The technique of Critical Chain Method (CCM) is mentioned in the previous versions of the PMBOK. There is no mention of Critical Chain Method is PMBOK 6th Edition, so from PMP examination point of view it is unlikely that you will see questions on Critical Chain. But, from a knowledge point of view lets discuss this concept briefly.
We have already discussed the Critical Path Method, which is a technique for developing a Project Schedule. Critical Chain Method (CCM) is also another technique for developing project schedule.
First, let us see what a Critical Chain is, then we shall look into the Critical Chain method.
In simple words, A resource constrained Critical Path is called a Critical Chain.
A Critical Chain Method (CCM) allows the project team to place buffers on any of the project schedule paths to account for the limited resources and project uncertainties.
PMBOK defines CCM as “a schedule method that allows the project team to place buffers on any project schedule path to account for limited resources and project uncertainties.”
CCM follows the same approach of CPM, however, unlike CPM, it considers the effects of resource allocation, resource optimization, resource leveling, and activity duration uncertainty on the critical path. To factor in these effects, CCM introduces the concept of Buffers and Buffer management.
What is a buffer ?
Buffer is similar to a reserve. It is something (time or money) that is set aside to manage uncertainty or risk.
CCM is a schedule related technique. So, buffers in CCM means “duration buffers”.
The critical chain method adds duration buffers that are non-work schedule activities to manage uncertainty.
There are 2 types of buffers based on where they are placed on the Critical Chain.
- Project Buffer
- It is placed at the end of the Critical Chain before END.
- Project buffer protects project target finish date from slippage.
- Feeding Buffer
- It is placed at each points where a Non-Critical chain feeds into the critical chain.
- It protects the critical chain from slippage along the feeding chains.
- Size of feeding buffers should be inline with the level of uncertainty in the duration of the chain of dependent activities.
In Critical Path Method (CPM), focus is on managing the total float along the network paths, while in Critical Chain Method (CCM), focus is on managing the buffer durations against the durations of the chains of activities.