pc networks 2 elements of a pc network
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PC NetworksPC Networks
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2Elements of a PC NetworkElements of a PC Network
ClientPC
ClientPC
ClientPC
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3Client PCsClient PCs
Sit on desks of ordinary managers, professional, or clerical workers
Usually begin life as stand-alone PCs
Add a Network Interface Card (NIC)
If operating system is not network-capable, must add client shell software
Do not confuse with client process
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4Client Operating SystemClient Operating System
Some PC operating systems are already network-capable– Windows 95, NT– No need to add additional software
Other client operating systems are not network-capable– Add client shell software
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5ServersServers
Provide services to client PCs
Usually High-End PCs– Add NIC– Add Server Operating System– Add service software
Can be low-end PCs for light services
Can be a UNIX workstation server
Can even be a mainframe or minicomputer
Examples: Dell, HP, Sun
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6Server SpecializationServer Specialization
Most PC networks have multiple servers– In a network with 200 client PCs, there are likely
to be 10-20 servers of different types
Why so many? Because servers are usually specialized by services– Optimized for needs of each service (power, disk
drive access, etc.)– Less expensive than using single large server– If one crashes, all do not crash
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7Server SpecializationServer Specialization
However, some offer multiple services– File storage– Remote printing– E-mail, etc.
The decision of how much to specialize each server is a matter of tradeoffs between the cost of adding a new server and the benefits of specialization.
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8Main Types of ServersMain Types of Servers
File Server
– Stores program and data files (acts like large hard disk drive)
– Programs run via file server program access E-mail Word processing, etc.
– Also handles remote printing
– Usually a fairly high-end PC
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9Main Types of ServersMain Types of Servers
Application Server
– Runs server program in client/server processing
– May be a workstation server rather than a PC, because client/server processing is platform-independent
– Database
– Webserver
Example: Oracle
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10Main Types of ServersMain Types of Servers
Communication Server
– For communication into, out of the PC network
– Dial in from home
– Go out to the Internet, a remote host computer, etc.
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11Main Types of ServersMain Types of Servers
Directory Server
– Knows locations of all resources on all servers
– Can be used to search for resources
– Can give user access to resources for which the user has access rights
Example: Novell
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12Server Operating SystemServer Operating System
Servers Need Operating Systems– Service applications run on these OSs– Optimized for running server services– Different optimization needs than client OSs
Usually Bundled with Some Applications– Email, webserver, etc. may be included
Usually Bundled with Management Software– May buy more from third parties
Server licenses
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13Server Operating SystemsServer Operating Systems
Novell NetWare
– Old market leader, less than 40% market share
– New sales: Netware 30%, Windows 40%, UNIX/Linux 30%
– Strong in directory service NetWare Directory Services NetWare strongest in mid-sized firms
– Newest versions called InterNetware
– Limited to PC servers
NetWare
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14Server Operating SystemsServer Operating Systems
UNIX/Linux
– 70% of market for webservers, database application servers
– Can run on workstation servers
– Weak in file service
– Difficult to administer: must hire new staff or retrain existing staff
– Dominant in large size organizations
UNIX
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15Server Operating SystemsServer Operating Systems
Microsoft Windows NT/2000 Server– Relatively new
– Easy to use, because based on Windows
– Priced attractively (Linux a threat)
– Can run on PCs or workstation servers
– Webserver software included
– Growing rapidly
– Now has directory service needed for large firms
– Strongest in small firms, department servers
WindowsNT
Server
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16Server Operating SystemsServer Operating Systems
A single PC network may have servers with different OSs– NetWare file servers– NetWare directory servers– Windows webserver– UNIX database server
NetWare
WindowsServer
UNIX
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17Service Application SoftwareService Application Software
The heart of PC networking File service (store, retrieve files) Electronic mail service Database service Web service Communication service Costs much more than the NOS
Examples: Microsoft BackOffice and IBM Lotus Software
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18Transmission NetworkTransmission Network
Need not be a LAN
– Can be a local internet or enterprise internet
– It may link thousands of client PCs and hundreds of servers
– So PC networking is not the same as local area networking
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19Independent Server Operating Independent Server Operating SystemSystem
Client A
DatabaseServer X
FileServer Y
FileServer Z
Login to Server X
Simultaneous Login to Server Y
FileA
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20Independent Server Operating Independent Server Operating SystemSystem
Servers do not even know that others exist
Easy on network administrators, who do not have to manage all information on an integrated basis
Hard for users who have to know what server holds a target file, then log into that server
Hard for users who have to know what server runs what service, then log into that server
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21Synchronized Server Synchronized Server Operating SystemOperating System
Client A
DirectoryServer X
FileServer Y
FileServer Z
Synchronized Server Network
Synchronizing Messages
SingleLogin
toDirectoryServer
FileA
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22Synchronized Server NetworksSynchronized Server Networks
Directory server maintains list of all resources
Easy on user: login once, to directory server. Access to all resources.
