xuxun_wuhan
join:2009-11-08
| Low Throughput of the Added AP?
I was told the throughput of an 11g router is only about 1/3 of the 100Mb CAT5 Ethernet. I am trying to utilize the unused Ethernet bandwidth by adding one more AP with different SSID and different channel. The result is quite surprising; if the traffic is heavy, the client connected to the main router gets roughly 15 mbps of bandwidth, and the client connected to the AP get only 5 mbps of bandwidth. What happened to the unused Ethernet bandwidth?
Here is my setting,
Main router, Airlink 101 AR525W, running FW v1.0.22
AP, Linksys WRT54G v6, running DD-WRT v24sp2
This is how I measured the bandwidth. I have got 3 computers and the router and AP in the same room. All 3 computers are running Windows XP.
Computer A is connected to the main router and the AP by 10/100Mb Ethernet.
Computer B is wirelessly connected to the main router.
Computer C is wirelessly connected to the AP.
Both computer B and C copy a large file from a shared folder on C. I calculate the bandwidth by the copying speed.
Thanks for any inputs. |
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No_Strings
Premium,Mod
join:2001-11-22
The OC
Host:
Wireless Networking
All Things Unix
Cox HSI
Qwest
Efficient
| The reason that the actual data throughput is limited is a function of half-duplex (vs. Ethernet's full-duplex) and wireless protocol overhead. There's no unused bandwidth to reclaim.
The best you can do is maintain a strong signal and maximize the transfer rate. |
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xuxun_wuhan
join:2009-11-08
| Thanks for your comment, No_Strings. But I am still confused.
If I hook up B to the main router by an Ethernet cable, the file transfer is a lot faster. So the bandwidth between A and the main router is a lot bigger than the wireless bandwidth. In this way, the main router functions like a switch and talks with A in full-duplex mode, am I right?
My test shows that if both B and C are connected the router and the AP wirelessly, Ethernet side of the transmission becomes the bottleneck. Do you mean the main router and the AP talk to A in half-duplex mode and compete for roughly 50mbps of bandwidth? Is there anyway to loosen it up by adding a switch or something?
Many thanks. |
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No_Strings
Premium,Mod
join:2001-11-22
The OC | I'm confused now, too.
Can you post a diagram of your configuration, please? |
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xuxun_wuhan
join:2009-11-08
| Don’t know how to post graph here. I just uploaded the connection graph to Picasa. Here are the URL and embedded link. Please let me know if you cannot see the picture.
»picasaweb.google.com/lh/photo/A3···rectlink
 From Misc
Ideally, both computer B and C will have a throughput of 20mbps. In another word, I have a combined throughput of 40mbps. But in my test, computer B got 15mbps, and C got only 5mbps. The combined throughput is as low as 20mbps. Is the Ethernet link the bottleneck?
Many thanks. |
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No_Strings
Premium,Mod
join:2001-11-22
The OC | That picture helped, thank you.
What's A doing? What's your Internet connection?
Variables that could be affecting B and C speeds:
Wireless cards/drivers, signal quality. |
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xuxun_wuhan
join:2009-11-08
| I use A as a media server. I want to stream video simultaneously to B and C. Internet comes in through the main router. But here my major concern is the A to B and A to C throughputs.
A's Ethernet Card: VIA Rhine II Fast Ethernet Adapter, Win XP default driver.
B's WIFI card:Belkin PreN CardBus Adapter, Win XP default driver
C's WIFI card:Intel(R) Pro/Wireless 3, Intel latest driver.
The signals are excellent. I have all the stuff in the same room to test.
If there's no A to C traffic, A to B can be 20mbps. A to C throughput can also reach 20mbps if there is no A to B traffic. I exchanged computer B and C, the result is the same. |
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xuxun_wuhan
join:2009-11-08 | Computer C's WIFI card is Intel Pro /wireless 3945 ABG adapter. Sorry for the typo. |
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stevech0
join:2006-09-17
San Diego, CA | reply to xuxun_wuhan
note the connection speed for the client PC. For example, strong signal, 54Mbps.
Multiply by 0.6 for what you can expect at the IP layer for "goodput", assuming there's little competition for the WiFi channel use. |
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tipstir
join:2004-11-14
Enfield, CT
 ·Cox HSI
| reply to xuxun_wuhan
10mbps = 6mbps
100mbps = 60mbps
G54 = 20-30mbps
Just buy external switch to dedicate lines from the main router to wired PC and and wired AP. You'll get better results. Also if you use third-party wireless client access disable the WZC you don't both running. If those wireless router and wireless AP uses WPS disable that feature and setup your wireless security manually. Again don't run both.
Otherwise your setup looks good just get external 10/100mbps with at least 128KB packet data buffer. |
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Full Power
join:2009-09-25
Houston, TX
| reply to xuxun_wuhan
said by xuxun_wuhan  :If there's no A to C traffic, A to B can be 20mbps. A to C throughput can also reach 20mbps if there is no A to B traffic. I exchanged computer B and C, the result is the same. Looks like you still may be out of available wireless spectrum. Set the AirLink to G mode only if it can do it. Then put one radio on CH 1 and the other on CH 11.
Using N mode on one radio will reach into the G radio's spectrum.
Other than that your plan should work just fine. Have you hard wired both client computers to the network to be sure the server can deliver 40 Mbps ? |
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xuxun_wuhan
join:2009-11-08
| Thank you for the comments, stevech0, tipstir and full power.
Tipstir, I didn’t use third party wireless client access software. Both B and C use Win XP default wireless utility. I manually set wireless security to WPA_PSK. Still have low combined throughput. For 128k packet data buffer, where am I supposed to set it, on Computer A or on the main router and the AP?
Full Power, I suspect wireless spectrum is the issue. Though the wireless links are on different channels, they are still competing for a narrow spectrum badly, especially when both the router and the AP sit in the same 12ftx12ft room.
I tried to set the main router to CH11 and the AP to CH1. Strangely, computer C cannot get connected on CH1. It can see the broadcasted SSID, but just cannot get hooked up. I tried with computer B, the same problem. Before, I used CH5 and CH8, no connection issue, but stuck with low combined throughput.
Ethernet links look fine in my WIFI solo test. If I replace the WIFI connection of computer B or C with a Ethernet link, the throughput instantly shoots up to 50mbps, and the remain wireless throughput drops from 20mbps to 18mbps. Pretty normal I think. |
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tipstir
join:2004-11-14
Enfield, CT | No, no don't touch buffer settings on wireless NIC. I was refering too buying external 5-port switch with 128KB packet buffer. |
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penypinch
Premium
join:2007-09-07
Henning, MN
1 edit | reply to xuxun_wuhan
What firmware release of DD-WRT are you running? r13064 is the latest
And are the routers in AP or WDS AP mode or are you trying WDS??
--
Mitch
support@abetterwireless.com |
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