# Does a 802.11b device slow down a 802.11g network?



## ForrestB (Apr 8, 2004)

April 6. 2008

Does an 802.11b Device on a 802.11g Network Slow the Network Down?

I often see this claim with four year old reports offered as proof. In the computing industry, a lot can change in four years. Is this still the case in April, 2008? I decided to test the theory using my newly purchased Netgear WGR614v9 802.11g router with the latest firmware.

My test setup consists of a series 2 DirecTV Tivo, Hughes SD-DVR40 hacked with the Zipper version 1.4 and upgraded with a Western Digital 250GB drive (17% empty). The DirecTivo is wired to a 4 port Linksys 10/100 hub thru a Netgear FA120 USB 2 Fast Ethernet adapter. The Netgear router is wired to the Linksys hub and 128 bit WEP encryption is enabled for all tests.

All test were performed on a 1.8 GHz G5 iMac with Airport Extreme(g) running OSX 10.4.11 and Tivotool 0.5.7. The same Tivo show, a 30 minute newscast 400 MB long was saved as an MPEG2 file with Tivotool in each test.

All tests were repeated three times to monitor repeatability.

Test 1: Netgear router set to b+g mixed mode and a computer with a wireless b card was active on the same network with a web browser running. 
Transfer times (minutes:seconds): 6:03, 5:41. 6:59. Average transfer time was 6:14.

Test 2: Netgear router set to b+g mixed mode, the computer with the wireless b card was deactivated.
Transfer times: 4:50, 4:32, 5:56. Average transfer time was 5:06.

Test 3: Netgear router set to g only, the computer with the wireless b card was deactivated.
Transfer times: 5:00, 6:18, 6:16. Average transfer time was 5:51.

Observations:
1. Tivo transfer times are not very repeatable, presumably due to Tivo background tasks. Average transfer time variation while performing the same test was 23%!
2. The Netgear router was 15% SLOWER when set to 802.11g only!
3. Averaging tests 2 and 3 together, having the 802.11b computer on the network slowed the 802.11g transfer down by an average of 14%. However this is LESS than the repeatability of the test! In three instances, transfer times were SHORTER with the wireless b computer on the network.

So my testing proves there is NO penalty for having an wireless 802.11b computer on your 802.11g network.

Forrest B


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## jbjabroni (Apr 3, 2008)

ForrestB said:


> April 6. 2008
> 
> Does an 802.11b Device on a 802.11g Network Slow the Network Down?
> 
> ...


TRUE DEPENDING ON THE NETWORK. However its all determinate on the Network Traffic during the test period.

802.11b devices can only transfer at a max of 11 Mbps compared to the 54 Mbps of a G device. So inevitably the network will slow when a B Device is on the network. But if a B device is using minimal transfer speed (IE, surfing the web) then its more than likely not going to effect the network all that much.

Also while Netgear produces great routers, I wouldn't reliably do such a study without also comparing them to a linksys or cisco router.


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## ForrestB (Apr 8, 2004)

jbjabroni said:


> TRUE DEPENDING ON THE NETWORK. However its all determinate on the Network Traffic during the test period.
> 
> 802.11b devices can only transfer at a max of 11 Mbps compared to the 54 Mbps of a G device. So inevitably the network will slow when a B Device is on the network. But if a B device is using minimal transfer speed (IE, surfing the web) then its more than likely not going to effect the network all that much.
> 
> Also while Netgear produces great routers, I wouldn't reliably do such a study without also comparing them to a linksys or cisco router.


Thanks for your reply.

Keep us posted on how the linksys and cisco testing is progressing


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## 100Tbps (May 12, 2006)

ForrestB said:


> April 6. 2008
> 
> Does an 802.11b Device on a 802.11g Network Slow the Network Down?
> 
> ...


This isn't very clear. The Tivo is hardwired to a linksys hub which is hardwired to the netgear. Somewhere, there is a computer with wireless with an open browser. Was that your mac? What was the browser doing? I understand the wireless variable wasn't the tivo's connection, but rather this other computer, but if that was where you hosted tivotool, none of this makes any sense.

I believe the studies you referenced mentioned the AP will lower all it's connection speed in a mixed environment. This meant if every device was 802.11g and a machine logged on at 802.11b, all the other devices would be throttled down - perhaps not all way down to the slowest speed - but slower nonetheless. This has to do with backwards compatibility in a mixed environment.

