panko_bdnt7e_ch11

7/27/2019 panko_bdnt7e_ch11

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2009 Pearson Education, Inc. Publishing as Prentice Hall

NetworkedApplications

Chapter 11Updated January 2009

Raymond PankosBusiness Data Networks and Telecommunications, 7th edition

May only be used by adopters of the book


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ApplicationArchitectures

An application architecture describes howapplication layer functions are distributed

among computers to deliver service to users.


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2009 Pearson Education, Inc. Publishing as Prentice Hall 11-3

11-1: Simple TerminalHost System


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Client/Server Computing

The client does at least some of the work

Made possible by growing PC processing power

ServerClient PC

Client ProgramServer Program


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11-2: Client/Server Computing

File Server

Client PC

Highly scalable: Use larger server as number of clients increases

Client/Server Processing with Request-Response Cycle

Client Program Server Program

Request Message

Response Message

Does Light I/O andPost-DownloadProcessing

Does HeavyDatabase

and Other HeavyProcessing

3


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11-3: Web-Enabled Application (E-Mail)

E-Mail Server

Client PC

Client is Browser Server Program

HTTP Request Message

HTTP Response Message

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.


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E-Mail


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Each e-mail user has a mail server.

The sender transmits a message to its mail server.

The senders mail server delivers the messageto the receivers mail server.

The receivers mail server delivers the messageto the receiver.

The E-Mail Delivery Process

SendingE-MailClient

ReceivingE-MailClient

Senders MailServer

Receivers MailServer


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11-5: E-Mail Standards: Sending

2.SMTP

To Send1.SMTP

To Send

SendingE-Mail Client

(Outlook, etc.)

ReceivingE-Mail Client

(Outlook, etc.)

Senders MailServer


Simple Mail Transfer Protocol

(SMTP) is used to transmit mailin real time to a users mail

server or between mail servers

Sender-initiated


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11-5: E-Mail Standards: Receiving

Senders MailServer


3.POP orIMAP

to Receive

POP or IMAP to download mail to

receiver when the receiver next

downloads mail

Receiver-initiated

Sending

E-Mail Client(Outlook, etc.)

Receiving

E-Mail Client(Outlook, etc.)


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Figure 11-5: E-Mail Standards

SendingE-MailClient

ReceivingE-MailClient

Senders MailServer


MessageRFC 822 or 2822HTML bodyUNICODE

Message Body Format Standard

Most applications have standards for delivery and also document syntax.

For e-mail, the document (message) syntax usually is one of three standards


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On the left, we have just seen thattraditional e-mail clients send withSMTP and receive with POP or IMAP.

On the right, Web-based e-mail clientsonly need a browser and use HTTPboth to send and to receive.

Server-server communication alwaysuses SMTP.

11-5: E-Mail Standards: Web-Based E-Mail

TraditionalE-Mail Client

(Outlook, etc.)

Web-BasedE-Mail

ClientBrowser

SMTP

POP or

IMAP

HTTP

SMTP


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Figure 11-5: E-Mail Standards

Message Body Standards RFC 822 and RFC 2822 for all-text bodies

HTML bodies

All of the richness of a webpage UNICODE

Can represents the characters in multiple languages

Chinese, Japanese, Sanskrit, German, Arabic, etc.


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11-6: Interactions in the Simple Mail Transfer

Protocol (SMTP)

Actor Command Comment

ReceivingSMTPProcess

220 Mail.Panko.ComReady

When a TCP connection isopened, the receiver signals thatit is ready.

SendingSMTPProcess

HELOvoyager.cba.hawaii.edu

Sender asks to begin sending amessage. Gives own identity.(Yes, HELO, not HELLO.)

Receiver 250 Mail.Panko.Com Receiver signals that it is readyto begin receiving a message.

Opening a connection


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Protocol (SMTP)


Sender MAIL FROM: [email protected]

Sender identifies the sender (mailauthor, not SMTP process).

Receiver 250 OK Accepts author. However, mayreject mail from others.

Sender RCPT TO:

[email protected]

Identifies first mail recipient.

Receiver 250 OK Accepts first recipient.Sender RCPT TO:

[email protected] second mail recipient.

Receiver 550 No such user here Does not accept second recipient.

However, will deliver to firstrecipient.

