Chapter 9LAN Software

Part II: Understanding Internet Access Technologies

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Topics Addressed in Chapter 9

LAN application software LAN system software functions LAN workstation software LAN NOS functions Major network operating systems Software license agreements Server software interoperability

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LAN Software Categories

LAN software falls into two major categories (see Table 9-1): LAN application software: this category includes user-

oriented programs that enable business users to perform their work activities. Two types of application programs exist:

General-purpose LAN applications that are widely used across the business’s divisions or departments (e.g. word processing and spreadsheet applications)

Special-purpose LAN applications that support the activities of specific divisions/departments of subsets of users. Examples include groupware, transaction processing programs, and project management software

LAN system software consists of operating systems, utilities, drivers and other background programs that enable application programs to run smoothly on LAN hardware

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Table 9-1

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Work-group Software

Work-group software (aka groupware) supports multiple users working on related tasks. LAN implementations provide the hardware platform needed for its use

Groupware facilitates the activities of groups of users by reducing the time of time and effort needed to perform group tasks

Work-group software includes messaging, document sharing, group calendaring, threaded discussions, videoconferencing, and work-flow management applications

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E-Mail Administration

E-mail has become a fundamental means of communication within and between businesses. As a result, e-mail administration has become an important network management activity

Key e-mail standards have emerged including: X.400 which provides a framework for worldwide

electronic message-handling services (see Figure 9-1)

X.500 which outlines global directory systems for maintaining user names and network addresses

Global directory services used by network operating systems are modeled after X.500

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Figure 9-1

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Key Groupware Applications

Important groupware applications include: Electronic conferencing applications (including

videoconferencing) Work-flow automation software Document coauthoring systems Document management (aka image processing

systems) Including electronic document management

systems (EDMS) Group decision support systems Time-staged delivery systems

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LAN System Software Functions

LAN system software is found in both clients and servers

Key software components of LAN system software found in workstations are depicted in Figure 9-3. These include: Media interface software Redirector software

The redirector intercepts all application I/O requests

If the request is for a local device, the request is passed to the client’s operating system

If the request is for a network resource, the request is sent to the media interface software for transmission over the LAN’s communication medium

This process is illustrated in Figure 9-4

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Figure 9-3

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Figure 9-4

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Key Workstation Software Interfaces

Application software in client workstations rely on system software to perform hardware-oriented tasks such as interfacing with disk drives and printers

When an application requests a service from the workstation’s operating system (OS) or the client network operating system (NOS), it issues an interrupt. Each interrupt is interpreted by the redirector to determine if it is a local or network request

The compatibility of an application with a particular OS or NOS depends on whether the application issues interrupts and requests for server-based resources in the format required by the OS’s or NOS’s application program interface (API)

The medium-interface portion of the client NOS has two key functions: placing data onto the communication medium and receiving data from the network. The former must be done using the message block format(s) required by LAN servers

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Server System Software Functions

Servers often receive multiple simultaneous requests for network resources; the server must be able to keep track of the progress of each request and to manage the request queue (see Figure 9-5)

Most of today’s servers support multithreading, the ability to have multiple concurrent streams of execution with each stream being treated as a different transaction

A database server spends most of its time accepting requests, issuing reads or writes to satisfy the requests, reacting to read/write completions, and sending results to requesters

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Figure 9-5

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Universal Clients

A universal client is a client workstation that is able to transparently interact with multiple servers that run different network operating systems or applications

Universal client capability requires support for: Multiple network redirectors Multiple file systems Multiple network transport protocols Multiple MAC-level clients and network drivers This is illustrated in Table 9-2.

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Table 9-2

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Supporting Remote Clients

Telecommuting and mobile computing has increased the need for remote users to access LAN servers and computing resources

This is often addressed by installing a remote access client on the remote user’s computer Remote access clients enable users to connect to

remote access servers responsible for controlling access to shared resources in the LAN

Password systems or more sophisticated mechanisms are used to authenticate the identities of remote users

Messages between remote clients and remote access servers may be encrypted

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Peer-to-Peer Networking Functions

Today’s client operating systems support peer-to-peer network capabilities including file and printer sharing

File sharing enables LAN users to create shared directories on their workstations that can be accessed by other LAN users

Windows users can do this via Network Neighborhood Password control options include read-only and full

Printer sharing enables a LAN user to use a printer that is physically attached to another workstation

Passwords can be used to control access When printer or file sharing is enabled on a workstation,

it becomes a nondedicated server Client OSs that support peer-to-peer networking include

