Subject: [NEXTEL-1] Re: Advice on using spread spectrum link in critical communications

From: [email-masked]
Date: Wed, 19 Nov 2003 00:21:54 -0500

-------- Original Message --------
From: Jack Daniel <[email-masked]>
Subject: Re:  Advice on using spread spectrum link in critical communications

Kevin,

I can't verify this personally but I was told by a dealer (whom I trust)
they had to urgently replace several unlicensed point-to-point links
last year due to interference from other unlicensed transmitters. This
occured about 13 months ago.

Seems a major Los Angeles water utility had installed unlicensed band
radios as critical system control links between pump stations north of
LA. On a weekend, someone fired up a high powered unlicensed system in
the area and intermittently jammed the utility's control system. 

To keep part of LA from running out of water and avoid damage to the
pump stations, the utility had to dispatch operators to maually control
the system until the unlicensed equipment was replaced with "real"
point-to-point microwave. This took several days.

Apparently the use of unlicensed equipment was a financial choice, not a
lack of licensable microwave channels.

Hope your client doesn't rely on unlicensed bands for anything
important.

===========================================================

Kevin Graybill wrote:
> 
> You guys are really helping me out with my cause.  Keep the great
> information coming if you can.
> 
> Kevin

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---

From: [email-masked]
Date: Wed, 19 Nov 2003 01:10:39 -0500

Last year PSWN reviewed 802.11b/ 2.4 Ghz / 5Ghz  protocols & spectrum for Public
Safety applications they noted the following disadvantages:

• Commercial vendors operating as wireless Internet service providers (WISP) can
deploy multiple APs within an area, creating substantial interference or
rendering
existing unlicensed 802.11b compliant networks unstable or unusable.

• Adequate and appropriate security features are not presently found in the
wireless
network equipment thus requiring use of additional third-party products at
additional
costs.

• Depending on the manner of the wireless deployment, the usability and
functionality
may not be seamless for the user community, which could create some resistance to
its
use and requirements for additional training.

• Appropriate management tools for the wireless APs are limited and immature and
may
require increased manual efforts for troubleshooting.

• Interference from other WLANs, cordless telephones, microwave ovens, Bluetooth
enabled devices, or other wireless devices or sources can disrupt or obliterate
connections.

• Coverage can be impacted by the composition of structures or materials around
APs,
as well as the existence of other WLANs in the area.

• The 5 GHz spectrum used for 802.11a compliant network equipment is more
susceptible than the 2.4 GHz spectrum to fading and decreases in coverage due to
signal absorption during rain events or in areas where water is present.

• 802.11b compliant equipment operates in the very crowded 2.4 GHz unlicensed
spectrum, which can contribute to vast opportunities for interference with other
equipment using the same area of spectrum.

• 802.11b compliant equipment, operating in the 2.4 GHz range, incorporates only
three
available channels, making it less desirable to install multiple APs near each
other
because of potential overloading of the limited bandwidth.

• Existing 802.11 standards are currently under revision and are poised to change

rapidly, which could make existing products obsolete in the near term.

• Presently, some manufacturers’ devices do not interoperate well with those of
other
manufacturers, possible making those devices prone to losing data packets as
users
move between dissimilar APs or multiple WLANs.

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