On 13-10-24 12:49 PM, Jim Thompson wrote:
If those wireless links are for exterior paths, and not simply 802.11
LANs, then you’re in for a huge amount of trouble, as wireless isn’t
reliable. At all.
I have to disagree, at least partially. In the wireless world,
reliability costs!
Wireless reliability also depends heavily on the specific environment
you're running it in, and the quality of link engineering that went into
each installation.
Also making a big difference is whether it's point-to-point (dedicated)
or point-to-multipoint (typical for WISPs), or multipoint-to-multipoint
(omnidirectional broadcast, i.e. mesh).
I have a 68' tower in my back yard anchored into 80 cubic feet of
concrete with fairly cheap Ubiquity 2.4Ghz gear up top, running
point-to-point using directional (closed parabolic dish) antennas at
both ends (2' my end, 3' far end).
With this setup, I have yet to experience any (non-self-inflicted)
outages. I do notice that available channel throughput varies from
~18Mbps to ~30Mbps depending on RF and atmospheric conditions, although
latency stays low at around 1msec.
If I upgraded to a better-quality unit, or switched to licensed
spectrum, I could probably eliminate the variability and increase speed
simultaneously. I'm told to expect intermittent service in the case of
a whiteout (blizzard), which hasn't happened yet.
Within the Ubiquity line, the AirFiber apparently would get me to
~99.99% reliability at ~600Mbps, or ~99.9% reliability at ~1Gbps. Still
using unlicensed spectrum, using the built-in directional antennas.
Of course, my personal link is only 6.8km long - not exactly a
worst-case scenario.
I also used Dragonwave (5GHz, licensed) equipment mounted on cell towers
to cover ~500,000 square kilometers at speeds of up to 800Mbps on links
of up to 60km, and the only failures or outages we had on a regular
basis were power-related. (Yes, some of the radios failed over time.
Cisco switches failed about four times as often, in the hostile and
lightning-prone environment we were running in.) We did experience some
link flapping during a severe ice storm, because the ice was forming on
some of the dishes faster than the RF power and/or heater could melt
it. Turns out even Dragonwave radios can't transmit or receive very
well through solid water :-).
Rough rule of thumb boils down to:
1. If you aren't spending at least $5000 per link, then wireless
will be noticeably unreliable.
2. Point-to-point (dedicated) is always more reliable than
point-to-multipoint (shared).
3. WiFi (802.11) equipment pretty much always sucks.
If you're spending enough money, wireless can be made more reliable than
copper or fiber (but not necessarily faster). We weren't spending quite
that much money, but our Dragonwave radio links were still 99.99+%
reliable as a rule.
Dragonwave and Alvarion(?) radios are considered to be the cream of the
crop; telcos regularly use them for backhaul in areas where it's too
expensive or difficult to trench cable. I do not have personal
experience with Alvarion, but I can unreservedly recommend Dragonwave.
--
-Adam Thompson
[email protected]
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