Describe Critical Chain Scheduling

Question

Examlex · Accepted Answer

The Answer is The critical chain method is used if activities contend for limited resources. When using the critical chain method, the critical path is first identified, independent of resource availability. Entering resource availability might then reveal conflicting activities, which were planned to be completed in parallel but draw upon the same (limited) resource. Based on resource availability, a new (altered) critical path is created. This new path, based on both task dependencies and resource dependencies, is referred to as a critical chain. If resources were unlimited, the critical path and the critical chain would be equal. So far, this process to some extent resembles resource leveling techniques. However, another advantage of the critical chain method is that it helps to minimize uncertainty in a project's schedule, therefore leading to a shorter overall completion time. The following paragraphs explain how critical chain scheduling can be used to influence a project's completion date.

People assigned to multiple concurring tasks often resort to multitasking, that is, working a bit on one task, going on to the next, working a bit on a third task, and so on, before restarting work on task one. Unfortunately, this approach often wastes time because of setup for the individual tasks. Therefore, critical chain scheduling prohibits multitasking with the goal of arriving at a shorter overall completion time. Another factor often leading to long project durations is the uncertainty inherent in any project. To cope with this uncertainty, a project's activities often contain duration buffers (i.e., additional time allocated to an activity to account for any unforeseen circumstances). As this buffer is added to every activity, the entire project contains more reserve time than is usually needed. Further, there is often the tendency to fill the allotted time; in other words, if a certain amount of time is allotted for an activity, people tend to use it (also known as "Parkinson's Law"). If a buffer is added to an activity, people tend to use this buffer as well, no matter whether the additional time is needed or not. CCM thus suggests
following aggressive target duration schedules to reduce over- allocation of time, placing buffers at more strategic locations in the project timeline, avoiding multitasking because there are switching costs, emphasizing resources and the contention for resources when planning, and finally tracking the status of buffers managing both their depletion and replenishment.
Critical chain scheduling eliminates any buffers from the individual activities; instead, a general project buffer is created. Eliminating individual buffers helps to decrease the entire duration of the project, while the project buffer protects the final due date. The removal of individual buffers serves the additional purpose of discouraging people from engaging in multitasking or other distractions. As the duration estimates (without the individual buffers)are very aggressive, people focus on the task at hand in order to finish the task in the allotted time.
In addition to the project buffer, critical chain scheduling uses feeding buffers to protect the activities on the critical path. Usually, in complex projects, many noncritical activities feed into critical activities. As the individual safety buffers are eliminated using critical chain scheduling, a change in duration of a noncritical activity feeding into a critical activity would influence the critical path and, thus, the duration of the entire project. To prevent this, a feeding buffer is added to any noncritical activity feeding into a critical activity. The project manager can easily monitor the use of the feeding buffers and the project buffer to determine whether the project is on schedule. Project management software frequently employs third-party add-ons for critical chain scheduling.
When using any of these techniques, a project manager should always monitor the project calendars and resource calendars. In a large software development project of a multinational corporation, virtual teams located in different regions of the world might be working on completing a certain task; thus, teams could work in three continuous shifts. The resource calendar would specify these working times. On the other hand, the client organization might be available only during certain times, so that, for example, during requirements generation, the project team members cannot get in contact with it. Such times would be specified in the project calendar.
Another factor to be considered during schedule network analysis is the use of leads and lags. In the activity sequencing stage, the leads and lags of the different activities have been established. To review, a lead is the time between the start of one activity and the start of an overlapping activity; a lag is the time between the finish of one activity and the start of a succeeding activity. As these leads and lags can significantly influence the schedule, their use should be carefully double-checked to minimize potentially negative impacts on the schedule.

Describe Critical Chain Scheduling

Definitions: