Networked Applications, Notes from Business Data Communication CSI120, describes applications used for networking ther functions, benefits, and how they work. (download document for ease of reading)

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Application architectures

        How application layer functions are spread among computers to deliver service to users

Thanks layering ability to separate function at different layers most application architecture can run over

TCP/IP, IPX/SPX and other standards below the application layer

Note: if you use TCP it does not care what application architecture you are using.

Important networked applications



world wide web

electronic commerce

Application layer

The only layer whose functionality users see directly


Terminal-host systems, client/server architectures (both file server program access and client/server processing.

Hosts with Dump terminals

        The first step beyond stand-alone machines still place the processing power on a single host computer but distributed input/output (I/O) functions out to user sites.

        It placed these functions in dumb terminals which sent user keystrokes to the host an painted host information on the terminal screen but did little else


        Computer was often overloaded by the need to process both applications and terminal communication

And this resulted in slow response times


        Resulted in high transmission cost. All keystrokes had to be sent to the host computer for processing

Generated a great deal of traffic.

To reduce transmission costs, most terminals limited the information they could display to monochrome text (one color against a contrasting background) graphics were seldom available


                Uses a more complex design for their terminal-host systems that added other pieces of equipment beyond terminals and hosts.

        This extra equipment reduced cost and improved response time. In addition, IBM terminals-host systems had higher speeds that traditional terminals and so were able to offer limited color graphics.

        These advances extended the life of terminal-host systems, even these advanced IBM systems were less satisfactory than subsequent developments, including the client/serve systems described next.

Client/Server Systems

After terminal hosts systems

A big breakthrough came in form of client/server systems

They placed some power on the client computer

This was made possible by the emerge of personal computers in the 1980

File Server Program Access

The server's only role is to store programs and data files.

For processing the program is copied across the network the to the client PC along with data files

The client PC does the actual processing of the program and data files

Many client Pc's are operatively underpowered

Even the faster are usually fairly slow compared to servers

File server program access is only sufficient for word processing, email and other small application

It is not useful for large database applications.

Client/Server processing

        In contrast in full client/server processing the work is done by programs on two machines

        There server does the heavy processing needed to retrieve information.

        The client normally focuses on the user interface and on processing data delivered by the server


        Client/server processing is highly scalable

        Scaling merely involves replacing the existing server with a larger server

        Or the server platform can be changed without the user noticing it.

        An application can start on a small Pc Server and then be moved successively to a large PC server, a workstation server, and even a mainframe.

Web-enabled Applications

Client/server processing requires a client program to be installed on a client PC.

Used to be extremely time-consuming and expensive

There is one client program that almost all PCs have today.

This is a browser

Many client/server processing applications are now web-enabled meaning they use ordinary browsers as a client programs

Electronic Mail/A Universal Service on the Internet

Provides mail even if not online

Offers the speed of a fax

Instant communication is possible but only if the other party is in and can take calls

Less intrusive than a telephonically

E-Mail Standards

        Message body standards

RFC 822 and RFC 2822 for all-text bodies

Html bodies

Unicode for multiple languages s

Simple Mail transfer Protocol (SMTP)

Message delivery

Client to sender's mail host

Message deliver: sender's mail host to receivers mail host

Downloading mail to client

Post Office Protocol (POP) is simple and widely used

Internet Message Access Program (IMAP) is less widely used and very powerful


Rare to use different standards

Key issue application layer standards

Message body standards        ÂÂ

RFC 2822 (originally RFC 822)         Initial standard for e-mail has been updated to 2822

Plain text, no graphics no bold.

HTML bodies

Html became widespread on the WWW

Richly formatted text and graphics

UNICODE         Rfc822

specified the use of the ASCII code to represent printable characters

Was developed for English

Even European languages need extra characters

The UNICODE standard allows characters of all languages to be represented

Note most mail readers cannot read all UNICODE

Simple Mail Transfer protocol (SMTP)

Standards are also needed for delivering RFC2822. HTML and Unicode messages

        Senders outgoing hosts sends the message to the receivers incoming mail host again using SMTP

        The receiving host stores the message in the receiver's mailbox until the receiver retrieves it.

Receiving Mail (POP and IMAP)

Two standards are used to receive e-mail

Post office protocol (POP)

is the simpler standard and is more popular

mail host downloads some or all new mail to the users' client e-mail program

After a user deletes new email, email only exists on the users. Client Pc (after deletion)

Internet Message Access Protocol (IMAP)

Offers more features not as popular than POP

Web-enabled E-mail

Almost all PCs have browsers. Many mail hosts are now web-enabled,

Meaning that users only need browsers to interact with them in order to send receive and manager their e-mail.

Especially good for travelers

No special e-mail software is needed.

Any computer with a browser in an Internet cafe, home, or office will allow users to check mail.


Tends to be very slow all the processing is done on the distant and often overloaded web server wit its server-asked main processing program.


