Presentation on theme: "5/4/20151 NETWORK SCHEDULING TECHNIQUES. 5/4/20152 Network Diagrams PMI defines the scheduling process as: “the identification of the project objectives."— Presentation transcript:
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.
5/4/201510 Precedence Network in a Gannt Chart TASKS12345 4 MONTHS AFTER GO-AHEAD 3 2 1 5
5/4/201511 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
5/4/201512 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
5/4/201513 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
5/4/201514 Node Labels Early Start Activity Float Activity Descriptor Late Start ID Number Activity Duration Late Finish Early Finish
5/4/201515 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
5/4/201516 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
5/4/201517 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
5/4/201523 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
5/4/201524 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
5/4/201525 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)
5/4/201526 Forward Pass 0 A 5 Contract 5 5 B 10 Design 5 5 C 11 Market ID 6 11 D 24 Survey 13 11 G 20 Demog. 9 24 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
5/4/201527 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)
5/4/201528 Backward Pass 0 A 5 Contract 0 5 5 5 B 10 Design 6 5 11 5 C 11 Market ID 5 6 11 11 D 24 Survey 11 13 24 11 G 20 Demograph. 19 9 28 24 F 28 Analysis 24 4 28 10 E 16 Dev. Present 22 6 28 28 H 30 Presentation 28 2 30 Activities A, B, and C are burst points
5/4/201529 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.
5/4/201530 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.
5/4/201531 Complete Activity Network 0 A 5 0 Contract 0 5 5 5 B 10 1 Design 6 5 11 5 C 11 0 Market ID 5 6 11 11 D 24 0 Survey 11 13 24 11 G 20 8 Demograph. 19 9 28 24 F 28 0 Analysis 24 4 28 10 E 16 12 Dev. Present 22 6 28 28 H 30 0 Presentation 28 2 30
5/4/201532 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
5/4/201533 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.
5/4/201534 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
5/4/201535 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.
5/4/201536 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)
5/4/201537 Hammock Activities Used as summaries for subsets of activities 0 A5 0 55 5 B15 5 1015 15 C18 15 318 0 Hammock18 01818 Useful with a complex project or one that has a shared budget