For your study, get some devices with more accuracy. If you can't control the background tasks on the tivo, it shouldn't be a "control" in your test. Also, there needs to be a third computer doing some consistent traffic on both 802.11b and 802.11g if you're to claim there's no difference. The third machine injects traffic onto the network while you test the speeds to your mac and the transmitting source.

The fact your test showed having a mixed enviroment made your transfers faster just shows the controls in your test weren't controls at all. In an all G environment (and using a wireless router of any decent quality) you should have seen G-only faster than mixed. Don't test with a tivo and you may find very different results.


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## ForrestB (Apr 8, 2004)

100Tbps said:


> This isn't very clear. The Tivo is hardwired to a linksys hub which is hardwired to the netgear. Somewhere, there is a computer with wireless with an open browser. Was that your mac? What was the browser doing? I understand the wireless variable wasn't the tivo's connection, but rather this other computer, but if that was where you hosted tivotool, none of this makes any sense.
> 
> I believe the studies you referenced mentioned the AP will lower all it's connection speed in a mixed environment. This meant if every device was 802.11g and a machine logged on at 802.11b, all the other devices would be throttled down - perhaps not all way down to the slowest speed - but slower nonetheless. This has to do with backwards compatibility in a mixed environment.
> 
> ...


I don't understand your comments - maybe you should reread my post.

I performed the test in response to MrOrange677 comments here http://www.tivocommunity.com/tivo-vb/showthread.php?t=389325


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## 100Tbps (May 12, 2006)

ForrestB said:


> I don't understand your comments - maybe you should reread my post.
> 
> I performed the test in response to MrOrange677 comments here http://www.tivocommunity.com/tivo-vb/showthread.php?t=389325


I read your post several times. If I understand what you tested and how, the path you took to arrive at your conclusion was flawed, even if your final conclusion is reasonably sound.

There is a minor performance degradation in a mixed environment. The average user won't notice it.

The fact that your testbed resulted in noticeably better performance in a mixed environment proves your set-up wasn't controlled because the Tivo's processes represents too many variables. This is substantiated by the ~10% delta in each test run. Seriously, it took you up to a minute longer under like-conditions to send a 400MB file three times in a row, a few minutes apart?? Unless there was another device on the network causing congestion or just adding noise, these kinds of results have nothing at all to do with the network.

If you're serious about testing this, replace the Tivo with a source device (linux, mac, windows, whatever) doing as little as possible other than the test. Test streams to a remote station. A third device operating at 802.11b should join the network. The simple fact of it's presence and association to the AP will force the AP (in mixed mode) to fall back to backwards compatible framing, and you could see a small throughput impact. Based on what I've read, you might see a 2-5% performance hit in throughput speed.


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## Tiger (Aug 15, 2000)

100Tbps said:


> If you're serious about testing this, replace the Tivo with a source device (linux, mac, windows, whatever) doing as little as possible other than the test. Test streams to a remote station. A third device operating at 802.11b should join the network. The simple fact of it's presence and association to the AP will force the AP (in mixed mode) to fall back to backwards compatible framing, and you could see a small throughput impact. Based on what I've read, you might see a 2-5% performance hit in throughput speed.


I believe that's assuming the 802.11b device doesn't have any network activity. If it does, it will slow the network down more than an 802.11g device using the same network bandwidth would, since the 802.11b device uses the frequency longer to send the data than an 802.11g device.


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## jonbig (Sep 22, 2003)

My understanding is that in order to enable g devices to talk to b devices, some of the "network overhead" traffic sent by g devices must be sent at b speed instead of at full g speed. So if there's even one b device, all the g devices must transmit some of the time at only b speeds so that the b device can follow along. I don't think this is a very large problem, though.


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## ForrestB (Apr 8, 2004)

Folks, this forum is called Tivocommunity - we are Tivo users. It would be foolish to repeat this test on anything but a Tivo.

Jonbig is the only one that truely comprehended the results of the test. That being, if you're a Tivo user, it makes no difference if there's a 802.11b user on your 802.11g network - it won't slow down transfers on your 802.11g networked Tivo.


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## 100Tbps (May 12, 2006)

ForrestB said:


> Folks, this forum is called Tivocommunity - we are Tivo users. It would be foolish to repeat this test on anything but a Tivo.
> 
> Jonbig is the only one that truely comprehended the results of the test. That being, if you're a Tivo user, it makes no difference if there's a 802.11b user on your 802.11g network - it won't slow down transfers on your 802.11g networked Tivo.


The title of your thread is misleading. You did not successfully test whether or not 802.11b & 802.11g technologies can get along. You simply ran multiple data transfers over different permutations of similar networks.