Easy on user: no need to ask which server has the file or service
Harder on network administrator, who must plan and manage an integrated directory
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23Communication Between Client Communication Between Client PC and ServerPC and Server
LAN
Internetting
Transport
Application
LAN
Internetting
Transport
Application
LAN Protocol
IP or IPX
TCP or SPX
Service
WindowsPC Server
PC networking is an application layer issue
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24Communication with Three Communication with Three ServersServers
Client PC
WindowsNT Server
ServerUNIX
ServerNetWare
File Server
IPX/SPXTCP/IP
TCP/IPODI
NDIS
NFS
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25Communication with Multiple Communication with Multiple ServersServers
Adaption Layer SoftwareAdaption Layer Software
NICNIC
Printing throughNetWare Server
Request for datato UNIX server
Multiplexes Transmissions
Places inside subnet (802.2, 802.3)frames
SPX, NCPSPX, NCP
IPXIPX
TCPTCP
IPIP
IPX/SPXProtocol
Stack
TCP/IPProtocol
Stack
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26File ServiceFile Service
Local DrivesA:B:C:
Virtual DrivesF:S:Y:Z:
File Save andRetrieve
Commands;Disk
ManagementCommands
Client PCFile Server
File Save andRetrieve
Commands;Disk
ManagementCommands
Virtual drives aredirectories on the file
server’s hard disk drives
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27Data File Storage: BackupData File Storage: Backup
A C
File Server
B
NetworkAdministration
PC
Tape BackupUnit
File Saves
Backup
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28BackupBackup
End users rarely back up their hard disks
File servers usually are backed up nicely
Storing files on a virtual drive means that they will be backed up
A real problem in large installations (think about UBmail with 5,000 user accounts)
Tape backup
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29Virtual Drive Access from Virtual Drive Access from AnywhereAnywhere
OwnDesktop PC
Notebook inCar or Hotel
PC at Home
Files OnVirtual Drive H:
PC inAnother Office
File Retrieval
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30Shared Virtual DriveShared Virtual Drive
Haraj Sidhu
Tod Kimura
SharedVirtualDrive(S:)
Luz Ochoa
NoAccessX
Save
Retrieve
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31Shared Virtual DrivesShared Virtual Drives
Potential Problem– First A retrieves and edits the file– Then B retrieves and edits the file– Then A saves– Then B saves– Whose changes are now in the file?
Locking– When one person starts to use a file, it is locked– Nobody can change it– Others, however, can read the old version
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32Program Storage on a File ServerProgram Storage on a File Server
Single Copy ofProgram Stored
On VirtualDrive ZSmall "Stub"
Program onClient PC
Download forExecution
vs Winstall
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33Program Execution Via File Server Program Execution Via File Server Program AccessProgram Access
Network
Client PCRAM andProcessor
ProgramClient PC
HardDiskDrive
FileServerHardDiskDrive
ServerRAM andProcessor
Copy fromServer Disk
to ClientRAM for
Execution
Client PC File Server
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34Redirection in a Network-Capable Redirection in a Network-Capable Operating SystemOperating System
Network-Capable Operating System
Application Program
2. Calls for Local Drives (C:) are Handledby the Client Operating System
PC HardwarePC Hardware Network Interface CardNetwork Interface Card
1. Call to access data file (includes name of drive)
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35Redirection in a Network-Capable Redirection in a Network-Capable Operating SystemOperating System
Application Program
3. Calls for Virtual Drives (F:) areRedirected to the File Server
PC HardwarePC Hardware Network Interface CardNetwork Interface Card
FileServer
viaNetwork
Network-Capable Operating SystemNetwork-Capable Operating System
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36Print ServicePrint Service
Client PC
PrinterFile Serverwith PrintQueue
Network PrintServer
Printout goes from the client PCto a print queue on the file server, not to the print server.
A print queue is a directory with associated control software
Printout goes from theprint queue to
a print server.
Network Printers
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37Client/Server ProcessingClient/Server Processing
NetworkClient PC Application Server(need not be a PC)
Client Program(Excel)
Server Program(Oracle)
Request
Response
Application Layer Interactions
Concepts: introduction and details
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38Program ProcessingProgram Processing
File Server Program Access– Processing is done only on client PC– File server stores program– Limited to small programs
Client/Server Processing– Processing shared by client PC and server– Application server rather than file server– Good for larger applications– Platform independent
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39Remote Access ServerRemote Access Server
Remote Client PC
Remote AccessServer
ModemModems
TelephoneLine
Remote Access Software
LAN
NT FAQ - RAS
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40Remote AccessRemote Access
Remote Control Software– Remote control server acts like a PC attached to the
network locally. Processing is done on access server.
– What appears on the remote access server “screen” appears on the remote screen
– Simple but very slow: screen images must travel across network
PC NetworkPC NetworkRemote
PC
Access Server
Example: pcAnywhere
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41Remote Access ServerRemote Access Server
Remote Node Service
– Remote PC is a full network node
– Processing is done on the remote PC, for fast screen changes
– File opens and saves cause file transfers over network
PC NetworkPC Network
AccessServer
File Server
RemotePC
outside of the network
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42
53
Gateway ServerGateway Server
IBMMainframe
Synchronous CommunicationGateway Server
SNA Communication
IPX/SPXCommunication
Gateways translate between networks with different standards architectures -- in this case, IPX/SPX and SNA
ClientPC
inside the network
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43Internet AccessInternet Access
Client PC connects to router– Connection is via TCP/IP– Router links user to the Internet
Router
TCP/IP Communication
Connection tothe Internet
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44Connecting to the InternetConnecting to the Internet
Firewall– Stands between Internet and the company– Limits unauthorized access
Router
TCP/IP Communication
Connection tothe Internet