7-1© 2001 by Prentice Hall

Local Area Networks, 3rd EditionDavid A. Stamper

Part 3: Software

Chapter 7

LAN System Software

7-2© 2001 by Prentice Hall

Chapter Preview

• Generic LAN system software functions

• Workstation system software functions

• Server system software functions

• Printer software

• Backup software

In this chapter you will study:

7-3© 2001 by Prentice Hall

Server/Workstation Communications

• The first problem the workstation must address is connecting to a server. Once a client has a server connection, the user at the client can log onto the network. Depending on the LAN OS being used, a user can log onto a single server, a collection of resources called a domain, or the entire corporate network.

• Regardless of the environment—single server, domain, or network directory—the user’s network software must find a server resource that can authenticate the logon request.

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Server/Workstation Communications (cont.)

• The address of the server with which the workstation must communicate is essential because the address is part of the data link message header.

• The network layer protocols determine the format of addresses. Leading transport/network layer protocols include the transmission control protocol/internet protocol (TCP/IP) used on the Internet, and the sequenced packet exchange /internet packet exchange (SPX/IPX) protocol used on many Novell and Microsoft LANs.

7-5© 2001 by Prentice Hall

IP and IPX Header Formats

VersionIP

HeaderLength

DestinationAddress

SourceAddress

HeaderChecksum

Typeof

Service

PacketLength

Identification FlagsFragment

Offset

Timeto

LiveProtocol

ChecksumSourceSocket

SourceNode

SourceNetwork

LengthTransport

ControlPacketType

DestinationNetwork

DestinationNode

DestinationSocket

IP Header

IPX Header

7-6© 2001 by Prentice Hall

Services Advertising Protocol

• In Novell NetWare LAN implementations, the services advertising protocol (SAP) is implemented at the OSI application layer. Inherent in this protocol is the presence of a server table in each server and router.

• When the server is initiated, one of its startup functions is to broadcast a SAP message. A broadcast message has a distinct destination address that allows it to be accepted by all nodes. The SAP message identifies the server’s name, address, and the types of services it can provide.

7-7© 2001 by Prentice Hall

A Generic Server Table

MktgSvr

AcctSvr

SWDevSvr

HRSvr

MfgSvr

RanDSvr

ExOffL

Unused

File

File

File

SQL

File

File

Printer

1

2

0

1

1

0

1

A12B634A

DDC3958B

DD84A124

A12C583D

29837CAB

834AB3E7

5602C0A1

Server Name Address Server Type Hops

7-8© 2001 by Prentice Hall

The Network Directory

• In a large LAN with hundreds of users, hundreds of e-mail addresses, dozens of printers, and 5 to 10 servers, keeping track of the names and locations of people and equipment is a significant effort.

• A network directory is fundamentally a database of LAN objects, properties of those objects, and values for properties.

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Possible Contents of a Network Directory

Server

User

Printer

Disk volume

Network address

Full name

Location

Print server

Server name

Manufacturer

Location

Telephone

E-mail address

Operator name

Capacity

Name

Login name

Address

Name

Print queues

Name

Interface

Object Properties

7-10© 2001 by Prentice Hall

Client/Server Dialogue

• Once the client and server have connected, a client/server dialogue can begin.

• When an application requests a service from the OS, it does so by issuing a signal called an interrupt. The redirector reacts to the interrupt and decides whether it is a LAN request or a local request. The redirector must know which interrupts to intercept.

• Once the redirector has the request, it must formulate a server message to indicate which service is to be provided. It formats a message with the proper request codes and sends the message to the LANCom process.

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Redirector Implementations

ClientOperating

SystemRedirector

LANComApplicationProgram

Redirector receives application requests and routes local request to the client OS and network request to LAN communication process.

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Redirector Implementations (cont.)

ClientOperating

SystemRedirector

LANComApplicationProgram

Client OS gets request and sends network requests to the redirector.

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LAN Operating System Functions

• Optimized I/O– One of the main services provided by a server is disk access. Disk

access consists of three components: seek, latency, and transfer. I/O optimization attempts to reduce one or more of these disk access components.

• Disk Configurations– One of the functions of an OS is to implement a file system. This

involves allocating and deallocating disk space and keeping track of space allocated to each file.

– Partitioning• sometimes it is beneficial to divide a single disk drive in two

or more partitions; each partition can be managed separately

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LAN Operating System Functions (cont.)

– Single Disk Volume• a volume is a logical disk (a partition or collection of partitions) or physical

disk that has been formatted and can be used to store data by an OS.

– Multiple Disk Volumes or Volume Sets• Most LAN OSs allow multiple partitions or disks to be combined to

form a single logical partition. A volume created from multiple partitions is called a volume set.

– RAID Level 0—Striping without parity• Another capability provided with some LAN OSs is called a

Redundant Array of Inexpensive Disks (RAID) Level 0 or striping without parity. Multiple partitions on different disks can be combined to proved a single logical disk; striping with parity differs from a volume just described in that data is written to all partitions simultaneously.

7-15© 2001 by Prentice Hall

Fault Tolerance

• A LAN with fault tolerance allows the server to survive some failures that would ordinarily be disabling. Fault tolerance usually is provided by a combination of backup hardware components and software capable of using the backup hardware.

• A level of fault tolerance also can be provided by using redundant arrays of inexpensive disks (RAID). There are six levels of RAID, but for fault tolerance we are concerned only with RAID Level 1 and RAID Level 5.

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Mirrored Disk Drives

Controller 1 Controller 2

File 1 File 1

File 2 File 2

DuplexedControllers

1 2

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Raid Level 5 Technology

File 1 Part 1 File 1 Part 3File 1 ParityFile 1 Part 2

File 2 Part 2 File 2 Part 3 File 2 Part 1 File 1 Parity

Server

1 2 3 4

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A Fault-Tolerant Duplexed Server

Dedicated High-SpeedConnection

Duplexed Servers

Disk Drive Disk Drive

Mirrored Disk Drives

7-19© 2001 by Prentice Hall

Logical and Physical Printers

• In discussing the operation of a printing environment, we need to make a distinction between logical printing and physical printing. The application’s job stream is sent to a logical printer. Logical printers collect print streams from one or more applications. Logical printers are connected to zero, one, or several physical printers that Microsoft call a printing device.

7-20© 2001 by Prentice Hall

LAN Printing Configurations

• Because printing requirements vary among companies using LANs, a wide range of implementation options exist. Among these are:– Private printers attached to a user’s computer and not shared– Shared printers attached to file servers– Shared printers attached to users’ workstations– Shared printers attached to computers that are dedicated to the printing

task– Shared printers attached to special-purpose print servers– Shared printers attached directly to the LAN via an on-board LAN adapter

and print server

7-21© 2001 by Prentice Hall

Some Spooler Options

Collect printed output

Hold hobs in disk queue after printing

View jobs on hold in print queue

Delete jobs from print queue

Se/change job priorities

Start/stop printers

Print banners

Print statistical reports

Direct print jobs to designated printers

Hold jobs in disk queue before printing

Set number of print copies

Attach/detach printers from print queue

Add/delete printers

Start/stop spooler process

Close print jobs based on time-out interval

7-22© 2001 by Prentice Hall

Backup Software

• The software used to perform the backups is as important as the hardware. Backup software is responsible for reading the files being backed up and writing them to the backup device.

• Backup devices often come with a backup/restore program (both capabilities are contained on one program), and most LAN system software includes a backup/restore module.

• Some LAN administrators choose to purchase a separate, more functional backup system than the LAN or backup device versions.