View source for Network Planning


== Abstract ==
The success of a project's realization depends heavily on the effectiveness of the planning phase. This article will present how to use network planning in project management, which can be very challenging, and requires careful planning, managing, and controlling. The ability to break down work and segment it into different assignments can be critical for project success. Having a comprehensive plan can explain the project's complexity and keep it on track <ref name="PMBook"/>. Network planning is a common term for methods where projects are studied as a series of interrelated activities to plan, manage, and control projects <ref name="NP"/>. 

According to Guide to the Project Management Body of Knowledge, project schedule management includes various processes required to manage the project's timely completion. These processes refer to, among other things, how to sequence activities and estimate activities duration. Moreover, they include developing and controlling the schedule. Network planning methods help in this processing. The main objectives of network planning are determining the project duration and the Critical Path. Moreover, find out how to speed up a project if that becomes necessary. As a result, it is a basis for scheduling <ref name="PMI1"/>.

The most well-known network planning techniques are the Critical Path Method (CPM) and the Program Evaluation and Review Technique (PERT). These methods include describing each of the activities involved in the project, the order in which must carry out the activities, and the activities carried out in tandem with other activities. Using network planning methods results in showing activities that can be completed simultaneously and increases efficiency. Moreover, it helps in decisions making and saves time, and therefore decreases cost. Conversely, creating it uses merely estimates, which may be inaccurate. Furthermore, large scale projects are often complex and detailed, and thus performing network planning on them, can be time-consuming <ref name="NP"/>.

The focus of this article will be introducing network planning and describing different methods of it. Moreover, identify how to apply network planning techniques to project management and choose the right method for various projects. Finally, this article will describe the limitation of network planning.
 

== Why Use Network Planning in Project Management? ==
 
=== History ===
Network planning methods were first developed in the late 1950s. The most known network planning techniques are the Program Evaluation and Review Technique (PERT) and Critical Path Method (CPM), which were also the first methods developed. Initially, PERT was built to prepare and control the Polaris rocket, an extensive project involving thousands of operations, using more than 3,000 contractors. As a result, the project’s duration was reduced by two years. Many government contracts also involve the use of PERT or a similar technique because of its effectiveness. CPM was designed initially for the preparation and coordination of chemical plant maintenance programs <ref name="OpBook"/>.

=== Description of Network Planning in Project Management ===
Network planning can research various issues such as project scheduling, risk analysis, cost minimization, or net present value maximization. Therefore, it can find the most appropriate balance between risk, quality, length, and cost. Moreover, using network planning in project management allows project teams to visualize all the tasks that need to be done during a project’s lifecycle. It also provides essential context, such as length of the job, sequence, and dependence on the project schedule. Furthermore, it helps to find the critical path, slack, and max float, among other things <ref name="NP"/>. 

From the complexity perspective, the central part of ISO 21500 discusses project and project management. It suggests structural, technical expertise to be implemented in a particular sequence in the form of activities. Thus, projects operate smoothly, effectively, and efficiently. Moreover, activities related to complexity are linked to the planning processes and involve the functions necessary to manage and control various project-related activities. The primary purpose of network planning in project management is to aid in the planning, managing, and controlling of projects <ref name="PMBook"/>. 

Network planning is a sequential categorization of the activities involved in the project's execution, accompanied by a graphical presentation of the actions required for the project as a whole. Therefore, network planning is a distributed model of work to be done in a project. A hierarchy of interdependent job elements, which are processes, tasks, and activities, is sequenced and prioritized to identify and describe the overall project effort. Typically, the project network is constructed and built using charts and hierarchical diagrams or often termed project network diagrams <ref name="PSNP"/>.

Each terminal element represents an operation at the lowest level of the work breakdown structure (WBS) related to a work package. However, although the WBS does not attempt to decide the sequence of events or the length of any activity, the network planning diagram attempts to determine the series of activities that take place and the other activities (if any) on which the activity depends. When conducting network planning diagram, there is a range of techniques used. Critical Path Management (CPM) and the Project Evaluation and Review Technique (PERT) are some of the most widely used methods. Every terminal element (or activity) is represented by a node on a graph in some techniques, while it is characterized by an edge in others (the line connecting two nodes). Only one path for every terminal element must lie through the network <ref name="Techno"/>. 

Multiple sequences of activities are included in the network planning that specifies one or another aspect of work, for example, a process or phase. The main criterion for the network planning efficiency is that each sequence of activities should have a finite and measurable outcome and never contain circular references. If there is a circular reference in an operation chain, it creates a closed-loop, resulting in an endless cycle <ref name="PSNP"/>.

