Welcome to the 90s! It's a great time to be automating our offices—we have so many choices. More and more, those choices are going to involve networking our offices. Unfortunately, given so many choices, it's sometimes difficult to decide what to do. You may have heard about the capabilities and possibilities in linking your office PCs together. You may have even been reading up on the subject. Many magazines specialize in networking. You may have also found out the limitations of these sources of information. Simply: much of this information is aimed at the networking of an entire office, business, or firm, dealing with hundreds or thousands of PCs.
September 1998
As we saw in my last three columns, my practical suggestion for a small office or home office installation of a network (under a dozen computers) is to install Thin EtherNet (RG-58 A/U) cabling according to specific rules. The key rules are: keep length below 100%' total, terminate both ends with a 50-ohm resistor, keep a few feet between each computer, always have BNC T's connecting directly to the computer, and make sure you have one constant, unbroken stretch of network cable from one end to another (no loops or drops). Take a look at the illustration—the top and bottom schematics are A-OK; the middle one is no good. But, the bottom illustration "looks" like the middle one, if the two legs of the cable going to each computer are wrapped in a single bundle. If you like this effect, and need a more foolproof and businesslike installation (jacks and all), go for the AMP Thinnet Tap System.
Presumably, you've now got the idea of how to cheaply wire your home or office. Remember, our goals are an inexpensive and easy installation. Wiring problems are the easiest to cause and the hardest to solve, so following the rules will give you a great boost. Another difficult area is selection and installation of a network card in your PC. A few lucky readers will have a LAN adapter already installed or built in. Most of you, though, will have to buy some for yourselves. This column will discuss the various factors involved, and suggest how to proceed. For our purposes, we'll concentrate on EtherNet cards.
There are three basic ways EtherNet cards interface with your network wiring—three different kinds of jacks on the outside of the card. The first is the AUI port, which looks like a funny game port. The "Autonomous Unit Interface" was the original, standard method of connecting the network to the computer. You bought, separately, the real network connection gadget, called a transceiver. The AUI cable connects the transceivers to the EtherNet port. Yes, you certainly can do this today—but it's so much more expensive, we can ignore it totally. For the remaining two choices, the transceiver is built into the EtherNet card in the PC itself, saving you lots.
The second possibility for the connector would be a telephone jack. This is for UTP (Unshielded Twisted Pair) connections. To use this, you need a dedicated run of four wires, properly twisted, no more than 185 feet, to a "hub", at some central location. The hub has one jack for every possible computer, and interconnects the different computers together inside itself. In the past columns, my recommendation has been that this is an effective method if and only if you are installing new construction (and can run the correct wire at that time), or have it already installed. For our purposes, small, simple, and cheap, you probably don't want to fool with it. (One way around this is to get an EtherNet card for your server that is also a UTP hub, having a bunch of phone jacks on it. Then, run pre-purchased lengths of UTP direct from there to each other machine. It's still more expensive.)
This leads us to the third possibility: BNC coax. This takes the form of a BNC jack on the back of the card. Into this jack, you MUST plug the BNC T-connector (or equivalent). Some EtherNet cards have only one of the above three possible jacks. Others have two, or even all three—these are called "combo" cards (you can only use one jack at a time). For your purposes, it doesn't matter whether you have a BNC card or a combo, you can only use the BNC jack. Shop on price. However, if you get a combo card, you may have to physically set one or more jumpers on the card, or use the setup program included, to set the card to the "BNC" mode.
Now, the EtherNet card has to communicate with the computer somehow. There are two basic techniques: one is to use an I/O port, and the other is to use shared memory. The first technique is easier but slower. The standard PC has a bunch of input/output port addresses available, between 200 and 3FF (in hexadecimal). Some of these ports are used for built-in and standard add-in features of the PC: serial and parallel ports, VGA adapters, floppy and hard drives, and so forth. Some of these addresses are unused in a standard PC, especially address 300 hex. Therefore, it's usually easy to find one—I always start with 300.
The second technique is used by accelerated EtherNet cards. It generally uses something like 16K of memory space, usually in your Upper Memory Blocks (UMBs). This is the space between the memory address space where your display adapters go (segments at A000 and B000 hex) and the addresses your computer's BIOS fits (segment F000). Some of this space is occupied by your VGA BIOS, a SCSI disk controller BIOS, and other special occupants (such as a video capture card buffer). To use this space, you will have to investigate everything else in your machine, to determine what is free and what is not. Then, you will have to tell your memory manager NOT to control that space—for instance, with an X= specification in your EMM386.EXE command line in CONFIG.SYS. And, you will have to set up the EtherNet card so it knows to use the memory addresses you just selected. (Note that all this will reduce the amount of upper memory you can LOADHI into, thus reducing your free DOS space available for running programs.)