HTTP         Hypertext Transfer Protocol used in interactions between the browser and web server application programs

To give analogy

An e-mail message may be created using RFC 2822 standard but will be delivered using SMTP

Many application standards consist of a document standard and transfer standard.

Complex WebPages

Consist of several files

A master text-only HTmL file plus graphics files, audio and others

The HTML file merely consists of the pages text plus tags to show where the browser should render graphics files and so forth

Several HTTP request-response cycle may be needed to download a single webpage.

HTTP request response cycle example

Clients role

Clients role send HTTP request messages asking for the file and to draw the webpage on-screen

If the webpage has a java applet or another active element

The browser will have to execute it as well

the web servers role

        the basic job is read each HTTP request message

        retrieve though desired file from memory and create an HTTP response message that contains the requested file or a reason why it can not be delivered

HTTP request and Response Messages

        Both request messages and response headers use text formats.

        MIME is a standard for describing diffent types of file formats , so that the receiver will know how to process the file delivered in an HTTP response message (or an e-mail attachment

Electronic Commerce (Ecommerce)        ÂÂ

The buying and selling of goods and services over the internet

Adds extra functionality to a web servers basic file retrieval function

Catalog         Must have electronic catalog showing the goods for sale

Can be created using basic HTML coding

Most merchants purchase e-commerce software to automate the creation of catalog pages an other e-commerce functionalities

Shopping cart, check out and payment functions         Two core e-commerce functions

Shopping cart for holding goods

Check out when buyer has finished shopping

Most merchandiser use e-commerce software

Including cart maintenance and check out capabilities, and payments

Customer Relationship Management (CRM)

Many firms use CRM software

T examines customer data to understand the preferences of their customers.

This allows a company to tailor presentations and specific market offers to its customer specific tastes.

The goal s to increase the rate of conversions

Browsers becoming buyers

And the rate of repeat purchasing

Small increases on both can have big impact on profitability

Links to other systems         External systems

Payments usually requires external links to tow outside organizations

a credit card verification service

checks validity of the credit card number the user has typed

bank settlement firm

handles the credit card payment

Internal Back-end systems        ÂÂ

For accounting, pricing, product availability, shipment, and other matters.

Application servers

Most large e-commerce sites use an application server

That accepts user data from a front=end web server

Some sites combing the web server and application server

Mist large sites separate these to functions on two machines

Retrievals for external systems

the application server         Contacts external systems and internal back-end database

Systems to satisfy the user's request.

It sends requests that these external systems can understand and then it receives responses.

This is complicated each system may have its own way of handling requests and responses.

Connecting to external systems is one of the most difficult tasks into the development of an e-commerce site.

Application Program Interfaces (APIs)         Modern client/server database systems have publish application program interface specifications to allow application server programs to interact directly with database systems.

Mainframe Interactions         Mainframe computers

have their own ways of communicating

With the outside world

Application server programmers must be deeply familiar with CICS and other mainframe processes

Creating a response

To document is findings the application server then crates a new webpage and passes it to the user via the web server.

Three-tier architecture

Terminal host systems perform processing on a single machine.

Most client/server systems do processing on two machines

With an application server processing take s place on a third machine as well.

E-Commerce security

SSL/TSL         Credit card numbers or other sensitive information over the internet is almost always protected by a secure communication system at the transport layer called Secure Sockets Layer (SDSL) security

It shout be called TLS transport Layer security because this is the new name given to it by the IETF with now controls its development

SSL provides merchant authenticating (rarely client authentication ) and encryption for confidentiality

SSL is not perfect but highly effective

Demilitarized Zones (DMZs)

Shows that public e-commerce servers (and other public servers) normally are pLaced "outside the firewall". N demilitarized zone

This means that even if hackers can take over the server they cannot get into the rest of the corporate network which is protected by a strong firewall.

Between the DMZ and the Internet ,

But is weak enough to allow widespread access while stopping simpler attacks

Hardened Servers

Hackers will probably be able to get into the DMZ to attack servers there.

Therefore -commerce servers and other servers must be specially hardened against attacks

Most credit thefts come from hackers taking over e-commerce serer or back-end systems and reading the credit card numbers out of files stored there.



Calls its implementation of web services .NET

Basic web service

Compares traditional web service (based on HTML with a simple web servers

Here the client is a browser


In programming terminology a web service is an object

It communicates with the outside world using a specific interface.

This interface exposes well-defined methods (actions it can take) to the outside world and ahs properties that can be changes

Clients communicate via messages directed to the interface

Simple Object Access Protocol (SOAP)

        Is a standardized way for a Web service to expose its methods on an interface to the outside world.

        SOAP is a message format that allows clients to send commands to Web services calling for methods these Web servers support.

        SOAP request specify a particular method and the specific parameters allowed or dictated for that methods

        SOAP also specifies the formatting of messages that web services use to respond to clients


The first line of each message begins with a header that says "xml version="1.)".

