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Buffer management

How to determine the critical chain:

  1. Critical Path vs. Critical Chain
    • The critical path is the longest sequence of dependent tasks that determine the minimum project duration, assuming unlimited resources.
    • The critical chain considers both task dependencies AND resource availability constraints.
  2. How to Calculate the Critical Chain
    • First establish the critical path (longest path through the network)
    • Next, identify resource conflicts along this path
    • Resolve conflicts by resource leveling (shifting tasks to when resources are available)
    • The resulting path, which includes both dependency and resource constraints, is your critical chain
  3. Steps in Detail:
    • Start with a forward and backward pass to determine early/late start and finish times
    • Identify resource overallocations
    • Apply resource leveling to resolve overallocations
    • After leveling, recalculate the critical path considering the resource constraints
    • This new path is your critical chain

CCPM methodology that goes beyond just identifying the critical chain.

Here's how we would approach this:

  1. Calculate Optimistic Task Durations:
    • For each task, we would reduce the "safe" estimates (which often include hidden buffers) to more aggressive, optimistic durations
    • Typically, this means reducing traditional estimates by 50% to remove the built-in safety margins
    • These optimistic durations focus on the most likely time needed, not worst-case scenarios
  2. Insert the Project Buffer:
    • Identify the end of the critical chain
    • Create a project buffer that's typically 50% of the total duration of the critical chain tasks
    • This buffer protects the project completion date from variations in the critical chain tasks
  3. Insert Feeding Chain Buffers:
    • Identify all non-critical paths (feeding chains) that merge into the critical chain
    • For each feeding chain, calculate a buffer (typically 50% of the feeding chain duration)
    • Place these buffers at the point where each feeding chain connects to the critical chain
    • These buffers protect the critical chain from delays in non-critical paths
  4. Buffer Management:
    • Once implemented, we would track buffer consumption rates to monitor project health
    • Buffer consumption can be visualized using fever charts with red/yellow/green zones

An algorithm that would:

  1. Take your critical chain network
  2. Calculate optimistic durations based on your risk tolerance
  3. Determine appropriate buffer sizes
  4. Position the buffers correctly in the network
  5. Provide a revised schedule with buffers properly placed