---
title: "Network diagram"
subject: "ICT Project Management"
chapter: 8
key: "semester_7/ict_project_management:network-diagram"
source: https://www.bctengineer.com/q/semester_7/ict_project_management/network-diagram
site: BCT Engineering
---

# Network diagram

ICT Project Management · Chapter 8: Project Time Management

- Asked in: year not given
- Video: [How to draw a CPM network diagram](https://www.youtube.com/watch?v=gEBMPP0SOnU) — Engineer4Free
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/ict_project_management/network-diagram
- Whole chapter: https://www.bctengineer.com/md/semester_7/ict_project_management/chapter-8

## Question

What do you mean by network diagram?

## Answer

A **project network diagram** is a schematic display of the logical relationships (dependencies) among the project activities. It shows the sequence in which activities are to be done, and is used to find the critical path, float and the project duration. It is produced in the "Sequence activities" process (precedence diagramming).

#### Types
1. **Activity-on-Node (AON) / Precedence Diagramming Method (PDM)**
   - Boxes (nodes) represent activities; arrows show dependencies.
   - Supports four relations: finish-to-start (FS), start-to-start (SS), finish-to-finish (FF), start-to-finish (SF), with leads and lags. Most commonly used.
2. **Activity-on-Arrow (AOA) / Arrow Diagramming Method (ADM)**
   - Arrows represent activities; nodes represent events. Uses only finish-to-start and may need dummy activities.

The same logic (B and C follow A; D follows both B and C) in both forms:
```text
AON:   [A 3d] --> [B 5d] --> [D 2d]
          \                   ^
           +-> [C 4d] -------+

AOA:  (1)--A-->(2)--B-->(3)--D-->(5)
                |        ^
                C        : dummy
                |        :
                +-->(4)..:
```
(In AOA, B and C cannot both join nodes 2 and 3, so a dummy from 4 to 3 shows that D also depends on C.)

#### Information in a node
Activity name, duration, earliest start (ES), earliest finish (EF), latest start (LS), latest finish (LF) and float.

#### Uses
- Show the order of work.
- Calculate the critical path via the forward pass (ES, EF) and backward pass (LS, LF).
- Float = LS − ES = LF − EF.
- Identify parallel activities, bottlenecks and schedule compression options.
- Basis for the Gantt chart and resource scheduling.

#### Steps to draw
1. List activities from the WBS.
2. Find the predecessors of each.
3. Draw a start node and arrange activities from left to right.
4. Link dependencies; avoid loops.
5. Add durations and calculate.

#### Advantages and limits
Clear logic and critical path identification; but large networks become complex.

| Dependency type | Example |
|---|---|
| Mandatory | Coding before testing |
| Discretionary | Preferred order |
| External | Vendor delivery |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does AON differ from AOA?
   A. AON uses nodes for activities; AOA uses arrows for activities and nodes for events
   B. Both use arrows
   C. AOA supports four dependency types and AON only one
   D. AON uses arrows for activities
   Answer: A. In AON (PDM) boxes are activities; in AOA (ADM) arrows are activities and nodes are events. (Key point: AON vs AOA)

2. How is float calculated?
   A. LS - ES (or LF - EF)
   B. ES + EF
   C. LF + LS
   D. EF - ES
   Answer: A. Float = LS - ES = LF - EF. (Key point: Float)

3. Which dependency type does AON support that AOA does not?
   A. Dummy activities
   B. Mandatory dependencies
   C. Only finish-to-start
   D. Start-to-start, finish-to-finish and start-to-finish relations
   Answer: D. AON supports FS, SS, FF and SF with leads and lags; AOA uses only finish-to-start. (Key point: Dependency types)

4. What does the forward pass calculate?
   A. LS and LF
   B. Float only
   C. ES and EF
   D. Cost baseline
   Answer: C. Forward pass gives earliest start and finish; backward pass gives latest start and finish. (Key point: Forward and backward pass)

## Related in other subjects

- [Block diagram and Vo/Vi of L-R ladder network](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Abd-l1-r1-l2-r2) — Control Systems, chapter 2
- [Block diagram model of R-L ladder network](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Abd-r1-l1-r2-l2) — Control Systems, chapter 2
- [Network errors; expected time of engineers](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Anetwork-errors-expected-time-engineers) — Project Engineering, chapter 3
- [CPM network, 9 activities (A=3 to I=1)](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-network-nine-act-b82) — Project Engineering, chapter 3, asked 5×