Suggestions for a short building-to-building hop

Discussion in 'Wireless Internet' started by Cloy, Aug 15, 2007.

  1. Cloy

    Cloy Guest

    I'm helping a downtown non-profit that operates a daycare center in
    the building next door to its main offices. They would like to bridge
    the Internet connection from the main building to the daycare so staff
    can check e-mail, web, etc. -- general purpose communication, nothing
    mission critical. [The daycare staff will have wifi cards on their
    desktops and laptops.]

    The two buildings are brick/stucco/steel and the distance between them
    is 10 or 15 feet of open space. There is also a furnace/plumbing room
    in the daycare building that seems to cause some attenuation.

    I've tried a couple Linksys WRE54g network extenders (one in each
    building) to bridge the distance, but the connection is weak and
    unstable at best. (Not sure if this is a problem with the extenders,
    or limits imposed by the architecture.)

    Any suggestions on an inexpensive way to connect between the buildings
    would be appreciated.

    Thanks, in advance!

    Cloy, Aug 15, 2007
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  2. I use to service a few non-profits. I don't any more. I now sleep 8
    hours per day and don't cringe when the phone rings.
    All the material you've listed are impervious to RF. Even at 10-15
    ft, the chicken wire under the stucco will block the signal. Do you
    have any opposing windows? If you put the wireless in the window, and
    there's no metal screen, it will pass nicely.
    Two repeaters are two hops and probably won't work even if you had a
    strong signal. One repeater maximum please.
    Over a distance of 10-15ft, you should be able to run CAT5 between the
    buildings somehow, even if you have to do some underground horizontal
    drilling, trenching, digging, or overhead building to building wiring.
    There's also a possibility that they're both on the same power
    xformer, in which case Power Line Networking (HomePlug) will work.

    However, if the wired alternative is impossible, then I suggest a
    simple dedicated wireless bridge between buildings. Get two identical
    wireless bridges, one for each building. At 10-15ft, you won't need
    any fancy antennas. Connect one bridge into the main office network.

    The other bridge you have to make a decision. If you want to connect
    via wireless, get a wireless access point and plug it into the
    wireless bridge. Use a different RF channel (1, 6, 11) for these
    radios to prevent mutual interference. Also, different SSID. Note
    that this is now a total of 3 radios. You can install an ethernet
    switch between the wireless bridge radio and the wireless access point
    for nearby desktops. Everyone else connects wireless to the wireless
    access point. Since they're on different channels, there's no speed
    loss as you would get with a store an forward repeater.

    Also, note that you don't have to buy an access point. A wireless
    router will suffice if you disable the DHCP server, and don't connect
    anything to the WAN (internet) port.
    Jeff Liebermann, Aug 15, 2007
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  3. Cloy

    Cloy Guest

    Thanks for the reply, Jeff!

    My understanding is that running ethernet lines outside (even well
    insulated ones) can risk equipment damage from lightening / stray
    voltage. Is that true?

    Thanks! -Cloy
    Cloy, Aug 16, 2007
  4. Twisted-pair without insulation would be a trick. I think they call that
    stuff "wire rope".

    "Stray voltage" in the form of ground potential differences between
    buildings on different supplies is a problem, yes.

    But there's no particular potential for a buried connection between
    buildings to invite lightning hits.

    Fiber eliminates both problems.

    Lloyd E. Sponenburgh, Aug 16, 2007
  5. Cloy

    stephen Guest

    i have had parts of a multiuser Unix box vaporised by a lightning strike
    over a copper cable (this was high speed twisted pair for a distributed
    terminal mux system - no fibre option then).

    the hit was on a tarmac road (someone there during the storm described the
    hit area, and we found the melt pool after the storm) - the duct was buried
    about a meter under the surface........
    only if the strike doesnt induce a big pulse via ground or power supply into
    the electrics and get into equipment that way....
    stephen, Aug 16, 2007
  6. Generally true. Any conductor can attract lightning, act as an
    inductive pickup, or become part of the lightning's path to ground.
    Let's take them one at a time.

