Extending the UTP Ethernet: A Special Report
by
Robert Bruce Thompson
Other reports by Thompson:
Extending the UTP Ethernet
One of the drawbacks of living on the bleeding edge is that you always pay too much for stuff and then end up stuck with it once better stuff becomes available. For example, I notice that "home networks" are now all the rage in the mainstream PC periodicals like PC Magazine. Well, I've had a home network up for a decade or so now. Furthermore, many of my friends have had home networks up for similar periods. The home networking phenomenon is perhaps not quite as leading-edge as PC Magazine would have you believe.
I brought my home network up back when a "cheap" clone Ethernet card cost $250. Unfortunately, the only realistic option back then was using 10Base2 "thinnet" coax. I could have installed 10BaseT UTP, but hubs were extremely expensive back then--a couple hundred dollars a port for 10 Mbps, or $1,500+ for an eight-port hub. With RG-58 thinnet coax, you can simply daisy-chain from one computer to the next--no hub required. So, I have RG-58 strung around the house, including from my office back to my wife's office.
If I'm going to install the new Pentium II box I've just built in Barbara's office, I need some way to get the 100 Mbps PCI Ethernet card in it connected to the hub in my office. Although there's no technical reason why 100 Mbps Ethernet can't run on coax, it's never been implemented simply because coax is inferior mechanically and topologically to a star-wired bus like 10BaseT. Mechanically, in that coax connectors fail frequently. Topologically in that 10Base2 is a true bus, logically and physically, which means that a failure anywhere on the chain knocks down the whole network. 10BaseT is a logical bus, but uses star wiring. This means that the bus actually exists within the hub. If someone kicks a 10BaseT cable loose, the machine it connects loses its network connection, but the rest of the network continues to function uninterrupted.
So, I have two options:
- Install a 10BaseT to coax adapter in her office, connect her 10BaseT/100BaseT Ethernet card to it, and use the existing coax run from her office to mine.
- Install a run of unshielded twisted pair (UTP) cable from my office to hers and connect her normally to the 10BaseT network.
I'd probably choose the first option as a quick-and-dirty fix if I had such an adapter handy, but I don't. Buying an adapter is not an attractive alternative, although they're not that expensive. Although doing it this way would solve the immediate problem, two problems would remain:
- Barbara's is the last 10Base2 link in the house, and I'd just as soon convert to 100% UTP.
- Using the adapter would limit Barbara to 10 Mbps throughput.
The 10 vs. 100 Mbps is not a major issue right now, because the hub that serves the rest of the network is a 3Com TPC eight-port 10BaseT hub with one coax connector on it. However, I've been installing dual-speed 10/100BaseT cards in all my machines for some time now, and 100BaseT hubs are getting to be reasonably priced. I just saw a LinkSys eight-port 100BaseT hub for under $200, so the day when I upgrade the network here to 100 Mbps is not far off. So it looks like running new cable is the way to go.
Choosing the Cable
The first consideration is the type of cable I'll install. There are about a gazillion types of UTP cable available in a wide variety of pair counts, sheath types, etc., but for data communications the important consideration is the "Category" rating of the cable. EIA/TIA defines three categories of cable, designated Category 3, 4, and 5 (with 6 on the way). Category 3 is fine for 10BaseT (and short runs of 16 Mbps Token Ring); Category 4, also called "extended distance LAN cable" is just slightly better than Cat 3, and is now essentially obsolete; Category 5 is good for 100BaseT.
I have about a mile (literally) of Cat 3 cable in boxes down in the basement, and it'd be perfectly usable for the existing 10BaseT network. However, I don't want to have to re-run cable when I upgrade to 100BaseT, so it makes sense to install Cat 5 initially. The price differential between Cat 3 and Cat 5 cable is much smaller than it used to be.
Two or three years ago, when I bought most of this Cat 3, I paid something like $35 per 1,000 foot box of the PVC sheath (plenum-rated sheath is much more), while the same box of Cat 5 was closer to $200. Since then, the price of Cat 3 has gone up some and the price of Cat 5 has dropped quite a bit. Now, you'll probably pay $50+ for a box of Cat 3, and under $100 for a box of Cat 5. Although some people still run Cat 3 for voice-grade stuff, at that price differential it's worth running all Cat 5, if only for the future flexibility it provides.
