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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
4
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
5
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
6
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.
7
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
8
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
9
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.
10
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
11
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
12
Server Operating Systems
Novell
13
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
14
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
15
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
16
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
17
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
18
Independent Server Operating
System
Database
Server X
Client A
File
Server Y
Login to Server X
Simultaneous Login to Server Y
File
A
19
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
20
Synchronized Server
Operating System
21
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
22
Communication Between Client
PC and Server
23
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
24
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
25
File Service
File Save and
Retrieve
Commands;
Disk
Management
Commands
File Server
Client PC
Local Drives
A:
B:
C:
26
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
27
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
28
Virtual Drive Access from
Anywhere
29
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
30
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
31
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
32
Program Execution Via File Server
Program Access
File Server
Client PC
Client PC
Hard
Disk
Drive
Client PC
RAM and
Processor
33
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
34
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
35
Print Service
Client PC
File Server
with Print
Queue
A print queue
is a directory
with
associated
control
software
36
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)
37
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
38
Remote Access Server
Remote Client PC
Remote Access Software
Remote Access
Server
Modems
Modem
Telephone
Line
LAN
NT FAQ - RAS
39
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
40
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
41
Gateway Server
42
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
53
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
43
Connecting to the Internet
Firewall
– Stands between Internet and the company
– Limits unauthorized access
Router
TCP/IP Communication
Connection to
the Internet
44