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I need to connect two buildings to share LAN and internet connection between them. They are 20m apart, but from the two end points I would need about 90m of cable. I know that the maximum of UTP is 100m, so it would be feasible with it, but I don't know how to connect the two buildings. As far as I know, UTP is vulnerable to weather, so it wouldn't be wise to just stretch the cable in the air between the two. Optical cable is out of the question because of the high costs.

What would be the best?

Edit: Ok, I think WIFI is a good alternative, but I'll still need to pull a cable from the endpoint to the other end of the building. Is it a good way if I get about 50m of UTP to a WIFI bridge and then the two wifi bridges will connect the two bldgs? Wouldn't this make the network unstable?

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migrated from electronics.stackexchange.com Jan 15 '13 at 19:51

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About the edit: Why would that make network unstable any more than a single cable? Also what do you consider "stable"? Good cable can easily run for rated distance and there shouldn't be many (usually any) physical layer problems int the cable itself. It's the WiFi part that can be problematic due to weather and interference from other sources (which is why I recommended 5 GHz, since it's usually less crowded, unless you're near radars). –  AndrejaKo Jan 15 '13 at 23:04
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6 Answers

If you want gigabit, a laser link should be more than capable of the job. Many have wifi backup systems built in to fall back down to slower speeds if needed.

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Would weather or haze/smog affect them? –  K.A Jan 15 '13 at 20:51
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If the OP can't afford 90m of fiber, I think a laser link will be a tad out of his price range. –  HikeOnPast Jan 15 '13 at 21:00
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I missed that last sentence about cost. As soon as you start cutting corners though, all bets are off. –  Sirex Jan 15 '13 at 21:17
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Take a look at the Ubiquity AirGrid M. They also have other options if you need faster links.

You get an outdoor directional antenna with the wifi bridge built right in. All you have to do us run the ethernet cable. There is a PoE injector. You will install that inside. Probably next to the switch.

Ethernet is fine to run outdoors, but do note a few things:

  1. Use a cable with outdoor rated weather proof jacket
  2. Make sure the cable has a ground connected to earth ground. If your outdoor ethernet cable does not have a ground wire, it is okay to run a separate ground wire in parallel.
  3. Use a drip loop for the condensation
  4. Use a surge protector for the Ethernet line. Something similar to a Gigaguard.

About the configuration of the antenna. When you get it, there are a few things you should know. Since this will be a dedicated link, and not a general access point for Wi-Fi clients you have the advantage of configuring it to run 40MHz channels. That will get you a faster connection. Lastly, do not use the max power. After you get a link, turn down the power a bit. Since these are designed for much longer distances, you will probably get the fastest connection will less than full power. Just tweak it during your install.

Note: I am not affiliated with Ubiquity, but have been very happy with all of their products I've used.

EnGenius, 3COM (as mentioned) and others also make outdoor wifi bridges.

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You can use a WiFi LAN to LAN bridge for this.

For example, 3COM has the 54 Mbps Wireless LAN Building-to-Building Bridge, and most other major network vendors probably offer similar products.

The key advantage will be eliminating the concern of weather deterioration. Also, installation is relatively painless, no pulling cables between buildings, or having to replace said cables when someone decides to have some fun tossing stuff onto them.

The key disadvantages are a slower inter-LAN speed, and concerns about data security.

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Just to add onto this bit, you can use an OpenWRT or DD-WRT based router to bridge your network as well. –  dext0rb Jan 15 '13 at 19:22
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This is a really outdated answer. Today for higher speeds much better option would be to use IEEE 802.11n equipment, preferably in the 5 GHz spectrum using 2:2x2 or better antenna configuration. Directional antennas would be a bonus. As mentioned, for even more cost savings, two good routers could be set up using free firmwares to work as a bridge. Speeds in from 150 Mb/s to 450 Mb/s could be obtained this way, although 450 Mb/s eqipment is a bit harder to obtain and more expensive than 300 Mb/s equipment. –  AndrejaKo Jan 15 '13 at 20:28
    
In any case it should be kept in mind that Wifi is still half-duplex and despite higher nominal speed will be slower in practice than Fast Ethernet. –  AndrejaKo Jan 15 '13 at 20:29
    
Data security is not an issue in my case. There wouldn't be any highly confidential data transferred and there are only a few industrial buildings nearby, so I think a WIFI with WPA2 ecryption would suffice. –  Moha Jan 15 '13 at 20:47
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@David Schwartz I agree. It really does look like a good representative of what would be needed. That particular unit does however use proprietary Power over Ethernet (which might be a problem) and comments say that it doesn't support VLAN tagging. –  AndrejaKo Jan 16 '13 at 9:54
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I would need about 90m of cable. I know that the maximum of UTP is 100m, so it would be feasible with it

Are you sure about this? It's unlikely you'll be able to run this cable directly... you'll add some distance going around corners and bends here and there. If you don't get this right, some very weird things can happen. I recommend placing a small switch at the near end of the outdoor gap in one or both buildings to act as a bridge, and thus ensure you're not anywhere close to your distance limit.

I also want to address how you run the wire between the buildings. You cannot just string copper wire through the air, as you see done with telephone or power lines. Over time you can build up a voltage differential from one side of the link to the other, even with simple/short building to building links. I've heard this can even build to level of potential electrocution, and while that might be urban legend I know you can burn out equipment this way. Now you could just do the same kinds of things the phone and power companies to do to handle this issue, but I really prefer to just have the cable buried. Last time I had this done I was quoted $14 per foot to have a underground conduit bored, though that pricing can vary wildly depending on where you are and what you have to deal with. I've seen it as cheap as $8 per foot and as high as $26, but I don't doubt it could get much higher yet. Still, I think this is by far the way to go. If it's all grass and private property, you might also be able to just trench it, but 20m is at the edge of where you're likely better off with a boring machine.

There is some cheap wifi bridging equipment out there now. A wifi bridge will be easier to set up outdoors, but it's less ideal in terms of performance, ability, and security. At your distance I would expect it to be reliable enough, but you will be subject to rf interference. Still, even the low-end stuff is gonna cost at least $250 by the time you consider radios and power for both ends. Depending on where you are, that might be enough to make the cost of a boring your conduit seem reasonable, and again, I think this should be your first choice.

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Aerohive makes some very nice units that are 802.11n compatible, and they feature dual-radios. One radio is for the bridge itself, and the other one is available for user comsumption. They can be powered by POE or from wall warts. You will still need to run a cable from your closet to wherever you place these(preferably as close to one antoehr as possible). Even better is they are centrally administered from the web, so it is very easy to reconfigure and monitor them. We have 8 various model aerohives deployed in a seamless mesh network.

http://www.aerohive.com/

And the length of cable runs has no real effect on the "stability" of the network, unless you exceed the maximum recommend distance by a large amount like 50-100ft, and even then you typically just lose gigabit connectivity. If it's like most offices you can run the cable through the drop ceiling and no one will have a chance to damage it. You could even hide your wireless bridge in the ceiling if it is POE powered.

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Just run a wire. Put a powered switch as close to the other building as possible and another switch at the other end of the cable. Run it thorugh the air use outdoor CAT-6 cabling. It will work fine.

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This can be physically dangerous. You can't just string copper wire through the air without taking steps to mitigate voltage build-up. Otherwise you'll burn out equipment. If you're really unlucky, you might even burn out YOU. –  Joel Coehoorn Jan 16 '13 at 15:59
    
hmmm, I wonder what phone companies have been doing all these years. –  Toby Allen Jan 17 '13 at 10:43
    
See @Pablo Maurin's answer. It's not that you can't do it at all... it's that there are extra steps you must take, and if you don't do them properly the cable run is not safe. You'll be fine at first, and if you're lucky you might never have a problem, but large voltange differentials can build up and discharge. "Just run a wire" doesn't cut it. –  Joel Coehoorn Jan 17 '13 at 14:17
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