Network Diagrams
 It is defined 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.
 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

Network Diagrams
Show
interdependence
Facilitate
communication
Help
schedule
resources
Identify
critical
activitiesDetermine project
completion
Show
start &
finish
dates

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)
 Graphical Evaluation and Review Technique
(GERT)

Advantages of network scheduling
techniques include:
• They form the basis for all planning and
and help management decide how to use its
resources to achieve time and cost goals.
• They provide visibility and enable management
control programs.
• They help management evaluate alternatives
answering questions
o Such as how time delays will influence
completion, where slack exists between
elements, and what elements are crucial
meet the completion date.

Advantages of network scheduling
techniques also include:
• They provide a basis for obtaining facts for
making.
• They utilize a time network analysis as the basic
method to determine manpower, material, and
requirements, as well as to provide a means for
checking progress.
• They provide the basic structure for reporting
information.
• They reveal interdependencies of activities.
• They facilitate “what if ” exercises.
• They identify the longest path or critical paths.

Networks are composed of events and activities. The
following terms are helpful in understanding networks:
• Event: Equivalent to a milestone indicating when
an activity starts or finishes.
• Activity: The element of work that must be
accomplished.
• Duration: The total time required to complete the
activity.
• Effort: The amount of work that is actually
performed within the duration. For example, the
duration of an activity could be one month but the
effort could be just a two-week period within the
duration.
• Critical Path: This is the longest path through the
network and determines the duration of the
project. It is also the shortest amount of time

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.

AOA vs. AON
activities on arch
C
ED
B F
E
C
D
B F
activities on node

PERT/CPM
 PERT was developed in the late 1950s in
collaboration between the US Navy, Booz-Allen
Hamilton and Locked 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.

Precedence Diagramming
Method (PDM)
 PERT/CPM networks do not allow for leads and
lags between two activities;
o 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.

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

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

Node Labels
 Nodes representing activities should be labeled
with the following information:
 Identifier
 Description
 Duration
 Early StartTime
 Early FinishTime
 Late StartTime
 Late FinishTime
 Float

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 + Duration
 Late Start (LS) – Latest possible date an activity
may begin without delaying a specified milestone
(usually project finish date).
 Late Finish (LF) = LS + Duration

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

Serial Activities
Parallel Activities
Merge Activities
Activity
A
Activity
B
Activity
C
Activity
D
Burst Activities
Activity
C
Activity
B
Activity
A
Activity
D

Example
Activity Description Predecessors Duration
A Contract signing None 5
B Questionnaire design A 5
C Target market ID A 6
D Survey sample B, C 13
E Develop presentationB 6
F Analyze results D 4
G Demographic analysis C 9
H Presentation to clientE, F, G 2

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
Activity Description Predecessors Duration
A Contract signing None 5
B Questionnaire design A 5
C Target market ID A 6
D Survey sampleB, C 13
E Develop presentation B 6
F Analyze results D 4
G Demographic analysis C 9
H Presentation to client E, F, G 2
 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

 There are two terms related to Critical
Path that one may encounter. These the
terms are
Forward Pass
Backward Pass.
 These terms are related to ways of
determining the early or late start [forward
pass] or early or late finish [backward pass]
for an activity.
 Forward pass is a technique to move forward
through a diagram to calculate activity
duration.
 Backward pass is its opposite.

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:
o Add all activity times along each path as we move through the
network (ES + Dur = EF)
o 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
o 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)

Forward Pass
Activity D is a merge point for B and C
Activity H is a merge point for E, F, and G
0 A 5
Contract
5
5 C 11
Market ID
6
5 B 10
Design
5
11 G 20
Demog.
9
10 E 16
Dev.
Present.
6
11 D 24
Survey
13
24 F 28
Analysis
4
28 H 30
Present
2

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:
o Subtract activity times along each path through the
network (LF – Dur = LS).
o 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.
o 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)

Backward Pass
Activities A, B, and C are burst points
0 A 5
Contract
0 5 5
5 C 11
Market ID
5 6 11
5 B
10
Design
6 5
11
11 G 20
Demograph.
19 9 28
10 E 16
Dev. Present
22 6 28
11 D 24
Survey
11 13 24
24 F 28
Analysis
24 4 28
28 H 30
Presentation
28 2 30

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.
 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.

Complete Activity Network
0 A 5
0 Contract
0 5 5
5 C 11
0 Market ID
5 6 11
5 B
10
1 Design
6 5
11
11 G 20
8 Demograph.
19 9 28
10 E 16
12 Dev.
Present
22 6 28
11 D 24
0 Survey
11 13 24
24 F 28
0 Analysis
24 4 28
28 H 30
0
Presentation
28 2 30

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

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.

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

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.

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
A1(1) A2(1) A3(1)
B1(2) B2(2) B3(2)
C1(3) C2(3) C3(3)

 Draw the complete activity network for both the projects
and identify the critical pathActivity Preceding Activity Time (Weeks)
A — 4
B — 6
C A, B 7
D B 8
E B 5
F C 5
G D 7
H D, E 8
I F, G, H 4
Activity Preceding Activity Time (Weeks)
A — 7
B — 8
C — 6
D A 6
E B 6
F B 8
G C 4
H D, E 7
I F, G, H 3

Lec 09 network scheduling_techniques