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Introduction to CICS Transaction Server

Introduction to CICS Transaction Server. for OS/390 – Unit 4. Unit 4: CICS intercommunication. Topics: 4A. Intercommunication facilities 4B. Interregion and intersystem communication 4C. CICS and the Internet. Unit 4 overview.

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Introduction to CICS Transaction Server

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  1. Introduction to CICS Transaction Server for OS/390 – Unit 4

  2. Unit 4: CICS intercommunication Topics: • 4A. Intercommunication facilities • 4B. Interregion and intersystem communication • 4C. CICS and the Internet

  3. Unit 4 overview Many organizations have resources such as terminals, application programs, and data spread out over one or more systems or CICSPlex setups. CICS TS for OS/390 supplies several facilities to allow you to access CICS resources across a CICSPlex, over an intranet, or over the Internet. This unit describes these facilities and the advantages that they offer. It also introduces several products that provide a range of options in configuring a CICS setup for Web browser access.

  4. Unit 4 objectives This is what you should be able to do upon completing this unit: • Describe the intercommunication facilities that allow the sharing of CICS resources across regions and systems • List the advantages of distributing transactions and programs across regions and systems • Identify the applications of multiregion operation in CICS TS for OS/390 • Describe the possible system configurations for setting up intersystem communication • List and describe the facilities available in CICS TS for OS/390 for making CICS available over the Internet or an intranet

  5. 4A. Intercommunication facilities In previous units, you learned that every CICS setup controls its own resources, such as files, terminals and local application programs. However, through CICS intercommunication facilities, a CICS system can establish links to other systems and gain access to remote resources. Such intercommunication permits the sharing of resources and transferring of data across several systems. CICS employs these methods for communicating between systems: • Function shipping • Asynchronous processing • Transaction routing • Distributed program link (DPL) • Distributed transaction programming

  6. 4A. Function shipping Function shipping allows multiple systems to share resources such as files, temporary storage or application programs. When function shipping is used, a program is invoked in a local CICS system and accesses resources owned by a remote system. The program operates as though the resources are resident on the local system. Access gained through function shipping allows both reading from and writing to the resource, as well as restarting and recovery operations.

  7. 4A. Function shipping In developing applications, CICS systems programmers can specify that a required resource is not located on the local or requesting system, but on a remote or owning system.

  8. 4A. Function shipping When a file-control command is issued for a resource, first the EXEC interface program determines where the resource is located.

  9. 4A. Function shipping If the resource is on another system, the request is passed to the owning system. The owning system runs the request in a mirror transaction, a local re- creation of the original request. Application programs can use EXEC CICS commands to perform These function shipping operations: • Shipping file control requests to another CICS system • Shipping transient data and temporary storage requests to another CICS system for data transfer • Initiating transactions in another CICS or IMS system by shipping START commands (called asynchronous processing)

  10. 4A. Function shipping Once the request is completed, a reply is sent back to the originating CICS system.

  11. 4A. Function shipping Some transactions that involve function shipping: • EXEC CICS READ FILE (‘RFILE’) – A simple read request is passed from one CICS system to another and returned. • EXEC CICS READ UPDATE FILE – A request to read file updates is passed from one CICS system to another and returned. • EXEC CICS REWRITE FILE – A request to rewrite a remote file is passed from one CICS system to another.

  12. 4A. Function shipping Asynchronous processing is a type of function shipping where a transaction is initiated in a remote CICS system by shipping an EXEC CICS START request to a remote system. The processing is asynchronous because the performance of the request on the remote system proceeds independently of any implementation on the initiating system. To return a reply when the transaction is completed, the remote system can initiate a transaction in the local system.

  13. 4A. Transaction routing Another type of intercommunication in CICS is transaction routing, which allows terminals connected to one CICS system to run transactions within a remote CICS system. This means that you can distribute terminals and transactions throughout a network of systems and still have the ability to run any transaction from any terminal.

  14. 4A. Distributed program link Distributed program link (DPL) enables a CICS program to call a program on a remote system or CICS region. The DPL exploits the LINK command by allowing the linking and linked-to application to reside in different systems or regions. This potentially reduces the number of data transfers between systems, thus improving performance.