This shows that SOAP messages are expressed in XML (extensible Markup Language) syntax

XML allows communities of users to create their won tags for example Price and price that have semantic meaning to the community

Web services and HTTP

        Overall web services are server programs that communicate with clients using HTTP to deliver SOAP messages written in XML syntax

        instead using HTTP to deliver HTML messages

        HTTP is advantageous because it is simple to support and widely understood.

Web Services and Firewalls

Most firewalls pass HTTP messages on Port 80

Makes web service communication easier

SOAP specifies the addition of a few new HTTP header lines that firewalls can use to control access

Universal Description, Discovery and Integration (UDDI) protocol

In the future

Some web services will be offered on a fee-per-use basis

Many firms are now adopting the Universal Description Discover and Integration protocol to advertise themselves to the world


is a distributed database meaning that there will be many interconnected UDDI servers that cooperate with one another


Will offer tree basic search options

UDDI white pages

Allow users to search the web services by name like telephone books

UDDI yellow pages

Like telephone yellow pages by type

UDDI Green pages

Allow companies to understand how to interact with specific web services

In object-oriented terminology, green pages specify the interfaces on which a Web service will respond, the methods it will accept and the properties that can be changed or returned

Payment methods are also part of UDDI green pages



The newest application architecture

Is peer to peer in which most or all o the network is done by cooperating user computers such as desktop PCs.

If servers are present at all they only serve facilitating roles and do not control the processing

Advantage Central Control

All communication goes through the central server

There can be good security and policy-based control over communication


Traffic Overload at the server         All traffic passes through can cause network overloads at the central location

Underused client PC capacity

Client/server computing often uses expensive server capacity while leaving clients underused.

Clients are usually modern PCs

Central Control         Can be problem form the end users point of view.

Limits what end users can do

Peer-to-Peer Applications

User PCs communicate directly with one another at least for part of their work

All of the work involves P2P interactions.

2 user computers work without the assistance of a central server and also without its control


Client users are freed fro central control for better or worse network traffic is spread more evenly and less user computer capacity is wasted


Transient Presences         Another problem is that each time a user PC uses the Intent its DHCP server is likely to assign it a different IP address

No permanent phone numbers or IP address on the server


Without centralized filtering on servers security will have to be implemented on all user PCs, or chaos will result

Pure peer-to-peer applications: Gnutella

Viral networking for searches


        Gnutella is a pure P2P file-sharing application that addresses the problems of transient presence and transient IP addresses without resorting to the use of any server.

        The user's PC connects to one or a few other user PCs

        Which each connect to several other user PCs and so forth

        When the users PC first connects it sends and initiation message t introduce itself vi viral networking

        Subsequent search queries sent b the user also are passed virally to all computers reachable within a few hops

Direct File downloads

Actual file downloads are done using strictly peer-to-peer communication between the user's PC and the PC holding the file to be downloaded. There is no viral networking in actual file downloads

Super Clients

Gnutella cheats

It relies on the presence of many super clients that are always on

That have fixed IP address that have many files to share and that are each connected to several other super clients

They are not precisely servers

Using Servers to Facilitate P2P interactions

Most p2p do not even try for a pure P2P approach

Rather they use facilitating servers to solve certain problems in P2P interactions but allow clients to engage in P2P communicating for most of the work.


Used an index server

When stations connect to napster they first upload a list of files available for sharing to an index server

Later when they search, their searches go to the index servers and are returned form there

Once a client receives a search response it selects a client who has the desired file and contacts that client directly.

The large file transfer usually on to five megabytes is done entirely peep-to-peer.


In videoconferencing and IP telephony communication is governed by the H.323 standard.

The calling party knows the called party's IP address it can connect to the called party directly.

The communicating typically uses gatekeeper servers

The called party s gatekeeper authenticates the caller and then facilitates the connection to the called party

If there is a gatekeeper in a terminal's zone, the terminal is required to use the gatekeeper to communicate

Another type of server, a gateway connects and IP network to the Public Switched Telephone Network.

If all communication goes through the gatekeeper after the initial connection is made, additional services are possible, such as call waiting etc.

This spectrum of capabilities illustrates the type of flexibility that would be desired able in other P2P programs to allow individual firms to select the degree of client-server versus P2P functionality that would be best for their organization.

Processor Utilization:


PC processors sit idle most of the time

This is even true much of the time when a person is working at their keyboard. This is especially true when the user is a way form the computer doing something else.

One example of employing P2P processing to use this wasted capacity is SETI@HOME

Is the search for Extraterrestrial intelligence projects.

Many volunteers download SETI@HOME screen savers that really are programs .

When the computer is idle the screen saver awakens asks the SETI@home server for work to do and then processes the data.

Processing ends when the user begins to work which automatically turns off the screen saver ,

The future of P2p

it is so new that it is impossible to forecast its future with any certainty when should note that many more p2p applications are likely to appear in the near future offering a much broader spectrum of services than we have seen here


Market realities

There will be one bullion intent users by 2005

Europe and Asia-pacific region will vie to have the largest number of intent users

United states is third place

The United States is expected to account for 36 percent of e-commerce revenues