What are the main communication protocols supported by ISC?

ISC supports multiple protocols including LU6.1 for basic SNA communication, LU6.2/APPC for advanced program-to-program communication, TCP/IP for internet protocol communication, and XCF for cross-system coupling facility communication.

What is the difference between LU6.1 and LU6.2/APPC?

LU6.1 provides simple, reliable data transfer with basic error handling, while LU6.2/APPC offers full-duplex communication, advanced flow control, sophisticated error handling, session management, and security features.

What are the key benefits of using ISC?

ISC provides distributed transaction processing, cross-system application integration, enterprise-wide data sharing, improved system scalability, and support for complex communication patterns like request-response, asynchronous, and publish-subscribe.

How do you configure security in an ISC environment?

ISC security is configured through authentication and authorization mechanisms, network security measures, data encryption, secure communication protocols, and comprehensive audit logging of cross-system operations.

What performance considerations are important in ISC?

Key performance considerations include connection pooling (MAXCONN), session management (MAXSESS), buffer sizing, timeout configuration, monitoring response times, and optimizing resource utilization across systems.

CICS Intersystem Communication (ISC)

Q: What is CICS Intersystem Communication (ISC)?

CICS Intersystem Communication (ISC) is a facility that enables communication between different CICS systems, mainframe subsystems, and external applications, supporting distributed transaction processing and enterprise application integration.

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Intersystem Communication (ISC) is a fundamental CICS capability that enables communication between different CICS systems, mainframe subsystems, and external applications. ISC provides the foundation for distributed transaction processing, allowing CICS applications to interact with systems across different platforms, networks, and architectures.

What is Intersystem Communication (ISC)?

Intersystem Communication (ISC) is a CICS facility that enables communication between CICS systems and other mainframe subsystems or external applications. It provides a standardized way for CICS applications to exchange data, execute programs, and coordinate transactions across system boundaries.

ISC is essential for building distributed applications that span multiple systems, enabling enterprise-wide transaction processing, data sharing, and application integration. It supports various communication protocols and provides robust error handling and recovery mechanisms.

Key Concept: ISC enables CICS systems to communicate with other systems, supporting distributed transaction processing, cross-system program execution, and enterprise application integration.

ISC Architecture and Components

ISC consists of several key components that work together to provide reliable communication between systems:

ISC Manager

The ISC Manager is the central component that coordinates all intersystem communication activities. It handles:

Connection establishment and management
Message routing and delivery
Protocol translation and conversion
Error handling and recovery
Performance monitoring and tuning

Communication Protocols

ISC supports multiple communication protocols to accommodate different system requirements:

LU6.1: Logical Unit 6.1 for SNA communication
LU6.2: Logical Unit 6.2 for APPC communication
TCP/IP: Internet Protocol communication
XCF: Cross-system Coupling Facility
Channel: Direct channel communication

Resource Definitions

ISC requires various resource definitions to establish and manage connections:

CONNECTION: Defines communication links between systems
SESSIONS: Manages active communication sessions
PROFILES: Defines communication characteristics
MODEL: Templates for connection definitions
GROUP: Logical grouping of related resources

LU6.1 Communication

LU6.1 (Logical Unit 6.1) is a basic SNA communication protocol that provides reliable data transfer between CICS systems. It's suitable for simple, point-to-point communication scenarios.

LU6.1 Characteristics

LU6.1 provides the following features and characteristics:

Simple, reliable data transfer
Point-to-point communication
Basic error detection and recovery
Limited flow control mechanisms
Suitable for batch and simple transaction processing

LU6.1 Configuration

Configuring LU6.1 communication requires several resource definitions:

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RDO Commands for LU6.1:
 
DEFINE CONNECTION(LU61CONN) -
       GROUP(ISCGROUP) -
       NETNAME(LU61NET) -
       PROTOCOL(LU61) -
       SECURITY(USERID) -
       TIMEOUT(300)
 
DEFINE SESSION(LU61SESS) -
       GROUP(ISCGROUP) -
       CONNECTION(LU61CONN) -
       MAXSESS(5) -
       AUTOCONN(YES)
 
DEFINE PROFILE(LU61PROF) -
       GROUP(ISCGROUP) -
       TYPE(ISC) -
       MAXCONN(10) -
       MAXSESS(20)

LU6.1 Programming

Programming with LU6.1 involves using specific CICS commands for communication:

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. LU61-COMMUNICATOR.
       
       ENVIRONMENT DIVISION.
       DATA DIVISION.
       
       WORKING-STORAGE SECTION.
       01  COMMUNICATION-AREA.
           05  MESSAGE-TYPE        PIC X(10).
           05  MESSAGE-DATA        PIC X(100).
           05  RESPONSE-STATUS     PIC X(4).
       
