An Introduction to Buffer Management
Asta PowerProject includes many exciting features to help you manage projects efficiently so that you complete your projects on time and within budget. Buffer Management is one of the features included in Asta PowerProject that helps you protect your strategic project deadlines. Buffer Management , based upon the Theory of Constraints (TOC) and Critical Chain Project Management (CCPM) concepts proposed by Dr. Goldratt in 1990, provides a method to more effectively manage activity durations. Buffer Management assists you in generating a project plan that protects you against uncertainties and reduces the impact of potential changes.
According to Andrew Willard, International Business Director of ASTA Development PLC, in his white paper “Using Asta PowerProject for Critical Chain and Buffer Management”: “Critical Chain is defined as the longest sequence of activities from several different paths, connected by activities performed by common resources. The contingency period in the Critical Chain is removed from individual activities and is utilized to create a project buffer. These buffers provide the necessary cushions to individual activities enabling them to accomplish the final goal of completing the Critical Chain in the least possible time”.
Buffer or contingency activities can be setup to protect important deadlines and reduce excess float. Buffers activities do not have float, and they shrink or expand in duration as required without moving beyond their finish date or the start date of the successor activities.
Asta PowerProject includes two types of buffer activities:
- project buffers to protect a project finish date
- feeder buffers to protect the start date of successor activities
According to Andrew Willard in the above mentioned white paper, the following steps should be performed when incorporating buffer activities and Critical Chain Project Management:
- Plan the schedule utilizing traditional Critical Path Method (CPM)
- Identify the protective duration estimate or cushion incorporated for each activity
- Determine the “reasonable” estimated duration for each activity
- Remove the cushion or safety estimates for each activity based upon steps 2 and 3.
- Identify the critical chain as the longest chain of dependent activities
- Add a “project buffer” at the end of the project
- Add “feeder buffers” in non-critical chains that merge into the critical chain
- Include resource buffers as necessary to ensure resource availability
- Verify the critical chain
This tutorial provides a very simple illustration of Buffer Management in Asta PowerProject.
Step 1. The image below depicts a project consisting of 2 phases. Phase 1 is a non-critical path connecting to activities in Phase 2, which is the critical path. Notice that the activities in Phase 1 have significant float, which may indicate that safety or cushion duration has been included in those activities. Also notice that the project finish date, which we want to protect, is April 4.
Step 2. The image below reflects that the safety or cushion duration has been removed from the activities in Phase 1 and a “feeder buffer” activity has been with a duration of 6 days. This buffer activity will expand or shrink based upon the other activities in Phase 1. Notice that the feeder buffer is connected to an activity in the critical path.
The safety or cushion duration has also been removed from the activities in Phase 2. Additionally, a “project buffer” of 20 days has been added to the end of the project to protect the finish date of April 4.
Step 3. The image below reflects that the duration of Phase 1 Task 3 increased from 8 to 10 days. Notice that the duration of the Feeder Buffer task has been reduced to 4 days from 6 days in response to the increased duration Task 3.
Step 4. When the duration of Phase 1 Task 3 is increased to 15 days, the duration of the buffer task (which was originally 6 days) has been consumed and the buffer task is now reflected as a milestone. Also notice that the duration of the project buffer activity (in Phase 2) has been reduced from 20 to 19 days.
Step 5. The image below reflects the original project plan after adding the buffer activities. We will now begin to explore the behavior of the project buffer activity. Notice the original duration is 20 days.
Step 6. In the example below, the duration of Task 3 in Phase 2 has been increased from 13 to 20 days and the project has been rescheduled. Notice that the project buffer has been decreased from 20 days to 13 days. Also notice that the feeder buffer has increased from 6 days to 13 days.
Step 7. When we increase the duration of Task 4 in Phase 2 from 13 days to 20 days and reschedule the project, the project buffer is completely consumed and is now reflected as a milestone.
Asta PowerProject is one of the only project scheduling tools that comes equipped with Buffer Management functionality out of the box. Do you want to experiment with Asta PowerProject’s Buffer Management functionality? Click on the link to access a free 7 day trial of Asta PowerProject.
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