1. An Introduction to Client/Server Architecture
Dr. Farid Farahmand

2. A Brief History: Open Platform
The good old days
Octopus-like mainframes
Only a few venders to choose from
Farms of disks where required
Applications were specific for each machine
Open platform
New client/server architecture
Open system allowed mix-and-match
Different application technologies could be purchased from different venders
Examples: server platform, client platform, network protocols, middleware software, etc.

3. What is Client/Server (C/S) Computing
It started as PCs became more powerful
PCs were no longer dumb terminals
Provided an open and flexible environment
C/S is considered as a form of distributed software

4. Distinct characteristics of C/S
Client-server is a computing architecture which separates a client from a server
It is almost always implemented over a computer network
The most basic type of client-server architecture employs only two types of nodes: clients and servers.
This type of architecture is sometimes referred to as two-tier.
It allows devices to share files and resources.
Server provides the service
Client is considered as the customer requesting the service
The server service can be shared among a number of clients
Clients must request or initiate the service
The location of the server in the network is transparent to clients
Transaction between C/S is message-passing based
C/S architecture is scalable
horizontally (more clients can added)
Vertically (more servers can be added)
The server is centrally maintained where as clients are independent of each other

5. Systems with C/S Architecture
File servers
File sharing and file processing
Data base servers
Passing file results
Example: Query in DBMS server
Typically one single request/reply
Transaction servers
Transaction server includes DBMS and transaction monitoring
Server has remote procedures run online by the client
web servers
Super-fat servers and thin clients
Uses HTTP protocol
Java was first to introduce interactive C/S forms
Client
Server
Internet
Application
Client
HTML
Server
Client
JAVA

6. Client/Server Models Where to push the application to Fat clients
The bulk of the application is running on the client
The client knows how the data is organized and where it is
Different clients access the same applications different ways
Fat servers
The server more complicated
The clients are less complex
More of the code runs on the server
The network interaction is minimized
Application
Client
Server

7. Middleware Software
It is the (/) between client and server which glues them together
Allowing the client request for a service and the server providing it
Middleware can also be between server/server
Two broad classes
General
LAN servers, TCP/IP, Communication stacks, Queuing services, etc.
Application specific
Used to accomplish a specific task
Groupware specific: SMTP
Internet specific: HTTP
Database specific: SQL

8. Two-Tier vs. Three-Tier Architecture
Same basic idea as fat-client versus fat-server
Depends on how the application is divided between the server and the client
Two-tier servers
Examples: file servers and database server
In this case the process (application logic) is buried within the client or server (or both)
Three-tier servers
Examples: Web and distributed objects
In this case the process is run on the middle-tier – separated from the user and data interface
They can integrate the data from multiple sources
More robust and more scalable

9. Client/Server Building Blocks
Middle
ware
Purpose
How to divide the application between the client and server
What are different functionalities of client and server
Basic client server model
Fits various applications
Small office
Small business
Enterprise
Global
Single Machine
Middle
ware
Client
Server
Middle
ware
Client
Server
Server
Client
Middle
ware
C/S
C/S
C/S
C/S

10. Servers and Client Building Blocks
Middleware
Web Browser
GUI
DSM OS
Web server
Groupware
DMBS
Etc.
Service-Specific; DSM
NOS (securit, peer-to-peer,
directory, distributed files);
Transport stack (TCP/IP)
NOS=Network operating system

11. Server Scalability PC Server  Asymmetric Multi- processing 
Superserver
symmetric Multi-
Multiservers

12. Server Scalability Superserver Multiprocessing Multiservers
A very powerful server
Single-server or multiserver
Each server can have a single processor or multiprocessor
Multiprocessing can be Asymmetric or Symmetric
Multiprocessing
Asymmetric: each processor is dedicated to a specific task
Fully symmetric (SMP): applications are divided into threads and threads are sent to available processors
Examples: 32-bit NT, Unix, NetWare
Requires 3 basic functionalities:
Global scheduling
I/O sharing structure
OS access sharing
Multiservers
Pool of servers, providing more processing power (also called a cluster)
They divide the task between different servers
Server lite
As opposed to full blown servers
Provides a background process on the client machine that can accept unsolicited networks request (refreshing database, synchronizing time, etc.)

13. OS Wars General trends Operating system applications OS players
More powerful PCs (fat PCs, Network PCs, Multimedia PCs)
Operating system applications
Embedded devices (cell phones)
Clients
Super clients
Servers
SMP servers
Clusters
OS players
DOS and Windows 3.x/95
JAVA OS
OS/2 Wrap
NT/XP/2000/2003/VISTA
NetWare (Novell’s, poor application server, fast file server)
Unix
Linux
Specialized parallel OS for clusters

14. Client/Server Networking Model
Networking in Linux follows the client/server model
Server provides the resource (web server)
Client talks to the server (browser, program)
Server has a corresponding program that communicates with the client (runs in the background)
In Windows the server program called service
In Linux the server program called daemon in Linux

15. UNIX/Linux UNIX was introduced in 1969 Linux is from the early 1990s
Based on MINIX
Three basic components
Kernel – central portion of OS
File system – provides input and output mechanisms
Shell – provides user interface

16. Linux Introduction Source code is freely available
Developers can make changes
Available from a number of organizations (called disro)
Red Hat
Mandrake
SuSe

17. Linux Resource List of Linux compatible hardware:
List of hardware issues and forums for Linux
Third-party utilities allowing Windows to read the drives of a Linux installation on the same machine

18. Fedora Linux Two ways to obtain Obtain a copy
Installation CD
Download and burn your own CD – Read to see how to burn a DVD
Obtain a copy
Fedora core 6, i386 Intel x86 processor compatible, first CD – ISO image
FC-6-i386-disc1.iso
When you have dowloaded the ISO images, you need to burn them on CD/DVD
Popular Windows CD burning tools:
You can also use CD BurnerXP Pro

19. Summary
Got it?

20. Homework 1 – Linux Monday
Visit Fedora Core Web cite. What is the latest version of Fedora?
Burn a copy of Fedora Core 4 on CDs or DVD. You must have this in order to install Linux on your machine – You are not allowed to do the lab without your own CD.
Search for Linux Commands and obtain a one or two-page long list of some of Linux commands used with Fedora Core 4 version
In your own words, list 5-10 differences between Fedora Core 4 and Fedora Core 7 version. You must tabulate your answer.
Do a little research and briefly explain the sequence involved in installing Windows and Linux. What will you do if Windows is already installed?
NOTE: Submit a hardcopy only.

21. references
on ISDN
Learn about 2-Tier and 3-Tier systems: