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From: Bob on 9 Jun 2010 04:20
I have just been reading the review on smallnetbuilder.com
<http://www.smallnetbuilder.com/wireless/wireless-reviews/31164-lots-more-features-lots-less-performance-netgear-wnr3500l-with-dd-wrt-reviewed>
It was interesting to see how badly the routing performance was hit
using DD-WRT. I was also interested in the wireless performance test
where the "Spectrum Expert card and software" were used, I am surprised
there was no comment on just how much potential "interfering" noise was
generated by tweaking the o/p power to max in DD-WRT.
From: Jeff Liebermann on 9 Jun 2010 21:41
On Wed, 09 Jun 2010 09:20:34 +0100, Bob <bob(a)invalid.invalid> wrote:

>I have just been reading the review on smallnetbuilder.com
><http://www.smallnetbuilder.com/wireless/wireless-reviews/31164-lots-more-features-lots-less-performance-netgear-wnr3500l-with-dd-wrt-reviewed>
>It was interesting to see how badly the routing performance was hit
>using DD-WRT. I was also interested in the wireless performance test
>where the "Spectrum Expert card and software" were used, I am surprised
>there was no comment on just how much potential "interfering" noise was
>generated by tweaking the o/p power to max in DD-WRT.

Careful... Tim ran a test that simultaneously tested both the wireless
and router performance. I can't tell from the results whether the
rather drastic drop in performance was due to slothish packet
processing and filtering, or due to the wireless. What worries me
more is that the router crashes when too many streams are run
simultaneously.

The TX power test was interesting but not very useful. At 250mw, the
xmitter probably goes out of spec for the FCC spectrum mask. It also
generates some non-linearities that are going to have an effect on
speed. Worse, it creates an "alligator" where the TX range is much
more than the RX range. It does no good to crank up the TX power, if
you can't hear the responses from the other end of the link. It would
take *TWO* WNR3500L boxes, acting as a bridge (i.e. no routing), where
the transmit power is cranked up on both bridge boxes, to do a proper
test.

The maker of the $4,000 Spectrum Expert Card, Cognio, was purchased by
Cisco and is now "Cisco Spectrum Expert".
<http://www.cisco.com/en/US/products/ps9393/tsd_products_support_series_home.html>

Despite my usual pot shots about methodology and conclusions, the
tests performed by Tim Higgins on SmallNetBuilder.com are the best
(and most creative) that I've seen anywhere and should be considered
seriously.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl(a)cruzio.com
# http://www.LearnByDestroying.com AE6KS
From: Bob on 10 Jun 2010 02:55
On 10/06/2010 02:41, Jeff Liebermann wrote:
> On Wed, 09 Jun 2010 09:20:34 +0100, Bob<bob(a)invalid.invalid> wrote:
>
>> I have just been reading the review on smallnetbuilder.com
>> <http://www.smallnetbuilder.com/wireless/wireless-reviews/31164-lots-more-features-lots-less-performance-netgear-wnr3500l-with-dd-wrt-reviewed>
>> It was interesting to see how badly the routing performance was hit
>> using DD-WRT. I was also interested in the wireless performance test
>> where the "Spectrum Expert card and software" were used, I am surprised
>> there was no comment on just how much potential "interfering" noise was
>> generated by tweaking the o/p power to max in DD-WRT.
>
> Careful... Tim ran a test that simultaneously tested both the wireless
> and router performance. I can't tell from the results whether the
> rather drastic drop in performance was due to slothish packet
> processing and filtering, or due to the wireless. What worries me
> more is that the router crashes when too many streams are run
> simultaneously.
A list has been started on DD-WRT of throughput tests for "N" products .
<http://www.dd-wrt.com/wiki/index.php/Wireless-N_Throughput_Testing>

There was also this on the forum
"It really depends on what features you use. If you run anything that
puts a high load on the CPU then it will cut into your routing
throughput. For instance, if you set up a VPN tunnel that's encrypted
then using the tunnel will put a lot of load on the CPU. If you're
running default settings then it shouldn't be as drastic as in that
article, somewhere around 30% less throughput off the top of my head."
"http://www.dd-wrt.com/phpBB2/viewtopic.php?p=448942>

30% drop in throughput expected.

>
> The TX power test was interesting but not very useful. At 250mw, the
> xmitter probably goes out of spec for the FCC spectrum mask.

It was a pity he didn't use the same settings that are used for testing
the 802.11 "Spectral Mask" but I would guess the "Spectrum Card" was on
the limit and went into auto RBW.
> It also
> generates some non-linearities that are going to have an effect on
> speed. Worse, it creates an "alligator" where the TX range is much
> more than the RX range. It does no good to crank up the TX power, if
> you can't hear the responses from the other end of the link. It would
> take *TWO* WNR3500L boxes, acting as a bridge (i.e. no routing), where
> the transmit power is cranked up on both bridge boxes, to do a proper
> test.

I was more interested in the possible consequences to nearby networks
rather than whether it improved a link in a network.
>
> The maker of the $4,000 Spectrum Expert Card, Cognio, was purchased by
> Cisco and is now "Cisco Spectrum Expert".
> <http://www.cisco.com/en/US/products/ps9393/tsd_products_support_series_home.html>
>
> Despite my usual pot shots about methodology and conclusions, the
> tests performed by Tim Higgins on SmallNetBuilder.com are the best
> (and most creative) that I've seen anywhere and should be considered
> seriously.
>

From: Jeff Liebermann on 10 Jun 2010 11:54
On Thu, 10 Jun 2010 07:55:25 +0100, Bob <bob(a)invalid.invalid> wrote:

>A list has been started on DD-WRT of throughput tests for "N" products .
><http://www.dd-wrt.com/wiki/index.php/Wireless-N_Throughput_Testing>
If you filter on Netgear, you'll see the results for the WNR3500L and
others.

Thanks, but not very useful. The 2MByte window is cheating as many IP
device stacks are limited to the same as ethernet (1500 bytes). The
exact Iperf/Jperf command lines should be supplied so that the test
are reproducible. Testing at 1 meter range is not exactly indicative
of "typical" operations.

How SmallNetBuilder tests:
<http://www.smallnetbuilder.com/content/view/30488/98/>

There should also be a test for:
- Ethernet to ethernet to prove the wire speed is possible.
- LAN ethernet to wireless bridging (not through router) Up/Down.
- WAN ethernet to wireless routing Up/Down.
- Wireless to Wireless bridging Up/Down.
The last is amazingly lousy on some devices I've tested.

This might be more informative:
<http://www.smallnetbuilder.com/component/option,com_wireless/Itemid,200>

WRN3500L (not DD-WRT) results table:
<http://www.smallnetbuilder.com/index.php?option=com_wireless&Itemid=200>

Incidentally, the maximum simultaneous connections test results are
kinda amusing:
<http://www.smallnetbuilder.com/index.php?option=com_chart&Itemid=&chart=124>
This has not been a problem as the routers usually limit the number of
available IP addresses to 253. However, when used as a bridge, the
approx 200 connection limit is fatal as many more MAC addresses are
used. Many routers also don't do a proper job of clearing the MAC
address table from old addresses to make room for new addresses. Extra
credit for those that hang when the limit is reached.

>There was also this on the forum
>"It really depends on what features you use. If you run anything that
>puts a high load on the CPU then it will cut into your routing
>throughput. For instance, if you set up a VPN tunnel that's encrypted
>then using the tunnel will put a lot of load on the CPU. If you're
>running default settings then it shouldn't be as drastic as in that
>article, somewhere around 30% less throughput off the top of my head."
>"http://www.dd-wrt.com/phpBB2/viewtopic.php?p=448942>
>30% drop in throughput expected.

Well, yes... that's true. Terminating the VPN in the router is a
great way to overload the CPU. Excessive packet filtering and VLAN's
also has a big effect. Multiple SSID's seems to slow the wireless
speeds a little. For the WRT54G series of routers, CPU overload is a
serious problem. However, the later routers have much faster and more
efficient processors. I don't know what the WRN3500L uses, but I
would assume is faster than the older Broadcom chips.

>> The TX power test was interesting but not very useful. At 250mw, the
>> xmitter probably goes out of spec for the FCC spectrum mask.
>
>It was a pity he didn't use the same settings that are used for testing
>the 802.11 "Spectral Mask" but I would guess the "Spectrum Card" was on
>the limit and went into auto RBW.

I would have settled for a spectrum analyzer photo at various power
levels with the spectrum mask overlay, as in the FCC Part 19 tests.
Incidentally, some of the newer PA chips are now using cellular PA
tricks of pre-distorting the AM linearity in order to get more power
at less distortion.
<http://www.atheros.com/pt/whitepapers/11nNetworksSustainingSignals_whitepaper.pdf)
(440KBytes) See Pg 7.

>I was more interested in the possible consequences to nearby networks
>rather than whether it improved a link in a network.

I'll be blunt. I think that 40MHz on 2.4Ghz was a bad idea and should
be banned. It works well on 5.7GHz. I also have some nasty things to
say about channel bonding between the two bands. The entire effort is
only to get more speed, something most users don't need or want. If
this additional speed is at the price of additional interference, it's
a bad tradeoff.

I'm not too worried about 802.11n 40MHz interference. If the
rules/guidelines are followed, where 40MHz is only allowed in a
"greenfield" environment on 2.4GHz, any interference will immediately
switch everyone to 20MHz mode.

--
Jeff Liebermann jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: Bob on 10 Jun 2010 12:24
On 10/06/2010 16:54, Jeff Liebermann wrote:

>
> I would have settled for a spectrum analyzer photo at various power
> levels with the spectrum mask overlay, as in the FCC Part 19 tests.
> Incidentally, some of the newer PA chips are now using cellular PA
> tricks of pre-distorting the AM linearity in order to get more power
> at less distortion.
> <http://www.atheros.com/pt/whitepapers/11nNetworksSustainingSignals_whitepaper.pdf)
> (440KBytes) See Pg 7.

I had seen something similar before:-
<http://sigma.ucsd.edu/research/articles/2004/2004_5.pdf>
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