PTP wireless Bridge

Posted on 2012-09-12
Last Modified: 2013-01-07
I am looking for some advice on a Wireless project.  I am looking for a PTP wireless solution either indoor or outdoor to connect two buildings next to each other.  They are about 50 feet apart wall to wall but can spread that distance to 75 to 100 feet on the roof.

The main building needs to share its 30 Mb Internet connection with the remote building for VoIP and data.  There is little LAN traffic except DHCP from the main building.  When you run most apps across the bridge they are fine but VoIP is suffering from enough packet loss that it is effecting call with dead spots and some drops.

The current bridge is a Teletronics TT5800 that has been tweaked as much as it can but can't stop the packet loss, also this unit is connected at its full 54 Mb speed but it is only capable of half duplex.  Any help would be most welcome.
Question by:Collins26050
    LVL 44

    Expert Comment

    by:Craig Beck
    Get one of these...'ll get 300Mbps radio link between the sites and 100Mbps full duplex throughput.

    The key here is to prioritise VoIP traffic, so your LAN needs to run QoS.
    LVL 1

    Expert Comment

    The nanobridge is extreme overkill for a 50 foot link with line of site.  The nanobridge is designed to go 10+ kilometers.  Instead go with the nanostation M5 or LocoM5.  Same radio but designed for shorter distances.  Keep your received signal around -50 and you should be able to easily get a 50Mbps full duplex connection using only 20Mhz of spectrum.  Go to 30Mhz or 40Mhz wide channels if you need more.  If your in the states they can be had for about 80 bucks per end.  YMMV.

    LocoM5 and the Nanostation M5 both show to be in stock at in their TX warehouse.  But you can also get from  out of Kansas or in CA.
    LVL 44

    Expert Comment

    by:Craig Beck
    @jeffster... Did you actually follow the link I posted?

    It's a NanoBridge M and its tiny!  I've deployed lots of these so I definitely wouldn't say it's overkill compared to your suggestion - but rather the other way round.  The M5 you suggest is sold as an 'up-to 15Km' bridge, and the Loco isn't a fully transparent bridge as its a CPE device so I wouldn't spec it to bridge a segment which requires VoIP from multiple clients.
    LVL 1

    Expert Comment

    Craig.  What did the links I put up take you to because it seems like you are talking about a different product (PowerBridgeM5)?

    Yes, I did follow your link and it took me to the NanoBridge M5.  It comes in two versions, a 13" dish and a 16" dish.  Not tiny, but not huge either.  

    The Airmax M5 product line includes the NanoBridgeM5 (NBM5), NanostationM5 (NSM5), LocoM5, PowerBridgeM5(PBM5) and RocketM5.  The NBM5, NSM5, and locoM5 all have the same processor, sdram and internal flash specs.  The differences show up when you start going over the antennas and power output.  They all use the exact same firmware download and have the same feature set.  Whatever you can do with the NBM5 you can do with the LocoM5 and NSM5, but there's a right tool for each job.  

    NBM5-22 (@13 inch dish) - 200mw radio and a 22dBi antenna.
    NBM5-25 (@16 inch dish) - 200mw radio and a 26dBi antenna.
    NSM5 (11.5 x 3 inches) - 500mw radio and a 16dBi antenna <-- My suggestion
    LocoM5 (6.5 x 3 inches) - 200mw radio and a 13dBi antenna <-- My suggestion
    PBM5 (17 x 16 inches)- 500mw radio and a 25dbi antenna  <-- 15KM bridge you referenced????

    "the Loco isn't a fully transparent bridge as its a CPE device so I wouldn't spec it to bridge a segment which requires VoIP from multiple clients."

    You are wrong here.  The LocoM5 has the exact same hardware specs as the NBM5, runs the exact same firmware and it can do exactly the same thing feature wise (obvious distance limitations).  I actually am working off a pair of LocoM5's right now that are setup as a transparent bridge.  One is setup as an Access Point with WDS enabled (Transparent Bridge Mode) and the other is setup as a station with WDS enabled.  I have another link using a pair of NBM5-22's spanning roughly 5km that uses the exact same config (with different SSID's).  I also consider the NBM5 to be a cpe too.  But I only use them when I have to because I hate having to deal with the feedhorn in the off chance I have to replace or service one.  Removing the assembled feedhorn is a pain in the arse.

    Again, I stand by my words.  The NBM5 is extreme overkill for a 50 foot link.  That much power, that close up and you will overdrive the receiver and cause other issues with your link.  Hell it's overkill for anything less than 500ft unless you aim the antennas off of each other to attenuate the signal.

    Now, I'll back it up.
    Let's say he is able to spread the distance to 75ft which is just .014 miles.  With the nanobridge set to it's minimum power output of -8dBm the rssi is calculated at -38dBm (22db antenna at both ends).  Ubiquiti and anyone who knows will tell you that the RSSI sweet spot is -55dBm.  -38dBm will only cause you headaches eventually.

