Mobile agents can be described as pieces of software that are capable of acting autonomously within a network in the name of a user. Furthermore, agents can decide where in a system they are best fit to execute their tasks and, for this purpose, can migrate from one computer to another if there is an agent system installed on both machines. In the context of the Mole project, the department 'Distributed Systems' is currently researching and developing a system that allows the implementation of mobile agents.

As in all distributed systems, it is equally important in mobile agent systems to recognize agents which no longer have references to an owning entity. These orphans can subsequently be terminated to minimize the usage of resources in the system. Resources the agent might be carrying (e.g. electronic cash) can be returned to the owner. Several protocols have been developed in the department that allow the functionality of orphan detection. Among them is the shadow protocol.

In this thesis, we will first regard the concept of orphan detection including several existing approaches that have been developed to handle the task. The core of this thesis is the concept of mobile shadows for orphan detection, named the groundhog protocol because of the efficient search for and positioning of shadows. The protocol is designed with respect to special factors affecting distributed networks, fault tolerance and reliability.

After the design and implementation of the mobile shadow protocol, the system's performance is analyzed in comparison to behavior without this mechanism. Not only are timing issues the topic of the analysis, but also the effect of the mechanism with regards to fault tolerance and reliability. Test results illustrate the usability, efficiency and robustness of the developed mobile shadow concept.