       01  CONNECTION-NAME         PIC X(8) VALUE 'LU61CONN'.
       01  SESSION-NAME            PIC X(8) VALUE 'LU61SESS'.
       
       PROCEDURE DIVISION.
       
       MAIN-LOGIC.
           EXEC CICS CONNECT PROCESS(CONNECTION-NAME)
               SESSION(SESSION-NAME)
           END-EXEC
           
           IF EIBRESP = DFHRESP(NORMAL)
               PERFORM SEND-MESSAGE
               PERFORM RECEIVE-RESPONSE
               EXEC CICS DISCONNECT END-EXEC
           ELSE
               PERFORM ERROR-HANDLING
           END-IF
           
           EXEC CICS RETURN END-EXEC
       
       SEND-MESSAGE.
           EXEC CICS SEND
               FROM(COMMUNICATION-AREA)
               LENGTH(LENGTH OF COMMUNICATION-AREA)
               SESSION(SESSION-NAME)
           END-EXEC
       
       RECEIVE-RESPONSE.
           EXEC CICS RECEIVE
               INTO(COMMUNICATION-AREA)
               LENGTH(LENGTH OF COMMUNICATION-AREA)
               SESSION(SESSION-NAME)
           END-EXEC.

LU6.2 / APPC Programming

LU6.2 (Logical Unit 6.2) and APPC (Advanced Program-to-Program Communication) provide advanced communication capabilities for distributed applications. They offer sophisticated features for complex communication scenarios.

LU6.2/APPC Features

LU6.2/APPC provides advanced communication features:

Full-duplex communication
Advanced flow control and pacing
Sophisticated error handling and recovery
Session management and pooling
Security and authentication features
Performance optimization capabilities

APPC Programming Model

APPC programming follows a specific model with distinct phases:

APPC Communication Phases

Allocate Phase: Establish communication session
Send Phase: Transmit data to partner program
Receive Phase: Accept data from partner program
Deallocate Phase: Terminate communication session

APPC Commands

APPC programming uses specific CICS commands for communication:

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. APPC-COMMUNICATOR.
       
       ENVIRONMENT DIVISION.
       DATA DIVISION.
       
       WORKING-STORAGE SECTION.
       01  APPC-CONVERSATION.
           05  CONVERSATION-ID     PIC X(8).
           05  PARTNER-LU          PIC X(8).
           05  PARTNER-TP          PIC X(8).
           05  CONVERSATION-STATE  PIC X(1).
       
       01  MESSAGE-DATA.
           05  MESSAGE-HEADER      PIC X(20).
           05  MESSAGE-BODY        PIC X(100).
           05  MESSAGE-TRAILER     PIC X(10).
       
       01  RESPONSE-STATUS         PIC X(4).
       
       PROCEDURE DIVISION.
       
       MAIN-LOGIC.
           PERFORM ALLOCATE-CONVERSATION
           IF EIBRESP = DFHRESP(NORMAL)
               PERFORM SEND-MESSAGE
               PERFORM RECEIVE-RESPONSE
               PERFORM DEALLOCATE-CONVERSATION
           ELSE
               PERFORM ERROR-HANDLING
           END-IF
           
           EXEC CICS RETURN END-EXEC
       
       ALLOCATE-CONVERSATION.
           EXEC CICS ALLOCATE
               CONVERSATION(CONVERSATION-ID)
               PARTNER(APPC-CONVERSATION)
               SYNCLEVEL(1)
           END-EXEC
       
       SEND-MESSAGE.
           EXEC CICS SEND
               CONVERSATION(CONVERSATION-ID)
               FROM(MESSAGE-DATA)
               LENGTH(LENGTH OF MESSAGE-DATA)
               STATE(CONVERSATION-STATE)
           END-EXEC
       
       RECEIVE-RESPONSE.
           EXEC CICS RECEIVE
               CONVERSATION(CONVERSATION-ID)
               INTO(MESSAGE-DATA)
               LENGTH(LENGTH OF MESSAGE-DATA)
               STATE(CONVERSATION-STATE)
           END-EXEC
       
       DEALLOCATE-CONVERSATION.
           EXEC CICS DEALLOCATE
               CONVERSATION(CONVERSATION-ID)
           END-EXEC.

Cross-System Communication

Cross-system communication enables CICS applications to interact with systems beyond their immediate environment, supporting enterprise-wide integration and distributed processing.

Communication Patterns

ISC supports various communication patterns for different application requirements:

Request-Response Pattern

The request-response pattern is the most common communication model:

Client sends request to server
Server processes request and sends response
Client receives and processes response
Suitable for synchronous operations
Easy to implement and debug

Asynchronous Pattern

Asynchronous communication allows non-blocking operations:

Client sends request without waiting for response
Server processes request independently
Response sent when processing completes
Improves system responsiveness
Requires callback or polling mechanisms

Publish-Subscribe Pattern

Publish-subscribe enables event-driven communication:

Publishers send messages to topics
Subscribers receive messages from topics
Decoupled communication between systems
Supports multiple subscribers
Ideal for event notification systems

Error Handling and Recovery

Robust error handling is essential for cross-system communication:

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. CROSS-SYSTEM-COMM.
       
