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'[EE]: 802.11b - Comments sought'
2002\05\21@184135 by Russell McMahon

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No PICs here (yet).
I'd be interested in hearing from people who have experience with 802.11b
networking over significant distances. Offlist if too OT but I suspect many
would be interested to know what has been achieved. Any comments on specific
points covered below would be welcome. This is not the best forum for vast
discussions on this topic - whether we should take this offlist depends on
response and general interest.

I'm about to venture into playing with 802.11b wireless networking. A major
longer term aim is establishing reasonably long distance 1 to 10 Mbit
communications links. Initially the aim is to get a feel for what's involved
by establishing successively longer medium range links (A = 400 metres / not
quite LOS, B = 3 km / will be LOS when I find a high point, C = 6 km / will
be LOS when I climb that pine tree at the far end) and then work up to
getting as much range as possible. One longer term aim is to extend one leg
to a city H about 130 km / 80 miles South of here using as many hops as it
takes and as few as possible. I have access to one high point D on the South
side of my city with a clear line of sight over water to a higher point E
about 30 km / 20 miles South. From there it's 85 km to the final destination
H with some variably hilly country in between so I am going to have to find
some suitably interested farmers along the way :-). From my location to H
(on the water) is only about 11 km but high ground between means there will;
need to be at least one intermediate point. (One PICLister mentioned
achieving 46 miles (AFAIR) on a single hop but this was with powers well
above the NZ legal limit.)

Our regulations limit effective power to 36 dBi or 10 milliwatts into a 26
dBi parabolic (about 0.8 metre diameter).
There is no restriction on receiver antenna gain and I will look at larger
dishes for the relay point although maximum size is limited by aesthetics
and cost. Surplus satellite TV dishes from "the early days" should be
available at reasonable cost.

This is essentially a "hobby" venture at this stage although something
commercial may grow from it in due course. I'm keen to spend as little as
reasonable on hardware at this stage as long as labour requirements are not
vast as a consequence. A tour of some of the vast amount of web resource on
802.11 suggests that extremely useful aerials can be made with very little
work (eg coffee can and an N connector gives a 16 dBI waveguide antenna for
10 minutes work after you've spent N days getting the first one right).  I
have my doubts about the Pringles Can designs. Driving a surplus 65 cm
parabolic antenna should allow gains in the 22 - 28 dBi range. (There are
some VERY poor "designs" published as well).

I'm considering with DLink USB  cards to start as these are available
locally, are the lowest cost in this market and have RF specs (TX level, RX
sensitivity) similar to most others generally available. The USB versions do
not have an external aerial connector but there are numerous "how to" pages
on adding one to various cards. (Technically this is a trivial task but in
practice knowing that many people have modified 2.4 GHz gear like this is
comforting.).

I favour USB cards initially due to flexibility - hey can be operated in
desktop or laptops and if desired may be mounted near the aerial with feed
by USB cable rather than using longer potentially lossy coax runs. There is
a potential loss in throughput due to the USB interface being specd somewhat
below 11 Mbps but this loss of throughput is irrelevant during initial
investigations.
.
I'm probably not buying an access point to start as I can ascertain the
practicality of longer ranges without one. Various open source solutions are
becoming available.



Thoughts ???



           Russell McMahon

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2002\05\21@190250 by Jon Baker

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> No PICs here (yet).
> I'd be interested in hearing from people who have experience with 802.11b
> networking over significant distances.

I have a friend involved with long distance wireless networking in
australia. http://www.wireless.org.au . They are setting up quite an impressive
wide area network. They seem like a friendly bunch of guys if you want to
get in touch with them. I'll pass your email address onto him.

> getting as much range as possible. One longer term aim is to extend one
leg
> to a city H about 130 km / 80 miles South of here using as many hops as it
> takes and as few as possible.

> Thoughts ???

I've got thousands of them !. Wireless is something I'd love to get involved
with but nothing much seems to be happening around where I am ( UK ). Would
be nice to have a 802.11b module we could use with the pics...
Perhaps a pic<>pcmcia interface would do the trick

Jon Baker

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2002\05\21@204834 by Patrick J

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Hi Russell,
This sounds just like a project i am currently trying to tie toghether.

One nice cheap access point you should look into is D-Link's DWL-900AP
It has external antenna outlet and can work in many different setups, which
client 802.xx cards can't. See http://www.dlink.com
Also they have a new 802.11a access point: DWL-6000AP. Speed 54Mbps.
The problem with the D-Link products I face is that they are for indoor use.
Read the datasheet for the temp-range.

http://www.netgear.com have simular products. Breezecom have equipment that is
built for ISPs. Outdoors use, VoIP, security, loadbalancing etc... As
expected
their prices is a sad story.

My primary issues are load balancing, QoS, VoIP, security etc.. basically as
I understand it, traffic-managment sucks... There will always be someone
that will take all the bandwith, if not controlled. I'd like to allow full
speed
within the LAN, but be able to control the speed each user gets to the
internet.

You won't get more than 5 Mbps from a 802.11b radiolink at 5 km, as the
distance increase the speed drops. At 10 km u'll get like 1 Mbps.
(Actually you won't get more than 5-6 Mbps even at 0-5 meters, i've tried)


> I'm about to venture into playing with 802.11b wireless networking. A
major
> longer term aim is establishing reasonably long distance 1 to 10 Mbit

If you even have a single tree in the LOS forget it... Might work fine in
the
winter, but will be crap in the summer. (fire up the chainsaw :-)

> ...mounted near the aerial with feed
> by USB cable rather than using longer potentially lossy coax runs. There
is
> a potential loss in throughput due to the USB interface being specd
somewhat
> below 11 Mbps but this loss of throughput is irrelevant

Since 5 Mbps is max you will get from the link, USB2.0 might be ok.
(I don't know what the USB standards say about the lenght of the cable)
The problem is that you can't mount the D-link AP outdoors... which leaves
you with 2 alternatives:
1. long coax
2. environmental controlled box to put the AP in. (expensive stuff)
3. other brand of AP which is made for outdoors use (even those seems to
have
a bad temp-range. Here summer is +50C in the sun and winter -30C)

Here is a 39 meters high tower that I will mount sector-antennas in the top
of.
From that there is another 200 meters to the router. That adds up to ~250m
coax... might be tricky to do. [*looking into alternatives*]

/PJ

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