    If you run the CAT5 in the air between buildings, you've increased the
    effective area of the "ground" that is seen by the charge cloud.
    However, lightning is more likely to hit the buildings than the wire
    because of their larger surface areas. If the CAT5 is buried, it's
    not an issue.

    Inductive pickup is a problem with any conductor. If there's a nearby
    lightning strike, the CAT5 can become part of a transformer. The "one
    turn" primary is the lightning strike itself between the clouds and
    the ground at 20,000 amps. The secondary is the CAT5 where the
    current varies with just about everything, but can still be
    substantial. The primary effect is to destroy electronics or fuse the
    copper wires. If the CAT5 is buried, it's less of a problem because
    the earth absorbs much of the charge. The induced voltage can also be
    substantial. EIA-568A/B specifies 2500volt isolation, which is a huge
    help. The twisted pairs also allow considerable induced current in
    the wires, but since they're the same in each pair of wires, they
    cancel at the transformers at each end.

    You can obtain better isolation using an ethernet isolator:
    (lots more). Note that this is NOT a "surge protector", which is
    un-necessary. The idea is to isolate the ends of the cable so that if
    one building gets a lightning strike which temporarily raises the
    ground potential a few thousand volts, the current will not go through
    the CAT5 and into the circuitry in the other building. It will also
    protect users in the unlikely even that one building AC power ground
    goes away (which happened here after the 1989 earthquake). You only
    need one ethernet isolator.

    Ground current is what fries most electronics. What happens is that
    the CAT5 and its associated electronics is grounded at both ends. A
    lightning hit to the ground will dissipate the charge over a wide
    area. If one building is closer to the lightning ground hit than the
    other, there will be a differential voltage produced between buildings
    as the charge dissipates through the ground. The induced voltage (and
    current) can be substantial. After having a few expensive ethernet
    switches vaporized by this effect, I've take to installing cheap
    sacrificial ethernet hubs or switches at each end. If they blow up,
    they get replaced by another sacrificial switch or hub.

    I suggest you do NOT use shielded CAT5 cable. If you do decide to use
    shielded CAT5 (because buriable waterproof gel filled CAT5 is most
    commonly offered as shielded cable), ground only one end of the
    shield, not both. If you're seriously worried about lightning, you
    might invest in two (one for each end) CAT5 lightning protectors:
    Jeff Liebermann, Aug 17, 2007
  7. I must be slipping in my old age. My previous rant is all about
    copper wire (CAT5). Fiber optic cable has none of the problems
    mentioned and is completely lightning proof. Depending on sheathing,
    you can bury it, or run it between buildings (with a messenger wire
    for support). No worries about lightning or ground faults with fiber.

    You'll need two 100baseTX(copper) to 100baseFX (fiber) "media
    converters", one at each end. Over the <50ft distance you're working
    with, almost any fiber technology will work. Note that there are
    different types of fiber and many different types of connectors. I
    would go with cheap dual mode fiber, with either ST or SC connectors.

    If you feel ambitious, you might even go with 1000SX gigabit fiber
    links (which costs more):

    Plenty more vendors can be found by googling for:
    "ethernet fiber media converter"

    Also, look on eBay. This looks close. However you'll need a pair of
    them plus buriable fiber cable:

    Pricewise, I suspect you want to do this cheaply. Brand new buriable
    fiber is not cheap. However, if you can bury waterproof conduit
    (sprinkler pipe?), you can use any flavor fiber cable inside. If you
    settle for slow 10baseT transceivers, you can probably find a used
    pair for about $25/ea. 100baseT will be about $100/ea. No clue on
    Jeff Liebermann, Aug 17, 2007
  8. Cloy

    Bob Smith Guest

    I agree with Jeff, First choice, run a piece of outdoor cat5 betwen
    the buildings.. Short and sweet

    Second, the wireless bridges are ok, but you now how the problem of
    waterproofing them, or at least the antenna and coax that 'might' be
    outside. You could also purchase two wireless bridges in waterproof
    boxes with antennas built inside the box. But you have to waterproof
    the entry into the building (the hole where the coax goes into the

    here's a place you can get a decently priced wireless bridge like I
    described using above:

    Yes I know they say CPE, but they are all able to be configured as a
    CPE, a Bridge, or an AP/CPE, just with the firmware. I've used alot
    of them for building to building bridges because of asphalt parking
    lots between the building, ec.

    take your choice, if lightning is a big factor in your area, the the
    buildings are probably a bigger target with the AC overhead, the pipes
    out the top of the building, etc. I really don't think lightning is
    going to find the CAT5 before the building.. And since you have to
    run cat5 to the wireless bridges on each side of the building, another
    15' of cat5 ain't no big thing.

    Bob Smith

    Robert Smith Consulting
    "Wireless Installations -- Government, Businesses & ISP's"
    F.C.C. Licensed-Commercial & Amateur Services
    A.R.S NA6T
    ARRL Life Member
    1-707-964-4931 w/answering machine
    Fort Bragg, California 95437

    "On The Air-Conditioned Mendocino Coast, In REAL Northern California"
    No trees were destroyed in the sending of this message.
    However, a large number of electrons were terribly inconvenienced.
    Bob Smith, Aug 17, 2007
  9. Cloy

    stephen Guest

    2 issues.

    1. - you have to pull it thru the pipe. Some kinds of fibre will not take
    lots of mechanical stress, so a good choice, plenty of grease, and bit of
    2. around here at least the pipe will spend a lof of time full of water.
    Ideally, you actually need fibre cable with waterproofing built in, as over
    time hydrogen ions can degrade the glass (may not be an issue in practice
    with a short run, but replacing it will be a pain, and 1st you would need to
    figure out what is happening).

    Finally - you can get fibre cables with no metal inside, which removes the
    issue of grounding and lightning pulse induction from that route into the

    If you
    i hate media convertors - had lots of hassle getting them to work, making
    them work again when they stop, or the power gets cycled.....

    A fair few switches now have SFP connectors which take modular optics -
    mainly GigE these days, but some 100 Mbps ones around as well.
    stephen, Aug 17, 2007
  10. Nobody uses grease. They use some kind of soapy goo that washes off
    with water. For example:
    Lots of fun when someone spills a gallon of the stuff on the concrete

    Pull strength on buriable fiber is about 600-1000 lbs per cable.
    That's a problem when pulling a bundle, where the totally pull stress
    for the bundle may be transfered to a single cable. However, a spring
    scale can usually be employed to avoid getting near the tension limit.
    For an estimated 15ft pull, lube and tension are not even an issue.
    Then, you're doing it wrong. For a 15ft run, almost any type of
    conduit will work. Properly sealed and terminated with end points
    forming an inverted siphon, the system is essentially waterproof. If
    there is a danger of flooding, install a drain at an intentional low
    point. It would be tempting to use flexible water pipe to avoid
    cracking caused by asphalt movement, but I'm not familiar with the
    code requirements.
    What water damage I've seen has been either in the connector area,
    where the water pressure has displaced the optical gel outer coating
    on the fiber. The gel is necessary to fill in micro-cracks in the
    fiber and to act as refractive boundary layer to enhance internal
    reflections. When displaced by water, the cable losses increase
    dramatically. It takes substantial heat and water pressure to do
    this, but flooding will do. The best defense is to simply keep the
    end points, splices, and terminations elevated and dry.

    Again, for a 15ft run, the cable losses are so minimal, that even if
    water incursion causes additional losses, they would not affect
    performance much.
    Well, I only have about 10 pairs of Milan and Allied Telesyn media
    converters in service. Mostly at radio sites, where RF pickup in the
    networking cable is a problem. I've lost a few to lightning hits and
    mechanical damage. Several are in outdoor NEMA boxes and have
    suffered corrosion damage. I don't recall any of them hanging or
    having power problems. For me, they're all plug-config-n-play. Any
    particular type, brand, or model that you were having problems with?

    If I had anything to complain about, it's the tendency for all the
    media converter manufacturers to use power supplies with odd voltages.
    I often have to connect these to -48VDC telecom power buses or
    12/24/48VDC solar power systems using DC-DC converters.

    Duh. I almost forgot. My ability to properly attach a connector to
    fiber (using 3M hot melt method) is rather marginal. I did have some
    reliability problems with what I thought was a media converter issue,
    but turned out to be my sloppy termination job.
    Yep. You can buy modules to plug into the "backbone" port on most
    managed ethernet switches. These make a very nice media converter.
    However, for the single wireless device that needs to be bridged in
    this case, methinks a modular fiber switch might be a bit overkill.
    Jeff Liebermann, Aug 17, 2007
  11. Cloy

    Cloy Guest

    Thanks to everyone for the replies... I appreciate the time you took
    to respond.

    Given the location of the offices and connections -- and the
    construction of the buildings -- I'm thinking a cabled/fiber solution
    is going to involve a hell of a lot of cable pulling and jerry-built
    surface mounting.

    I'm actually wondering if the "power line networking" option might be
    the best way to go, given our budget. It looks like the Homeplug AV
    system might do the trick.

    A couple questions on PLN solutions:

    1. I understand that both buildings need to be on the same
    transformer. Am I correct in assuming an electrician or the power
    company can tell us that?
    2. Are there other obvious compatibility issues that can be
    identified (before we get too far down the road with this solution)?
    3. Is there some sort of testing process/equipment to check if PLN
    will work for us?
    4. I understand that the Homeplug AV standard supposedly provides
    200 Mbit/s half-duplex. What can I actually expect?

    Any other comments on a Homeplug solution would be appreciated.

    Excelsior! -Cloy
    Cloy, Aug 17, 2007
  12. Yes. They have to be on the same transfomer and the same phase. If
    the building are adjacent, there's an excellent chance that's the
    case. If you can see the transformers on the power pole, you can
    trace the wires visually. If not, you can borrow a circuit tracer and
    check for yourself.
    It puts a tone on the power line that does not go through the
    transformer. If you can hear the tone on a power plug in the other
    building, you win.

    You might ask the electrician how much it would cost to run
    communications conduit between buildings.
    Speed and performance has not been discussed. In general, the power
    line networking is make for running in a single building, where the
    wire runs are relatively short. Even though your two buildings are
    fairly close together, the AC power run to the transfomer may be a
    substantial length of wire. HomePlug will go to 1000ft, but is rather
    slow at that distance. You need to specify a minumum throughput
    Yep. Buy a pair of HomePlug bridges. Try it. If it doesn't work,
    return it to the store where you bought it in sellable condition. It's
    called fly before you buy.
    There should be some test benchmarks on various review sites (CNet,
    SmallNetBuilder, etc). Here's a random performance test of one
    200Mbit/sec HomePlug AV box:
    HomePlug is worth a try. However, if these are large office
    buildings, and someone else has a similar system using the same
    frequencies, you're going to have a problem. I would still make an
    effort to try fiber optic cable, because of the performance benifits.
    Jeff Liebermann, Aug 17, 2007
  13. Cloy

    stephen Guest

    OK - bad terminology....
    Agreed - but you said "any fibre" - indoor patch leads?
    great theory - but this Manchester UK. Famous for rain, and when it isnt
    raining, mist, drizzle.

    anyhow - good engineering paranoia to assume the water will get in - and if
    you seal it well it stays there....
    stephen, Aug 17, 2007
  14. As a reference point I've had 30mtrs of CAT5e clipped to the top of my
    garden fence for the last year, with no ill effects. This is common
    CAT5e, not any sort of external-grade stuff. According to ipef I get
    75-80Mbps which seems ok to me. At some point I'll upgrade to
    powerline networking, if I can be bothered.
    Mark McIntyre, Aug 17, 2007
  15. Not necessarily in the UK,
    but watch out for different phases. The pole near my Dad's house has
    all three (we get 'em all for my Dad's circular saw..., the neighbours
    get one each)
    Mark McIntyre, Aug 17, 2007
  16. I'm not sure what it's called in the fiber biz, but in the land mobile
    radio biz, it was called "slime".

    In the early 1970's, some company invented a product called "instant
    banana peel" (Riotril) that was used for riot control. It was
    positively amazing stuff and worked far better than the soapy products
    available at the time. It came as a white powder which was mixed with
    water. What we forgot about was that the soapy products would
    eventually evaporate, while this stuff would slowly ooze out of the
    pipe, puddle on the floor, and create a serious footing hazard. Slip,
    slide, and swear became a serious and almost permanent problem. At
    one point, the radio shop had to have the concrete floor steam
    cleaned. No amount of washing would get rid of the stuff.
    Maybe. For a 15ft run, patch cable would probably be strong enough.
    However, the pull tension increases with the cable length. My guess
    is 15ft would be about the maximum that could be used. Anything
    longer would require buriable fiber or reinforced fiber.
    Ok, that's different. I guess you have to be more careful in dealing
    with water problems. We get about 80 inches of rain per year on the
    California central coast, but no flooding.
    Yep. I'm not BISCI certified, but I try to follow their guidelines:
    Unfortunately, my printed book was three revisions out of date, and I
    loaned it to someone, and forgot whom.

    [media converters]
    You didn't answer my question. Which media converters were you having
    problems with? They're fairly simple inside and I can't imagine any
    form of reliability problem that isn't externally induced (i.e. my
    crappy fiber terminations).
    Jeff Liebermann, Aug 18, 2007
  17. You mean like this?
    Locally, the residential areas usually get 2 phase power, while the
    business and industrial districts get 3 phase. Most office buildings
    get 3 phase (mostly to run the HVAC motors).

    I'm still wondering why I can't find any "phase couplers" for HomePlug
    frequencies. The various FAQ's imply that there's enough coupling
    between parallel wires to couple between phases.
    Jeff Liebermann, Aug 18, 2007
  18. Cloy

    stephen Guest

    missed that. Over 5 years i used to help look after several campus networks
    that were in love with the things for 100 Mbps Ethernet links, so i dont
    have the part numbers any longer.

    there were a few different flavours - allied telsyn was common, and several
    that i think were rebadged via RS and Black Box.
    They were plugged into Cisco, 3Com, Bay networks and Allied Telesyn switches
    in different places, but the problems didnt seem to be switch specific, the
    common factor was the media convertors.

    we had endless trouble with intermittent auto negotiation going wrong on the
    UTP side - usually triggered by a switch reboot, or a power fail. The things
    were hidden all over the networks and not always documented, so these faults
    were difficult to find sometimes.

    the biggest site had around 200 wiring locations and hundreds of the things.
    They finally did a "LAN refresh" to migrate most backbone links to GigE,
    with 100M to small satellite switches on built in ports - nearly all of our
    intermittent issues & spanning tree instability evaporated after that.
    stephen, Aug 18, 2007
  19. Ok, there's the difference. The few that I deal with were all 1:1
    connections with no switches involved. The few that are plugged into
    something usually go to a hub or EtherTap, which are convenient for
    traffic monitoring. Since hubs don't do NWAY, the media converter is
    manually configured for the correct speed and never gets lost.
    I haven't had any NWAY negotiation failures that I know about.
    However, I make it habit of nailing down the connected speeds and
    protocols on my managed switches as I've had problems with some
    ethernet cards (3c509b) doing NWAY all wrong and requiring a power
    cycle to recover. Yeah, I can see where there might be a problem. As
    none of these systems have media converters in the line, I've
    apparently missed that adventure.
    OK, got it. I guess if you're relying on NWAY, there may be a
    problem. However, for a 1:1 connection, where the installer can lock
    down the rate and protocol, I don't see a problem with using a media
    Jeff Liebermann, Aug 18, 2007
  20. In answer to #1, get the right type of fiber and it pulls just fine. Also,
    NEVER use grease. There is a water based lube that you use, and only in
    instances where you go through 2 90 degree turns. (Grease will break down
    the jacket coating and eventually damage the fiber.)
    Richard Johnson, Aug 19, 2007
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