    Same calculations with LocoM5's at .014 miles with integrated 13dBi antenna.  One of the differences is the minimum power on mine only lets me set -4dBm.  It might be that I need to upgrade the firmware to get the -8dBm like the nanobridges but we will just go with it for now.  The LocoM5 has an integrated 13dB antenna which gives a calculated RSSI of -53dBi which is pretty much the sweet spot.  If I could get the -8dBm then I could get an RSSI of -56dBi.

    The NSM5 shows a calculated RSSI of -46dBm at it's minimum, still not the -55dBm we are looking for, but no where near as hot as the NBM5.

    ThePBM5 is just ridiculous with it's  26dB antenna and RSSI of -28dBm at minimum.

    Anyways, to the original poster.... All four products will do the same thing but the LocoM5 is the cheapest of the group and signal wise is the right tool for the job.  

    No sense in trying to use a sledge hammer to put a thumb tack into a corkboard......
    LVL 44

    Expert Comment

    by:Craig Beck
    Hmmm I don't know why we appear to be seeing different things here!?  I'm talking about the NanoBridge M, not the PowerBridge.  I don't even think the box that the NanoStation M5 comes in isn't even 13" even though the spec says the dish is that big!

    It was my understanding that the transparent bridge couldn't be configured in client mode?  If I'm wrong, I apologise, however you appear to be using WDS and not client mode.

    Still, I've deployed these radios where other links were affected by weather, for example, over distances ranging from 100 - 7000ft and I've never had a problem with link reliability due to high receive signal.

    However, saying that, if the Loco does WDS in transparent mode there's no problem ;-)

    Accepted Solution

    I ended up getting a Point to Point wireless backhaul, 5.1-5.8 GHz frequency with 23dBm integrated antennas, 20MHz channel spacing, 50Mbps aggregate throughput (25Mbps full duplex). Complete Link.

    The Full duplex made the difference because it's been running fine and VoIP had drastically improved.
    LVL 1

    Expert Comment

    Glad to hear you found a solution.  

    But not to kick a dead horse, you should check your power levels.  If you put them up out of the box with the stock power levels you ARE overdriving the receivers at 75ft.  When they publish the specs of the radios they list the miniumum receiver sensivity which usually appears as numbers ranging from -70 to -96 dBm.  Notice those receiver sensitivities are negative values.  Lets convert these number to mW (milliWatts):
    -70dBm converts to .0000001 mW.  That is 1 ten millionth of a mW or .0000000001 watts
    -90dbm converts to .000000001mW.  That is 1 billionth of a mW or .000 000 000 001 which is a picowatt.
    Just for reference a hot wireless signal is usually considered anything above -40 (receiver are rated in negative values so a -40 is a much higher signal that a -70.)  -40dBm is .0001mW

    Point I am trying to make is that these radios are designed to go really far and listen to the most faint signal.

    Let's say your new bridge has a run of the mill atheros drivers and it's power output is conservative at 17dBm (50mW)  before the antenna.  Your antennas are theoritically radiating at (17dBm + 23dBm) +40dbm (10000mW) which is a conservative estimate.  The free space loss at 75 feet is about 74dB in the 5.2 to 5.8Ghz range.  Lets start with the original 40dBm and subtract the free space loss of 74dBm to come up with a -34dBm signal arriving in front of the antenna.  Now lets factor in the 23dB of antenna gain.  Take the -34 and add the 23dB of antenna to get a signal of -11dBm arriving at the receiver.  -11dBm is .079mW.  Lets take that a step further and say that the radio power output is 20dBm.  The receiver at the other end is seeing a signal of .166mW which are small numbers.

    Your receiver is designed to listen a very faint signal.  As quiet as .0000000001mW and a signal of .0001mW is considered very loud.  Now, you are screaming at your receiver at .079mW and it is working fine for now.  Imagine someone standing next to you with a bullhorn in your ear.  Sure it's effective, but how long can your eardrum hold out?  Granted the radio will hold out a lot longer, it's just when the intermittent issues start happening and you could have done something about it.

    Assuming you put the radios on the roof and they have line of site... you could take the radios and face one of the 180 degrees away from the the other and they would probably still link up (granted it wouldn't be very effective, I'm just proving a point).  

    Guys who deal with fiber optics have the same calcuations to worry about.  Too hot a signal into your optic receiver can eventually desensitize the receiver.  That's why they make attenuation pads for optical systems.  Just saying....  Best bet is to check with the manufacturer to find out if your signal is ok or if they say it is too hot.

    Author Closing Comment

    The hardware for the unit I chose was already in place so it was more cost effective than a lot of the other solutions.

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