Outdoor Wireless Antennas

I have been thinking of setting up 3 Dlink DI-624+ with 8db omni outdoor
antennas to connect to buildings as it is a cheaper option than fibre and
copper is not permitted (policy crap).

The wireless is solely for bridging the buildings which are no more than 15m
between them.

1. What are the outdoor antennas like in rain?

2. The 3 buildings are inline. Would it make any difference to use
directional antennas on the 2 outer buildings to point at the omni antenna
on the middle building (If possible)?


Thanks, James.

If you are trying to network the 3 buildings together what you will need is
a dlink that can act as a bridge such as the 2100ap.

Then an omni in the middle and directional on the other two would work
great. Buy antennas made for outdoors. Rain is not a big hindrance. Ice is
worst!


"James Collins" <(E-Mail Removed)> wrote in message
news:BDAC479D.7AEA%(E-Mail Removed)...
> I have been thinking of setting up 3 Dlink DI-624+ with 8db omni outdoor
> antennas to connect to buildings as it is a cheaper option than fibre and
> copper is not permitted (policy crap).
>
> The wireless is solely for bridging the buildings which are no more than
15m
> between them.
>
> 1. What are the outdoor antennas like in rain?
>
> 2. The 3 buildings are inline. Would it make any difference to use
> directional antennas on the 2 outer buildings to point at the omni antenna
> on the middle building (If possible)?
>
>
> Thanks, James.
>

> If you are trying to network the 3 buildings together what you will need is
> a dlink that can act as a bridge such as the 2100ap.

Thanks, its also the same price!

> Then an omni in the middle and directional on the other two would work
> great. Buy antennas made for outdoors. Rain is not a big hindrance. Ice is
> worst!

Since we are in Northern Australia, it is hard enough finding ice in the
freezer!

If I placed the unit in a waterproof plastic box (that is 2mm thick) on the
outside wall under the roof overhang, would the antenna on the bridge be
sufficient if the units where no more than 10m apart? (if I forget about the
third building for now)

James Collins wrote:
>>If you are trying to network the 3 buildings together what you will need is
>>a dlink that can act as a bridge such as the 2100ap.
>
>
> Thanks, its also the same price!
>
>
>>Then an omni in the middle and directional on the other two would work
>>great. Buy antennas made for outdoors. Rain is not a big hindrance. Ice is
>>worst!
>
>
> Since we are in Northern Australia, it is hard enough finding ice in the
> freezer!
>
> If I placed the unit in a waterproof plastic box (that is 2mm thick) on the
> outside wall under the roof overhang, would the antenna on the bridge be
> sufficient if the units where no more than 10m apart? (if I forget about the
> third building for now)
>
10m should be no problem for the bridge, but what are you going to be
communicating with? Will the other end be outside or in a building? An
external antenna would likely give you more than sufficient signal. A
cantenna or maybe a reflector may be in order.

On Mon, 01 Nov 2004 20:05:49 +1000, James Collins <(E-Mail Removed)>
wrote:

>I have been thinking of setting up 3 Dlink DI-624+ with 8db omni outdoor
>antennas to connect to buildings as it is a cheaper option than fibre and
>copper is not permitted (policy crap).

Omni antennas suck for such bridges. From a rooftop, you end up
picking up everything in the area as interference. Better to keep the
signal beamwidth narrow. At such short ranges, you don't really need
the gain, but the interference rejection is important.

The DI-624+ will NOT act as a transparent bridge. As a minimum, I
suggest DWL-2100AP, WAP54G, or similar box. However, you're probably
going to have a big problem. These cheapo transparent bridges will
only bridge 32 MAC addresses. That's probably not enough if you're
planning to band-aid three entire buildings together. You'll need
something that will do thousands. I suggest you look into various
Proxim, Alvarion, YDI, etc products specifically designed for
bridging. (Note: You will not enjoy the prices).

>The wireless is solely for bridging the buildings which are no more than 15m
>between them.

What kind of bandwidth were you expecting? If it's above commodity
wireless data rates, have you looked into FSO (free space optics)? At
only 30 meters, you can use the cheaper LED type systems that are good
to several hundred mbits/sec. If you have fog, forget it, but
otherwise, it's a good interference free solution.
http://www.freespaceoptics.org

>1. What are the outdoor antennas like in rain?

Like a sponge. Water is the enemy because at 2.4GHz, water literally
absorbs RF. I mean, that's why 2.4Ghz was selected for microwave
ovens. Spend the money on something decent so you won't be cleaning
antennas in a storm.

>2. The 3 buildings are inline. Would it make any difference to use
>directional antennas on the 2 outer buildings to point at the omni antenna
>on the middle building (If possible)?

Again, it depends on interference. From a metropolitan rooftop, I
guarantee you will have an interference problem, even in the smallest
cities. Put some effort into using directional antennas. If you
wanna do it right, the one in the middle should have two radios and
two direction antennas. Point to multipoint bridges will work but
will constipate the traffic as everything will need to be store and
foreward repeated from the middle bridge point. Things work best with
individual links between individual buildings which really means two
radios and two antennas on each building. It all depends on how much
traffic you expect. If it's low, then point to multipoint will work.
If it's high, individual links may be required.

If the buildings are truely inline, then you may have a clearance
issue. If the line of sight between the end buildings is blocked by
the middle building, then you may end up using the middle building as
a repeater. This isn't all that bad, but needs to be properly
engineered.

I suggest you find someone local that has had some experience
engineering telco bypass and WLAN bridges, and ask them to help.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> wrote:
> The DI-624+ will NOT act as a transparent bridge. As a minimum, I
> suggest DWL-2100AP, WAP54G, or similar box. However, you're probably
> going to have a big problem. These cheapo transparent bridges will
> only bridge 32 MAC addresses. That's probably not enough if you're
> planning to band-aid three entire buildings together. You'll need
> something that will do thousands. I suggest you look into various
> Proxim, Alvarion, YDI, etc products specifically designed for
> bridging. (Note: You will not enjoy the prices).

If there are more than 32 devices in the buildings, a switch is going to be
needed for connectivity anyway. Can't that be a router, providing a subnet
per building, reducing the traffic on the wireless that would be present if
it were a flat bridged network?

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

> Omni antennas suck for such bridges. From a rooftop, you end up
> picking up everything in the area as interference. Better to keep the
> signal beamwidth narrow. At such short ranges, you don't really need
> the gain, but the interference rejection is important.
>
> The DI-624+ will NOT act as a transparent bridge. As a minimum, I
> suggest DWL-2100AP, WAP54G, or similar box. However, you're probably
> going to have a big problem. These cheapo transparent bridges will
> only bridge 32 MAC addresses. That's probably not enough if you're
> planning to band-aid three entire buildings together. You'll need
> something that will do thousands. I suggest you look into various
> Proxim, Alvarion, YDI, etc products specifically designed for
> bridging. (Note: You will not enjoy the prices).

I find it hard to believe that Dlink would make such crap. We currently do
this with Apple Airports, however these are inside the buildings without
external antennas. The move to Dlink is to increase the bandwidth fron 11 to
108MBps. There are about 30 PC's per building, all connect to a 3Com switch
then the switch connects to the current Airport.

>> The wireless is solely for bridging the buildings which are no more than 15m
>> between them.
>
> What kind of bandwidth were you expecting? If it's above commodity
> wireless data rates, have you looked into FSO (free space optics)? At
> only 30 meters, you can use the cheaper LED type systems that are good
> to several hundred mbits/sec. If you have fog, forget it, but
> otherwise, it's a good interference free solution.
> http://www.freespaceoptics.org

The bandwidth of 54 - 108MBps is suffecient.

> Again, it depends on interference. From a metropolitan rooftop, I
> guarantee you will have an interference problem, even in the smallest
> cities. Put some effort into using directional antennas. If you
> wanna do it right, the one in the middle should have two radios and
> two direction antennas. Point to multipoint bridges will work but
> will constipate the traffic as everything will need to be store and
> foreward repeated from the middle bridge point. Things work best with
> individual links between individual buildings which really means two
> radios and two antennas on each building. It all depends on how much
> traffic you expect. If it's low, then point to multipoint will work.
> If it's high, individual links may be required.

> If the buildings are truely inline, then you may have a clearance
> issue. If the line of sight between the end buildings is blocked by
> the middle building, then you may end up using the middle building as
> a repeater. This isn't all that bad, but needs to be properly
> engineered.
>
> I suggest you find someone local that has had some experience
> engineering telco bypass and WLAN bridges, and ask them to help.

Again, I find it difficult that we can do the same setup using Apple
Airports with there builtin omni antennas, we are just looking to increase
the 11Mbps to 108MBps by upgrading our equipment and possibly external
antennas to decrease interference.

If I need to call in a telco then this will start to cost big $$$ so we
would just spend the extra and use fibre. At the moment we are finding the
wireless to be 1/4 less then the fibre alternative.


