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Connecting two LANs

Aug 02, 20043 mins
CablesCellular NetworksNetworking

 I would like to connect two LANs over a distance of 3 to 5 km. What equipment do I use for this task?– Via the Internet802.11b or similar technology. If you have a relatively clear line of sight between buildings (this make take a small tower at each end to accomplish), you can use 802.11b in a bridged configuration functioning as a point-to-point link. 

There are several options, depending on what country you’re in. I will list several options, some of which may not be possible depending on the laws or telco tariffs in your country. The first is a wireless connection using 

You will need wireless units made for this purpose with as strong a transmitter as possible (at least 100 mw – up to 1 watt if available in your area) and a directional antenna. The higher the gain on the antenna the more accurately it must be aligned at each location to work properly. If this is an option, all you’ll need to buy is a wireless unit for each and then plug it into your network. I would strongly encourage the use of encryption on this link to help keep prying eyes out. 

With the distance you mention, if the tariffs are available and your telco can accommodate your request, think about getting a dry copper pair between locations. Using technology currently available, you can create your own private DSL network and only have to pay for what should be a modest cost for a set of wires between locations.

A dry pair should have no voltage or other signaling from the telco on it for this to work. There is one other thing you’ll have to watch for, and you probably won’t know until you try to use this option. If there’s a T-1 in the binder that your copper pair is running through, this type of option may not work because of the T-1 signaling interfering with the DSL signaling. I’ve run into this problem more than once. Another thing to check is the gauge of wiring used by the telco. If it is in the 26 gauge or smaller area, you won’t be able to try this option as the surface area of the wire isn’t enough to carry the signal more than a few blocks. If you can use this option, you will have an Ethernet interface in the DSL unit to connect to your network at each end. Companies in the U.S., such as Blackbox and others, sell this kind of equipment. 

If neither of the two above options are viable, check with your local cable TV company to see if it offers Internet access over cable. This should be fairly reasonable in cost. Another option would be to talk to your telco about its DSL offerings, as well as conventional frame relay and point-to-point connections, comparing the cost vs. the speed you can afford.

I’ve been watching reports on a new technology called broadband over power lines (BPL), which basically amounts to Internet access over power lines. While an interesting idea, most of the reports I’ve read of the field trials have indicated substantial interference from existing radio communications in the areas where this has been installed, so it may take a while before this becomes a viable option.