© 2001 by prentice hall7-1 local area networks, 3rd edition david a. stamper part 3: software...
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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.
7-4© 2001 by Prentice Hall
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.
7-9© 2001 by Prentice Hall
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.
7-13© 2001 by Prentice Hall
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
7-14© 2001 by Prentice Hall
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.