Lot-sizing problems of manufacturers and transportation planning problems of forwarders are presented and analyzed in this thesis. These problems represent crucial planning tasks in supply chain management. Due to high fluctuations and competitive markets, companies within supply chains use internal and external resources for the fulfillment of tasks. The thesis claims to contribute to the following topics: (1) introducing mandatory tasks for the DULR, IOTPP, CTPP, and CIOTPP as well as (2) presenting computational studies that demonstrate how much the costs of companies increase due to mandatory tasks. Mandatory tasks are tasks, which have to be fulfilled by appointed resources due to contractual obligations. A lack of research is identified in terms of this topic. It is usually assumed that a task can be fulfilled by any internal or external resources. The thesis describes how these planning tasks with mandatory tasks can be solved by using operations research. Therefore, existing mathematical models and solution approaches have to be extended. The thesis focuses on the determination of the impact of mandatory tasks based on computational studies
