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test 2 material - -PROJECT NETWORKS FORWARD/BACKWARD PASS...

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9/27/2011- PROJECT NETWORKS –FORWARD/BACKWARD PASS CALCULATIONS Developing the Project Network A project network is a flow chart that graphically depicts the sequence, interdependencies, and start and finish times of the project job plan of activities that is the critical path through the network. Network Computation Process – Forward Pass/Back Pass Purpose – compute the start and finish times of activities Based on the activity time estimates from the WBS Forward Pass—Earliest Times o How soon can the activity start? (early start—ES) o How soon can the activity finish? (early finish—EF) o How soon can the project finish? (expected time—ET) Network Computation Process (computing start/finish times of activities) Backward Pass—Latest Times o How late can the activity start? (late start—LS) o How late can the activity finish? (late finish—LF) o Which activities represent the critical path? o How long can it be delayed? (slack or float—SL) Forward Pass Computation Add activity times along each path in the network (ES + Duration = EF) Carry the early finish (EF) to the next activity where it becomes its early start (ES) unless… o The next succeeding activity is a merge activity, in which case the largest EF of all preceding activities is selected Backward Pass Computation Subtract activity times along each path in the network (LF - Duration = LS). Carry the late start (LS) to the next activity where it becomes its late finish (LF) unless o The next succeeding activity is a burst activity, in which case the smallest LF of all preceding activities is selected. Determining Slack (or Float) Slack = The amount of time an activity can be delayed without delaying the entire project o This is the difference between the Late Start (LS) and the Early Start (ES) for an activity Critical Path = The sequence of activities that determines the shortest duration of the project o The critical path is the network path(s) that has (have) the least slack in common. Normally the path(s) with zero slack Determining the Critical Path Critical path: o It is the longest path through the network (activities add up to the longest overall duration) o It determines the shortest time possible to complete a project o Any delay of an activity on the critical path directly impacts the planned project completion date Project Networks - Practical Considerations Network Logic Errors – no looping, no conditional statements Activity Numbering – assign each activity a unique identifier Usually ascending order from beginning to end
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For large projects, good idea to leave gaps (e.g., 1, 5, 10…) Use of Computers to Develop Networks (e.g., MS Project) Calendar Dates – add in after specifying workdays, holidays, etc. Single start node
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This note was uploaded on 02/15/2012 for the course ISDS 4113 taught by Professor Staff during the Spring '08 term at LSU.

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test 2 material - -PROJECT NETWORKS FORWARD/BACKWARD PASS...

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