  15. 4A. Distributed program link

  16. 4A. Distributed transaction processing Distribution transaction processing (DTP) is the distribution of transaction functions over several programs within a network of systems. Application programs involving DTP are complex to develop because they are able to initiate and control their own intercommunication between transactions.

  17. 4A. Distributed transaction processing DTP differs from the other intercommunication facilities discussed thus far in that it employs synchronous processing. The communication is dynamic, and not predefined by transaction definitions. However, transactions in DTP are designed to communicate with other transactions as efficiently as possible.

  18. 4A. Distributed transaction processing In large or high-traffic Parallel Sysplex setups, complex CICS innovations such as DTP serve to reduce the potential problems associated with simpler, more transparent and slower transaction facilities. DTP serves to streamline and synchronize transactions, and allows complex programming conversations between CICS systems. This helps to prevent heavy system use from resulting in sluggish performance or system errors.

  19. 4A. Distributed transaction processing DTP is not suited to all systems. For smaller and less heavily used systems, DTP might not be necessary. The complexity of DTP might demand too much technical expertise to set up and maintain it in some user environments.

  20. 4B. Multiregion operation CICS multiregion operation (MRO) enables CICS systems that are running in the same OS/390 system or within a Parallel Sysplex setup to communicate with each other. MRO does not enable communication between a CICS setup and a non- CICS system, such as an IMS or DB2 system. MRO provides all five of the intercommunication facilities listed at the right.

  21. 4B. Multiregion operation These are some of the uses of multiregion operation (MRO): • Program development • Providing reliable database access • Setting up department-specific regions • Multiprocessing

  22. 4B. Multiregion operation MRO allows for easy and risk-free testing of newly written applications by making it possible to set up a separate CICS system that is designated specifically for testing.

  23. 4B. Multiregion operation MRO allows you to set up your system to reduce the possibility that unreliable applications will disable the system or other applications. You can also use it to increase the reliability of database access. You could divide your system into multiple regions, dedicating one region to less reliable applications, and thus separating them from more reliable applications. The applications in one region can still access resources in other regions through interregion communications (IRC). To increase the reliability of database access, you can designate a database- owning region that contains no user applications, and thus might not be subject to the effects of an unstable application.

  24. 4B. Multiregion operation MRO allows you to set up a CICSPlex where each department of an organization has its own CICS system. IRC allows one department to access another department’s resources and data. With transaction routing, any terminal can run a transaction on any system. Thus, terminals do not need to be designated as belonging to a specific department.

  25. 4B. Intersystem communication Intersystem communication (ISC) is the communication between a CICS system and another system or set of systems that are networked together. Communication between systems in ISC uses the telecommunication protocols of Systems Network Architecture (SNA).

  26. 4B. Intersystem communication There are three basic ways in which subsystems can be connected for intersystem communication: • ISC within a single operating system • ISC between physically adjacent operating systems • ISC between physically remote operating systems Communication can take place between CICS and non-CICS systems. For example, intersystem communication can take place between a CICS Transaction Server for OS/390 system and an IMS system. Intersystem communication can make use of the same facilities as MRO, including function shipping, transaction routing, DLP and DTP.

  27. 4C. CICS from a browser CICS TS for OS/390 provides you with the facilities for making transaction-processing services available over the Internet or an intranet. There are several different means by which a client application program or an Internet browser can communicate with CICS and request CICS services.

  28. 4C. CICS from a browser Web browsers can communicate directly with CICS application programs without an intermediate gateway or Web server through CICS Web support (CWS).

  29. 4C. CICS from a browser Instead of accessing CICS directly through CWS, you can also access CICS services through a server on the OS/390 platform. For example, you can obtain a secure connection with CICS through an IBM WebSphere Application Server for OS/390.

  30. 4C. CICS from a browser You can also access CICS TS for OS/390 via a non-OS/390 Web server that is connected via a network. Communicating with CICS in this way uses the External CICS Interface (EXCI). EXCI is a form of function shipping, where the incoming request is processed by a mirror transaction in the linked- to system.

