© Copyright Brian Brown, 1996-1999. All rights reserved.
This material may not be reproduced in printed or electronic format without the express permission of the author.

BASIC NETWORK COMPONENTS
There are a number of components which are used to build networks. An understanding of these is essential in order to support networks. This is a discussion on some of the elements which make up a network [LAN].

Network Adapter Cards
A network adapter card plugs into the workstation, providing the connection to the network. Adapter cards come from many different manufacturers, and support a wide variety of cable media and bus types [ISA, MCA, EISA, PCI, PCMCIA]. For an explanation about various bus types, click here

New cards are software configurable, using a software program to configure the resources used by the card. Other cards are PNP [plug and Play], which automatically configure their resources when installed in the computer, simplifying installation. With an operating system like Windows 95, auto-detection of new hardware makes network connections simple and quick.

On power-up, the computer detects the new network card, assigns the correct resources to it, and then installs the networking software required for connection to the network. All the user need do is assign the network details like computer name.

For Ethernet or 10BaseT cards, each card is identified by a twelve digit hexadecimal number. This number uniquely identifies the computer. These network card numbers are used in the Medium Access [MAC] Layer to identify the destination for the data. When talking to another computer, the data you send to that computer is prefixed with the number of the card you are sending the data to.

This allows intermediate devices in the network to decide in which direction the data should go, in order to transport the data to its correct destination.

A typical adapter card looks like,

A PCMCIA adapter card, suitable for connecting to a portable laptop computer to a network, looks like,

Peripheral cards associated with EISA and MCA are normally self configuring.

The major problem arises with cards for the ISA bus (found in the majority of AT type computers and clones). This is because the cards are configured by the user (using either jumpers or a software program).

Users make mistakes, and often configure cards so that they conflict with other cards already present in this system. This causes intermittent or immediate non-operation of the computer system.

For instance, a networking card that is allocated the same resources as a serial communications program may function perfectly, except when the user is logged into the network and then tries to use the serial port, at which time the machine will crash.

Resources Used By Peripheral Cards
We have already mentioned that resources used by ISA peripheral cards must not be shared (two cards cannot use the same). So what are the resources used by peripheral cards? Essentially, there are FOUR resources which are user configurable for peripheral cards. Some cards may only use one (a port location(s)), others may require all four.

The FOUR resources are

1. Input/Output Port Address
   In the PC, the port numbers used by peripheral cards range from 200h to 3FFh. The I/O port address is used by the PC to communicate with the peripheral card (issue commands, read responses, and perform data transfer).

2. Interrupt Request Line
   The interrupt request line is used by the card to signal the processor that the card requires the processors attention. ISA peripherals cannot share the same interrupt request line, and IRQ2 in AT/2386/486 computers should not be used (there are others which must also not be used). IRQ2 to IRQ15 appear on the ISA bus.

3. Direct Memory Request Line
   The DMA request line is used to transfer data between the peripheral card and the computers memory at high speed. DMA channel 0 cannot be used, as it is reserved for system use.

4. Buffer Memory Address
   Some peripheral cards prefer to use memory space rather than an I/O port address to transfer data to the processor. This memory space occupied by the peripheral card appears in the main system memory RAM area available to the processor (usually between C0000h to EFFFFh). Care must be taken to ensure this space is not being used for other purposes (like shadow RAM, EMS for windows, VBGA BIOS).

   This space is also sometimes used by a remote boot Eprom, which is used for diskless workstations which download the operating system from the server at boot time.

So How Do Peripheral Cards Work?
Peripheral cards require a software driver to function. This software driver provides the interface between the card and the operating system, making the services provided by the card available to the user.

The software driver is normally configured to match the resource settings of the card. This is done by a configuration utility, and stored either in the executable file, or a separate file (like .ini or .cfg).

It is obviously important for the configuration settings in the software driver to match those configured on the peripheral card.

The resources used by the card are either set by jumpers (or slide switches). New cards can also be configured using a software program, rather than by manually setting jumpers on the card. Where cards are software configurable, the cards retain their configuration when the power is turned off.

