Gabriel,
The combination of no mast and many links will probably give you very high
latency and jitter along with many sources of outages and potential
interference.
Before you select a technology (VSAT, Landline or Terrestrial radio) you
need to know what delays and packet losses will crash your application. VSAT
has long delays so systems are built to spoof the TCP/IP windowing
algorithm. Your application may not like that. It is typically okay in web
page downloads if there is little Flash, graphics or video type content
where large blocks of compressed data must be received with low error rates.
A VPN solution is also needed if you want to keep your data secure. Since
you own both ends of the link, secure key management is easy. If you use a
SW/Server based solution have the manufacturer verify that they can do line
rate encryption and keep stream straight. I have seen inexpensive firewalls
collapse under heavy load of encryption and pass thru 5 to 20% of line speed
when encrypting. The advantage of SW is Unix/Linux/other OS and cheap
hardware.
I like "real man" hardware encryption like HiFn chips or proprietary
solutions. Some firms like Watchguard and others have hardware that will run
at 1GE and above, so they know about the system issues.
While at Wireless, Inc (now owned by Alvarian), Frank Massa
(ex-DMC/Stratex, ex-Wireless, & ex-YDI) engineered a series of long range 6
GHz licensed links to run from New Orleans across the south to mid-Florida.
Signals were distributes from each tower to the local area with unlicensed
radios but the back-bone was licensed.
He engineered many systems with mixes of unlicensed and licensed radios.
I'm not going to propagate Frankie's email or cell number, you need to
search him out. He splits his time between Silicon Valley and L.A.
In the unlicensed bands you are limited by interference and maximum EIRP
allowed. The EIRP limit leads to a transmitting antenna size limit to stay
within the rules, typically a 2' dish or panel. As you increase the link
carrying capacity you also loose range.
If your radios are on a building top you will probably pick-up the local
Internet Cafe signal levels above your long range link levels unless you buy
a great antenna. You will also see reflections causing multi-path. Standard
802.11b has some other issues with long links. One trick is to separate the
TX from the Rv antenna and use a higher gain, tighter pattern Rv antenna.
There are other issues above 3 GHz with propagation characteristics you
should know, like ducting and ground reflections. The Harris website and
others have some downloadable tools you could look at. Typically you can
fake out the EIRP and Frequency to match the band you desire.
http://www.microwave.harris.com/systems/starlink/index.html
Also Kirt Blattenberger's excellent site, RFCafe, has calculators for VSAT
and Terrestrial links.
http://www.rfcafe.com/references/calculator_links.htm
Also the 802.11 standard protocols 802.11b has some other issues with
long links, that is why you want to purchase PT-PT links or configure a
PT-MPT into PT-PT mode.
Definitely look into the alternatives in terms of service costs, QoS,
Guaranteed vs. spot capacity and Up-Time. A two path solution may give you
the best solution like landline to fiber backed up by radio.
Good luck,
Bill Kunz
Principal
Broadband Enterprises
ex-HP, ex-Wireless, ex-CEL
-----Original Message-----
From: gekorhi [mailto:[EMAIL PROTECTED]
Sent: Wednesday, September 29, 2004 9:33 AM
To: [EMAIL PROTECTED]
Subject: [wirelesslan] RE: LONG RANGE LAN EQUIPMENT
PLEASE I NEED TO COVER A LONG RANGE OF ABOUT 450 - 500 KM TO LINK UP
WITH OUR SECOND OFFICE, TO SHARE A DATABASE.
1. WHAT EQUIPMENT DO I NEED TO HOOK UP AND EXTEND THE LAN TO THE OTHER
OFFICE WITHOUT STRESS.
NO MAST, NEEDED.
PLEASE HELP ME OUT
CHEERS
GABRIEL
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