       ENVIRONMENT DIVISION.
       DATA DIVISION.
       
       WORKING-STORAGE SECTION.
       01  COMMUNICATION-STATUS.
           05  STATUS-CODE         PIC S9(8) COMP.
           05  STATUS-TEXT         PIC X(80).
           05  RETRY-COUNT         PIC S9(4) COMP VALUE 0.
           05  MAX-RETRIES         PIC S9(4) COMP VALUE 3.
       
       01  ERROR-HANDLING.
           05  ERROR-ACTION        PIC X(20).
           05  RECOVERY-PROCEDURE  PIC X(20).
       
       PROCEDURE DIVISION.
       
       MAIN-LOGIC.
           EXEC CICS HANDLE CONDITION
               ERROR(ERROR-ROUTINE)
               INVREQ(INVALID-REQUEST)
               NOTAUTH(NOT-AUTHORIZED)
           END-EXEC
           
           PERFORM COMMUNICATE-WITH-REMOTE-SYSTEM
           
           EXEC CICS RETURN END-EXEC
       
       COMMUNICATE-WITH-REMOTE-SYSTEM.
           PERFORM UNTIL RETRY-COUNT >= MAX-RETRIES
               OR STATUS-CODE = 0
               ADD 1 TO RETRY-COUNT
               PERFORM ATTEMPT-COMMUNICATION
               IF STATUS-CODE NOT = 0
                   PERFORM ANALYZE-ERROR
                   PERFORM EXECUTE-RECOVERY
               END-IF
           END-PERFORM
           
           IF STATUS-CODE NOT = 0
               PERFORM FINAL-ERROR-HANDLING
           END-IF
       
       ERROR-ROUTINE.
           MOVE EIBRESP TO STATUS-CODE
           PERFORM ANALYZE-ERROR
           PERFORM EXECUTE-RECOVERY
           EXEC CICS RETURN END-EXEC
       
       ANALYZE-ERROR.
           EVALUATE STATUS-CODE
               WHEN 1001
                   MOVE 'RETRY-OPERATION' TO ERROR-ACTION
               WHEN 1002
                   MOVE 'FALLBACK-SYSTEM' TO ERROR-ACTION
               WHEN 1003
                   MOVE 'ROLLBACK-TRANSACTION' TO ERROR-ACTION
               WHEN OTHER
                   MOVE 'ABEND-TRANSACTION' TO ERROR-ACTION
           END-EVALUATE.

ISC Configuration and Setup

Proper configuration is essential for successful ISC implementation. This involves defining various resources and establishing communication parameters.

System Initialization Table (SIT) Parameters

ISC behavior is controlled through SIT parameters:

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SIT Parameters for ISC:
                  
ISC=YES                    # Enable ISC support
ISCINIT=YES               # Enable ISC initialization
ISCINITTO=60              # ISC initialization timeout
ISCINITRET=3              # ISC initialization retry count
ISCINITWAIT=10            # ISC initialization wait time
ISCINITPARM=              # ISC initialization parameters
ISCINITPROC=              # ISC initialization procedure
ISCINITUSER=              # ISC initialization user ID
ISCINITGROUP=             # ISC initialization group
ISCINITCLASS=             # ISC initialization class

Resource Definition Online (RDO)

RDO is used to define ISC resources and establish connections:

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RDO Commands for ISC Setup:
 
DEFINE GROUP(ISCGROUP) -
       TYPE(ISC) -
       DESCRIPTION('ISC Resources')
 
DEFINE CONNECTION(ISC-CONN1) -
       GROUP(ISCGROUP) -
       NETNAME(ISC-NET1) -
       PROTOCOL(LU62) -
       SECURITY(USERID) -
       TIMEOUT(300) -
       MAXSESS(10)
 
DEFINE SESSION(ISC-SESS1) -
       GROUP(ISCGROUP) -
       CONNECTION(ISC-CONN1) -
       MAXSESS(5) -
       AUTOCONN(YES) -
       STATE(INBOUND)
 
DEFINE PROFILE(ISC-PROF1) -
       GROUP(ISCGROUP) -
       TYPE(ISC) -
       MAXCONN(20) -
       MAXSESS(50) -
       SECURITY(USERID)

