PC Networks 2 Elements of a PC Network

PC NetworksPC Networks

2Elements of a PC NetworkElements of a PC Network

ClientPC

ClientPC

ClientPC

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

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

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

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

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.

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


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


Communication Server

– For communication into, out of the PC network

– Dial in from home

– Go out to the Internet, a remote host computer, etc.


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

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

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


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


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


A single PC network may have servers with different OSs– NetWare file servers– NetWare directory servers– Windows webserver– UNIX database server

NetWare

WindowsServer

UNIX

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

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

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

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

21Synchronized Server Synchronized Server Operating SystemOperating System

Client A

DirectoryServer X

FileServer Y

FileServer Z

Synchronized Server Network

Synchronizing Messages

SingleLogin

toDirectoryServer

FileA

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

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

24Communication with Three Communication with Three ServersServers

Client PC

WindowsNT Server

ServerUNIX

ServerNetWare

File Server

IPX/SPXTCP/IP

TCP/IPODI

NDIS

NFS

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

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

27Data File Storage: BackupData File Storage: Backup

A C

File Server

B

NetworkAdministration

PC

Tape BackupUnit

File Saves

Backup

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

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

30Shared Virtual DriveShared Virtual Drive

Haraj Sidhu

Tod Kimura

SharedVirtualDrive(S:)

Luz Ochoa

NoAccessX

Save

Retrieve

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

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

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

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)

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

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

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

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

39Remote Access ServerRemote Access Server

Remote Client PC

Remote AccessServer

ModemModems

TelephoneLine

Remote Access Software

LAN

NT FAQ - RAS

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

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

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

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

44Connecting to the InternetConnecting to the Internet

Firewall– Stands between Internet and the company– Limits unauthorized access

Router

TCP/IP Communication

Connection tothe Internet

PC Networks 2 Elements of a PC Network

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