Wireless bridge

Peter Boone NANOG at Aquillar.com
Thu Jun 18 20:46:08 CDT 2009


OK, from reading all the excellent feedback I've got on and off list I've
attempted to compile a "quick" summary of findings/ideas/products so far.

- RouterBoard is no good for this type of application.

- Get a unit with radio/antenna integrated, PoE from inside the building
(outdoor rated cat5, shielded I assume), lightning suppression for the PoE
(properly grounded), and ensure the mast is properly grounded.

- Get off the 2.4 GHz range. Move up to 5. As for licensed vs. unlicensed,
I'm getting mixed input. I'm fairly certain that if the price is right and
the frequency is 5GHz+, it won't be a factor. Also, I'll be very glad to
separate the bridge from the client access points so that allows for more
options. Every solution at this range can easily do 20+ Mbps so throughput
is no longer a factor.

- Products that support ARQ are highly recommended.

- I'm hearing the same products mentioned over and over:
	- Motorola
	- Ubiquiti
	- Aironet (Cisco)
	- Aruba
A number of individuals recommended products from other brands at low cost
that meet these mentioned requirements too.


I'm not going to bother with a spectrum analyzer. In the current
implementation we tried channels 1, 6 and 11 for a few days at a time and
found 1 to be the most reliable. Done. At this point an analyzer will tell
me what I already suspect: there's a problem.

I've researched the Fresnel zones and calculated out a few things with rough
numbers and worst case. For one, the Fresnel zone is disrupted most if the
obstruction is closer to the endpoints (e.g. antennas). In this case, this
is fine as the antenna are mounted at the outermost corner of the buildings
as close as possible to the other buildings, approximately 3 floors in the
air. Other buildings become a factor near the middle. Based on channel 1's
wavelength of 0.12438 m, and assuming 1 km apart (for simplicity sake. It's
actually less), the Fresnel zone is largest in the center at approx 5.6 m
radius. That could definitely be obstructed by rooftops, I'll have to take
another look though. This radius cuts in half when the frequency is doubled,
thus more evidence in favour of the 5 GHz+ range. Cool. Or we could just go
with a good line of sight optical solution but they look too expensive, and
this area can have very unforgiving fog/wind to disrupt things further. What
if we tilt each existing antenna up towards the sky 10-20 degrees? Please
correct me if I'm wrong.

The current antennas are plates. I'm pretty sure they are polarized. I used
to have a product sheet on these but a Google search doesn't turn up any
useful results anymore (SmartAnt PCW24-03014-BFL). The way they are mounted
to the poles might make it difficult to try rotating them 90 degrees, but
worth another look. The coax between the AP and antennas are no longer than
30 feet. I've often wondered if a Pringle or Coffee Cantenna would work
better than these!


For right now I'll have the coax line and ends inspected for
damage/softspots, check the grounding, and cover/re-cover the ends in large
amounts of rubber/electric tape. I think we might try the Ubiquiti Bullet2
for approx $100 per side (PoE supply/lightning suppression, wiring included)
and see what happens! If that doesn't work, no major loss and we'll move up
to something more serious (the PoE and wiring will already be ready to go).
I will have to look into pricing on some of these suggestions and figure out
if we should even bother getting a Bullet but instead go straight to a
better all-in-one solution.

Thank you guys very much for the tips. Feel free to keep them coming!

Peter





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