One of the classic problems for network designers is how to connect users and devices that are some distance away from the wiring closet -- at the far corner of a plant or a remote kiosk, for instance. For all practical purposes, over the last decade that distance has been about 100 meters. In this tip are several ways to get beyond that limitation, one of which is Cisco's Long Reach Ethernet switch.
Back in the late 1990s, the default answer here was to run fiber. It's simple enough to run 100BaseF spec, and not difficult to find switches and NICs to support that common technology, but it's quite expensive and it takes a while to run. Lately, if you're so inclined, it's probably cheaper to find Gigabit fiber interfaces.
Another pretty simple solution is to go wireless. IEEE 802.11 specs with the right antennae can go 10 miles. Four miles is pretty easy to do. For a typical user who just happens to be 150m or 200m away from the closest switch, you don't need anything special, but using quality equipment will save you some headaches. This idea may not be for everyone though, as the speed is obviously lower and the security issues add some complexity.
One thing to look for though, is if you already have phone cabling run to these remote stations. Most phone systems support lines far beyond 100m, so there's a good possibility you've got some long-distance CAT 3 in place already. If so, a great alternative is Cisco's Long Reach Ethernet (LRE) switch. This is a clever technology that encapsulates the Ethernet frames and only requires a single pair, so you can do some POTS splitting and have data and a phone from the same cable. Speeds are pretty comparable to 802.11, as it supports 15 Mbps out to 3500 feet and 5 Mbps out to 5000 feet. But it has the advantage of not being affected by weather, and not having security issues.
5000 feet would meet the needs of most organizations, but if you need to go a lot further, perhaps up to 18000 feet, and do it on a budget, you can use DSL. Although your speeds would be low, and it might not be a "future-proof" investment, running telephone wire around a plant or devices in a field, or to guard shacks, is a whole lot cheaper than fiber.
Tom Lancaster, CCIE# 8829 CNX# 1105, is a consultant with 15 years experience in the networking industry, and co-author of several books on networking, most recently, CCSPTM: Secure PIX and Secure VPN Study Guide published by Sybex.