Project network is the tool used for planning, scheduling, and monitoring project progress. The network is developed from the information collected for the WBS and is a graphic flow chart of the project job plan. Project network times are not schedule until resources have been assigned. And when we assign resources, we will found the problems of the following resources constraints:
1. Manpower: due to we have limitation of employees, but project want numbers of manpower not equal from start until finish the project. Some period peak-moderate-little belong to quantity and physical of works.
2. Materials: may be its not come as time specified or not enough so we must to plan them how much the quantity we need and when we want use.
3. Machine or equipment: we have limitation of machine/ equipment, but project want numbers and type machine/equipment not same from start until finish the project. So it needs to plan for project can run smoothly.
4. Money: we must to estimate the budget and plan cash flow to meet cost relative to manpower, material, machine/equipment.
After assigned resources to project network time, we will summarize the resources as used on project network time, we will see the peak of resources (you can put data/ computation in excel or see in resource graph/sheet if it applied by MS Project). In case of has constraint of resources; we can adjust some task as has slack or float time to earliest start or latest start, then the resources will balanced to meet with available resources. But some time tasks have not slack or float time, cannot adjust them to earliest start or latest start method. Another alterative can apply is, usually peak of resources not take long time (about 1, 2 or 3 months), 1st may be we can temporary allocate resources from another project, 2nd some task can sub-contract especially task as need many labors (labor force) and not so need skill. However in any case smoothly performance of project will belong to suitable of planning and analyzing of all tasks concern.