Wireless bridge

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1

Hi NANOG,

I'm looking for some equipment recommendations for a wireless bridge between
two locations approximately 500-800 meters apart. The current setup for this
company has been extremely unstable and slow. I don't have a lot of
experience in this area so I was hoping someone could give me a few
pointers.

Currently, both locations are using Linksys WRT54GL's flashed with DD-WRT
firmware (Yes, 802.11g. All extra bells and whistles are disabled in the
firmware. They were set up for WDS so other wireless clients could connect
to the same access point, with varying degrees of success. Not very
important). They are connected to SmartAnt 2300-2500 MHz 14 dBi directional
antenna mounted on the roof (extended pretty high for perfect line of
sight). I'm not sure when they got these antenna exactly but I'm told it was
when WiFi was very new. The network is very small so both locations share
the same subnet (192.168.1.0/24).

They have gone through numerous Linksys access points over the years. The
wireless settings are tweaked as best as possible, and we have found the
connection to be most stable when the TX is limited to 6-9 Mbps.

We have explored other options as well. An internet connection at each
location + VPN is out due to very slow upstream speeds (the buildings are in
an industrial area, ADSL is the only option.) The max they offer on regular
business accounts is 800 kbps up. T1 lines are even slower and even more
expensive. They won't offer us any other solutions such as fibre. We have
considered running fibre/coax but there is too much construction activity
and other property in the way.

I'm looking into RouterBOARD right now, considering a RB433AH and R52H
wireless card, but I'm not sure this will actually solve the problem. It's
difficult to determine if the issue is with the antennas or access points
(for example, after a good thunderstorm, the wireless link will be down for
at least 12 hours, but will fix itself eventually. Resetting either access
point will keep the link down for at least 30 minutes. Using an airgun on
the access points tends to make them more reliable, even if they are clean
and dust free. From the admin interface, each access point will report
seeing a very good and strong signal from the other, yet they refuse to
communicate until they feel like it a few hours later.)

Any suggestions welcome. I'm sure you can tell cost is a bit of a factor
here but it will be easy for me to justify a higher price if I'm confident
it will be effective.

While I'm at it, I've been reading along on the list for over a year now;
thanks everyone for sharing your real world experiences :slight_smile:

Peter

2

I've had good luck with Cisco Aironet gear running in repeater mode.

  I've done the cheap linksys thing as well and it just did not work
as well as using some equipment that was better designed.

  I have actually found the non-IOS software on the aironet 350/340 to
be more usable than the IOS software. You need to have your network be
consistent.

  You also have the obvious interference challenges with any unlicensed
deployment.

  - Jared

some of the equipment i've used:

http://cgi.ebay.com/5-Cisco-Aironet-350-WAPs-AP352E2R-A-K9_W0QQitemZ200351697798QQcmdZViewItemQQptZCOMP_EN_Routers?hash=item2ea5e44b86&_trksid=p3286.c0.m14&_trkparms=65%3A1|66%3A2|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A50

http://cgi.ebay.com/Cisco-AIR-AP1121G-A-K9-Aironet-1100-1121-Access-Point_W0QQitemZ190313803887QQcmdZViewItemQQptZCOMP_EN_Routers?hash=item2c4f96306f&_trksid=p3286.c0.m14&_trkparms=65%3A1|66%3A2|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A50

3

We've used aironet since before cisco owned it. We just recently went fiber
for most of the district, but still running one aironet connection a good
distance apart.

4

We use Nortel 7230 wireless bridges and are *very* happy with them.
They run at 5.8 GHz, 20 Mbps full duplex (really 18 Mbps data rate),
do transparent bridging, and pass VLAN tagged frames just fine. For
one particular link, we continually push the full 18 Mbps and they
work fine. They are PoE powered via a power brick in the network
closets, with a single Cat5 cable up to the outdoor unit which has the
antenna integrated. We've had very few failures over the
years--mainly a few infancy failures shortly after installation. We
have about 40 units (20 links), all less than 1 km apart, most of them
a few hundred meters across city streets.