A network planning diagram allows the project manager to assess a project's most likely sequence of events and provides the basis for a practical project schedule. It will enable the project manager to measure the total duration needed for the project, determine the order in which tasks need to be completed, and highlight those tasks vital to the project's timeline. Once the WBS is complete, the project manager will have a list of tasks at different decomposition stages to accomplish the project's goal. To allow a schedule to be generated, the project manager now decides the task dependencies and each task's length. Project management software is now available to perform the scheduling for project managers, measure the total time needed to complete the project, and define the schedule's critical path. Merely what project managers have to do is determine each task's length and consider any task dependencies. Based on the data they provide, the program can generate network activity charts <ref name="Techno"/>. 

== Application == 
It is important to break down projects into smaller activities for projects to become achievable. Furthermore, to coordinate these interdependent activities and finally, adapt the project and respond to changes. When the project has been broken down into smaller pieces and the activities defined, the scheduling of it can begin <ref name="PMBook"/>. In project management, there are two primary types used when drawing network diagrams, which are the Arrow Diagramming Method (ADM) and the Precedence Diagramming Method (PDM) <ref name="PMI2"/>.

The arrow diagramming technique (ADM) refers to a schedule network diagramming technique in which arrows represent schedule activities within a specified project. The arrow's tail or base defines the start of the operation in the schedule. The pointed end of the arrow illustrates the endpoint of a selected process within the schedule. The duration of the arrow will loosely reflect the time between. The points to which these planning operations are connected are referred to as nodes. To illustrate the sequence or order in which these activities should occur, the relation of these schedule activities is performed. This link point, or node, is typically represented by a small circle or sphere. An operation with a length of zero can be seen in the ADM graph below. These operations are referred to as dummy operations and are usually represented using dotted lines. Dummy activities express dependencies between tasks. The activity B-D in the below diagram is a dummy activity. An example of why a project manager might need a dummy activity is if activity C is about tiling a floor. It can only start once the concrete is poured (Activity B) and the permits are gotten in activity D. In contrast, activities B and D are not directly linked, the project manager needs to draw a dummy activity between B and D to demonstrate that C is dependent on D being finished. Moreover, there is also not possible for an ADM chart to encapsulate lead and lag times without new nodes and activities being implemented <ref name="PMI2"/><ref name="PMG"/>.

[[File:ADM.png|700px|Figure 1: The Arrow Diagramming Technique.]]

The precedence diagramming method (PDM) refers to a selected project management technique. The project manager employs a schedule network diagramming technique to graphically represent any known and preexisting schedule activities via the utilization of boxes (which also can be mentioned as nodes). Once all of these basic schedule tasks have been graphically displayed in this box or node format, all of the individual boxes are connected by using a line describing any logical relationship that is found to occur. The fundamental and most important advantage of using the precedence diagramming system's style methodology is that it helps the project manager view all plan tasks and their relationships with each other rapidly and efficiently <ref name="PMI2"/><ref name="PMG"/>.

[[File:PDM.png|700px|Figure 2: The Precedence Diagramming Method.]]

Networks flow from left to right in both arrow diagrams and precedence diagrams. Each activity is marked with a unique name, and once all its previous activities are complete, the activity may start. For example, as per the node diagram activity shown above, activity C can not begin until activity B and activity D has been completed. The nodes for start and stop should be distinctive <ref name="PMG"/>.

In network diagrams, four types of dependencies are primarily depicted. They are Finish to Start (FS), Finish to Finish (FF), Start to Start (SS), and Start to Finish (SF). It is possible to represent these four types of dependencies as shown below <ref name="PMG"/>.

[[File:TypesOfDependencies.png|700px|Figure 3: Four Types of Dependencies.]]

'''Finish to Start (FS):'''
The next activity (successor) in this relationship cannot be initiated before the first one (predecessor) is finished. In network diagrams, this is the most common form of the dependency used. An example of this kind of dependency is that it is impossible to begin floor tiling until the waterproofing is finished. In the ADM graph, the only relation between the nodes can be expressed by an activity that is of "finish to start" dependency <ref name="PMG"/><ref name="ND"/>. 
 
'''Finish to Finish (FF):'''
In this type of dependency, it is impossible to complete the second activity before the first activity ends. Typically, this connection is used to achieve a milestone at the end. For instance, if the project manager is asked to finish a concrete work and the client has put it as a milestone on the project manager’s schedule. This milestone will be automatically reached after the project manager completes the last task like poring on concrete <ref name="PMG"/><ref name="ND"/>.

