Monitor Control Loops

The most common model for defining control is the Monitor Control Loop. Although it is a simple model, it has many complex applications within IT Service Management. This section will define the basic concepts of the Monitor Control Loop Model and subsequent sections will show how important these concepts are for the Service Management Lifecycle.

Figure 5.2 The Monitor Control Loop

Figure 5.2 outlines the basic principles of control. A single activity and its output are measured using a predefined norm, or standard, to determine whether it is within an acceptable range of performance or quality. If not, action is taken to rectify the situation or to restore normal performance.

Typically there are two types of Monitor Control Loops:

• Open LoopSystems are designed to perform a specific activity regardless of environmental conditions. For example, a backup can be initiated at a given time and frequency – and will run regardless of other conditions.
• Closed Loop Systems monitor an environment and respond to changes in that environment. For example, in network load balancing a monitor will evaluate the traffic on a circuit. If network traffic exceeds a certain range, the control system will begin to route traffic across a backup circuit. The monitor will continue to provide feedback to the control system which will continue to regulate the flow of network traffic between the two circuits.

To help clarify the difference, solving Capacity Management through over-provisioning is open loop; a load-balancer that detects congestion/failure and redirects capacity is closed loop.

Date: 2014-12-29; view: 1111