CINIT - Cross-Domain Initiation

Enhanced Definition

CINIT (Cross-Domain Initiation) is a VTAM (Virtual Telecommunications Access Method) process where a logical unit (LU) in one VTAM domain requests to establish a session with another LU located in a different VTAM domain. It is a fundamental mechanism within Systems Network Architecture (SNA) that enables communication between applications and terminals across separate but interconnected z/OS Communications Server networks. CINIT (Cross-Domain Initiation) is an internal Systems Network Architecture (SNA) request issued by a Cross-Domain Resource Manager (CDRM) in one VTAM domain to another CDRM in a different VTAM domain. Its primary purpose is to initiate a session between two logical units (LUs) that reside in separate VTAM domains. It is a critical step in establishing cross-domain SNA sessions.

Key Characteristics

- Cross-domain communication: Specifically facilitates session establishment between LUs that reside in different VTAM domains.
- VTAM-driven: The entire CINIT process is managed and controlled by VTAM (now part of z/OS Communications Server) in the respective domains.
- Session establishment: It's the initial phase that leads to the setup of an SNA LU-LU session, allowing data exchange between the two LUs.
- SSCP-SSCP sessions: Relies on active System Services Control Point (SSCP) to SSCP sessions between the involved VTAM domains for control information exchange and resource resolution.
- Resource resolution: VTAM uses its network configuration knowledge to locate the target LU in the remote domain and route the session request.
- Security context: Can involve security checks at both the initiating and target VTAM domains to authorize the cross-domain access.

Use Cases

- Terminal access to remote applications: A 3270 terminal connected to VTAM A needs to access a CICS application running under VTAM B, requiring a cross-domain session.
- Application-to-application communication: A COBOL batch application in one z/OS system (VTAM A) needs to communicate with a DB2 stored procedure or another application in a different z/OS system (VTAM B) using SNA protocols.
- Network consolidation: Connecting multiple geographically dispersed z/OS systems, each with its own VTAM domain, to allow users seamless access to resources across the entire enterprise network.
- Disaster recovery setups: Enabling LUs in a recovery site's VTAM domain to connect to applications in the primary site's VTAM domain (or vice-versa) for business continuity.
- Distributed data access: Facilitating communication for data sharing or synchronization between applications running in different z/OS LPARs or sysplexes.

Related Concepts

CINIT is a core component of SNA (Systems Network Architecture) and is managed by VTAM (Virtual Telecommunications Access Method), which is now integrated into z/OS Communications Server. It relies heavily on SSCP-SSCP sessions between VTAM domains to exchange control information and facilitate resource location. Once CINIT successfully resolves the cross-domain path, it leads to the exchange of BIND requests between the LUs, which are the actual commands to establish the SNA session. It works in conjunction with CDRSC (Cross-Domain Resource) definitions, which inform VTAM about resources in other domains.

Best Practices:

Accurate VTAM definitions: Ensure all CDRSC (Cross-Domain Resource) and CDRMLIST (Cross-Domain Resource Major List) definitions are correctly configured and synchronized across all participating VTAM domains.
Network security: Implement robust SNA security measures, including APPL and LU definitions, and leverage RACF (Resource Access Control Facility) profiles to control and authorize cross-domain access.
Performance monitoring: Regularly monitor VTAM activity and cross-domain traffic using VTAM display commands (D NET,ID=lu_name, D NET,CDRSCS) and performance tools to identify and resolve potential bottlenecks.
Redundancy and resilience: Design the underlying network infrastructure (e.g., using Enterprise Extender (EE) or MPTN (MultiPath Transport Network)) to provide redundant paths for critical cross-domain communication.
Standardized naming conventions: Adopt consistent naming conventions for LUs and APPLs across domains to simplify configuration, troubleshooting, and management of cross-domain resources.