'''Start to Start (SS):'''
In the Start to Start dependency, the second activity cannot be initiated until the first activity begins. This is used to demonstrate that two activities will start simultaneously. This relationship is useful when crashing a schedule. If the paintwork is started on one floor, for example, then if ready, the project manager will begin painting on the other floor. In the project manager's schedule, this will save time <ref name="PMG"/><ref name="ND"/>.

'''Start to Finish (SF):'''
In this relationship, once the first activity begins, the second activity cannot be completed. This is an unusual dependency; however, an example of this dependency is before the project manager can start turning off the old system, the implementation of a new accounting system needs to be completed <ref name="PMG"/><ref name="ND"/>.

In order to create a network diagram, various requirements must comply. For the full scope of the project, tasks should be specified. There has to be logic between activities, and the time estimate of all the activities must be completed beforehand <ref name="ND"/>.


== Network Planning Tools ==

=== CPM & PERT ===
As mentioned before, the most common network planning tools are the CPM and PERT, and they both have similar characteristics. The first characteristic is that it is possible to break the project down into a well-defined set of activities or jobs. It is essential to perform these activities in a specific sequence. Lastly, the operation should be started and stopped within a given sequence <ref name="MH"/>.

However, the main difference between these network planning tools is that CPM is determinist structured and PERT probabilistic. Therefore, for traditional, routine projects with a comprehensively known and well-defined scope, and the possible changes and risks merely marginally affect the entire course of the project, CPM is recommended. Additionally, for the purpose of measuring a project with a technique like CPM, its length should be viewed as a single value for each activity, such as five working days. Conversely, reality often changes and is unpredictable, and therefore executing reasonable quality estimates is difficult and costly. Hence, a probabilistic approach and the use of PERT are suggested to represent better the effect of risk and uncertainty on a project and improve the reliability of the forecasts <ref name="Prob"/>.

The article, "Comparison between Deterministic and Stochastic Time Estimating Techniques" <ref name="DS"/>, explains the difference between deterministic and stochastic approaches. There it is mentioned that two-time dimensions influence time management, which is the actual time and calendar time. Furthermore, while there are numerous existing estimating techniques, the deterministic and stochastic are the most commonly used in the time estimation process. Historically, most project management practitioners use one or the other as their essential technique for estimating time. This article examines these two techniques and determines, like others have, that no specific method is more suitable in each estimating situation. As verified by others, it was recommended that CPM be used when activity times are predictable (deterministic) <ref name="DS"/>.

In contrast, PERT techniques should be used in cases where activity times are unpredictable (probabilistic). PERT gives a more reliable estimate for projects that allow for a more extended period of time for completion and difficult to estimate. On the other hand, CPM is a good alternative for traditional projects with predictable tasks and assignments. It is therefore inferred, on the whole, that PERT offers a better model for estimating than CPM <ref name="DS"/>.

=== GERT ===
Another standard network planning tool is GERT. The article, Project Management Using GERT Analysis, explains the modeling technique and simulation package of the GERT network and demonstrates its capabilities through an example of planning for R&D projects. Additionally, a summary of the use of GERT performance for management planning and control, including sensitivity analysis and implementation, is included <ref name="GERT"/>.

=== SNPM === 
Several studies have shown where projects fail due to uncertainty and inaccurate estimates. The network planning tool Stochastic Network Planning Method (SNPM) has some advantages over PERT and GERT. The benefit of SNPM is that it finds potential solutions with the aid of stochastic variables and that all possible successor relations are taken into account. In this process, if the effect on the project changes, the parameters can be modified due to changes in the market's technological conditions or tendencies. The SNPM may thus be useful as an expert system module <ref name="SNPM"/>.

== Limitations ==
Overall, network planning tools are created using only estimates, which may be inaccurate. It is often difficult to use it in large-scale projects as they can be complicated and detailed, and therefore, it can be time-consuming using network planning tools. Moreover, one of the challenges of network planning is it puts pressure on the manager to achieve deadlines, which may result in corners being cut and led to less quality in projects. Additionally, network planning does not illustrate how much the project will cost, or its quality.

PERT and CPM are helpful tools that graphically provide details about project schedules, but they do not tell the project manager everything. For instance, they do not tell the project manager what resources are needed for a specific task. Network diagrams of activities are snapshots of a project's status at a given moment. Updating the network diagrams as conditions shift would be necessary. If a job takes longer than anticipated, the overall project timeline will affect. For tasks that are performed ahead of time, the same is true. From looking at the network diagram alone, the effect on resources will not be evident. Other methods and techniques must be used to assess when the peaks and troughs will occur in terms of demand for vital project resources.

