Networked Applications

Chapter 11

Copyright 2001 Prentice HallRevision 2: July 2001

2

Web-Enabled Database Access

Problem: Database is on a “database server” Mainframe or client/server server need proprietary client software or a

terminal Problem: Most users only have

browsers Solution: an application server

User with Browser Database Server

3

Web-Enabled Database Access Step 1: User types URL of data entry

form Step 2: Webserver application sends

form

Step 3: User completes form, hits Send Browser puts data in a request line

User with Browser Database Server

URL

Form

Application Server

GET /cgi-bin/bogo.exe?last=Lee&first=Pat

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Web-Enabled Database Access

Step 3: Application server webserver software passes data form to intermediary program, Bogo.exe, on the webserver

Step 4: Bogo.exe puts the data into a query in the database server’s standard format

Application Server

WebserverApplicationSoftware

IntermediaryProgram

(Bogo.exe)

Database Server

StandardQuery

5

Web-Enabled Database Access Step 5: Database server sends standard format

response to intermediary program, Bogo.exe

Step 6: Application server intermediary software creates new HTML webpage containing response

User with Browser Database Server

StandardResponse

Application Server

(Bogo.exe)

Application Server

IntermediaryProgram

(Bogo.exe)

WebpageWebpage

6

Web-Enabled Database Access

Step 7: Application server intermediary software passes webpage to webserver application program

Step 8: Webserver application program passes webpage

to browserApplication Server

WebserverApplicationSoftware

IntermediaryProgram

(Bogo.exe)

WebpageWebpage

User with Browser

WebpageWebpage

7

Web-Enabled Database Access

Intermediary Program

Bogo.exe does actual translation work

CGI (Common Gateway Interface) standard Highly standardized communication between

Webserver & Intermediary Program SlowWebserverApplication

Program

WebserverApplication

Program

IntermediaryProgram

(Bogo.exe)

IntermediaryProgram

(Bogo.exe)

DatabaseApplication

Program

DatabaseApplication

Program

CGI

8

Web-Enabled Database Access

Application Program Interfaces (APIs) Database servers have proprietary

Application Program Interfaces (APIs) for communication with other application programs

Proprietary (not standardized) Faster than CGI

WebserverApplication

Program

WebserverApplication

Program

DatabaseApplication

Program

DatabaseApplication

Program

API

9

Web-Enabled Database Access Client-Side Processing

Webserver can download webpage with Java or Active-X program

Client can then communicate directly with the database server

User with Browser Database Server

Webpage withJava applet

Subsequent Interactions

10

Mainframes

Contain about 70% of corporate data from operations (accounting, payroll, billing, etc.)

Often the “database server” in web-enabled database applications

Mainframe marketdominated by IBM

11

Terminal-Host Communication Traditionally:Terminal, Host, & Line

Poor response time Poor user interface: sending graphics over a

distance is expensive (and lines usually are slow)

Inadequate for production workers who use their terminals hours per day

12

Mainframe Communication

User site has multiple terminal users Called “3270” Terminals Generically

High speeds, some color, some graphics

UserSite

3270 Terminal

13

Mainframe Communication Cluster Controller at User Site

Multiplexes terminals and printers traffic reduces transmission costs

expensive for higher-speed long-distance links

Provides limited on-screen text editing to terminals

This elimination of text editing work allows the mainframe to focus on high-value database chores

CentralSite

CentralSite

Long-Distance

Line

A A A A AA A

BB

B B

14

Mainframe Communication Communications Controller

Handles multiplexing to reduce transmission cost

Handles detailed interactions with cluster controllers, freeing mainframe to deal with database processing

CommunicationsController

15

Mainframe Communication

Reducing Response Time Text editing work is done locally Still delay for heavy database work on

mainframe

Reducing Transmission Costs Multiplexing, and

Cluster controller provides limited local screen editing, so fewer bits need to be transmitted to and from the mainframe

16

Mainframe Communication

Reducing Work the Mainframe Needed, so Focus is High-Value Database Processing Cluster controller handles most text-

editing chores freeing mainframe from having to support this work, and

Communications controller handles details of communication with cluster controllers, freeing mainframe from having to support this work

17

Mainframes Use SNA Standards Architecture

Not peer-to-peer control; Master-slave control under System Services Control Point program on a mainframe

SSCP program governs all sessions among devices

SSCP

18

Mainframes SNA Standards Architecture

Uses OSI standards at physical & data link layers

Path Control layer is like TCP/IP internet layer

Transmission Control layer is like transport layer

Data Flow Control layer is like session layer

Network Addressable Unit (NAU) Services layer is like presentation layer

There is no SNA application layer

19

Mainframes

SNA NAUs Communication takes place between

network addressable units (NAUs) Unit is a general name for a

communicating entity In networks, communicating entities must

have addresses; So they are network addressable units

20

Mainframes Logical Units

Deal directly with end users Terminals are logical units!

Connection points on mainframe (not mainframe itself) deal with application programs,which are considered to be end users

LU6Connection

Application

HumanUser

21

Mainframes

Physical Units Do not deal directly with end users

Mainframe, communications controller, cluster controller

Path control network connects cluster controller and communication controller

PathControlNetwork

PathControlNetwork

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Mainframes SSCP

Third type of NAU Program located on the mainframe In classic SNA, two other NAUs can only be

connected under the control of the SSCP

Advanced Peer-to-Peer Networking (APPN) Communication without SSCP permission

High-Performance Routing Classic SNA and APPN are difficult to route HPR improves routing, IBM focuses on

connection

23

Mainframes

SNA and Router Networks To link cluster controllers to

communications controller over routed networks (mainframe too)

Data Link Switching (DLSw) standard supports SNA transmission through routers

High-Performance Routing (HPR) is better

24

Mainframes Mainframes and TCP/IP Networks

TN3270E TN3270E servers communicate with

mainframe Users have PCs with TN3270E client

software that emulates 3270 terminals

TCP/IPNetwork

TCP/IPNetwork

PC withTN3270E

Client

TN3270E Server