

802.11g is designed to be backward compatible with 802.11b, so the amount of
overhead usually goes up since the system has to make the channel and data
comprehensible to the older, slower devices if they happen to be around.

but - there can be much more data going in 1 direction or the other
depending on load. the protocol is effectively demand driven, so apart from
overhead singalling, the channel is only occupied by either the AP or the PC
when there is actual data to send.

it sounds like you were testing the link, perhaps by moving a file or using
a test utility. such tests often move nearly all data in 1 direction, so the
results you saw is probably 90% or more of the total data moved.

the test you did might have included IP and MAC overhead rather than just
application data (depends on what got counted) and might have included data
in both directions - without knowing what you were measuring and where the
thruput numbers came from - we cant tell.
>
> "Robert" <(E-Mail Removed)> wrote in message
> news:lqkVd.139148$(E-Mail Removed) m...
> > I'm using IBM Thinkpad T40 with Intel Pro wireless LAN 2100 3B
> > mini card and a Linksys WRT54G wireless router. The best transfer
> > rate I can get is 5.5 Mbps which is half duplex. How can I make use
> > of the full bandwidth of 11 Mbps for 802.11b? What do I have to
> > do as far as device driver, firmware, configuration is concern to be
> > networked using full duplex?
> > Any suggestions would be greatly appreciated.
> >
> > Robert
--
Regards

Stephen Hope - return address needs fewer xxs

On Wed, 2 Mar 2005 10:36:28 -0600, in alt.internet.wireless , "Airhead"
<(E-Mail Removed)> wrote:

>Half duplex is all there is in wireless (over the air).

correct.

>5.5mbs throughput is normal for an 802.11b device.

Yes, thought thats the in-air bandwidth in any one direction. Then subtract
protocols, security etc. Expect to see 3-3.5 Mb/s

>The other 5.5 is overhead (protocol, security etc.)

What????? The other 5.5 is the traffic going the other way.... thats what
half-duplex means...

--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt>

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On Wed, 02 Mar 2005 23:23:37 +0000, in alt.internet.wireless , Mark
McIntyre <(E-Mail Removed)> wrote:

>On Wed, 2 Mar 2005 10:36:28 -0600, in alt.internet.wireless , "Airhead"
><(E-Mail Removed)> wrote:
>
>>Half duplex is all there is in wireless (over the air).
>
>correct.
>
>>5.5mbs throughput is normal for an 802.11b device.
>
>Yes, thought thats the in-air bandwidth in any one direction. Then subtract
>protocols, security etc. Expect to see 3-3.5 Mb/s
>
>>The other 5.5 is overhead (protocol, security etc.)
>
>What????? The other 5.5 is the traffic going the other way.... thats what
>half-duplex means...

I should have added: assuming symmetrical traffic. Obviously if you're
mostly transmitting then traffic is assymetric. A file copy is heavily
biassed in one direction, so you tend to see slightly better throughput. If
you've several things going on at once on your machine, or if you've
communication between several machines going on, traffic may be much more
symmetrical.

The other point to bear in mind is that not only is the above true, but
ALSO all devices on a given AP share the same channel -> two devices, both
busy sending data -> each sees half the bandwidth. You're then relying on
the same contention model that DSL uses, ie you're hoping that not every
device is simultaneously busy.

--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt>

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Mark McIntyre <(E-Mail Removed)> wrote in
news:(E-Mail Removed):

> On Wed, 02 Mar 2005 23:23:37 +0000, in alt.internet.wireless ,
> Mark McIntyre <(E-Mail Removed)> wrote:
>
>>On Wed, 2 Mar 2005 10:36:28 -0600, in alt.internet.wireless ,
>>"Airhead" <(E-Mail Removed)> wrote:

> The other point to bear in mind is that not only is the above
> true, but ALSO all devices on a given AP share the same channel ->
> two devices, both busy sending data -> each sees half the
> bandwidth. You're then relying on the same contention model that
> DSL uses, ie you're hoping that not every device is simultaneously
> busy.

Indeed - although as you say, it's contended rather than 'shared' in
the sense of 'divided evenly'.

This contention is one of the reasons why I use multiple access
points on different channels for my (fairly extensive) home/business
network, and specify this solution for others.

It is very instructive exercise to measure data transfer rates across
a busy wireless network

Hope this helps

--

Richard Perkin
To email me, change the AT in the address below
richard.perkinATmyrealbox.com

It's is not, it isn't ain't, and it's it's, not its, if you mean it
is. If you don't, it's its. Then too, it's hers. It isn't her's.
It isn't our's either. It's ours, and likewise yours and theirs.
-- Oxford University Press, Edpress News

On Wed, 02 Mar 2005 18:52:04 GMT, "Robert" <(E-Mail Removed)> wrote:

>Thanks for the replies. Does that mean if I switch to 802.11g
>I can only get at most 27 Mbps or does 802.11g uses full duplex?

From one of my previous postings:

I keep getting asked "how fast can it go" type questions. Perhaps
some numbers might help. This is stolen from an Atheros PDF at:
http://www.atheros.com/pt/atheros_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

The paper claims that encryption is enabled for these calculations,
but my numbers seem to indicate that these number are for encryption
disabled. Dunno for sure. The Max TCP and Max UDP are the
theoretical maximum thruput rates.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# (E-Mail Removed) AE6KS

On Wed, 02 Mar 2005 23:23:37 +0000, Mark McIntyre <(E-Mail Removed)> wrote:

~ On Wed, 2 Mar 2005 10:36:28 -0600, in alt.internet.wireless , "Airhead"
~ <(E-Mail Removed)> wrote:
~
~ >Half duplex is all there is in wireless (over the air).
~
~ correct.
~
~ >5.5mbs throughput is normal for an 802.11b device.
~
~ Yes, thought thats the in-air bandwidth in any one direction. Then subtract
~ protocols, security etc. Expect to see 3-3.5 Mb/s
~
~ >The other 5.5 is overhead (protocol, security etc.)
~
~ What????? The other 5.5 is the traffic going the other way.... thats what
~ half-duplex means...

Wrong - if you try a unidirectional transfer (say one-way UDP packet blast)
over "11Mbps" 802.11b, you will see about 5.5Mbps. The 50% reduction
in payload througput relative to nominal signaling rate really is due to
overhead.

Matthew Gast has an excellent explanation here:
When Is 54 Not Equal to 54? A Look at 802.11a, b, and g Throughput
http://www.oreillynet.com/pub/a/wire...hroughput.html

As far as whether 802.11 is "half duplex" - technically one
should call it simplex, if you use the appropriate (radio)
definition of simplex and not the telephony/serial definition.
See the ATIS Glossary http://www.atis.org/tg2k/ and check
out the definitions for "simplex operation", "duplex operation"
and "half-duplex (HDX) operation".

Aaron