== Annotated Bibliography ==

'''Kosztyán Z.T., Kiss J. (2010) Stochastic Network Planning Method. In: Elleithy K. (eds) Advanced Techniques in Computing Sciences and Software Engineering. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-3660-5_44:''' This article describes the Stochastic Network Planning Method (SNPM) and references several studies where projects fail due to uncertainty and inaccurate estimates. Moreover, this article explains the advantages of SNPM over some of the most known methods of network planning, PERT and GERT.

'''Briggs D. G. (2017) Comparison between Deterministic and Stochastic Time Estimating Techniques. In: International Journal of Advanced Research in Science, Engineering and Technology. IJARSET. http://www.ijarset.com/upload/2017/july/21-IJARSET-daketima.pdf''': This paper identifies the difference between the two main techniques of network planning, CPM and PERT. Time is one of the variables in project management that provides inputs for use in project scheduling. There are two dimensions of time that impact time management: real-time and calendar time. There are a variety of estimation techniques available. Two methods are most widely used in the time estimation process among the different methods: the determinist (single-point) estimation technique and stochastic (three-point) estimation technique. This article argues that in situations where activity times are predictable (deterministic), CPM should be used, while PERT techniques should be used in cases where activity times are unpredictable (probabilistic). Furthermore, it concludes that PERT offers a better model for estimating than CPM.

'''Taylor, B. W. (1978). Project management using GERT analysis. Project Management Quarterly, 9(3), 15–20.''': This article explains the modeling technique and simulation package of the GERT network and demonstrates its capabilities by planning for R&D projects. Additionally, a summary of the use of GERT performance for management planning and control, including sensitivity analysis and implementation, is included.

== References ==
<references>

<ref name="PMBook">J. Geraldi, C. Thuesen, & J. Oehmen. (2017). ''Doing Projects - Nordic flavour to managing projects''. Danish Standards Foundation. </ref>

<ref name="NP">Rand G.K., Tavares L.V. (2001) Network planning. In: Gass S.I., Harris C.M. (eds) Encyclopedia of Operations Research and Management Science. Springer, New York, NY. https://doi.org/10.1007/1-4020-0611-X_665 </ref>

<ref name="PMI1">Project Management Institute. (2010). ''A Guide to the Project Management Body of Knowledge (PMBOK Guide)''. Project Management Institute. ISBN: 9781930699458, 193069945X </ref>

<ref name="OpBook"> R. Dan Reid & Nada R. Sanders. (2013). ''Operations Management: An Integrated Approach, 5th Edition International Student Version''. Wiley. ISBN: 978-1-118-55566-8 </ref>

<ref name="PSNP">A. Shaddra. (n.d.). ''Project Scheduling and Network Planning (With Diagram)''. https://www.yourarticlelibrary.com/project-management/project-scheduling-and-network-planning-with-diagram/95024/. Visited: 15.02.2021 </ref>

<ref name="Prob">Wyrozębski, Paweł & Wyrozębska, Agnieszka. (2013). ''Challenges of project planning in the probabilistic approach using PERT, GERT and Monte Carlo''. Journal of Management and Marketing. 1. 1-8. </ref>

<ref name="DS">Briggs D. G. (2017). ''Comparison between Deterministic and Stochastic Time Estimating Techniques''. In: International Journal of Advanced Research in Science, Engineering and Technology. IJARSET. http://www.ijarset.com/upload/2017/july/21-IJARSET-daketima.pdf </ref>

<ref name="Techno">Technology UK. (n.d.) ''Project Networks''. https://www.technologyuk.net/computing/software-development/project-management/project-networks.shtml. Visited 15.02.2021 </ref>

<ref name="PMI2">Project Management Institute. (2004). ''A Guide to the Project Management Body of Knowledge (PMBOK Guide)''. Project Management Institute. ISBN: 978-1930699458 </ref>

<ref name="PMG">Project Management Guide. (n.d.). ''What is a Network Diagram in Project Management''. https://www.wrike.com/project-management-guide/faq/what-is-a-network-diagram-in-project-management/. Visited 16.02.2021 </ref>

<ref name="ND">Project PM. (15.11.2020). ''Network Diagrams''. https://project.pm/network-diagrams/. Visited 17.02.2021 </ref>

<ref name="MH">Management Hub. (n.d.). ''Planning, scheduling, and controlling a project effectively''. https://www.management-hub.com/project-management-planning.html. Visited 14.02.2021 </ref>

<ref name="GERT">Taylor, B. W. (1978). Project management using GERT analysis. Project Management Quarterly, 9(3), 15–20. </ref>

<ref name="SNPM">Kosztyán Z.T., Kiss J. (2010) Stochastic Network Planning Method. In: Elleithy K. (eds) Advanced Techniques in Computing Sciences and Software Engineering. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-3660-5_44 </ref/>