These are the third generation of wireless bridge products we have
used, and they far outperform the older ones, especially from a
reliability and maintenance perspective. We will be looking to
upgrade these over the next few years to get more bandwidth in some
locations, and I'm not overly optimistic about finding something that
matches these from a reliability and ease-of-use perspective--I would
appreciate it if you share a summary of any results you find.

5

Peter Boone wrote:

Hi NANOG,

I'm looking for some equipment recommendations for a wireless bridge between
two locations approximately 500-800 meters apart. The current setup for this
company has been extremely unstable and slow. I don't have a lot of
experience in this area so I was hoping someone could give me a few
pointers.

....

I have had good luck with Airaya. May be a bit pricy for your application but they are solid. The one I am on right now has to be at least five years old.

http://airaya.com

Whatever you do, move out of 2.4Ghz. That's probably 50% of your problems right there.

6

Cisco Aironet www.cisco.com
Alvarion www.alvarion.com
Aruba www.arubanetworks.com
bluesocket www.bluesocket.com

I've used all but bluesocket and they all worked pretty well. bluesocket gets good reviews. These are just a few. There are lots of them. Try to use one as and access point and use one as a client. Working in repeater mode will cut your bandwidth in half.

--Curtis

Peter Boone wrote:

7

Pair of Ubuquiti power station 2 or 5 bridges, 5 would be preferable,
under $200 per end.

http://www.ubnt.com/downloads/ps5_datasheet.pdf

Peter Boone wrote:

8

(for example, after a good thunderstorm, the wireless link will be down for
at least 12 hours, but will fix itself eventually.

Sounds like there are trees in the line of sight, and maybe they are getting
leafier over the years. The only solution to that is to change the path if
it is possible.

9

We're a WISP, so I have lots of experience with this kind of thing. The problem with using 2.4GHz equipment is that there's a whole lot of noise out there (run Network Stumbler sometime on a laptop with a wireless card, and you'll be shocked by just how many wi-fi APs are floating around).

You didn't mention your bandwidth requirements, but I'm assuming that you're trying to get more (and spend less), so I'll only recommend unlicensed gear. For that distance, you might want to consider using a 5.2GHz radio. The FCC limits their transmit power, so they only work well in short-range applications (>2 miles or so), and 5.2GHz doesn't propagate the way that 2.4GHz does, so there tends to be much less noise in that band.

The Motorola PTP400 series (http://www.motorola.com/Business/US-EN/Business+Product+and+Services/Wireless+Broadband+Networks/Point-to-Point+Bridges) is very good (Asymetric Dynamic Frequency selection means that each side can pick the best frequency to transmit on, and ARQ means that scrambled packets get handled at the wireless layer), and throughput tops out about 45Mbps (300Mbps for the PTP600 series), but they are expensive. They can be purchased in many different bands.

On the lower end, we've been using Ligowave (http://www.ligowave.com), and had good results from them, for the price. They also come in many bands, and run about $3000 (for the model with an integrated panel antenna), support throughput up to 45Mbps, and also support ARQ.

Hope this helps.

Tim Huffman
Director of Engineering
Business Only Broadband, LLC
O (630) 590-6012
C (630) 340-1925
tim@bobbroadband.com
www.bobbroadband.com

10

(for example, after a good thunderstorm, the wireless link will be down
for at least 12 hours, but will fix itself eventually.

Are you sure there's not a moisture problem in the antennae cabling? Get
an SWR meter that can handle the 2.4 GHz range and make sure that SWR is
very low (approaching 1:1 but certainly less than 2:1). Hook up the meter
in-line at the AP. Test this after everything is wet and again when
there's been a dry spell. Minimize the number of exposed connections and
use dielectric grease. Any exposed connections should be well wrapped
with that rubberized electricians tape first, then with regular.

Resetting either access point will keep the link down for at least 30
minutes.

This seems to point to signal quality issues. This could be interference
as others have suggested. Few things to try (in order of less work, less
$$$):

1.) Try different 802.11 channels. Pick one of 1, 6, or 12 as they are
the only non-overlapping spectrum. Set this manually on both ends

2.) if yaggi type antennas, try changing the polarity. If it's vertical
now, try horizontal or vice versa (both ends should be the same for
maximum gain!)

3.) Try even higher gain "dish" style antennas (these have circular
polarity)

4.) Use APs that do 802.11a or n. These are much less susceptible to
interference. This probably also means changing/adding antennas.

*.) Bonus idea: Google roll your own dsl (assuming both locations have
the same CO). Basically: get a dry pair (no dialtone) from the telco
going from location A to Location B; buy two sdsl modems and install at
each end; hopefully enjoy a few-several Mb connection!

~JasonG

11

From: Michael Dillon [mailto:wavetossed@googlemail.com]
> (for example, after a good thunderstorm, the wireless link will be
down for
> at least 12 hours, but will fix itself eventually.

Sounds like there are trees in the line of sight, and maybe they are
getting
leafier over the years. The only solution to that is to change the path
if
it is possible.

The line of sight is all clear, no trees. Only one building along the way
has a rooftop of similar height, but the antennas are extended far above the
roofline. We have used a rifle scope to confirm line of sight is all clear
at all angles.

From: Tim Huffman [mailto:Tim@bobbroadband.com]
We're a WISP, so I have lots of experience with this kind of thing. The
problem with using 2.4GHz equipment is that there's a whole lot of
noise out there (run Network Stumbler sometime on a laptop with a
wireless card, and you'll be shocked by just how many wi-fi APs are
floating around).

Oh I know. Luckily it's located in an industrial area just on the outskirts
of the city. There isn't a lot of other WiFi (in my opinion); 3-5 total
SSIDs spread across 2 of the 3 physical channels (1,6,11) depending on which
rooftop you measure from.

You didn't mention your bandwidth requirements, but I'm assuming that
you're trying to get more (and spend less), so I'll only recommend
unlicensed gear. For that distance, you might want to consider using a
5.2GHz radio. The FCC limits their transmit power, so they only work
well in short-range applications (>2 miles or so), and 5.2GHz doesn't
propagate the way that 2.4GHz does, so there tends to be much less
noise in that band.

Bandwidth requirements aren't too picky. If it can handle minimum 9 Mbps
full-duplex everyone will be happy. Of course, the faster the better.
I don't know if it makes a difference or not but this is all taking place in
Canada. I don't know of any regulations drastically different from the U.S's
regarding frequency use here. The biggest problem I've ever had though has
just been payment/shipping depending on the supplier (some don't ship to
Canada or are very specific about payment methods!).

Just to answer a few more questions I've been getting, the access points are
located inside, connected to a small UPS. The antenna wire is a very thick
coax up to the roof, BNC connectors to the access point and I'm fairly
certain BNC connectors on the antenna end as well. I'll double check
grounding on the poles but I'm somewhat afraid to turn it into a lightning
rod. I'm fairly certain that the ground in the antenna wire is clean but
again, something to double check.

Rain/moisture doesn't seem to cause problems. In fact the connection is more
reliable through the winter. The last 2 months here have been cold/warm,
dry/wet and there's been no pattern to the stability issues. The only
correlation between weather and stability that they have noticed there is
lightning related.

From: Jason Gurtz [mailto:jasongurtz@npumail.com]
Are you sure there's not a moisture problem in the antennae cabling?

I hope I just answered most of your questions Jason. Good tips to check for
too. I'll answer more of your specific questions ASAP.

Thanks everyone for the responses so far on and off list. I've been getting
lots of product suggestions as well as ideas for troubleshooting the current
implementation for the short term. I'm working on another project for today
so I've just been skimming through the responses. Later tonight I'll go
through all the options in more detail and report back/answer more
questions.

Keep 'em coming and thanks again,

Peter

12

2.4 and 5GHz license-free Wifi is license free because the frequencies
are shared with the ISM (Industrial/Scientific/Medical) services. In an
industrial area, competing WiFi is the least of your worries. These
frequencies are also used by industrial grade heating units. Got anyone
in the neighbourhood running a large plastic shrink wrap machine, for
example?