The software driver provides the follow functions

• initialization routine
• interrupt service routine
• procedures to transmit and receive data
• procedures for status, configuration and control

• card receives data
• card generates interrupt by asserting interrupt request line
• processor responds to interrupt request and jumps to service routine
• service routine instructs processor to read data from port location
• interrupt service routine releases processor to continue previous work

Common I/O Port Addresses

Port Address	Peripheral
200-207h	Game I/O Adaptor
210-217h	XT Expansion Unit
220h	SoundBlaster
278-27Fh	LPT2
2E8-2EFh	COM4
2F8-2FFh	COM2
300-30Fh	Color Video Adaptor
320-32F	XT Hard Disk
330h	SoundBlaster MIDI
378-37Fh	LPT1
3A0-3A9h	IBM Synchronous Adaptor
3B0-3BFh	Monochrome Video
3E8-3EFh	COM3
3F0-3F7h	Floppy Disk
3F8-3FFh	COM1

Common Interrupts

IRQ Line	Peripheral
2	EGA/VGA
3	COM2
4	COM1
5	LPT2, Bus mouse, Network
6	Floppy Disk
7	LPT1
13	Co-Processor
14	AT Disk Controller

Common Memory Addresses

Address	Peripheral
A0000-BFFFFh	EGA/VGA
B0000-B7FFFh	Monochrome
B8000-BFFFFh	CGA
C8000-CFFFFh	XT Disk
F4000-FFFFFh	AT ROM BIOS
F8000-FFFFFh	PC/XT ROM BIOS

Common DMA Lines

DMA Line	Peripheral
0	Memory Circuitry
1	Spare
2	Floppy Drive

1. Determine the resources used by the computer
   Use the previous tables to determine the interrupts, memory and port addresses used by the current hardware in the computer.

2. Read the install manual
   Check the disk for a read.me file (and read it). Read the manual and take note of the jumper switches used by the card. Identify where these are located on the card.

3. Determine resources to be used by the card
   Allocate resources to the card which do not conflict with existing hardware.

4. Observe electrostatic protection in handling the card
   Use a wrist strap and ground yourself properly before handling the card. Handle the card by the edges. Do not touch the components or edge connector. Use electrostatic bags or an electrostatic mat.

5. Configure the card jumpers
   Set the jumpers on the card

6. Insert the card
   Remove the system base unit cover and insert the card into a spare peripheral bus slot. Observe electrostatic precautions.

7. Load the software driver
   If the card was provided with a software driver, install the software driver. This might involve running an INSTALL program, or copying the drivers to the hard disk. It might also mean adding the driver name to the config.sys file (DEVICE=xxxxx.sys).

8. Configure the driver software
   If the driver software needs to be configured (specify which resources the card is using), this information might be stored in a separate file (.ini or .cfg). Often, when installing the software, it will ask for configuration details. These must be the same as the hardware jumpers used by the card.

9. Test card (run diagnostics where provided)
   If the card was provided with diagnostic software, run that now to test the card and driver. This is a good way to test if the installation was done correctly.

10. Test the machine
    Test some of the other software packages on the system (like networking, serial communications and printing) to see if they still work. If they don't, this indicates a probable conflict of resources. In Windows 95 or NT, run the diagnostic program to check for interrupt and resource conflicts (MSD or WINMSD).

Summary of Installing Network Cards in Servers and Workstations

• ISA cards are a problem
• check what resources are already being used
• do not share resources between two cards
• interrupts can only be shared on EISA and MCA cards
• run the diagnostics software after installation
• if the computer hangs, remove one board at a time until the problem disappears

• define a generic voice and data wiring system that is multi-purpose and multi-vendor
• help minimize cost of administration
• simplify network maintenance and changes

• horizontal wiring
• backbone wiring

• the wall outlet
• the horizontal cable
• cables used to interconnect components [cross-connects or patch cables] in the telecommunications closet (TC)

• uses star topology
• limit of 90 meters (295') from TC to wall outlet
• limit of 3 meters (10') to connect from wall outlet to PC
• patch cords and cross-connect leads are limited to 6 meters (20')
• minimum of two outlets per user (phone+data)
• standardized media, Outlet A=4pair 100ohm UTP, Outlet B=same or 2 pair 150ohm STP

• star topology
• maximum of two hierarchical levels
• interconnections between any two TC must not go through more than 3 cross connects
• use of recognized media
• adherence to distance limitations