Identifying recipients


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Protocol (SMTP)


Sender DATA Message will follow.Receiver 354 Start mail input; end with

.Gives permission to sendmessage.

Sender When in the course The message. Multiplelines of text. Ends with line

containing only a singleperiod: .

Receiver 250 OK Receiver accepts message.Sender QUIT Requests termination of

session.

Receiver 221 Mail.Panko.Com Serviceclosing transmission channel

End of transaction.

Sending the message.Ending the connection.


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11-4: E-Mail

Viruses, Worms, and Trojan Horses Widespread problems; often delivered through e-mail

attachments

Use of antivirus software is almost universal, but it isnever fully ineffective


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11-4: E-Mail

Viruses, Worms, and Trojan Horses Where to do scanning for viruses, worms, and Trojan

horses?

On the client PC, but users often turn off or fail toupdate their software

On the corporate mail server and application firewall;users cannot turn off

At an antivirus outsourcing company before mailreaches the corporation

Defense in depth: Filter at two or more locations withdifferent filtering software


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11-4: E-Mail

Spam Separating spam from legitimate messages is very

difficult

Many spam messages get through to users

Some legitimate messages are deleted

Some firms merely mark messages as probable spamand then deliver them to the user

Others periodically send a list of deleted spammessages that users can recover if they wish


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11-4: E-Mail

Spam Reputation-Based Filtering

Some domains are white-listed, and messages fromthem either bypass spam filtering or get limitedfiltering

Some domains are black-listed, and messages fromthem are either deleted automatically or filteredheavily

New:Not in the book.


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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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11-8: Downloading a Complex Webpage with Two

Graphics Files

Client PC

BrowserWebserver

Application

Webserver

Webpage Consists of Three Files

Rendered as a Single Page On-ScreenWebpage as

Displayed

TwoGraphics

Files

HTML

Document

C


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Graphics Files

1.HTML Document

Client PC

Browser Webserver

Application

Webserver

Download Requires 3

HTTP Request-Response Cycles;

Downloads HTML Page First

HTML Page Has Tags to Identify Other Files

AsDisplayed

2Graphics

Files

HTML Document

11 8 D l di C l W b ith T


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Graphics Files

Client PC

Browser WebserverApplication

Webserver

Based on Tags in HTML Document,Browser Requests Downloads of

Remaining Graphics or Other Files

Browser Renders Combined Webpage on Screen

AsDisplayed

2Graphics

Files

2.

3.

11 8 D l di C l W b


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11-8: Downloading a Complex Webpage

with Two Graphics Files

Quiz: Your browser downloads a webpage with threegraphics images, a sound sequence, and a Java applet.

How many files will your browser have to download?

11 9: Examples of HTTP Request and


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11-9: Examples of HTTP Request and

Response Messages

HTTP Request Message GET /panko/home.htm HTTP/1.1[CRLF]

Host: voyager.cba.hawaii.edu

Notes Two lines, all text

GET = method

/panko/home is the file to get

HTTP/1.1 is the version of HTTP the sender speaks CRLF (carriage return/line feed) starts a new line

Next Line: keyword, colon, value



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Response Messages

HTTP Response Message HTTP/1.1 200 OK[CRLF]

Date: Tuesday, 20-MAR-2009 18:32:15 GMT[CRLF]

Server: name of server software[CRLF] MIME-version: 1.0[CRLF]

Content-type: text/plain[CRLF]

[CRLF]

File to be downloaded. A string of bits that may be text,graphics, sound, video, or other content.



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Response Messages (Cont.)

MIME Multipurpose Internet Mail Extensions

Naming system for type of file contained in the responsemessage

Allows the receiver to know what type of file it will bereceiving so that the receiver can handle the file properly

Must specify MIME version and type of content

MIME-version: 1.0[CRLF]

Content-type: text/plain[CRLF]


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E-Commerce


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11-10: Electronic Commerce Functions

CustomerPC

Browser Webserver

Application

E-Commerce

Server

ExternalDatabase

InternalDatabase


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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

Bank settlement


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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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11-11: Application Server (3-Tier Architecture)

Client PCwithBrowser 1.

