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OPSM 639, C. Akkan1 Network Planning Purposes of network planning –Determine the intended timing of activities –Determine the estimates of resource requirements.

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Presentation on theme: "OPSM 639, C. Akkan1 Network Planning Purposes of network planning –Determine the intended timing of activities –Determine the estimates of resource requirements."— Presentation transcript:

1 OPSM 639, C. Akkan1 Network Planning Purposes of network planning –Determine the intended timing of activities –Determine the estimates of resource requirements –Develop of comprehensible picture of the project. –Take a proactive approach in order to prevent errors –Minimize the effects of uncertainties on the projects success factors. Note that timing and resources interact.

2 OPSM 639, C. Akkan2 Network Planning The fundamental element of time planning is developing a project network. The network depicts the tasks and the logical precedence structure between these activities.

3 OPSM 639, C. Akkan3 Time Planning A B B B A A Types of precedence relations between activities: Finish - Start: One task cannot start until the other has finished. Start - Start: Unless one of the tasks has started the other cannot start. Start- Start with time lag: A certain time has to pass after one task has started until the other starts.

4 OPSM 639, C. Akkan4 Time Planning Lets assume the following represent finish-start precedence relation: TaskImmediate predecessors A- BA CB, D D- ED FE

5 OPSM 639, C. Akkan5 Time Planning The following is called an activity-on-node network diagram (or PERT diagram) Start A D C E B Finish F

6 OPSM 639, C. Akkan6 Time Planning Time 11 A, 3 B, 5 D, 2 C, 3 E, 2 F, 5 Bar (Gantt) chart: ABCDEFABCDEF

7 OPSM 639, C. Akkan7 Developing Project Network Developing a network takes time (thus costs money). Is it worth it? –Provides a graphic display of the flow and sequence of work that is easy to understand. –Provides the basis for scheduling and resource planning. –Yields a realistic estimate for total project time. –Easy to update when unexpected events occur. –Helps identify critical activities (whose delay will most probably delay the entire project).

8 OPSM 639, C. Akkan8 Developing Project Network Level 1 - Milestone Plan ABCDEABCDE Time WP1 WP2 WP3 WP4 Level 4 Level 2 - Plans Level 3 - Plans M1M2M3M4

9 OPSM 639, C. Akkan9 Developing Project Network Integrating WBS and the network is crucial. The hierarchical nature of WBS allows different levels of managers to visualize the project plan at different levels of detail. –The milestone plan, in the form of a bar chart, shows the level of detail useful for top management, showing only the major deliverables. –Work-packages are used to develop a detailed network for the first-line managers.

10 OPSM 639, C. Akkan10 Developing Project Network Not only time, but also cost and resource plans can be rolled up from the work-package level to the top level. –Deliverables and sub-deliverable in WBS must be designed so that after roll-up managers at different levels can obtain plans/reports that can be useful for them.

11 OPSM 639, C. Akkan11 Developing Project Network Network terminology –Activity: Element of a project that takes time. Usually one or more work packages. –Merge activity: Activity with more than one immediate predecessor activity. –Burst activity: Activity with more than one immediate successor activity. –Parallel activities: Activities that can take place simultaneously. –Path: A sequence of connected activities. –Critical path: Longest path(s) through the network –Event: Represents a point in time.

12 OPSM 639, C. Akkan12 Developing Project Network Rules: draw networks from left to right Each activity has a unique identification number An activitys identification nbr should be larger than the activities preceding it. Loops (cycles) are not allowed. Conditional statement (e.g. if this happens then …) are not allowed. If there are multiple start or finish activities, a common start or finish node is used.

13 OPSM 639, C. Akkan13 Developing Project Network Laddering –Consider a pipe laying project. Three basic activities: dig a trench, lay the pipe, refill the trench –Lets say the pipeline is 5 km long: You cannot dig the entire trench before laying the pipe. TrenchLay pipeRefill

14 OPSM 639, C. Akkan14 Developing Project Network –Instead:break activities into segments and ladder them Trench 1/3 Lay pipe 1/3 Trench 1/3 Lay pipe 1/3 Refill 1/3

15 OPSM 639, C. Akkan15 Developing Project Network Calculating the earliest and latest times (numbers in the nodes represent activity durations): Start A,3 D,2 C,3 E,2 B,5 Finish F,5

16 OPSM 639, C. Akkan16 Developing Project Network Start A D C E B Finish F Time 11 A, 3 B, 5 D, 2 C, 3 E, 2 F, 5 Total slack (float) for an activity = LS - ES (or LF - EF) Free slack: Amount an activity can be delayed without delaying early-start (ES) of activities following it.

17 OPSM 639, C. Akkan17 Using Time Lags A lag is the minimum amount of time a dependent activity must be delayed to begin or end. Uses for start-to-start time lags –Instead of using laddering. –Concurrent engineering practice that compresses the total product development time. Uses for finish-to-start time lags –Modelling ordering of parts: 1 day takes to place to order, 14 days to receive it. Uses for finish-to-finish time lags –Painting multiple layers.

18 OPSM 639, C. Akkan18 Using Time Lags It is possible to have multiple time-lags attached to a pair of activities. –Usually an start-to-start and finish-to-finish Network calculations with time lags –forward and backward pass procedures are the same as the ones for finish-to-start case with no time lags. Difference is in checking the time lag relationships effects on the activities times.

19 OPSM 639, C. Akkan19 Forward Pass with Time Lags Start A,3 D,2 C,3 E,2 B,5 Finish F,5 Lag 2 Lag 6 Lag Would be 0 with no lag Would be 9 with no lag. 2 ? Would be 5 with no lag. 0

20 OPSM 639, C. Akkan20 Backward Pass with Time Lags Start A,3 D,2 C,3 E,2 B,5 Finish F,5 Lag 2 Lag 6 Lag 10 ? Would be ? with no lag ? 0 ? Would be ? with no lag.

21 OPSM 639, C. Akkan21 Estimating Activity Times Guidelines –Responsibility: at the work-package level estimates should be made by person(s) most familiar with the task. Those responsible for getting the job done on schedule should determine the estimated times. –They will have less bias due to imposed deadlines. –Their judgement will be based on experience. –They will do their best to materialize their estimates.

22 OPSM 639, C. Akkan22 Estimating Activity Times –Normal conditions: Estimates should be based on normal conditions, efficient methods and a normal level of resources. A consensus is required in the organization as to what normal conditions mean. –Time Units: All task time estimates need consistent time units. In practice workday is the most frequent choice. Other alternatives: –calendar days, workweeks, minutes, shifts

23 OPSM 639, C. Akkan23 Estimating Activity Times –Independence: Estimators should treat the task as independent of other tasks in the WBS. Top managers tend to aggregate many tasks into one estimate and deduce the durations of individual tasks from this aggregate. It is better to obtain estimates from first-line managers who consider tasks independently. If tasks are in a chain, opportunity should not be given to modification of estimates so that total chain time meets an arbitrary schedule (imposed).

24 OPSM 639, C. Akkan24 Estimating Activity Times –Contingencies Work package estimates should not include allowances for contingencies. –Estimate errors The project management culture should allow estimate mistakes and errors to occur. –Punishment leads to future estimates being inflated. –Trust in the project management culture will results in more realistic estimates.

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