CIR - Committed Information Rate

Enhanced Definition

Committed Information Rate (CIR) is a Quality of Service (QoS) parameter in wide area networks (WANs) that specifies the guaranteed minimum bandwidth a service provider will allocate to a customer's data traffic. In the mainframe context, it defines the assured data transfer rate for critical z/OS applications and data flows traversing a WAN link, ensuring predictable performance for enterprise-level transactions and data replication. CIR (Committed Information Rate) is a networking term that, in the mainframe context, refers to the guaranteed minimum bandwidth that a service provider commits to deliver for data traffic originating from or destined for a z/OS system over a Wide Area Network (WAN) connection. It ensures a baseline level of network performance for critical mainframe applications and data transfers, even during periods of network congestion.

Key Characteristics

- Guaranteed Bandwidth: Represents the minimum data rate that the network service provider commits to delivering under normal conditions, even during network congestion, for traffic within the committed profile.
- Traffic Prioritization: Traffic that exceeds the CIR (often referred to as Excess Information Rate - EIR) may be marked as "discard eligible" and dropped during network congestion, while traffic within CIR is prioritized.
- Service Level Agreements (SLAs): CIR is a fundamental component of network SLAs, providing a measurable metric for network performance and reliability for critical enterprise services connecting to or from the mainframe.
- Application Performance Impact: Directly influences the perceived performance of mainframe applications (e.g., CICS transactions, DB2 queries, batch file transfers) when their data travels over WAN links.
- Network Design Consideration: Network architects design enterprise networks connecting mainframes to remote sites, considering CIR to ensure sufficient bandwidth for peak and critical data requirements.

Use Cases

- Disaster Recovery (DR) Replication: Ensuring a guaranteed bandwidth for synchronous or asynchronous data replication between primary and DR mainframe sites (e.g., GDPS, XRC, Metro Mirror) to meet stringent Recovery Point Objectives (RPO).
- Remote User Access: Providing consistent performance for remote users accessing mainframe applications via terminals (e.g., TN3270) or web interfaces, where network latency and throughput are critical for user experience.
- Batch File Transfers: Guaranteeing a minimum transfer rate for large batch file transfers (e.g., using FTP, NDM/Connect:Direct) between z/OS and distributed systems or business partners over WAN.
- Distributed Data Access: Supporting distributed applications that access DB2 or IMS data on the mainframe, ensuring that queries and updates meet performance targets across the WAN.
- Hybrid Cloud Connectivity: When integrating z/OS workloads with hybrid cloud environments, CIR can be used to ensure dedicated bandwidth for secure and high-performance data exchange between the mainframe and cloud resources.

Related Concepts

CIR is closely related to network Quality of Service (QoS) mechanisms and Service Level Agreements (SLAs) that govern the performance of network links connecting z/OS systems to the broader enterprise or external networks. It works in conjunction with concepts like peak information rate (PIR) or maximum information rate (MIR), which define the absolute upper limit of bandwidth, and bursting, where traffic can temporarily exceed CIR up to PIR. For mainframe professionals, understanding CIR is crucial for capacity planning and troubleshooting performance issues related to network latency and throughput for