Form

Web-server Application

Server

Mainframe

DatabaseServer

Server ofExternal Company

2.Data

1.User fills in a formusing a browser

2.Webserver sendsform data onto anapplication server


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Client PCwith

Browser


Server

3.MainframeQuery andResponse

Mainframe

DatabaseServer


3.To get data needed to serve

the customer,the application server

queries a mainframe databaseand reads the information

in the response


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Client PCwithBrowser


Server

Mainframe

4.

DB ServerQuery andResponse

DatabaseServer


5. External Query/Response

Database Sever Interactions (4, 5)Application program interfaces (API)

Both internal and external database hosts


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Client PCwith

Browser 7.Webpage


Server

Mainframe

DatabaseServer


6.New

Webpage

6.From the

retrieved data, theApplication Server

creates a new webpage

7.Webserver sendsthe webpage to

the browser


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Web Services


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11-12: Web Service Versus Web Services

HTTP Response

HTTP Request

HTML or Other DocumentClient PC

Webserver

Browser WebserverApplication

Ordinary Webservice

Ordinary webservice was created to download documents


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HTTP Response

HTTP Request

Client PCWebserver

SOAP-CapableBrowser

ServiceObject

SOAP MessageUsing XML Syntax

Web services, in contrast to webservice,provide program-to-program communication.

Programs on the webserver are called service objects.

Messages follow the SOAP format.


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Result of Calculation

Parameters

Client PCWebserver

SOAP-CapableBrowser

ServiceObject

SOAP MessageUsing XML Syntax

The sending program sends parameters for the calculation.The service object does the calculations and sends back results.

11-12: Web Service Versus Web


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11 12: Web Service Versus Web

Services

Question: Distinguish between what the serverdoes when a webservice request arrives and whena Web service request arrives.

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11-13: Simple SOAP Request and


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11-13: Simple SOAP Request andResponse

Simple Object Access Protocol (SOAP) Message

Carried in HTTP request or response message

Formatted using XML Syntax

Similar to HTML syntax but

the sender and receiver can

create new tags that

they can then use intransactions, such as

$33

HTTP Header

SOAPBody

XMLFormatting



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11 13: Simple SOAP Request andResponse

Situation There is a pricing object that returns the price if another

object sends the part number, quantity, and shippingtype (rush, etc.) on an interface

Objects can be on different computers

SendingObject

PricingObject

Request(PartNum, Quantity, ShippingType)

Response(Price)

11 13 Simplified SOAP Req est and


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11-13: Simplified SOAP Request and

Response

SOAP Request Message

HTTP Request Header pointing to program

QA78d47Rush

Note: xmlns specifies an XML namespace for the object

Asks for price,

given part number, quantity,and shipping type



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11 13: Simple SOAP Request and

Response

SOAP Response Message

HTTP Response Header

$750.33

Response givesthe price quote

11 14 WSDL d UDDI


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11-14: WSDL and UDDI


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Peer-to-PeerComputing


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2009 Pearson Education, Inc. Publishing as Prentice Hall11-51

11-15: Traditional Client/Server Application

Client PC Client PC Client PC Client PCClient PC

Server Does Heavy Processing Work

Disadvantages:Network Overload at Server

Underused Client PowerCentral Control

Advantage:Central Control

P2P Applications


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P2P Applications

Direct service, although most P2P systems usefacilitating servers for some of the work

Peer Peer

Peer

PeerPeer

Peer

Figure 11-16: Simple Peer-to-Peer (P2P)


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Figure 11-16: Simple Peer-to-Peer (P2P)

Application

Client PC Client PC

Request

Response

Benefits:End User Freedom

No Network Bottleneck at ServerUses Client Capacity Better

Problems:Transient Presence of ClientsTransient Client IP AddressesSecurity (No Central Control)

Figure 11-17: Gnutella: Pure P2P Protocol


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Figure 11 17: Gnutella: Pure P2P Protocol

with Viral Networking

GnutellaClient

(Carol)Gnutella

Client (XYZ)Gnutella

Client (GHI)

GnutellaClient (ABC)

Gnutella

Client (DEF)

1. Init orSearch

Message

2.Init or Search

Message

3.Init or Search

Message

3. Init or

SearchMessage

4.

