[Voyage-linux] Extreme asymmetry/poor throughput on link - UPDATE

[Edwin Whitelaw]

All,

First, thanks for the several posts on my initial inquiry.

Here's a quick diagram of the link:

         5-port switch, other systems
                   ^
                   |
      5600m       eth0    6400m    (Both links are set to 7000m with 
athctrl)
A<----H-Pol----->B...B<---V-Pol---->C  (My upstream connection to the 
Internet)
ALIX,XR5    CM11,ALIX,CM11    CM11,ALIX

All antennas except C are Pac Wireless 26db grids.  C has a 22db grid.
None of the boards have had the ECN addition of the capacitor added.

The original problem was between A and B where A to B was great and B to 
A was horrible. The B to A antenna was only a few of feet above a 
flat-topped water tank so we tested from the ground nearby to prove 
there wasn't a weird reflection off the metal causing the problem.   We 
were able to duplicate the problem so have left the antennas alone.

As a final (desperate) measure, we switched the XR5 out for a CM11 at A 
and presto!, good and consistent performance.  Go figure. 

While I now have a workable backhaul with speeds from A to C between 
15-20mbs, there is still the interesting oddity that I can get 30+mbs on 
either of the links individually, ie A to B or B to C (either direction) 
but significantly less when going *through* B radio to radio.  A side 
note is that I can go through B to one of the systems on its the 
ethernet port with full speeds, the degradation only occurs when both 
radios on B are involved.  A potential workaround that may yet be worth 
the effort is to have two boards, B1 and B2, each with a single radio 
and connected to each other on the ethernet side.

Is it possible that the driver or CPU to PCI bus implementation could be 
causing the throughput drop?  I'm certainly not expert on board building 
or drivers but the testing seems to point to something like that as a 
cause.  Obviously, this is a real disappointment to have smoking speeds 
on each leg but not all the way through.  Would sure like to find a 
solution.

Hope this helps someone.

Edwin


-- 
<=+=+=+==+=+=+==+=+=+=+=+=+=+=+=>
Edwin Whitelaw, P.E.
New River Valley Unwired, LLC
2200 Lonesome Dove Dr
Christiansburg, VA 24073
540-239-0318