I should probably just go out and buy a box of Cat 5, but I only need 50 feet or so (maybe $5 worth), so buying a thousand foot box seems a waste. Being a cheap author, I'll see if I can scrounge some before I actually pay cash money for it. My friend Steve Tucker has several partially used boxes of Cat 5 sitting around his basement, so I can probably sweet-talk him out of the short piece I need. Yep, Steve says he has plenty, and I'm welcome to what I need. With that taken care of, it's time to run the cable.
Running the Cable
Actually getting the cable run isn't going to be much problem. We live in a ranch house with a partially finished basement. That portion of the basement under both Barbara's and my offices is unfinished, and there are already holes drilled in the footer plates to allow cable to be run up between the sheetrock that sheathes the walls upstairs.
All we'll need to do is feed the cable down through the hole in the footer plate from one office, string it across the basement ceiling, and then feed it back up through the existing hole to the other office. Both offices also have existing modular faceplates with available positions, so it'll be a simple matter to terminate the cable on both ends to snap-in Cat 5 modular connectors and insert them into the faceplates.
Securing the new cable to the joists is another matter. Doing so is one of those jobs that's trivially easy if you have the right tool and next to impossible if you don't. The right tool in this case is an Arrow T-25 staple gun. It looks just like the familiar T-50 staple gun that fires 1/2" flat staples, but the T-25 fires round-top staples that can be used to secure wire up to 1/4" diameter (like UTP or RG-58/59 coax). You can get one for about $25 or so at a well-stocked hardware store or DIY center. Pick up a box of staples while you're there. A box should cost you a couple bucks, and will likely last you forever. The staples come in various colors. The naked steel ones are fine for the basement, but the beige ones are better for use in most finished areas.
Some hardware stores carry only the T-50 stapler. If they carry one designed for stapling cable, it may be the T-18, which you don't want. The T-18 fires 3/16" round-top staples that are good only for securing the obsolete "quad" telephone wire that most places still sell to people who come in and ask for "telephone wire." Using a T-18 on four-pair UTP cable will at best damage the sheath and crimp the conductors. At worst, it may actually penetrate and short out one or more of the wires. If you can't find a T-25 at your hardware store, check your local Graybar or other electrical jobber.
Getting cable from Point A to Point B in most homes is usually pretty straightforward. Most homes use balloon-frame construction, with sheetrock or paneling covering 2X4 studs. Ranch houses are particularly easy to wire, because they ordinarily offer a choice of coming up from below in the basement or crawlspace, or coming down from above in the attic. There's almost always a way to get where you want to go, particularly if you're reasonable in your choice of where you want to go.
You can usually get the easy runs made with standard tools you're likely to have around the house. For situations that standard tools don't solve, there are two special tools you should know about:
Bellhanger bit - originally so named because they were used by people who hung bells in church steeples, the bell-hanger bit is a combination drill bit and cable puller. The business end of the bit has a small hole in it. You drill through the intervening material, attach a pull wire to the end of the bit, and then pull the bit back through. The result is that you have a hole and a pull wire--a very useful thing to have sometimes.
Bellhanger bits come in diameters from about 1/4" to more than an inch and in lengths from a few inches to 8 or 10 feet. The one I have is 3/8" diameter by 6 feet long. I got it from a specialty place named (disgustingly enough) Jack and Jills Drills. It cost about $20 for the bit itself. They also sell an L-shaped guide for about $15 that you use to guide the bit while it's turning. If you want one of these things, you'll probably have to order it specially. Your local hardware store will probably never have heard of it, and your local electrical supply house may or may not carry them. If it does, they may not have the size you need. If you need one quickly and all else fails, call your local alarm installer and ask them where they get theirs.
Fish tape - when you're working with cable, you want to pull it. Pushing it doesn't work well at all because it's too flexible. There are times, however, when "you can't get there from here" and that's when a fish tape is indispensable. A fish tape is a fairly rigid but flexible piece of spring steel wire contained on a spool, similar to a drain snake. You can push it from where you are to where you want to be. Once the end of the fish tape arrives at the remote location, you can attach the cable to that end of it and pull the cable back through the problem area.
The most common application of a fish tape in residential wiring is when you have to make a run to an exterior wall. Interior walls are not insulated, and so are relatively easy to route wire through. Exterior walls contain insulation, which makes it next to impossible to route cable through them unless you use a fish tape to lead the way.
A fish tape is definitely something you want to avoid buying unless you run cable very frequently. They come in a variety of thicknesses and lengths, but even the small ones typically cost $50 or more, and the larger ones may cost several hundred dollars. If you absolutely positively need one, there are a couple of possibilities:
- If you only need a short fish, a straightened coat hanger may do the job.
- For runs of six feet or so, you may be able to use a bell hanger bit as a substitute for a fish tape.
- If you have a box of Romex around the house, you can sometimes use it to substitute for the fish tape for longer runs of up to 10 feet or so. Romex is rigid enough to push through most insulation, but has neither the rigidity nor the springy flexibility of the fish tape. The Romex will often coil up within the wall, but if you can get any part of the Romex visible at the remote location, you can simply tie a piece of cord to it and pull the Romex back through, leaving you with a pull string that you can use to pull the cable through.
- For situations where only a real fish tape will do, you may be able to rent one by the day at one of those tool rental places. The price is usually outrageous (I've been charged $20 a day), but it's cheaper than buying one and using it only the once.
Installing Face Plates and Connectors
Although I already have the necessary face plates installed, I'll detail the process for those of you who don't.
You can buy faceplates that have various combinations of connectors (telephone, 10Base2 coax, 10/100BaseT, etc.) permanently attached, but I suggest that you avoid these. I prefer the modular faceplates that you can buy from AT&;T, Leviton, ICC, and many other vendors. The faceplates cost about a dollar each, and have from two to eight holes about 3/8" square. You can snap various modular connectors into these holes--everything from RJ-11 telephone jacks to network jacks to cable TV jacks. You won't find these faceplates and modular connectors at your local home center, but you can get them at a Graybar or similar supply house.
The jacks themselves range in price from a couple of dollars up, depending on their type, and are available in various colors, as are the faceplates themselves. You cover the unused holes with a blank cover that costs about 10 cents. Once you have the faceplates and connectors you need, there are a couple of ways of installing them.
The traditional method - cut a rectangular hole in the sheetrock and mount an old-work box (one of those blue plastic things you can pick up at Home Depot for 69 cents). The old-work box has small wings that spread as you drive a screw and clamp the box against the sheetrock. At the top and bottom rear of the box there are knock-outs through which you can route the cable. Using this method makes it much more difficult to add new cable runs later. Although you must use a box to meet code when you're running power lines, you don't need the box to meet code if all you're installing is low-voltage signal cables (like network cables). I suggest you dispense with the box and use one of the following methods.
The quick-and-dirty method - hold the faceplate against the sheetrock and use it as a template to mark the location of the screw holes in the faceplate. Use a pencil to trace the outline of the faceplate very lightly onto the wall. At the positions you marked, drill two small starter holes in the sheetrock and press in two plastic screw anchors to hold the screws that secure the faceplate. Drill a third larger hole midway between the two screw anchors, and insert a coathanger with a hook on the end through that hole. Use a sharp knife to score a deep line to define the cutout in the sheetrock, keeping inside the faceplate outline, and staying at least 1/4" to 3/8" from the screw anchors. Tap the cutout section sharply to break the sheetrock free, and use the coathanger to pull the cutout section clear.
The right method - ask the hardware store guy for "battleship clips". If he has no idea what you mean (which is likely), describe them for him. If he doesn't carry them, head for the electrical supply store. They'll know. A battleship clip is a thin metal template that fits a rectangular cutout you make in the sheetrock. Unlike a box, the battleship clip does not extend back past the rear of the sheetrock, and makes it easy to add cables later. The clip has a metal wing on each side that resembles the outline of a battleship as seen from above. You place the clip in the cutout and bend the wings back against the sheetrock to secure the clip. The clip itself contains the screw holes to which you secure the faceplate.
Copyright © 1998 by Robert Bruce Thompson. All Rights Reserved.Send feedback to: webmaster@ttgnet.com
—30—
