6-1© 2001 by Prentice Hall

Local Area Networks, 3rd EditionDavid A. Stamper

Part 3: Software

Chapter 6

Software Introduction

6-2© 2001 by Prentice Hall

Chapter Preview

• The distinction between the different classes of software

• The generic requirements of workstation software• The generic requirements of server software• Software requirements for shared access• How software can be protected on a LAN• Some of the standards covering LAN software• The need for and general provisions of software

license agreements

In this chapter you will study:

6-3© 2001 by Prentice Hall

Classes of Software

• Application Software• Operating System Software

– Memory management• The OS manages memory and allocates it among itself and the

requesting processes according to a memory management scheme adopted by the OS designers

– File management• The OS provides the ability to organize bits into files, files into

directories, and so on

– User interface• Creating user environments is an OS function

– I/O interfaces• The OS and file management system translate the request to access a

file into an address the disk can act on

6-4© 2001 by Prentice Hall

Classes of Software (cont.)

– Resource allocation• The OS has an algorithm that determines which ready

process gets access to the CPU and the conditions under which a running process maintains control of the CPU

– Accounting• CPU usage

• Lines printed

• Disk space used

• Transactions submitted (by type)

• Data communications medium usage

• bytes read from and written to disk

6-5© 2001 by Prentice Hall

Classes of Software (cont.)

– Protection/Security• The OS provides the base on which security is established. We expect

the OS to prevent user programs from crashing the system and to eliminate the intrusion of one program onto the memory occupied by another program’s data.

• Database Management– A database management system (DBS) extends the OS file management

capabilities. A DBMS provides software that allows the user or database administrator to:• Define records, files, and file relationships• Access, update, and delete data in the database• Set up security• Establish, maintain, and use a data dictionary• Use host language interfaces that allow the database to be

manipulated by standard programming languages

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Classes of Software (cont.)

• Utility Software– Utilities augment the function of the OS or other subsystem, such as the database

management system or the data communications subsystem.

• Development Software– Development software includes text editors, text formatters, compilers, interpreters,

link editors, cross-reference programs, testing utilities, and related programs and utilities

• Network Management Software– Network management includes a variety of activities such as backups, problem

resolution, capacity planning, and establishing user environments

• Network Access Software– Network access software for a LAN includes the components that allow us to access

LAN resources from directly attached workstations and remote workstations

6-7© 2001 by Prentice Hall

Generic Functions of LAN System Software

• LAN system software is essentially an extension of the OS. It carries out hardware-oriented LAN tasks, such as interfacing to the medium, and I/O-oriented tasks such as directing print jobs and disk read/write requests to a server.

• The purpose of system software is to insulate applications from hardware details such as I/O and memory management. System software provides an interface through which the applications can request hardware services without needing to know the details of how the services are carried out.

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LAN System Software in Server and Workstation

ApplicationProgram

A1Network

Redirector

MediumInterfaceSoftware

OperatingSystem

DiskDrive

ServerOperating

System

MediumInterfaceSoftware

ServerSystem

SoftwareDiskDrive

LAN Medium

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LAN Redirector Functions

ApplicationProgram

A1

NetworkRedirector

MediumInterfaceSoftware

OperatingSystem

LAN Medium

Disk

RedirectorinterceptsI/O requestand routes toappropriate softwaremodule.

NetworkRequest

6-10© 2001 by Prentice Hall

LAN Server Request Queue

ServerOperating

System

LANSystem

Software

Database ReadWrite to Printer

Download ApplicationDatabase ReadWrite to PrinterWrite to Printer

Queueof

WaitingRequests

ServerDisk

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User Configuration Options

Default disk drive

Default disk directory

Disk drive mappings

Disk drive/directory search paths

Printer mappings

Initial program/menu

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A Contention Problem

Record A

Karen readsRecord A with lock

Juan issues a readrequest for Record A

Record A is locked byKaren so Juan must wait

Record A

Karen's Application

Juan's Application

ReadRecord A

PendingRequest

Database

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Exclusive, Protected, and Shared Open Combinations

