9 Apr 1995

Do You have What it Takes

The Internet is a "network of networks" and can use almost any type of communications link. However, the desktop PC is an inexpensive device and is not a good match for exotic hardware. Assuming that the adapter card must cost less than $200, the only connection options are Ethernet, Localtalk, or a modem.

Localtalk is not a very good choice for PCs, but it can show up in areas with a large population of Macintosh machines. Apple made a Localtalk card for PCs, but it sold the business to another vendor. The software support is not good, and it seems to be getting worse. Yale is trying to phase out Localtalk. At this point, Localtalk on a PC is not a "do it yourself" proposition. Students who need access from a dorm should contact the Computing Assistants for hands-on assistance.This document will provide detailed support for installation of Ethernet and modem support. A portable machine can use both types of connection (Ethernet in the office, modem from home).

Modem Installation Planning

A modem converts computer data into sound so that it can be transmitted over the telephone system. The COM port is a device that either comes as a standard part of the system unit or is added as an adapter card. The COM port moves data between the computer I/O bus and the modem. In some cases the COM port and modem are combined on an Internal Modem card. Otherwise, the modem is an external device connected by a cable (the famous RS-232 cable) to the COM port plug.

Decent SLIP performance requires a fairly high speed modem. At Yale, standards require at least a modem operating at 9600 baud (a "V.32" modem). For a few extra dollars, it is possible to run at 14,400 baud (a "V.32 bis" modem). It will shortly be possible to get modems that run standardly at 28,800 baud ("V.34" or "V.FAST" modems).

Unfortunately, many clone vendors use substandard chips in their built-in COM ports. Older junk chips include the 8250 and 16450. A quality vendor will use only a proper 16550A (sometimes a few extra letters are added after the A). The simplest test is to use the MSD program (Microsoft Diagnostics) included with Windows and most recent versions of DOS. Type "MSD" at the DOS command prompt to display a menu. Option "C" will describe the COM lines.

The output will look something like:

                              COM Ports            

The last line (UART Chip Used) indicates if the chip is good (a "16550"). When the screen comes up, press "C" to display COM information. Press F3 to return here.

In OS/2, type the command "MODE COM1" (and/or "COM2") and look at the reply. If the last item reads "BUFFER=AUTO" then this is a good chip. If it reads "BUFFER=N/A" then it is a bad chip.

The bad chips start to miss characters at higher speed. This will generate errors and require the network to retransmit data. It can be tolerated, but the problem should be corrected. Better chips are typically found on internal modem cards, or they can be purchased on Serial Port Cards for around $35 at any computer superstore. Just remember to look for "16550A" on the box.

COM1 and COM2 are fairly standard. COM3 and COM4 ports can be installed, but it is necessary to assign them proper I/O addresses and interrupt levels. Where possible, assign the modem to COM1 or COM2. Otherwise,

Click on the Main Group
Click on Control Panel
Click on Ports
Click on COM3 or COM4)
Click on Advanced Settings

[Select this to view Windows COM Port Configuration Panel] Fill in the I/O Port address and IRQ value in the boxes. Pressing the dropdown arrow will provide a list of suggestions. This configuration will be used automatically by any program that uses the standard Windows services to access the COM ports. In particular, this include Trumpet WINSOCK SLIP support.

Ethernet Installation Planning

Before buying an Ethernet card, determine what type of wiring is used or will be used in your building to make the connection. There are three types of Ethernet connections:

Relatively few Ethernet cards support all three types of connections. Most cards today support two of the three. While it is possible to get an external adapter, it will be easier if the right card is ordered to directly support the local wiring.

You then need a supported Ethernet card. At Yale, we generally recommend the 3Com Etherlink III (3C509) card as a reliable, low cost choice. This is the one adapter supported by every operating system.

The old 3Com 3C503 card is still quite usable, but the newer cards are better and less expensive. There are a ton of cards claiming to be "NE2000" compatible. Just like multimedia cards that claim to be "Sound Blaster" compatible, the support may only extend to plain DOS programs. Clone adapters may fail when the system is upgraded to Windows 95 or OS/2 Warp.

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Copyright 1995 PC Lube and Tune -- Windows on the World -- H. Gilbert