  31. 4C. CICS from a browser Another way to access CICS from a Web browser is through the CICS Transaction Gateway. The CICS Transaction Gateway uses the CICS External Call Interface (EXCI) to pass requests to CICS.

  32. 4C. CICS Transaction Gateway IBM’s CICS Transaction Gateway for OS/390 provides a set of Java- based Web server facilities allowing access to CICS applications from a Web browser. These facilities include: • A JavaGateway application that interfaces with CICS applications running on CICS servers. This communication takes place through the CICS External Call Interface (EXCI). • A CICS Java class library that provides an application programming interface (API), and facilitates communication between the gateway application and a Java application or applet.

  33. 4C. CICS Transaction Gateway The Java classes and JavaBeans supplied by CICS Transaction Gateway allow you to write Java Web server code to handle browser requests for CICS services. You can also use these facilities to code applets.

  34. 4C. CICS Transaction Gateway One of the Java classes included in the CICS Java class library is the JavaGateway class, which is used to establish communication with the gateway process. Another class, the ECIRequest class, is used to specify external call interface (ECI) calls.

  35. 4C. CICS Transaction Gateway The steps involved in accessing CICS using the CICS Transaction Gateway from a Web browser: 1. Browser calls a Web server using HTTP to get HTML pages. 2. Browser finds an applet tag for the applet that will communicate with CICS, and calls Web server to get the applet and classes that it requires. 3. After the browser receives an applet, it runs the applet.

  36. 4C. CICS Transaction Gateway 4.The implemented applet creates a JavaGateway object, which calls the CICS Transaction Gateway for OS/390. The applet also creates an ECIRequest object to represent its request for a CICS program.

  37. 4C. CICS Transaction Gateway 5.The ECIRequest object is passed to the gateway, which then calls the CICS program. 6.When the program is finished, the results are returned to the browser by way of the gateway.

  38. 4C. CICS Web Interface The CICS Web support (CWS) is a set of CICS services that support direct access to CICS from a Web browser over a TCP/IP connection. CWS allows customers to use the transaction processing facilities of CICS for transactions conducted over the Internet without an intermediate gateway to separate Web server.

  39. 4C. CICS Web Interface With CICS you can build CICS HTML application utilities and provide Internet or intranet access to CICS without a Web server. However, the facilities provided by CWS do not replace those performed by a Web server. You should use a separate server if you need facilities that provide GIFs, applets, or other items that might be referenced from the CICS pages.

  40. 4C. CICS Web interface CWS accepts two types of requests: • Requests from Web browsers connected via a TCP/IP port that is designated for CWS • Requests from Web browsers connected to IBM WebSphere Application Server for OS/390. With CICS you can build application utilities and provide Internet or intranet access to CICS without a Web server. However, the facilities provided by CWS do not replace those performed by a Web server. You should use a separate server if you need facilities that provide GIFs, applets, or other items that may be referenced from the CICS pages.

  41. 4C. CICS Web interface For requests from Web browsers connected via a TCP/IP port that is designated fro CWS, a user-replaceable application translates the HTTP request into a request for CICS transaction processing services. For requests from Web browsers connected to IBM WebSphere Application Server for OS/390, A CICS-supplied WebServer plug-in operating within the server relates the HTTP request to the transaction processing services.

  42. Unit 4 summary This is what you learned in this unit: • MRO allows communication between different CICS regions within a single system or CICSPlex. • ISC connects separate systems, including non-CICS systems, for intercommunication. • CICS TS for OS/390 provides five facilities for intercommunication: function shipping, asynchronous processing, transaction routing, DPL and DTP. (continued)

  43. Unit 4 summary • Intercommunication permits the sharing of resources across systems and regions. • All five types of intercommunication are available in both MRO and ISC setups. • There are several possibilities for making CICS transaction processing services available over the Internet or an intranet: CICS Web Support provides access to CICS with or without an intermediate Web server or gateway; CICS Transaction Gateway serves as an intermediary between CICS and a Web browser.

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