5/4/20151 NETWORK SCHEDULING TECHNIQUES

5/4/20152 Network Diagrams  PMI defines the scheduling process as: “the identification of the project objectives and the ordered activity necessary to complete the project including the identification of resource types and quantities required.”  Project scheduling defines the network logic for all activities that must either precede or succeed other tasks from the beginning of the project until its completion.

5/4/20153 Network Diagrams  Provide a basis for planning and how to use the resources  Identify the critical path and project completion time  Identify where slacks (float) are  Reveal interdependencies of activities  Aid in risk analysis (what-if analysis)

5/4/20154 Network Diagrams Show interdependence Facilitate communication Help schedule resources Identify critical activities Determine project completion Show start & finish dates

5/4/20155 Network Scheduling Techniques  Network scheduling techniques provide a logical process to consider the order in which the project activities should occur.  The primary methods for developing project activity networks are:  Program Evaluation and Review Technique (PERT)  Critical Path Method (CPM) – Also called Arrow Diagram Method (ADM)  Precedence Diagram Method (PDM)

5/4/20156 Network Scheduling Techniques  There are two ways to show the network:  Activity-On-Node (AON) – nodes represent the activities  Activity-On-Arch (AOA) – archs represent the activities  AON is easier, and it used in commercial software.

5/4/20157 AOA vs. AON activities on arc C E D B F E C D B F activities on node

5/4/20158 PERT/CPM  PERT was developed in the late 1950s in collaboration between the US Navy, Booz-Allen Hamilton and Lockeed Corporation for the creation of the Polaris missile program.  CPM was developed at the same time by DuPont.  Over the years the differences between PERT and CPM have blurred, so it is common to refer these techniques as just PERT/CPM.

5/4/20159 Precedence Diagramming Method (PDM)  PERT/CPM networks do not allow for leads and lags between two activities; i.e. a preceding activity must be completely finished before the start of the successor activity.  Precedence Diagramming Method (PDM) allows these leads and lags.  Most project management software systems use PDM and show interrelationships on bar charts.

5/4/ Precedence Network in a Gannt Chart TASKS MONTHS AFTER GO-AHEAD

5/4/ Network Development Rules  All activities must be linked to each other  Network diagrams flow from left to right  An activity cannot begin until all preceding connected activities have been completed  Each activity should have a unique identifier (number, letter, code, etc.)  Looping is not permitted  It is common to start from a single beginning and finish on a single ending node

5/4/ Steps in Creating the Network  Define the project and all of its significant activities  Develop the relationship among activities  Decide which activities must precede others  Draw the network connecting all of the activities  Compute the longest path which is the critical path  Calculate activity slacks (float)  Use the network to help plan, schedule, and control the project

5/4/ Node Labels  Nodes representing activities should be labeled with the following information:  Identifier  Description  Duration  Early Start Time  Early Finish Time  Late Start Time  Late Finish Time  Float

5/4/ Node Labels Early Start Activity Float Activity Descriptor Late Start ID Number Activity Duration Late Finish Early Finish

5/4/ Node Labels  Early Start (ES) – Earliest possible date an activity can start based on the network logic and any schedule constraints.  Early Finish (EF) = ES + Dur  Late Start (LS) – Latest possible date an activity may begin without delaying a specified milestone (usually project finish date).  Late Finish (LF) = LS + Dur

5/4/ Project Scheduling Terms Successors Predecessors Network diagram Serial activities Concurrent activities E D C B A F Merge activities Burst activities Node Path Critical Path

5/4/ Project Scheduling Activities  Serial activities flow from one to the next  Concurrent activities are accomplished at the same time  Merge activities have two or more immediate predecessor  Burst activities have two or more successor activities

5/4/ Serial Activities

5/4/ Parallel Activities

5/4/ Merge Activities Activity A Activity B Activity C Activity D

5/4/ Burst Activities Activity C Activity B Activity A Activity D

5/4/ Example ActivityDescriptionPredecessorsDuration AContract signingNone5 BQuestionnaire designA5 CTarget market IDA6 DSurvey sampleB, C13 EDevelop presentationB6 FAnalyze resultsD4 GDemographic analysisC9 HPresentation to clientE, F, G2

5/4/ Example A Contract 5 C Market ID 6 B Design 5 G Demog. 9 E Dev. Present. 6 D Survey 13 F Analysis 4 H Present 2