--
James Collins
Technical Officer
Cairns School of Distance Education

Ph. 07 4050 8203
Fx. 07 4051 0336
Mob. 0402 866 972

On Mon, 1 Nov 2004 18:27:47 +0000 (UTC), (E-Mail Removed)
wrote:

>Jeff Liebermann <(E-Mail Removed)> wrote:
>> The DI-624+ will NOT act as a transparent bridge. As a minimum, I
>> suggest DWL-2100AP, WAP54G, or similar box. However, you're probably
>> going to have a big problem. These cheapo transparent bridges will
>> only bridge 32 MAC addresses. That's probably not enough if you're
>> planning to band-aid three entire buildings together. You'll need
>> something that will do thousands. I suggest you look into various
>> Proxim, Alvarion, YDI, etc products specifically designed for
>> bridging. (Note: You will not enjoy the prices).

>If there are more than 32 devices in the buildings, a switch is going to be
>needed for connectivity anyway. Can't that be a router, providing a subnet
>per building, reducing the traffic on the wireless that would be present if
>it were a flat bridged network?
>Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

Certainly. In fact, that's the preferred method for glueing large
numbers of different customers together. I didn't want to get into
implimentation, just take some pot shots at using cheapo wireless
bridges.

Actually, even a bridge that can only do 32 MAC addresses will sorta
work. Traffic on both sides of the bridge will rapidly fill up the
MAC address to port bridging table. Most bridges are smart enough to
expire old addresses. Some are even smart enough to push out old
addresses when a new one appears. I have a custom packet generator
program (not for distribution) that will belch large numbers of unique
MAC addresses for testing bridges. The better bridges (usually
managed with SNMP) can handle it with ease because they timestamp
their bridging table and will expire the least recently used entry.
Commodity bridge suck by comparison. A pair of DWL-900AP+ boxes, in
transparent bridging mode, take about 10 seconds to lock up solid with
an excessive number table entries. The first 32 pass, and then
everything just sits there until the table entries expire. I vaguely
recall that was about 3 minutes. Then, I can hit it with the next 32
MAC addresses. In practice, on small networks, this isn't all that
bad as the most commonly used devices will eventually force the
scarcely used entries out of the table.

Using routers instead of bridging has some really big advantages.
1. It eliminates the MAC bridging table limit problem as it only uses
one MAC address per radio link.
2. Because it only uses one MAC address, there is no need for an
overpriced wireless bridge pair of radios that use proprietary
bridging protocols. A cheapo access point and ordinary client radios
can be used.
3. Multiple subnets and static routes can be used to keep unrelated
customer seperate (without resorting to a VLAN).
4. Bridging can be simulated using a VPN router on both ends.
5. Bandwidth management by IP is much much much much much easier by
IP than by MAC address.
6. The customer can still get routeable IP addresses by first
delivering an RFC-1918 private addresse, and then redirecting traffic
from an incoming routeable IP to the private address. Most wireless
ISP's charge extra for this. I can't seem to recall the exact Cisco
IOS incantation, but can dig it out if necessary.
7. The customer can still use NAT on their router to connect multiple
computahs.
8. Multiple connections to the internet, through multiple border
routers is much easier, offering improved reliability.
11. There's far more control over traffic and services at the IP level
than at the MAC address level.
10. Whatever else I forgot.

So, with all these advantages, why do people do bridging? Well, it's
easier, much simpler, cheaper, and good enough for most applications.

Anyway, the real unanswered question is what duz the original poster
plan to do with the wireless links? VoIP, video, internet, telco
bypass, sell bandwidth, play WISP, private WLAN, build a metro LAN,
fiber replacement, broadcast, etc? At the bottom end, almost anything
can be made to work. When the number of client radios, customers, or
traffic become large, solutions tend to be far more complex.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

James - to avoid the use of "D-Link crap:, or other lower cost alternatives
that work reasonably well, why not just upgrade to the Apple Extreme product
http://www.amazon.com/exec/obidos/tg...s&vi=tech-data.
It allows an external antenna.

--
Bob Alston

bobalston9 AT aol DOT com
"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Mon, 1 Nov 2004 18:27:47 +0000 (UTC), (E-Mail Removed)
> wrote:
>
>>Jeff Liebermann <(E-Mail Removed)> wrote:
>>> The DI-624+ will NOT act as a transparent bridge. As a minimum, I
>>> suggest DWL-2100AP, WAP54G, or similar box. However, you're probably
>>> going to have a big problem. These cheapo transparent bridges will
>>> only bridge 32 MAC addresses. That's probably not enough if you're
>>> planning to band-aid three entire buildings together. You'll need
>>> something that will do thousands. I suggest you look into various
>>> Proxim, Alvarion, YDI, etc products specifically designed for
>>> bridging. (Note: You will not enjoy the prices).
>
>>If there are more than 32 devices in the buildings, a switch is going to
>>be
>>needed for connectivity anyway. Can't that be a router, providing a
>>subnet
>>per building, reducing the traffic on the wireless that would be present
>>if
>>it were a flat bridged network?
>>Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
>
> Certainly. In fact, that's the preferred method for glueing large
> numbers of different customers together. I didn't want to get into
> implimentation, just take some pot shots at using cheapo wireless
> bridges.
>
> Actually, even a bridge that can only do 32 MAC addresses will sorta
> work. Traffic on both sides of the bridge will rapidly fill up the
> MAC address to port bridging table. Most bridges are smart enough to
> expire old addresses. Some are even smart enough to push out old
> addresses when a new one appears. I have a custom packet generator
> program (not for distribution) that will belch large numbers of unique
> MAC addresses for testing bridges. The better bridges (usually
> managed with SNMP) can handle it with ease because they timestamp
> their bridging table and will expire the least recently used entry.
> Commodity bridge suck by comparison. A pair of DWL-900AP+ boxes, in
> transparent bridging mode, take about 10 seconds to lock up solid with
> an excessive number table entries. The first 32 pass, and then
> everything just sits there until the table entries expire. I vaguely
> recall that was about 3 minutes. Then, I can hit it with the next 32
> MAC addresses. In practice, on small networks, this isn't all that
> bad as the most commonly used devices will eventually force the
> scarcely used entries out of the table.
>
> Using routers instead of bridging has some really big advantages.
> 1. It eliminates the MAC bridging table limit problem as it only uses
> one MAC address per radio link.
> 2. Because it only uses one MAC address, there is no need for an
> overpriced wireless bridge pair of radios that use proprietary
> bridging protocols. A cheapo access point and ordinary client radios
> can be used.
> 3. Multiple subnets and static routes can be used to keep unrelated
> customer seperate (without resorting to a VLAN).
> 4. Bridging can be simulated using a VPN router on both ends.
> 5. Bandwidth management by IP is much much much much much easier by
> IP than by MAC address.
> 6. The customer can still get routeable IP addresses by first
> delivering an RFC-1918 private addresse, and then redirecting traffic
> from an incoming routeable IP to the private address. Most wireless
> ISP's charge extra for this. I can't seem to recall the exact Cisco
> IOS incantation, but can dig it out if necessary.
> 7. The customer can still use NAT on their router to connect multiple
> computahs.
> 8. Multiple connections to the internet, through multiple border
> routers is much easier, offering improved reliability.
> 11. There's far more control over traffic and services at the IP level
> than at the MAC address level.
> 10. Whatever else I forgot.
>
> So, with all these advantages, why do people do bridging? Well, it's
> easier, much simpler, cheaper, and good enough for most applications.
>
> Anyway, the real unanswered question is what duz the original poster
> plan to do with the wireless links? VoIP, video, internet, telco
> bypass, sell bandwidth, play WISP, private WLAN, build a metro LAN,
> fiber replacement, broadcast, etc? At the bottom end, almost anything
> can be made to work. When the number of client radios, customers, or
> traffic become large, solutions tend to be far more complex.
>
>
> --
> Jeff Liebermann (E-Mail Removed)
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 AE6KS 831-336-2558


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James Collins <(E-Mail Removed)> wrote:
> I find it hard to believe that Dlink would make such crap. We currently do

Oops. Comparing apples to ...

> this with Apple Airports, however these are inside the buildings without
> external antennas. The move to Dlink is to increase the bandwidth fron 11 to
> 108MBps. There are about 30 PC's per building, all connect to a 3Com switch
> then the switch connects to the current Airport.

Aha! There is a switch already. That is part of Jeff's concern. But you
say "a 3com switch". Is there one switch in each building?

I picture three buildings with a switch each, and wireless links between
them. Most switches will relieve quite a bit of the traffic between
buildings that is targeted for specific other systems, but theer might be a
lot of general broadcasting on the network that will get repeated between
the buildings. If these were routers, the wireless portion would be even
less cluttered, and only pass the traffic that needs to pass.

> Again, I find it difficult that we can do the same setup using Apple
> Airports with there builtin omni antennas, we are just looking to increase
> the 11Mbps to 108MBps by upgrading our equipment and possibly external
> antennas to decrease interference.

If what you have already works, that eliminates a lot of the concerns that
Jeff is trying to hide. He is overengineering so that you won't be
disappointed, but you already have empirical test results from the existing
setup.


--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5