P2P File DownloadHTTP Request-ResponseCycle

2. Init orSearch

Message 3. Init orSearch

Message

3


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Figure 11-18: Napster

NapsterIndex Server

2.Search Query

3.Response

1.Uploads List

Of Available FilesWhen Connects

4.Large P2P

Download

File List

List ofAvailable

Files

From AllCurrent Clients

User A User B User C

2

11 19: Use of Servers in Instant Messaging


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11-19: Use of Servers in Instant Messaging

Client PC A Client PC B

Pure P2P IM

Ongoing IM

Communication

In pure P2P IM, there are no servers.The clients communicate directly.

Finding each other can be difficult because DHCP maygive each client PC a different IP address

each time the client uses the Internet.

Setup



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Client PC C Client PC D

Use of a Presence Server

3.Ongoing IM

Communication

1.Presence

Information

2.Presence

Information

Clients register with presence servers.Presence servers notify other clients as appropriate.Clients use this information to communicate directly.

Ongoing communication dominates.Most communication is peer-to-peer.

Presence Server



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Client PC E Client PC F

Use of a Relay Server

All Communication

Goes through theRelay Server

IMCommunication

Relay servers route all IM messages.This permits security filtering and other services.

It limits privacy because the relay server sees everything.

Relay Server

IMCommunication

11 20: SETI@home Client PC Processor Sharing


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11-20: SETI@home Client PC Processor Sharing

Perspective on Application


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Perspective on ApplicationArchitectures

Driven primarily by the evolution of clientprocessing power

Terminal-Host: Client processing power was

uneconomical

Client/Server: Client PCs could handle some ofthe load

P2P: Clients have rich power to do most things


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Cloud Computing

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Cloud Computing New:


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Cloud Computing

A Term that Emerged Just as the Book was Goingto Press

Characteristics

All services are provided by servers owned by service

providers

Software is executed on servers or downloaded to theclient

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Cloud Computing


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Cloud Computing

Advantages

The user organization is freed from maintaining theservers and applications that run on them

Browser-based, so no need to install or configure

applications on client PCs

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Cloud Computing


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Cloud Computing

Pricing Subscription-based pricing (fixed cost per month or year)

Up to a maximum amount of use

This gives predictability spending for customers

Pay per minute (hour, day, etc.)

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Cloud Computing


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Cloud Computing

Other Characteristics Use of Web services interaction standards to simplify

use

If large increases are needed for a short time, the serviceprovider can provide it

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Cloud Computing


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Cloud Computing

Concerns

What happens when the network is unavailable?

Quality of service concerns: response time, etc.

Comprehensibility of pricing schemes

Security of corporate information stored in the cloud

Vendor bankruptcies

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Topics Covered

Topics Covered


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Topics Covered

Application Architectures Terminal-host

Client/server

Client/server processing with request/response cycle Web-based client/server processing only needs a

browser

Peer-to-peer (P2P)

Evolution of architectures driven by growing desktopcomputer power

Topics Covered


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Topics Covered

E-Mail Sending: Simple Mail Transfer Protocol (SNMP)

Retrieving: POP and IMAP

Document format standards: RFC 822/2822, HTML, andUNICODE

Viruses, worms, and Trojan horses

Where to do antivirus filtering?

Spam

Topics Covered


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Topics Covered

HTTP and HTML Webpages consist of an HTML document and multiple

graphics, etc., files

Message transfer: HTTP

Multiple downloads for the multiple files in a webpage

MIME

Topics Covered


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Topics Covered

E-Commerce E-Commerce : webservice with additional functionality

Webserver interacts with customer browser

Application server interacts with back-end databases,passes webified response to the webserver for deliveryto the customer

Topics Covered


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Topics Covered

Web Services Regular webservice: retrieve stored files

Web Services: use HTTP and extended HTML tohandle program-to-program interactions on different

machines

SOAP request message passes parameters to aservice object on another machine

SOAP response message brings the reply SOAP messages are written in XML

WSDL and UDDI for documenting actions

Peer-to-Peer (P2P) Applications


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Peer to Peer (P2P) Applications

Clients provide services to other clients Facilitating servers may provide some functionality

However, MOST work is done by the peer PCs

File sharing

Instant messaging

Processor sharing


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All rights reserved. No part of this publication may be reproduced, stored in aretrieval system, or transmitted, in any form or by any means, electronic,

mechanical, photocopying, recording, or otherwise, without the prior writtenpermission of the publisher. Printed in the United States of America.

Copyright 2009 Pearson Education, Inc.Publishing as Prentice Hall

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