How can you double-check a suspected free memory area to see if it's really free? Try this. Let's say we suspect that 16K (we need) is free at segment D000. Thus, we boot the computer WITHOUT running a memory manager (MS-DOS version 6.X allows you to hit the F5 key when it says "Loading MS-DOS..." to bypass everything in CONFIG.SYS). Then, run DEBUG. It will prompt you with a "-". Type the command "D D000:0 L 4000" and press ENTER. This command dumps memory in hexadecimal, starting at segment D000, address 0, and continuing for 4000 hex bytes, which is 16K. It will scroll by pretty fast, but it should ALL be the same thing repeated endlessly—usually, "FF". This indicates that nothing exists at this memory address, and means you can use that for your EtherNet accelerator card.
If you are prepared for the extra trouble, and don't mind the extra work, feel free to go with a card using memory. For greatest ease of installation, chose the I/O port-only type of card, which will make installation a cinch. You'll pay somewhere around 20-40% of maximum speed—but in a small network, you may never work the cards close enough to capacity to tell the difference. (Note that a card with more RAM on the card itself will be better, regardless of how that RAM is used—and it can be used for either method above.)
The next decision you need to make is what kind of card to buy. EtherNet packets are transmitted over the network slower than the speed your bus can transmit the data inside the computer, so at first, it may not seem important. But, EtherNet can be "bursty". In other words, the EtherNet card usually has some memory in it, and will send or receive a bunch of packets to or from this memory. What you want is for the computer to read or write this entire buffer at one shot—using only one interrupt to handle the whole buffer, rather than one interrupt for each packet. Reducing the number of interrupts really speeds up your computer (an interrupt INTERRUPTS everything, and is the bane of Windows—there's lots of overhead). Thus, a 16-bit ISA (standard) card is a minimum. You can also get EISA cards, but you probably don't have an EISA motherboard, so forget that! VL-bus EtherNet cards are available now, too, but are hard to find, although they are much faster. One assumes PCI-based cards will be available soon, but I haven't seen any yet. (If you go the VL-bus route, make sure your motherboard supports VL BUS MASTER cards, or can be upgraded to do so. Cheaper VL motherboards only support non-master cards, such as VGA adapters!)
Almost any EtherNet card will require an interrupt. You must figure out which interrupts are available. Generally, IRQ 5 is unused for anything, and usually, IRQ 7 is available too. (They're reserved for LPT2: and LPT1: ports, respectively, but there's practically nothing out there that uses interrupts for LPT work. You may have to set your I/O card jumpers or your motherboard's BIOS setup to disable these IRQs, though.) If you only have one serial port (and no internal modem card), IRQ 3 is usually available. Most IRQs above 7 are also available—try 10, 11, 12, and 15. Use the MSD program that came with Windows 3.1 and MS-DOS 6 to check IRQ status and see what's unused.
The final choice to make is between a card with jumpers and a jumperless card. The latter lets you run a program to set the card. Don't lose the program, or you can never change your settings. A jumpered card doesn't have this problem, but if the purpose of each jumper is not labeled on the card itself, you still have to keep the manual for the card. Some cards compromise: they use jumpers, but provide an install program that tells you what to set the jumpers to. Just remember: remove power from the computer before removing or installing the card. Don't physically move jumpers when the power is on. And, make sure you are working stationary at a static-free area when holding the card—a little spark from your hand to the card can ruin it.
Now that you've figured out what I/O port address and IRQ number is free (along with memory segment if applicable), you can set the jumpers and install the card, or install the card and run the setting program (if available). Be sure you also set the card to BNC mode if it's a combo card. If you have any advanced settings to fool with, don't! Many cards have a diagnostic program to test them after installation—give it a whirl.
Pricing? You can get EtherNet cards for up to $300 or as low as $29. Quality cards can be had in the $80s if you shop around. I think you will find EtherNet cards easy to install as long as you know what you're going to deal with. Next month, we'll look into the different compatibilities, and some other issues, that EtherNet cards involve. See ya!
Six Easy Lessons
Here's how to set up a simple network in your small office.