JCL for ISC Startup

ISC requires specific JCL parameters for proper initialization:

jcl

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//CICSISC  JOB (ACCT),'ISC CICS',CLASS=A,MSGCLASS=X
//* CICS Intersystem Communication Startup
//STEP1    EXEC PGM=DFHSIP,REGION=0M
//STEPLIB  DD  DSN=CICS.SDFHLOAD,DISP=SHR
//DFHCSD   DD  DSN=CICS.DFHCSD,DISP=SHR
//DFHSTART DD  DSN=CICS.DFHSTART,DISP=SHR
//DFHPARM  DD  *
SYSIDNT=ISC1
ISC=YES
ISCINIT=YES
ISCINITTO=60
ISCINITRET=3
ISCINITWAIT=10
ISCINITPARM=ISC-PARMS
ISCINITPROC=ISC-PROC
ISCINITUSER=ISCUSER
ISCINITGROUP=ISCGROUP
ISCINITCLASS=ISC
//DFHCXRF DD  DSN=CICS.DFHCXRF,DISP=SHR
//DFHLOG  DD  DSN=CICS.DFHLOG,DISP=SHR
//DFHSNAP DD  DSN=CICS.DFHSNAP,DISP=SHR
//DFHAUXT DD  DSN=CICS.DFHAUXT,DISP=SHR
//DFHTEMP DD  DSN=CICS.DFHTEMP,DISP=SHR

ISC Security Considerations

Security is a critical aspect of ISC, requiring careful configuration and monitoring to protect sensitive data and system resources.

Authentication and Authorization

ISC security begins with proper authentication and authorization:

User ID validation across systems
Resource access control and authorization
Cross-system security profiles
Audit logging of cross-system operations
Security token management

Network Security

Network security protects ISC communication channels:

Encryption of sensitive data
Secure communication protocols
Network isolation and segmentation
Firewall configuration and access control
Intrusion detection and prevention

Data Protection

Protecting data in transit and at rest is essential:

Data encryption standards
Secure data transmission protocols
Access logging and monitoring
Data backup and recovery procedures
Compliance with security standards

ISC Performance and Tuning

Optimizing ISC performance requires understanding various tuning parameters and monitoring techniques:

Connection Pooling

Connection pooling improves performance by reusing connections:

MAXCONN parameter controls maximum connections
Connection pooling reduces establishment overhead
Monitor connection utilization and adjust pool size
Balance between resource usage and performance
Consider workload patterns when sizing connection pools

Session Management

Effective session management optimizes resource usage:

MAXSESS parameter controls maximum sessions
Session pooling improves response times
Monitor session utilization and adjust parameters
Consider session timeout and cleanup procedures
Implement session recovery mechanisms

Buffer Management

Proper buffer sizing is crucial for ISC performance:

Buffer size affects throughput and memory usage
Larger buffers improve throughput for large data transfers
Smaller buffers reduce memory usage and improve response time
Buffer size should match typical transaction data volumes
Monitor buffer utilization and adjust as needed

ISC Monitoring and Troubleshooting

Effective monitoring and troubleshooting are essential for maintaining ISC system health and performance:

Performance Monitoring

Monitor key ISC performance metrics:

Cross-system communication response times
Connection and session utilization
Buffer usage and efficiency
Error rates and failure patterns
Resource consumption and availability

Common Issues and Solutions

Be prepared to address common ISC issues:

Connection failures and timeouts
Authentication and authorization errors
Performance degradation and bottlenecks
Resource contention and deadlocks
Network connectivity problems

Diagnostic Tools

Use available diagnostic tools for troubleshooting:

CICS transaction monitoring (CEMT)
Performance monitoring tools (RMF, SMF)
Network diagnostic utilities
Log analysis and correlation
System trace and dump analysis

CICS Intersystem Communication (ISC)

What is Intersystem Communication (ISC)?

ISC Architecture and Components

ISC Manager

Communication Protocols

Resource Definitions

LU6.1 Communication

LU6.1 Characteristics

LU6.1 Configuration

LU6.1 Programming

LU6.2 / APPC Programming

LU6.2/APPC Features

APPC Programming Model

APPC Communication Phases

APPC Commands

Cross-System Communication

Communication Patterns

Request-Response Pattern

Asynchronous Pattern

Publish-Subscribe Pattern

Error Handling and Recovery

ISC Configuration and Setup

System Initialization Table (SIT) Parameters

Resource Definition Online (RDO)

JCL for ISC Startup

ISC Security Considerations

Authentication and Authorization

Network Security

Data Protection

ISC Performance and Tuning

Connection Pooling

Session Management

Buffer Management

ISC Monitoring and Troubleshooting

Performance Monitoring

Common Issues and Solutions

Diagnostic Tools

Knowledge Check: CICS Intersystem Communication

Question 1: What is the primary purpose of CICS Intersystem Communication (ISC)?

Question 2: Which communication protocol provides full-duplex communication and advanced flow control?

Question 3: What is the primary benefit of connection pooling in ISC?

Answers:

Related Concepts

CICS Multi-Region Operation (MRO)

CICS EXEC CICS Commands

CICS Programming Models

CICS Data Passing

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