[blacklionpt]

Hello everyone. I've been a long time lurker on this forums, and i've obtain great deal of information just from reading them.

However now i'm faced with an issue: I found a weird performance issue with my home network, and i can't quite find the reason why.

I operate a small network: It consists of 13 TP-Link TL-WR841N and TL-WR841ND routers, all flashed with DD-WRT. (Long story short: there's no good internet provider where i live (best one is 0.7 Mbps, yay), so we invested a bit and now have a stable 40 / 12 Mbps link that we all share. I alsp have QoS implemented!).

Here's a visual map of the network.

Now, i've found a pretty weird performance issue:

On the map, you can see Router 10 receives a WDS signal from Router 6 and then gives signal by cable to Router 11. Same happens with Router 16 to Router 30 and 31.

To test the speeds i usually use one of these ways:

- Copy a file from my home server to a computer connected to the router;
- Use this command to download 2 files in the telnet session of the router i want to test the speed of: wget -O /dev/null http://MY_PC_IP_HERE/test.zip & wget -O /dev/null http://MY_PC_IP_HERE/test.zip (This downloads to null a 150 MB file).

To monitor the speeds, i check the Windows Task manager and check what speeds the ethernet card is having.

Now the weird issue:

If i do a speedtest using the Wget command on Router 10, i get around 90-95 Mbps. However if i do the same test on router 11, i get around 70-80. There's a huge drop in performance (around 20 Mbps difference). Same happens with Router 30 and 31.

Here's another image showing a speedtest made to Router 30 (highest in the graphic) and then a test made to Router 31.

I've searched all over and i can't find a similar issue happening. Weird thing is, if i plug a client by cable on Router 6, it gets 100 Mbps from my server.

I even tested connecting by cable a computer on Router 10 and then copying a file from it on Router 11 (using another computer connected by wireless): I got 98 Mbps both ways.

This seems to only happen on the bridges: if the traffic comes from the WDS Wi-Fi to the LAN. (I also tried with Client (Routed) instead of WDS, same thing happens).

Does anyone know what could be causing this performance issue?

Thank you for your time.

[mrjcd]

Looks like 11 & 31 are only units going from wired >> wireless >> wired.
That little extra change in protocol is probably what causes the decrease.
You can test this by adding in another wireless >> wired after #11 or #31 and probably see similar drop.
All in all looks like you have a decent setup

[ramblin]

blacklion, your my hero. I been impressed with the reliability of these cheap units for a while but your network is the best !

[blacklionpt]

Hello. Thank you for answering and the support These devices are indeed really great, they are incredibly cheap and become such awesome routers using this firmware!

I'm kind of disappointed that such a deep cut in speed manifests like this just from a protocol change though. This also makes it sort of nonviable for me to keep pushing the network further using more wireless bridges, as the speed would deteriorate even further (didn't test yet, but it seems to lose speed every time it passes a wireless bridge.

Strange thing though, I've done a few more tests and ended up improving the stations speed by a little more. The tests i made where the following ones:

- Tested Router #30 as Client (Routed): Making a Speedtest using wget to Router 31, Router 30's CPU would fire up to 100% during the test. Speeds where also noticeably slower (40-50 Mbps).

- Tested Router #30 as WDS Station: Making a Speedtest using wget to Router 31, the Router's CPU would sit around 8%, speeds where around 60-70 Mbps.

- Tested passing a file in my Router #1 from LAN to a Wi-Fi Client: Pretty stable at 98.9 Mbps

Now the fun part: I played a bit with the ACK timings and ended up actually improving all my bridges speeds!

- Speeds on Router #30 and #31 with ACK 2000 (Default): 70-80 Mbps | around 50-60 Mbps

- Speeds On Router #30 and #31 with ACK 500: pretty stable between 85-90 (!) | also stable between 78-82 Mbps (!)

Tested on my other bridge (Router's 6 10 and 11 and so on) and also saw a performance increase in the router's performance. This was kind of unexpected, as i remember once playing around with ACK and didn't notice much difference.

I need to get a bit more free time to do some more tests. I want to try using a Client mode option (instead of routed) to see if the speed decrease also occurs.

I just find it weird because passing a file between a LAN computer and a Wireless one i can get 98 Mbps, and then just by having another router receive the signal i have this huge drop in speeds (almost 20 Mbps difference, now reduced with the ACK timings changes).

Again, thank you for your support, if you have any suggestions about changes i could make to improve the speed of the network i'm all ears

Any question about how i have it set up just fire them up, i'll be happy to answer them. When i have time to do more tests i'll report back with the results!

[mrjcd]

since WDS looks to be just point to point w/ no other wireless connected you can set becon interval up high should increase your rate also.
you will have to fiddle with that to see what's best.
used to run mine with becon interval higher than 15000 but some recent builds last couple months didn't do as well ...now running WDS (PtP) becon interval at 512

Edit:
Yea ack timing as true as can get seems best for WDS.
AFAIK these units do ack in 450 intervals so your 500 probably actually 450 and that will be great as long as wirless signal round trip is not over 450 meters.
Mine is set 900 which is really very very close to my range. Run them at 1350 for couple years but seems 900 is actually better for me now.....Think this is also related to changes made in New dd-wrt last few months.... Running two wrt160NL....So everything I mentioned may/may not apply to you

[blacklionpt]

Hello. Sorry, i noticed after, it was at 900 instead of 500. 450 drooped my performance really bad, from the values i tested, 900 actually seems to be the best performing one for all my routers, improved speeds greatly.

I also tweaked the beacon interval: Set it to 2000 ms, so far everything seems to be working on the network, but so far i can't really tell if there's any improvements or not.

I'm still wrapping my head around losing 20 Mbps due to WDS. Need the weekend to come to do some more tests, because i'd really like to get the network up to the 90 Mbps the main router receives instead of 70 due to loses. Need to keep tweaking and messing around till i find a better performing configuration.

Thank you for your help and tips, will keep you guys posted on my mini-network adventures

[mrjcd]

while you are tinkering around I'll tell you one more thing I've done on my WDS.
Enabled both RTS/CTS and set threshold to 2304.
Probably will not help your rate any but seems to be a better consistency for me moving large files around. Not that I had many errors ...well you really had to hunt for them to find one ...The lower threshold is better in my case.
Speed is good but if it's running into itself it don't make a hoot how fast it is....faster just hides it bettet