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Our business is taking over some new premises (currently housing multiple companies) and for at least the first year will be operating out of a pair of portacabins, around 50 metres apart.

Users in both cabins will need to be on our internal LAN, and our phone system. What's the most cost-effective way to link these buildings?

Stringing fibre between poles has been discussed but seems expensive; a trench/duct for underground fibre even more so (~£100/metre) -- so it seems like WiFi is my best option, but does this have reliability issues over this sort of range -- given there will be commercial vehicles and heavy plant crossing the direct LoS between the buildings, do I need to get the WiFi kit high off the ground, or can I just use high powered and/or directional wifi equipment?

Similarly, should I be looking at cordless handsets for one of the buildings, or should I be looking at just getting a data connection and using IPT for internal telephony?

James Green
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    Thanks to all those who answered -- we've had a rethink and are moving the mountain to mohammed instead, moving one of the cabins next to the other... – James Green Dec 31 '09 at 11:00

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It would seem to be hard to cost-justify a fiber link between the buildings for only a year's time. I'd probably go with WiFi, in such a case. I'd put the antennas as high as I could, and use directional antennas.

My main problems with WiFi in these kinds of situations have been interference from other systems (yes-- even with directional antennas), poor latency with crappy access points, and failures due to lightning. WiFi has worked very well, all things considered.

When I can get fiber into the budget, I push for it-- especially when the Customer is going to be in the facilities for a long time. In your case, that's not true...

If you can get a reliable WiFi connection, using the data network for the telephones is probably more cost-effective than cordless handsets. I'd compare the costs. For reliability, I might consider putting one cordless handset in the remote office even if I did use VoIP, just for fail-safe purposes. (If everyone on the site is carrying their own privately-owned wireless telephones that might be less of an issue...)

There are a variety of radios out there. I'll put in a plug for the Ubiquiti Bullet radios. I don't work for them or anything. I've used their radios in a couple of sites and rather like them (particularly the unfetted access to the Linux OS on the device). These particular radios are weatherproof and aimed at the outdoor point-to-point market. You attach an antenna to them, power-over-Ethernet on the other (with a lightning arrestor!) and you're good to go.

Evan Anderson
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  • Thanks for this -- it looks like it's now a 3 way decision between a) WiFi, if we can get our new-found power and water issues sorted, b) a trench, since we'll have multiple utilities to consider, and c) completely changing the site layout to avoid having disconnected portacabins... – James Green Dec 21 '09 at 14:04
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Jimbo, I've got a mate in Sheffield who specialises in laser-based point-to-point systems. They look like CCTV cameras, you just put one on each building, point them at each other and plug an ethernet cable into each one. They're not that cheap but given you only need them for a year I would imagine some kind of lease/rental package could be done. Let me know if you want me to put you in touch.

Chopper3
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  • Does that work on a rainy day? – ceejayoz Dec 20 '09 at 15:23
  • over the distances discussed in this post yes they do, perhaps not over 500m in torrential rain etc. and quite badly in very foggy areas but they're not bad really. – Chopper3 Dec 20 '09 at 17:24
  • I'd briefly talked to a supplier about a laser link -- but we were worried about the height issue, if they're mounted on the buildings directly there are going to be trucks or cranes passing through the LoS pretty frequently, which seemed to be an issue (I guess, unsurprisingly) – James Green Dec 21 '09 at 02:28
  • Interesting, you'll be affected in a similar way if you use wifi too then. Might have to cable. – Chopper3 Dec 21 '09 at 08:59
  • Perhaps naively, I'd hoped WiFi frequency would be less affected than whatever frequencies lasers run at... I'm not sure I had any real basis for that assumption though! – James Green Dec 21 '09 at 13:09
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100M is the limit for 100baseT, so you're well within spec to just run Cat5 before the two places. (I'd run cat5e or cat6 to reduce the noise, though). I'm not sure what the limit for gigE is, but I've run it a little over 100M without much problems -- we just put a switch at each end as soon as it entered the buildings. If you can trench between the two points, this might be the easiest.

Call whatever utility companies to get the existing lines marked, rent a ditch digger (looks like a big chainsaw blade on a cart), glue some PVC conduit together (while running some pull line), and once it's all together, pull the copper and terminate it. If you don't have other obstructions in the way, it'll take a team of two a day to complete, and a few hundred dollars of supplies.

...

If that fails:

I can't remember the name of the guy, or the name of the site where he put up all of his information, but there was someone in Hawaii who had a lot of information about squeezing longer range out of wireless ethernet. I think he was using 802.11b, but it might've been 802.11a, this was before the term 'wifi' became popular, so I don't think it was 802.11g ... this would've been about the time when the pringles can trick was noticed (2001?2002?).

Hopefully, someone else can remember and provide a link. I want to say he was connecting public schools in Hawaii, and they had a school bus that would act as an access point for laptops and had a long-haul link back to the school.

... it's possible, as it was older, that he was using other wireless technology (wavelan?), which might be harder to get ahold of this year, or difficult to put to use.

update: it might've been ALOHAnet, but from what I can find while wrestling with free airport wifi trying to frame my screen screwing up everything, it was out of service by the time I was remembering it (and I could've sworn it was ethernet-based). It's possible that I'm remembering whatever was the followup to ALOHAnet.

Joe H.
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  • If you run copper between the buildings you absolutely, positively *must* put lightning arrestors on the ends of the cable. – Evan Anderson Dec 20 '09 at 19:05
  • I think we've ruled out a trench -- the £100/metre cost wasn't for the fibre itself, but for a trench and ducting. Apparently tarmac is hard to dig through to a ~1m depth, and to re-lay... Wifi is starting to sound like the best (or least bad...) option -- I'll keep looking in that sort of area. Thanks! – James Green Dec 21 '09 at 02:30