Exclusive

Protected

Shared, update

Shared, read-only

Denied

Denied

Denied

Denied

Denied

Denied

Denied

Granted

Denied

Denied

Granted

Granted

Denied

Granted

Granted

Granted

Open Mode Requested Exclusive Protected

Shared Update Shared Read-only

Currently Opened As

6-14© 2001 by Prentice Hall

Waiting for Lock Release

Record A

Application 1 readsRecord A with lock

Application 2 issues a readrequest to Record A

Record A is locked byApplication 1, so Application 2 must wait

Record A

Application 1

Application 2

ReadRecord A

PendingRequest

Database

6-15© 2001 by Prentice Hall

Deadlock Situation

Record A

Record BLocked by A2

Application 1 has readand locked Record A

Application 2 has readand locked Record B

Application 1 is waitingfor Application 2to release Record B

Application 2 is waitingfor Application 1to release Record A

Application 1 and 2 aredeadlocked andwill wait forever

Record A

Application 1

Application 2

ReadRecord A

PendingRequest

Database

Record B

6-16© 2001 by Prentice Hall

Software Standards

• Most of the LANs in operation today are called open networks, meaning that they adhere to a set of standards formulated by organizations such as ISO, ANSI, IEEE, and EIA. These standards are placed in the public domain and are called open standards.

6-17© 2001 by Prentice Hall

Software Protection

• Software is protected in seven basic ways:– The code is kept secret so other software houses cannot use special

algorithms developed by the company to write a competing system.– The code is copyrighted to prevent another company from copying the

code and writing a competing system.– Legislation penalizing those who do not adhere to the copyright and

license restrictions is enforced.– The software is copy-protected to deter someone from making an illegal

copy.– License agreements are used to establish the terms of ownership and use.– The software requires WAN/Internet verification before it is activated.– The software requires a special hardware device to run.

6-18© 2001 by Prentice Hall

Software License Agreements

• The license agreement states the conditions under which you are allowed to use the product.

• In general, license agreements take one of the following forms:

– Single-user, single-workstation licenses• A single-user, single-workstation license agreement is the most

restrictive. It specifies that the software is to be used on one workstation only and by only one person at a time.

– Single-user, multiple-workstation licenses• The constraints of the single-user, single-workstation agreement are

relaxed by the single-user, multiple-workstation license agreement. It usually relies on the honor system for enforcement. The purchase of a single copy of the software allows the owner to install it on several systems.

6-19© 2001 by Prentice Hall

Software License Agreements (cont.)

– Restricted number of concurrent users licenses• Most LAN-compatible software is designed for multiple

users; however, some software vendors limit the number of concurrent users with a restricted number of concurrent users license agreement. The main idea behind this strategy is to charge by the number of users.

– Server licenses• A server license allows an application to be installed on

one server. All users attached to that server may use the application. If a company has several servers, say three, and wants to use the application on each of them, the company must purchase three licenses or three copies of the software.,

6-20© 2001 by Prentice Hall

Software License Agreements (cont.)

• Site licenses– A site license gives the user unlimited rights to use the

software at a given site. The site may be a single LAN or multiple LANs at one location.

• Corporate licenses– A corporate license gives the corporation unlimited use

of the software at all locations. Some companies restrict a corporate license to all locations within one country. Sometimes, the right to reproduce documentation is also granted.

6-21© 2001 by Prentice Hall

License Agreement Owners’ Rights

• The license agreement is intended primarily to protect the rights of the manufacturer. However, the owner of a license agreement also has certain rights:– The owner can transfer or assign the license to another user.– The owner can get a refund if the product is defective or does not work as

stated.– The owner has legal rights granted by certain states or countries

regarding the exclusion of liability for losses or damage resulting from the use of the software.

– The owner can terminate the license by destroying the software and documentation.