The rest of us didn't fail to "truly comprehend" your results. Had you re-titled the thread to something more appropriate, I doubt anyone would have given it a second thought or debated with you.

We're all in agreement: Tivos can MRV files using many types of topologies, and some conditions permit faster transfer rates than others. But your test conditions and your conclusions don't amount to anything useful. You may have well tested at noon and midnight on your 802.11g network and drew the same results and conclusions - with or without an 802.11b node.


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## ForrestB (Apr 8, 2004)

Blah blah blah - I don't see anyone else doing any testing and posting results.


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## ciper (Nov 4, 2004)

I've tested this in a corporate LAN with PCs and the speed of the G devices was only impacted when the B device was a decent distance away and sending large amount of traffic. 

Because of this I only purchased WAPs that were ABG compatible and gave the power users A cards on an as needed basis.

The DD-WRT forums or the LinksysInfo forums would be a great place for additional real world data.


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## JWThiers (Apr 13, 2005)

ForrestB said:


> Blah blah blah - I don't see anyone else doing any testing and posting results.


blah, blah, blah -


Because its not a tivo issue, its a network issue.
The network testing has already been done. And the answer is that connecting a B device will slow down the *overall* network performance. Proof is the old reports you mentioned. Things haven't changed much, if at all, on that front.

The reason you were getting contradictory results is because you didn't have good controls on the variables involved. If you want to do that you need to use something other than a tivo in your home. Did you proved that having your router in mixed mode makes your network faster? No, you proved that at the time you performed the test with the uncontrolled variables that you had at the time your mixed mode network performed better for some reason. What the reason is is unknown because the variables were not controlled. Plus there are environmental variables that you didn't account for, (interference sources, power fluctuations, someone with a foil hat standing in the way, etc)


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## ForrestB (Apr 8, 2004)

The only uncontrolled variable was the Tivo. There was nobody else on the network, except me casually browsing the web on the 802.11b machine. I ran this test to dispute the claims by some members that simply having an 802.11b machine on the network reduced ALL network activity to 802.11b speeds - which is clearly NOT the case.


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## Sherminator (Nov 24, 2004)

However, My Tivo is connected to the network via a DLink 802.11b USB adapter, in order to stream SD video to my XBox 360 I have to remove the adapter to avoid video stutter and the "Network Congestion" error message.

So, in my experience having an 802.11b device connected to the network (regardless of it transfering anything) does slow down a 802.11g network.


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## ForrestB (Apr 8, 2004)

Sounds like Microsoft needs to work on their streaming code. No stuttering problems streaming from my DirecTivo to my 6 year old 700 MHz G3 iBook equipped with the original Airport (802.11b) network card.


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## JWThiers (Apr 13, 2005)

ForrestB said:


> The only uncontrolled variable was the Tivo. There was nobody else on the network, except me casually browsing the web on the 802.11b machine. I ran this test to dispute the claims by some members that simply having an 802.11b machine on the network reduced ALL network activity to 802.11b speeds - which is clearly NOT the case.


Lets see, was there a microwave oven operating in the area how about cordless phone, drill motor anything that might interfere. Not just at your house but any nearby source like your neighbor.Also you might not see the OVERALL performance hit until the network gets loaded up a bit when the network is working harder. Specifically the wireless network is loaded up. Also, for a better understanding, try running in B mode only, How does that compare to B+G mixed mode and G only mode? Your posted data has some serious repeatability issues (or lack there of). The fact that just deactivating the b card decreased transfer times proves that connecting a B device adversely affects the network, But switching to G only mode negatively affecting it makes no logical sense. Decreasing the overhead should increase transfer speeds not decrease them.


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## ForrestB (Apr 8, 2004)

I see everyone else is still too lazy to do their own testing. Put up or shut-up.


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## Da Goon (Oct 22, 2006)

ForrestB said:


> Put up or shut-up.


Wow. Do you expect any cooperation with this attitude?

And, as pointed out already, your tested was significantly flawed (and not everyone has a wireless b device on their network any more.) Also you referenced "the Zipper version 1.4." Jesus christ, show a lack of understanding of hacking your box why don't you  What was going on in the background, do *you* even know?


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## JWThiers (Apr 13, 2005)

ForrestB said:


> I see everyone else is still too lazy to do their own testing. Put up or shut-up.


Not Lazy just more important things to do. But If it makes you happy we can go along with what your data implies. Your data confirms that a mixed B+G network runs faster than a G only network. Lets take the next step I bet to really speed things up you need an N network and also have a mix of B and G devices as well. That should run faster than a straight N network, right?


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