Windows 9x, Windows NT/2000/XP, Macintosh OS, and Linux

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Server Software Functions

LAN server software is more complex than client NOS software Server software usually supports multithreading to efficiently

respond to client requests Other important functions supported by LAN server software

include: I/O optimization Fault tolerance Directory services Application services File services Networking services Network management services Security services Print services Backup services

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I/O Optimization

I/O optimization refers to a variety of approaches to improve server performance by optimizing file and data access tasks

Techniques include: Disk caching Disk seek enhancement: rearranging disk

read/write requests to efficiently position read/write heads (see Table 9-4)

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Table 9-4

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Fault Tolerance

A server has fault tolerance if it is able to survive some failures that ordinarily would be disabling; generally a combination of hardware and software is used

Specific approaches include: Read-after-write Mirrored disks (see Figure 9-6) RAID (redundant arrays of independent disks) Server duplexing (see Figure 9-7) Server clusters Hot-swappable components

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Figure 9-6

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Figure 9-7

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Directory Services

LAN NOSs have a file or database that stores information about users and system resources such as servers, printers, and applications

Two major kinds of directory services used in LANs are: Global directory services (such as Novell’s NDS and

Microsoft’s AD) that store information about network users and resources in a single database (see Figure 9-8 and Table 9-5)

Domain directory services, such as Windows NT’s, that subdivide network linked subdivisions called domains

Each domain has a server called a primary domain controller (PDC) that maintains the directory of users and resources in that domain

LDAP (Lightweight directory access protocol) enables interoperability among different directory services

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Figure 9-8

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Table 9-5

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Application Services

Client/server computing and the emergence of 3-tiered and n-tiered C/S architectures have made it important for NOSs to provide high-quality application services

Support for symmetrical multiprocessing (SMP),and preemptive multitasking is typical in high-performance application servers

Windows NT/2000 Server has developed a solid reputation for application services

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File Services

NOSs vary in the kinds and number of file systems that they support

Commonly supported file systems include: FAT FAT32 NTFS NFS

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Networking Services

Server NOSs must be able to interface with a variety of client operating systems. Server NOS support for wireless device operating systems is also increasing

Additional NOS networking services include: Support for multiple network-layer protocols Ability to support multiple simultaneous

connections Support for multiprotocol routing Remote access support Gateway services

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Network Management Services

Common NOS network management services include: Directory management tools User account creation/management tools Tools for simultaneously managing multiple

servers Tools for monitoring server performance and CPU

utilization Network traffic analysis tools Network file system management tools Tools for managing backups Tools for recovering from server failures

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Security Services

Today’s network operating systems include a number of mechanisms for ensuring network security. These include: Authentication services: such as requiring network

users to provide authentication credentials to log on

Authorization services: such as access control lists (see Table 9-6 and Table 9-7)

Data encryption Auditing services: such as keeping track of all

network log-on attempts, both successful and unsuccessful(see Table 9-8)

Data access security services (see Table 9-13)

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Table 9-6

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Table 9-7

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Table 9-13

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Other NOS Services

Other important NOS services include: Spooler operations (see Figure 9-9 and Table

9-9) Backup services (see Table 9-10) Network resource sharing services

including: Configuration management (see Table 9-11) Application setting management Contention management (see Table 9-12

and Figure 9-10)

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Figure 9-9

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Table 9-9

Table 9-10

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NOS Products

A number of NOS products exist (see Table 9-3)

Among the most important are: NetWare 4.x, 5.x, and 6

All support NDS (see Figure 9-12) Windows NT/2000 Server (see Table 9-14)

Also see Figure 9-13 and 9-14 Linux (see Figures 9-15 and 9-16) UNIX (see Tables (9-15 and 9-16)

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Table 9-3

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Table 9-14

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Table 9-16

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Software License Agreements

Software license agreements are important issues in LAN software selection and management

A license agreement is legal agreement between manufacturer and purchaser that stipulates the rules under which the purchaser is allowed to use a product. It is one of the primary steps taken by software vendors to protect their investments

Types of software license agreements include: Single-user, single-workstation agreements Single-user, multiple-workstation agreements Restricted number of concurrent user agreements Server license agreements Site license agreements Corporate license agreements

Open-source software (e.g. Linux) may not be addressed by license agreements

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Server Software Interoperability

Because it is typical for large LANs to have multiple servers that run two or more different NOS, server interoperability is an issue in many organizations

Interoperability is the ability of network components to communicate with shared network resources and to work together

Interoperability challenges in LANs with mixed server and workstation platforms stem from the need to support:

Multiple application and file systems Multiple network transport protocols Multiple MAC specifications

Other interoperability challenges are outlined in Table 9-17

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Table 9-17

Chapter 9LAN Software

Part II: Understanding Internet Access Technologies