Transcript Chapter 7

Local Area Networks, 3rd Edition
David A. Stamper
Part 3: Software
Chapter 7
LAN System Software
© 2001 by Prentice Hall
7-1
Chapter Preview
In this chapter you will study:
• Generic LAN system software
functions
• Workstation system software
functions
• Server system software functions
• Printer software
• Backup software
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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.
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IP and IPX Header Formats
IP
Type
Time
Packet
Fragment
Header Source Destination
Version Header
of
Identification Flags
to Protocol
Length
Offset
Checksum Address Address
Length Service
Live
IP Header
Checksum Length
Transport Packet Destination Destination Destination Source Source Source
Control
Type
Network
Node
Socket Network Node Socket
IPX Header
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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.
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A Generic Server Table
Server Name
Address
Server Type
Hops
MktgSvr
A12B634A
File
1
AcctSvr
DDC3958B
File
2
SWDevSvr
DD84A124
File
0
HRSvr
A12C583D
SQL
1
MfgSvr
29837CAB
File
1
RanDSvr
834AB3E7
File
0
ExOffL
5602C0A1
Printer
1
Unused
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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
Object
Properties
Server
Name
Network address
Location
User
Login name
Full name
Telephone
Address
Printer
Disk volume
E-mail address
Name
Location
Print queues
Print server
Name
Server name
Interface
Manufacturer
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Operator name
Capacity
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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
Client
Operating
System
Redirector
Application
Program
LANCom
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.)
Client
Operating
System
Redirector
Application
Program
LANCom
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.
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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
Duplexed
Controllers
Controller 1
Controller 2
File 1
File 1
File 2
File 2
1
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Raid Level 5 Technology
Server
File 1 Part 1
File 1 Part 2
File 1 Parity
File 1 Part 3
File 2 Part 2
File 2 Part 3
File 2 Part 1
File 1 Parity
1
2
3
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A Fault-Tolerant Duplexed Server
Duplexed Servers
Dedicated High-Speed
Connection
Disk Drive
Disk Drive
Mirrored Disk Drives
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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.
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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
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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 timeout interval
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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.
© 2001 by Prentice Hall
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