Transcript Basic Concepts

Networked
Applications
Chapter 11
Updated January 2009
Raymond Panko’s
Business Data Networks and Telecommunications, 7th edition
May only be used by adopters of the book
© 2009 Pearson Education, Inc. Publishing as Prentice Hall
Client/Server Computing
• The client does at least some of the work
Server Program
Client Program
Server
Client PC
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11-2
11-2: Client/Server Computing
3
Client/Server Processing with Request-Response Cycle
Request Message
Client Program
Response Message
Does Light I/O and
Post-Download
Processing
Client PC
Server Program
Does Heavy
Database
and Other Heavy
Processing
File Server
Use larger server as number of clients increases
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11-3
11-3: Web-Enabled Application
HTTP Request Message
Client is Browser
Client PC
HTTP Response Message
Server Program
Web-enabled applications:
Form of client server processing
that uses browsers as clients.
Almost all client PCs
now have browsers.
No need to install new software.
E-Mail Server
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11-4
E-Mail
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The E-Mail Delivery Process
Sender’s Mail
Server
Receiver’s Mail
Server
Each e-mail user has a mail server.
Sending
E-Mail
Client
The sender transmits a message to its mail server. Receiving
The sender’s mail server delivers the message
E-Mail
to the receiver’s mail server.
Client
The receiver’s mail server delivers the message
to the receiver.
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11-6
11-5: E-Mail Standards: Sending
2.
SMTP
To Send
1.
SMTP
To Send
Sender’s Mail
Server
Sending
E-Mail Client
(Outlook, etc.)
Receiver’s Mail
Server
Simple Mail Transfer Protocol
(SMTP) is used to transmit mail
in real time to a user’s mail
server or between mail servers
Receiving
E-Mail Client
(Outlook, etc.)
Sender-initiated
Note that SMTP provides immediate delivery—usually in a few seconds.
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11-5: E-Mail Standards: Receiving
3.
POP or
IMAP
to Receive
Sender’s Mail
Server
Sending
E-Mail Client
(Outlook, etc.)
Receiver’s Mail
Server
POP or IMAP to download mail to
receiver when the receiver next
downloads mail
Receiving
E-Mail Client
(Outlook, etc.)
Receiver-initiated
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11-5: E-Mail Standards: Web-Based E-Mail
SMTP
HTTP
SMTP
POP or
IMAP
Traditional
E-Mail Client
(Outlook, etc.)
On the left, we have just seen that
traditional e-mail clients send with
SMTP and receive with POP or IMAP.
On the right, Web-based e-mail clients
only need a browser and use HTTP
both to send and to receive.
Web-Based
E-Mail
Client
Browser
Server-server communication always
uses SMTP.
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11-9
HTML and HTTP
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11-7: HTML and HTTP
The Hypertext Transfer Protocol (HTTP)
is the standard for transferring messages between
the client (browser) and the server (webserver).
The Hypertext Markup Language (HTML)
is a standard for text documents that have tags to indicate
formatting and other files to be downloaded
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11-11
E-Commerce
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11-10: Electronic Commerce Functions
Browser
Webserver
Application
E-Commerce
Server
Customer
PC
External
Database
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Internal
Database
11-13
11-10: EC Functions
• Webserver Functionality, Plus…
• E-Commerce functionality
– Online catalog
– Shopping cart
– Checkout, including payment
– Customer resource management (CRM)
– Links to External Systems
• Credit card number checking
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11-10: EC Functions
• E-Commerce functionality
– Links to internal systems
• Accounting
• Pricing
• Warehousing (product availability)
• Shipment
• Etc.
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11-15
Three-Tier Architecture
presentation tier
web
browser
logic tier
web
server
and
programs
• Three-tier model is a software architecture
•Data transfer between tiers is part of the architecture
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data tier
database/
file system
Three-Tier Architecture
Presentation
Business Logic
Web browser
Payment
User/Admin
Content
Modules
Data
Database
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11-11: Application Server (3-Tier Architecture)
Client PC
with
Browser
1.
Form
Webserver
Application
2.
Server
Data
Mainframe
1.
User fills in a form
using a browser
2.
Webserver sends
form data onto an
application server
Server of
External Company
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Database
Server
11-18
11-11: Application Server (3-Tier Architecture)
Client PC
with
Browser
Webserver
3.
Mainframe
Query and
Application
Response
Server
Mainframe
3.
To get data needed to serve
the customer,
the application server
queries a mainframe database
and reads the information
in the response
Database
Server
Server of
External Company
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11-19
11-11: Application Server (3-Tier Architecture)
Client PC
with
Browser
Webserver
Application
Server
4.
DB Server Mainframe
Query and
Response
5. External Query/
Response
Database Sever Interactions (4, 5)
Application program interfaces (API)
Both internal and external database hosts
Database
Server
Server of
External Company
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11-20
11-11: Application Server (3-Tier Architecture)
Client PC
with
Browser
7.
Webpage
Webserver
Application
Server
6.
New
Webpage
6.
From the
retrieved data, the
Application Server
creates a new webpage
7.
Webserver sends
Mainframe
the webpage
to
the browser
Server of
External Company
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Database
Server
11-21
Peer-to-Peer
Computing
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11-15: Traditional Client/Server Application
Client PC
Client PC
Advantage:
Central Control
Client PC
Client PC
Client PC
Disadvantages:
Network Overload at Server
Underused Client Power
Central Control
Server Does Heavy Processing Work
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P2P Applications
• Direct service, although most P2P systems use
facilitating servers for some of the work
Peer
Peer
Peer
Peer
Peer
Peer
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Figure 11-16: Simple Peer-to-Peer (P2P)
Application
Request
Client PC
Response
Benefits:
End User Freedom
No Network Bottleneck at Server
Uses Client Capacity Better
Client PC
Problems:
Transient Presence of Clients
Transient Client IP Addresses
Security (No Central Control)
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