You can't directly detect these other users with a Wifi transceiver.
Depending on the nature of the interference you *might* be able to hear
it directly on a scanner (if you can find one that covers those
frequencies), but you really need a good spectrum analyzer to tell
what's going on.

Anyway, don't assume the competition for spectrum is only other Wifi
units.

--lyndon

13

The line of sight is all clear, no trees. Only one building along the way
has a rooftop of similar height, but the antennas are extended far above
the
roofline. We have used a rifle scope to confirm line of sight is all clear
at all angles.

Unfortunately, you can't necessarily rely on visual line of sight. At 800meters, the Fresnel Zone on your radio is about 14ft in diameter at the midpoint. You need to make sure that this is free of obstructions.

Oh I know. Luckily it's located in an industrial area just on the
outskirts
of the city. There isn't a lot of other WiFi (in my opinion); 3-5 total
SSIDs spread across 2 of the 3 physical channels (1,6,11) depending on
which
rooftop you measure from.

Make sure you're using the channel that doesn't have an AP on it!

Bandwidth requirements aren't too picky. If it can handle minimum 9 Mbps
full-duplex everyone will be happy. Of course, the faster the better.
I don't know if it makes a difference or not but this is all taking place
in
Canada. I don't know of any regulations drastically different from the
U.S's
regarding frequency use here. The biggest problem I've ever had though has
just been payment/shipping depending on the supplier (some don't ship to
Canada or are very specific about payment methods!).

Canadian and US regulations are very similar in the unlicensed bands. I'd still pick 5.2GHz if you were replacing the radio.

Just to answer a few more questions I've been getting, the access points
are
located inside, connected to a small UPS. The antenna wire is a very thick
coax up to the roof, BNC connectors to the access point and I'm fairly
certain BNC connectors on the antenna end as well. I'll double check
grounding on the poles but I'm somewhat afraid to turn it into a lightning
rod. I'm fairly certain that the ground in the antenna wire is clean but
again, something to double check.

How long is your cable run, and what kind of cable is it? It's probably LMR-400 (the most common) loses about 6.6dB of your signal for every 100 feet. Also, you should check the waterproofing on the connector at the antenna. We normally use a 'courtesy wrap' of electrical tape, followed by a thick layer of Mastic tape, followed by another layer of electrical tape. Also, check your cable for nicks or kinks.

Rain/moisture doesn't seem to cause problems. In fact the connection is
more
reliable through the winter. The last 2 months here have been cold/warm,
dry/wet and there's been no pattern to the stability issues. The only
correlation between weather and stability that they have noticed there is
lightning related.

Moisture in the cables doesn't necessarily show up during rain! That moisture can seep throughout the cable, and cause attenuation when it gets cool and the moisture condenses, for example.

You haven't said what kind of antennas you are using, but if they are yagi's, they probably have very poor back-to-front ratios, which means that you could be picking up interference from behind you, or on the sides, especially if the antennas are up above the tree cover. You might try horizontal polarization on the antennas (just rotate them 90 degrees, but make sure you do it on BOTH sides!) to see if that helps. Cross-polarization is usually good for about 20dB of noise rejection.

The fact that there doesn't seem to be any pattern to your loss means that it's probably either interference (somebody changing channels), hardware failure, or software failure.

Hope this helps.

14

To come up with an accurate recommendation one really needs to know your
budget, on that distance speeds up to 1 gbit/sec are possible if you
spend enough on the radios... Do you have some cost and desired
throughput parameters to guide everyone's recommendations?

15

From: Lyndon Nerenberg [mailto:lyndon@orthanc.ca]
Sent: June 18, 2009 12:11 PM
To: Peter Boone
Cc: nanog@nanog.org
Subject: RE: Wireless bridge

> Oh I know. Luckily it's located in an industrial area just on the
> outskirts
> of the city. There isn't a lot of other WiFi (in my opinion); 3-5
> total
> SSIDs spread across 2 of the 3 physical channels (1,6,11) depending
on
> which
> rooftop you measure from.

