Lesson 3: Device Drivers and OSI
NICs play an important role in connecting a computer to the physical part
of the network. No discussion of networking standards is complete without
including drivers, the small software programs that enable a computer to
work with a network card or other device. In this lesson we look at device
drivers and how they relate to the OSI reference model.
The Role of Drivers
A driver (sometimes called a device driver) is software that enables
a computer to work with a particular device. Although a device might be
installed on a computer, the computer's operating system cannot communicate
with the device until the driver for that device has been installed and
configured. The software driver tells the computer how to drive or work
with the device so that the device performs the job it is assigned in the
way it is supposed to.
There are drivers for nearly every type of computer device and peripheral
Usually, the computer's operating system works with the driver to make
the device perform. Printers provide a good illustration of how drivers
are used. Printers built by different manufacturers all have different
features and functions. It would be impossible for computer makers to equip
new computers with all the software necessary to identify and work with
every type of printer. Instead, printer manufacturers make drivers available
for each printer. Before your computer can send documents to a printer,
you must install the driver for that printer on your computer's hard drive.
Input devices, such as mouse and keyboard devices.
SCSI and IDE disk controllers.
Hard and floppy-disk drives.
Multimedia devices such as microphones, cameras, and recorders.
Network interface cards (NICs).
Printers, plotters, tape drives, and so on.
As a general rule, manufacturers of components, such as peripherals
or cards that must be physically installed, are responsible for supplying
the drivers for their equipment. For example, NIC manufacturers are responsible
for making drivers available for their cards. Drivers generally are included
on a disk with the equipment when it is purchased, included with the computer's
operating system, or made available for downloading from an Internet service
provider such as the Microsoft Network (MSN), CompuServe, or others.
The Network Environment
Network drivers provide communication between a NIC and the network redirector
running in the computer. The redirector is the part of networking software
that accepts input/output (I/O) requests for remote files and then sends,
or redirects, them over the network to another computer. During installation,
the driver is stored on the computer's hard disk.
Drivers and the OSI Reference Model
NIC drivers reside in the MAC sublayer of the OSI reference model's data-link
layer. The MAC sublayer is responsible for providing shared access to the
physical layer for the computer's NICs. As shown in Figure 5.10, the NIC
drivers provide virtual communication between the computer and the NIC.
This, in turn, provides a link between the computer and the rest of the
Figure 5.10 Communication between the NIC and network software
Drivers and the Networking Software
It is common for a NIC manufacturer to provide drivers to the networking-software
vendor so that the drivers can be included with the network operating software.
The hardware compatibility list (HCL) supplied by operating-system manufacturers
describes the drivers they have tested and included with their operating
system. The HCL for a network operating system might list more than 100
NIC drivers. This does not mean that an unlisted driver won't work with
that operating system; it means only that the operating-system manufacturer
has not tested it.
When purchasing a new hardware device, always make sure that it
contains the correct drivers for the specified computer operating system
on which it will be installed. If in doubt, or if you are missing the appropriate
driver, consult the manufacturer before you install the device. Updated
drivers or drivers for various operating systems often are available over
the Internet for downloading.
Even if the driver for a particular card has not been included with
the network operating system, it is usual for the manufacturer of the NIC
to include drivers for most popular network operating systems on a disk
that is shipped with the card. Before buying a card, however, make sure
that the card has a driver that will work with a particular network operating
system. Installation and configuration of drivers is discussed in detail
in Chapter 8, "Designing and Installing a Network."
Network Driver Interface Specification (NDIS)
Network Driver Interface Specification (NDIS) is a standard that
defines an interface for communication between the MAC sublayer and the
protocol drivers. By permitting the simultaneous use of multiple protocols
and drivers, NDIS allows for a flexible environment of data exchange. It
defines the software interface, known as the NDIS interface. Protocol drivers
use this interface to communicate with the NICs. The advantage of NDIS
is that it offers protocol multiplexing, so that multiple protocol stacks
can be used at the same time. Three types of network software have interfaces
described by NDIS:
Microsoft and 3Com jointly developed the NDIS specification for use with
Warp Server and Windows NT Server. All NIC manufacturers make their boards
work with these operating systems by supplying NDIS-compliant software
Protocol stack Provides network communications. A stack generates
and disassembles frames (control information and data) that are sent to
and received from the network.
Adapter driver Controls the network interface hardware. Works in
the MAC sublayer and moves frames between the protocol stack and the interface
Protocol Manager Controls the activity between the protocol stack
and the MAC.
Open Data-Link Interface (ODI)
Open Data-Link Interface (ODI) is a specification adopted by Novell
and Apple to simplify driver development for their network operating systems.
ODI provides support for multiple protocols on a single NIC. Similar to
NDIS, ODI allows Novell NetWare drivers to be written without reference
to the protocol that will be used on top of them. All NIC manufacturers
can make their boards work with these operating systems by supplying ODI-compliant
Bridging NDIS and ODI
ODI and NDIS are incompatible. They present different programming interfaces
to the upper layers of the network software. Novell, IBM, and Microsoft
offer ODI-to-NDIS translation software to bridge the two interfaces. Two
examples are ODI2NDI.SYS and ODINSUP.SYS.
Most network card manufacturers supply both NDIS- and ODI-compliant
drivers with their boards.
Define ODI and describe the role it plays in Novell and Apple NOSs.
Printer manufacturers are responsible for writing _______________ for their
Drivers described in an operating system manufacturer's ________ have been
tested and included with their operating system.
NIC drivers reside on the computer's _________ _________.
Protocol drivers use an _________ interface to communicate with the NICs.
Translation software is required to _____________ ________________ NDIS
The following points summarize the main elements of this lesson:
A driver is a device-specific control program that enables a computer to
work with a particular device, such as a printer or a disk drive.
In networking, drivers are needed to provide the connection between the
computer and the NIC.
NIC drivers reside in the MAC sublayer of the data-link layer of the OSI
NDIS is a standard that defines the interface for Windows NT Server and
ODI is a standard that defines the interface for Apple and Novell systems.