5/4/ Example  Path One: A-B-E-H = 18 weeks  Path Two: A-B-D-F-H = 29 weeks  Path Three: A-C-D-F-H = 30 weeks  Path Four: A-C-G-H = 22 weeks Path three is the critical path

5/4/ Forward Pass  Forward pass determines the earliest times (ES) each activity can begin and the earliest it can be completed (EF).  There are three steps for applying the forward pass:  Add all activity times along each path as we move through the network (ES + Dur = EF)  Carry the EF time to the activity nodes immediately succeeding the recently completed node. That EF becomes the ES of the next node, unless the succeeding node is a merge point  At a merge point, the largest preceding EF becomes the ES for that node (because the earliest the successor can begin is when all preceding activities have been completed)

5/4/ Forward Pass 0 A 5 Contract 5 5 B 10 Design 5 5 C 11 Market ID 6 11 D 24 Survey G 20 Demog F 28 Analysis 4 10 E 16 Dev. Present 6 28 H 30 Present 2 Activity D is a merge point for B and C Activity H is a merge point for E, F, and G

5/4/ Backward Pass  The goal of the backward pass is to determine each activity's Late Start (LS) and Late Finish (LF) times.  There are three steps for applying the backward pass:  Subtract activity times along each path through the network (LF – Dur = LS).  Carry back the LS time to the activity nodes immediately preceding the successor node. That LS becomes the LF of the next node, unless the preceding node is a burst point.  In the case of a burst point, the smallest succeeding LS becomes the LF for that node (because the latest the predecessor can finish is when any one of the successor activities should start)

5/4/ Backward Pass 0 A 5 Contract B 10 Design C 11 Market ID D 24 Survey G 20 Demograph F 28 Analysis E 16 Dev. Present H 30 Presentation Activities A, B, and C are burst points

5/4/ Slack Time (Float)  Since there exists only one path through the network that is the longest, the other paths must either be equal or shorter.  Therefore, there are activities that can be completed before the time when they are actually needed.  The time between the scheduled completion date and the required date to meet critical path is referred as the slack time.  The activities on the critical path have zero slack time.

5/4/ Slack Time (Float)  The use of slack time provides better resource scheduling.  It is also used as warning sign i.e. if available slack begins to decrease then activity is taking longer than anticipated.  Slack time is equal to: LS – ES or LF – EF  Activities on the critical path have 0 slack; i.e. any delay in these activities will delay the project completion.

5/4/ Complete Activity Network 0 A 5 0 Contract B 10 1 Design C 11 0 Market ID D 24 0 Survey G 20 8 Demograph F 28 0 Analysis E Dev. Present H 30 0 Presentation

5/4/ Reducing the Critical Path  Eliminate tasks on the Critical Path  Convert serial paths to parallel when possible  Overlap sequential tasks  Shorten the duration on critical path tasks  Shorten  early tasks  longest tasks  easiest tasks  tasks that cost the least to speed up

5/4/ Lag  Lag is the time between Early Start or Early Finish of one activity and Early Start and Early Finish on another activity.  For example, in a Finish-to-Start dependency with a 10-day lag, the successor activity cannot start until 10 days after the predecessor activity has finished.  Lags are not the same as slacks. Lags are between activities whereas slacks are within activities.

5/4/ Finish to Start Lag Most common type of sequencing Shown on the line joining the modes –Added during forward pass –Subtracted during backward pass 0 A 6 Spec Design 6 6 B 11 Design Check 5 15 C 22 Blueprinting 7 Lag 4 This lag is not the same as activity slack

5/4/ Lead  Lead allows an acceleration of the successor activity. We can expedite the schedule by not waiting a preceding activity to be completely finished before starting its successor.  For example, in a Finish-to-Start dependency with a 10-day lead, the successor activity can start 10 days before the predecessor activity has finished.

5/4/ Laddering Activities Project ABC can be completed more efficiently if subtasks are used (Fast Tracking) A(3)B(6)C(9) ABC=18 days Laddered ABC=12 days A 1 (1)A 2 (1)A 3 (1) B 1 (2)B 2 (2)B 3 (2) C 1 (3)C 2 (3)C 3 (3)

5/4/ Hammock Activities Used as summaries for subsets of activities 0 A B C Hammock Useful with a complex project or one that has a shared budget