I have a moderately complex home network that serves me well for internet connectivity, but has a major problem when I try to transfer files within the network. I am a novice when it comes to networking, but I learn quickly, so hopefully I can learn from the pros on this forum. I set up this network piecemeal as my needs changed over the past few years, so it may not be the cleanest design, but I hope I can modify it a bit to get it working without doing a major redesign/hardware upgrade.

First I'll describe the network basically. Please ask any questions necessary to clarify important points necessary to fix my issue.

[DSL Modem]--ethernet--[Belkin Router A]--ethernet--[EnGenius EOC-5610 AP]--3.5 miles wireless bridge--[EnGenius EOC-5610 AP]--ethernet--[Belkin Router B]--wireless repeater bridge--[Belkin Router C]

All the hardware is off the shelf, with the exception of Router C which has been modified by DD.WRT to enable the wireless repeater bridge feature. But if you like you can ignore the connection to Router C altogether, because the issue was present even before I added it to the network.

The 3.5 mile wireless bridge is a slow (but stable and reliable) link in the chain and operates at just 2.5 Mbps, but this is normally not an issue because I rarely transfer large files across this bridge, and my internet is only 1.5 Mbps.

Ok, so the problem: Normally when transferring small amounts of data around the network, or just using the internet, I notice no issues. But when I try to transfer a large file between 2 computers on Router B (or C) it transfers very slowly...somewhere in the area of 7 Mbps...far short of the 56 Mbps wireless or 100 Mbps wired speeds I should be seeing. Also, while the file is transferring, my 3.5 mile wireless bridge is filled with traffic. So much so that the internet becomes unusable on computers connected to Routers B & C during the transfer.

So my best theory is that some sort of data is traveling all the way back to Router A during the transfer, even though Router A should have nothing to do with data traveling between 2 computers connected to Router B. Clearly not all the data is making the round trip as the link is only good for 2.5 Mbps and yet the transfer runs at around 7 Mbps, so if all the data were making a round trip through Router A I'd be seeing around 1.25 Mbps. But something is clogging my long distance bridge during the transfer, and waiting for this data to make the round trip is slowing the overall transfer as well.

Well that's the best I can explain it for now. Please ask for any more details you need. I realize there are a lot of variables here, but I'm hoping someone has seen something like this before and can point me in the right direction. My data clearly isn't being routed properly, but I can't figure out why. Thanks much for any advice!

is the bridge at 3.5 miles setup in layer 2 ?
Any thing between router B and c will be slow as death because of the repeater mode. I use that NEVER!
Router B is it plugged in with the WAN port or a lan switch port?

Yeah, I know the repeater mode cuts down my speed between Routers B & C, but the slow down I'm experiencing is even occuring just in transfering data between 2 computers on the same router (B for example).

Router B is connected to the long distance bridge AP by ethernet plugged in to a regular LAN port...I did not use the WAN port.

As far as the long distance bridge being in layer 2....? I don't know. I'm not familiar with that term. I'll have to do some research.

Thanks for your questions...let me know if you think of anything.

edit: Ok, looked up layer 2, but I don't understand it yet. The long distance bridge APs ais set up with a WDS link to the specific MAC address of its partner at the other end, if that helps...

wds with the mac address's is normally on most brands a layer2 bridge setup.
The slow speeds on router B could be because it's setup differently so router c can act as a repeater, or just because C is a repeater and is there. I know repeater mode wds will cut speeds by 1/2 or more.

You could be right. But when I take Router C out of the equation altogether, the problem still persists. Router B had the problem before I even bought Router C. Two computers that are connected to Router B with ethernet cords transfering data between themselves will transfer at just 7 Mbps and the long distance bridge is filled with 2.5 Mbps of traffic (which is its operating limit). This causes the long distance bridge to be useless during a large data transfer. Pretty weird....

Indeed
The switch in router B should not send traffic down the bridge. If you have another switch 5 port or so plug it too the bridge radio and wire up the 2 pc's try a transfer.
I get my internet from a wireless bridge with Nanostation M5's
On my end I have 16 port Giga switch almost full 3 desktops 3 camera servers 1 whs server xbox and laptops on an AP. I send 2 GB across the wire in under a couple minutes too seconds