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Network Planning

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

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Network Planning

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  1. 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 project’s success factors. • Note that timing and resources interact. OPSM 639, C. Akkan

  2. 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. OPSM 639, C. Akkan

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

  4. Time Planning • Let’s assume the following represent finish-start precedence relation: Task Immediate predecessors A - B A C B, D D - E D F E OPSM 639, C. Akkan

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

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

  7. 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). OPSM 639, C. Akkan

  8. Developing Project Network Level 1 - Milestone Plan Level 2 - Plans ABCDE Time M1 M2 M3 M4 Level 4 Level 3 - Plans WP1WP2WP3WP4 OPSM 639, C. Akkan

  9. 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. OPSM 639, C. Akkan

  10. 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. OPSM 639, C. Akkan

  11. 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. OPSM 639, C. Akkan

  12. 5 9 3 1 0 8 11 7 2 4 6 10 Developing Project Network • Rules: • draw networks from left to right • Each activity has a unique identification number • An activity’s 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. OPSM 639, C. Akkan

  13. Developing Project Network • Laddering • Consider a pipe laying project. Three basic activities: • dig a trench, lay the pipe, refill the trench • Let’s say the pipeline is 5 km long: You cannot dig the entire trench before laying the pipe. Trench Lay pipe Refill OPSM 639, C. Akkan

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

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

  16. C A B Start Finish D E F Developing Project Network 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. A, 3 B, 5 C, 3 D, 2 E, 2 F, 5 11 Time OPSM 639, C. Akkan

  17. 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. OPSM 639, C. Akkan

  18. 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. OPSM 639, C. Akkan

  19. Forward Pass with Time Lags Would be 5 with no lag. Would be 0 with no lag. Lag 10 2 5 5 10 2 ? A,3 B,5 C,3 0 Start Finish Lag 2 2 4 0 2 4 10 D,2 E,2 F,5 Would be 9 with no lag. Lag 6 OPSM 639, C. Akkan

  20. Backward Pass with Time Lags Lag 10 2 5 5 10 2 ? A,3 B,5 C,3 2 5 0 12 15 5 10 Start Finish Lag 2 Would be ? with no lag. 15 ? 2 4 0 2 4 10 D,2 E,2 F,5 7 9 10 15 ? 7 Lag 6 Would be ? with no lag. OPSM 639, C. Akkan

  21. 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. OPSM 639, C. Akkan

  22. 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 OPSM 639, C. Akkan

  23. 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). OPSM 639, C. Akkan

  24. 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. OPSM 639, C. Akkan

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