2.4 and 5GHz license-free Wifi is license free because the frequencies
are shared with the ISM (Industrial/Scientific/Medical) services. In an
industrial area, competing WiFi is the least of your worries. These
frequencies are also used by industrial grade heating units. Got anyone
in the neighbourhood running a large plastic shrink wrap machine, for
example?

Within range of the beam, not that I know of. The biggest building is just a
supplier, there's 2 other small buildings, not 100% sure what they do
though.

You can't directly detect these other users with a Wifi transceiver.
Depending on the nature of the interference you *might* be able to hear
it directly on a scanner (if you can find one that covers those
frequencies), but you really need a good spectrum analyzer to tell
what's going on.

Anyway, don't assume the competition for spectrum is only other Wifi
units.

--lyndon

I don't have a spectrum analyzer available to me (I've found a USB one for
$200 designed for WiFi that will pick up any non-wifi noise around the
frequency range too). Each access point reports a good signal. From what I
recall (not on site today) the noise is very minimal. Noise anywhere from
-98 to -85 with the signal at -20 to -40. The SNR is 30+, even when the
connection isn't working. The DDWRT firmware reports a Signal Quality as a
percentage as well: it's generally high, 80%+ (not sure exactly how it's
calculated though, I've seen it fluctuate while the Signal and Noise remain
about the same). These readings are consistent at both access points, and
remain about the same on each of the 3 physical channels. Hard to tell for
sure since the firmware doesn't keep any averages or historical statistics
on the signals, and no one has the time to sit around and take a reading
every few minutes.

Peter

16

Jason Gurtz wrote:

Are you sure there's not a moisture problem in the antennae cabling? Get
an SWR meter that can handle the 2.4 GHz range and make sure that SWR is
very low (approaching 1:1 but certainly less than 2:1). Hook up the meter
in-line at the AP. Test this after everything is wet and again when
there's been a dry spell. Minimize the number of exposed connections and
use dielectric grease.

Use dielectric grease sparingly on the outer threads of the connector. Don't let it get in contact with the inside where it bridges the center pin and the shield. This will cause nasty impedance bumps. The inside of the connector should be dry. The grease on the threads helps to ensure this.

Any exposed connections should be well wrapped
with that rubberized electricians tape first, then with regular.

Yep, the stretchy stuff. 3M type 23.

17

Jason Gurtz wrote:

Are you sure there's not a moisture problem in the antennae cabling? Get
an SWR meter that can handle the 2.4 GHz range and make sure that SWR is
very low (approaching 1:1 but certainly less than 2:1). Hook up the
meter
in-line at the AP. Test this after everything is wet and again when
there's been a dry spell. Minimize the number of exposed connections and
use dielectric grease.

Alternatively using an antenna with integrated ap like the one's I
referred to previously (they have a nice cast enclosure for radio and a
screw down bulkhead with gasket for the cable) eliminates the need for
runs of rf coax at all and also deals handily with the necessity for an
outdoor enclosure for the linksys ap. I would use outdoor rated cat-5
for the run up to the ap.

18

Might I suggest Ubnt.com ?

Or a vendor that I use.... http://www.wlanparts.com/category/ubiquiti/

Couple of these http://www.wlanparts.com/product/BULLET2-D13/Ubiquiti_BULLET2_and_13dBi_24GHz_Panel_Antenna__BULLET2D13.html

(100.00 per side or so).

Peter Boone wrote:

19

Lyndon Nerenberg wrote:

  

Oh I know. Luckily it's located in an industrial area just on the
outskirts
of the city. There isn't a lot of other WiFi (in my opinion); 3-5
total
SSIDs spread across 2 of the 3 physical channels (1,6,11) depending on
which
rooftop you measure from.
    
2.4 and 5GHz license-free Wifi is license free because the frequencies
are shared with the ISM (Industrial/Scientific/Medical) services. In an
industrial area, competing WiFi is the least of your worries. These
frequencies are also used by industrial grade heating units. Got anyone
in the neighbourhood running a large plastic shrink wrap machine, for
example?

Motion sensors also run in the 2.4GHz range.

20

+1 for Ubnt gear!

Joel Jaeggli wrote: