VDSL2 bridges for 600 meters wired Ethernet
March 25, 2010 5:33 AM   Subscribe

VDSL2: We'd like to bridge two 100Mbps LANs together. They are located at buildings approximately 600 meters apart by cable distance. I've found a few VDSL2 Ethernet bridge products that will do 90/70Mbps full duplex on 24 AWG POTS phone wiring at 600 meters. Wireless point to point links are not an option.

The main product I'm looking at is the Planet VC-234. It's reasonably affordable. We have cooperation from the local POTS phone company to install outdoor rated UV resistant cat6 23AWG cable along the route between the two buildings. The cost for the cable is not excessively high, and it should perform better than 24AWG phone wiring in regards to crosstalk.

Does anyone have experience with this product or similar VDSL2 bridges, whether used on existing POTS/PSTN wiring (dry pair) or self-installed cable? Any suggestions?
posted by thewalrus to Technology (10 answers total) 2 users marked this as a favorite
Response by poster: Oops, I forgot to mention in the original post that whatever we use, maybe one of these Zhone modems would be compliant with ITU G.993.2. This should mean that we can specify the modems should operate in symmetric mode for 70Mbps/70Mbps at 600 meters.
posted by thewalrus at 5:38 AM on March 25, 2010

If you've got line of sight between the two buildings, check out the Canon Canobeam's. We had a client in LA who's been really happy with them, and it saved them a fortune over the long run on the cost of the wires from PacBell. When we went back 4 years later for their upgrade they reported less than a day's downtime in that 4 year period.
posted by Runes at 6:02 AM on March 25, 2010

Copper between buildings is a Bad Idea - a lightning strike will fry everything. If you're going to run cabling, use fiber.
posted by djb at 6:32 AM on March 25, 2010

Seconded on the Fiber, especially if you're going to be laying new cable as it is.
posted by schmod at 7:03 AM on March 25, 2010

Be sure and get a proper router/bridge that only lets the right traffic through. Design the network so that users on one side don't *need* something on the other side, rather that then can get to the other side if they need to. (Login servers on both ends, for example.)

If a dry pair is an option, could two pairs also be an option? Might be better throughput per dollar than other solutions.

Copper between buildings: if you have power lines and phone lines, there is no difference between them and a private line. Especially if the right equipment is used. Yes, it is a risk, but no more a risk than you already have. I believe the Right Way to do this kind of thing is to use differential signalling on the pair, rather than single ended. The ground floats around between buildings like that, so you don't want to use it as a reference.

Wireless not an option: because you have a security concern, or because you don't have line of sight? They have products that work in the microwave frequencies where you mount a little panel to each building, and then rent space on a tower somewhere for a repeater. Might be an option to consider. Or optical line of sight- almost impossible to tap into, because the attacker would have to get in the middle somehoe.
posted by gjc at 8:04 AM on March 25, 2010

Yeah, you really wanna do fiber. You can get pretty cheap, decent switches from Dell that will take fiber transceivers and run gigabit over it... it should be enough for quite a number of years, and then the fiber will be re-usable for a higher bit rate with better transceivers sometime in the future.

It'll cost more, but not a TON more, maybe $1500 total, and you'll avoid all kinds of later headaches. Long distance runs is specifically what fiber is good for. Do it right and you'll only have to do it once. Doing it with copper is hacky and will probably give you pain.

Call some local network guys and get quotes. It really shouldn't cost that much, and you'll avoid so much hassle if you let professionals do it. They should be able to run the fiber, put the right ends on it, provide the switches, and tie it into your network however you want it done. And your needs are simple enough that you probably won't need more than an hour or two by the expensive network guy.

If they quote you on Cisco gear, which is common, it'll be vastly more expensive, so explain that you're trying to do it on the dirt-cheap, and that you're competing with a copper run as far as your budget is concerned. For this application, Dell switches will be just fine. They have fewer features, but your needs are so simple that they'll be more than adequate. If they have other recommendations in a similar price range, you can talk to them about it.

*delay while I look up stuff on the Dell website*

Ok, it's not quite as cheap as I thought, because your buildings are a bit too far apart.

You'd need 2 Powerconnect 2824s, at $179 each.
Unfortunately, it looks like you can't use the cheap Short-wavelength SFP Connector, at $86 each, because they only do 500m, and you're at 600. That means you have to use the much more expensive Long-wavelength SFP Connector, at $370 each. These will do 10km.

So, your total hardware is two switches at $179, two transceivers at $370, plus fiber, plus labor, plus configuration time if you pay someone to do it. $1200 for hardware, probably $1k for fiber and labor.

It's a shame your buildings aren't closer; if they were 500m instead, you could probably get quite close to the $1500 I was originally thinking.
posted by Malor at 8:12 AM on March 25, 2010 [1 favorite]

Response by poster: Clarification on the wireless is not an option: Not because of security, but because we have absolutely no hope of achieving line of sight or even NLOS. Free space optical bridges are really cool but far beyond the budget and there is also no hope for line of sight. I'm aware of the great options available these days from companies like Ubiquti for point to point 2.4GHz or 5.7/5.8GHz wireless bridges.

The application is between two offices in the densely populated and highly unplanned city center of a third world developing nation. The area has been spaghettied with RG6 75 ohm cable for cable TV services, run rooftop to rooftop, and that's how the PSTN wiring is also installed. It will be relatively trivial from a cost standpoint to pay the local "cable TV" guy to pull the cat6 or even 21AWG two-pair phone cable between the buildings.

We are not concerned about lightning strikes because none of the equipment that will be connected to the bridges at each end is particularly valuable, and because the area presents a dozen more attractive targets for lightning to strike. It's full of 20 meter high steel GSM mobile phone service towers with lightning rods atop them.

I would also prefer to use fiber and a pair of 1310nm SFPs at each end. There is little to no chance of running singlemode cable between the buildings, because whatever copper is installed will need to be installed by illiterate untrained third world "cable tv" dudes. The fiber would not survive being strung across rooftops, walls, poles, ziptied to the existing RG6 cable TV and PSTN lines. The cost to buy 600 to 700 meters of semi-armored bend resistant G.657 type singlemode fiber is prohibitive for the project.
posted by thewalrus at 8:43 AM on March 25, 2010

I'm not sure the run-lengths supported, but there is also relatively inexpensive equipment for running home networks over existing home coax (MoCA). It can even coexist with CATV signals on the same cable. A downside, as I understand it, is that there is only one chipset provider, so if it doesn't work well, you may not have many options for trying different equipment.
posted by Good Brain at 10:09 AM on March 25, 2010

Response by poster: I think the coax idea is worth looking into:

this thing seems to use the HomePNA standard for full duplex ethernet over 75 ohm cable, up to 4000 feet. Quad shield RG6 which is relatively cheap would be used.
posted by thewalrus at 1:15 AM on March 26, 2010

Can you rent space on one of those GSM towers for a point to point wireless repeater? I can't imagine your wires would last long in that kind of environment.
posted by gjc at 3:51 AM on March 26, 2010

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