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PC Networks
Elements of a PC Network
Client
PC
Client
PC
Client
PC
2
Client PCs
 Sit
on desks of ordinary managers,
professional, or clerical workers
 Usually
 Add
begin life as stand-alone PCs
a Network Interface Card (NIC)
 If
operating system is not network-capable,
must add client shell software
 Do
not confuse with client process
3
Client 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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Servers
 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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Server 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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Server 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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Main 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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Main 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 platformindependent
– Database
– Webserver
Example: Oracle
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Main 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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Main 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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Server 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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Server Operating Systems
 Novell
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NetWare
– Old market leader, less than 40% market share
– New sales: Netware 30%, Windows 40%,
UNIX/Linux 30%
– Strong in directory service
 NetWare
 NetWare
Directory Services
strongest in mid-sized firms
– Newest versions called InterNetware
– Limited to PC servers
NetWare
Server Operating Systems
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 UNIX/Linux
– 70% of market for webservers, database
application servers
UNIX
– 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
Server Operating Systems
 Microsoft Windows
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NT/2000 Server
– Relatively new
– Easy to use, because based on Windows
Windows
NT
Server
– 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
Server Operating Systems
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 A single
PC network may have servers with
different OSs
–
–
–
–
NetWare file servers
NetWare directory servers
Windows webserver
UNIX database server
UNIX
NetWare
Windows
Server
Service 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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Transmission 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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Independent Server Operating
System
Database
Server X
Client A
File
Server Y
Login to Server X
Simultaneous Login to Server Y
File
A
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File
Server Z
Independent Server Operating
System
 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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Synchronized Server
Operating System
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Synchronized Server Network
Client A
Single
Login
to
Directory
Server
Directory
Server X
File
Server Y
Synchronizing Messages
File
A
File
Server Z
Synchronized 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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Communication Between Client
PC and Server
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Service
Application
Windows
PC
Transport
Application
TCP or SPX
Transport
Server
Internetting
LAN
IP or IPX
LAN Protocol
Internetting
LAN
PC networking is an application layer issue
Communication with Three
Servers
NetWare
File Server
Client PC
IPX/SPX
ODI
UNIX
Server
TCP/IP
NFS
Windows
NT Server
Server
TCP/IP
NDIS
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Communication with Multiple
Servers
Printing through
NetWare Server
IPX/SPX
Protocol
Stack
Request for data
to UNIX server
SPX, NCP
TCP
IPX
IP
TCP/IP
Protocol
Stack
Adaption Layer Software
Multiplexes Transmissions
NIC
Places inside subnet (802.2, 802.3)frames
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File Service
File Save and
Retrieve
Commands;
Disk
Management
Commands
File Server
Client PC
Local Drives
A:
B:
C:
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File Save and
Retrieve
Commands;
Disk
Management
Commands
Virtual Drives
F:
Virtual drives are S:
directories on the file Y:
server’s hard disk drives
Z:
Data File Storage: Backup
File Server
Backup
Network
Administration
PC
File Saves
Tape Backup
Unit
A
B
C
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Backup
 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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Virtual Drive Access from
Anywhere
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Files On
Virtual Drive H:
File Retrieval
Own
Desktop PC
PC in
Another Office
Notebook in
Car or Hotel
PC at Home
Shared Virtual Drive
Shared
Virtual
Drive
(S:)
Save
Retrieve
Haraj Sidhu
X
No
Access
Luz Ochoa
Tod Kimura
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Shared 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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Program Storage on a File Server
Small "Stub"
Program on
Client PC
vs Winstall
Single Copy of
Program Stored
On Virtual
Drive Z
Download for
Execution
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Program Execution Via File Server
Program Access
File Server
Client PC
Client PC
Hard
Disk
Drive
Client PC
RAM and
Processor
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Program
Copy from
Server Disk
to Client
RAM for
Execution
Network
File
Server
Hard
Disk
Drive
Server
RAM and
Processor
Redirection in a Network-Capable
Operating System
Application Program
1. Call to access data file (includes name of drive)
Network-Capable Operating System
2. Calls for Local Drives (C:) are Handled
by the Client Operating System
PC Hardware
Network Interface Card
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Redirection in a Network-Capable
Operating System
Application Program
Network-Capable Operating System
3. Calls for Virtual Drives (F:) are
Redirected to the File Server
PC Hardware
Network Interface Card
File
Server
via
Network
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Print Service
Client PC
File Server
with Print
Queue
A print queue
is a directory
with
associated
control
software
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Printer
Printout goes from the
print queue to
a print server.
Network
Print
Printout goes from the client PC
Server
to a print queue on the file server, not to the
print server.
Network Printers
Client/Server Processing
Client Program
(Excel)
Server Program
(Oracle)
Request
Response
Application Layer Interactions
Client PC
Network
Concepts: introduction and details
Application Server
(need not be a PC)
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Program 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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Remote Access Server
Remote Client PC
Remote Access Software
Remote Access
Server
Modems
Modem
Telephone
Line
LAN
NT FAQ - RAS
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Remote 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
Access Server
Remote
PC
Example: pcAnywhere
PC Network
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Remote 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
File Server
Remote
PC
Access
Server
outside of the network
PC Network
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Gateway Server
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Gateways translate between networks with
different standards architectures -- in this case,
IPX/SPX and SNA
SNA Communication
Client
PC
IBM
Mainframe
IPX/SPX
Communication
inside the network
Synchronous Communication
Gateway Server
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Internet Access
 Client
PC connects to router
– Connection is via TCP/IP
– Router links user to the Internet
Router
TCP/IP Communication
Connection to
the Internet
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Connecting to the Internet
 Firewall
– Stands between Internet and the company
– Limits unauthorized access
Router
TCP/IP Communication
Connection to
the Internet
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