Networked Applications Chapter 11 Copyright 2001 Prentice Hall Revision 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 BrowserDatabase 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 BrowserDatabase Server URL Form Application Server GET /cgi-bin/bogo.exe?last=Lee&first=Pat

4 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 Webserver Application Software Intermediary Program (Bogo.exe) Database Server Standard Query

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 BrowserDatabase Server Standard Response Application Server (Bogo.exe) Application Server Intermediary Program (Bogo.exe) Webpage

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 browser Application Server Webserver Application Software Intermediary Program (Bogo.exe) Webpage User with Browser Webpage

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 Slow Webserver Application Program Webserver Application Program Intermediary Program (Bogo.exe) Intermediary Program (Bogo.exe) Database Application Program Database Application 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 Webserver Application Program Webserver Application Program Database Application Program Database Application 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 BrowserDatabase Server Webpage with Java 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 market dominated 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 User Site 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 Central Site Central Site Long- Distance Line AAAAAAA B B BB

14 Mainframe Communication Communications Controller Handles multiplexing to reduce transmission cost Handles detailed interactions with cluster controllers, freeing mainframe to deal with database processing Communications Controller

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 LU6 Connection Application Human User

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 Path Control Network Path Control Network

22 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/IP Network TCP/IP Network PC with TN3270E Client TN3270E Server