Interconnect

Enhanced Definition

In the mainframe context, an interconnect refers to the high-speed, dedicated hardware and software mechanisms that enable communication and data transfer between various components within a single mainframe system (e.g., CPU to I/O devices), between logical partitions (LPARs), or between multiple mainframe systems. These links are crucial for resource sharing, data access, and overall system coordination, ensuring low-latency and high-bandwidth communication.

Key Characteristics

- High Bandwidth and Low Latency: Designed for extremely fast data transfer and minimal delay, essential for mission-critical applications and high-volume transaction processing.
- Dedicated Hardware Paths: Often implemented using specialized hardware like I/O channels (e.g., FICON, ESCON) or Coupling Facility links (e.g., ICB, ICF).
- Redundancy and Resilience: Typically configured with multiple, redundant paths to ensure continuous operation and fault tolerance in case of a link failure.
- Protocol-Specific: Utilizes specific protocols tailored for mainframe environments, such as FICON for storage, ISC (Intersystem Communication) for CICS, or proprietary protocols for Coupling Facility communication.
- Scalability: Allows for the addition of more communication paths or higher-capacity links to accommodate increasing workload demands.
- Security and Isolation: Provides secure and often physically isolated communication channels, minimizing exposure to external threats.

Use Cases

- CPU-to-I/O Device Communication: High-speed channels (e.g., FICON) interconnect the mainframe processor complex with external storage devices (DASD, tape) and network adapters (OSA).
- LPAR-to-LPAR Communication: Within a single mainframe CEC, LPARs can communicate via internal shared memory, HiperSockets, or through a Coupling Facility for shared data and workload balancing.
- Mainframe-to-Mainframe Communication (Sysplex): Multiple z/OS systems in a Parallel Sysplex are interconnected via Coupling Facility links to share data, lock structures, and manage workload distribution across the sysplex.
- Network Connectivity: Open Systems Adapters (OSA) act as interconnects, linking the mainframe to external IP networks (LAN/WAN) for client access, distributed applications, and internet connectivity.
- Storage Area Network (SAN) Integration: FICON channels provide the interconnectivity between z/OS systems and Fibre Channel-based SANs, allowing access to shared enterprise storage.

Related Concepts

Interconnects are fundamental to the operation of a Parallel Sysplex, enabling multiple z/OS systems to function as a single logical entity by sharing resources via a Coupling Facility (CF), which itself relies on high-speed interconnects. I/O Channels like FICON are specialized interconnects that link the mainframe to DASD and tape storage, while Open Systems Adapters (OSA) provide network interconnectivity, allowing z/OS to participate in TCP/IP networks. Without robust interconnects, the high availability, scalability, and data sharing capabilities of modern z/OS environments would not be possible.

Best Practices:

Design for Redundancy: Always configure multiple, diverse interconnect paths for critical components (e.g., dual FICON paths to storage, multiple CF links) to eliminate single points of failure.
Monitor Performance and Utilization: Regularly monitor channel utilization, Coupling Facility link activity, and network adapter throughput using tools like RMF or SMF data to identify bottlenecks and ensure optimal performance.
Capacity Planning: Proactively plan for future growth by ensuring sufficient interconnect bandwidth and port availability to accommodate new workloads, devices, or sysplex members.
Physical Separation: Where possible, route redundant interconnect cables and paths through different physical conduits or racks to protect against localized damage.
Security Configuration: Implement appropriate security measures for network interconnects (e.g., OSA) including firewalls, intrusion detection, and encryption, and ensure proper logical partitioning of internal interconnects.