In the past decade, overlays have emerged and have been deployed in various application scenarios ranging from content delivery over voice communication to interconnecting sensors. Thereby, overlays have proven to be a solid abstraction layer that is able to provide important functional primitives for applications running on top, while hiding the complexity of the underlying network. In addition, overlays are able to cope with various degrees of distribution of network entities that provide and consume services. This comprises scenarios of a centralized service provision and distributed consumption as well as scenarios that are characterized by a fully decentralized service provision and consumption . The service provision and consumption thereby involves a rising number of different devices ranging from static, powerful and broadband connected servers over desktop PCs to mobile, energy-constrained and wireless devices such as smartphones and tablet PCs. This increasing degree of heterogeneity and mobility leads to rapidly changing dynamic environmental conditions and user contexts that an application has to deal with. Prominent examples for such changing environmental conditions are changes of the network access due to mobility or varying power supply due to different device types. A user might, for example, switch between a PC and a smartphone while continuously running the same application. The increased complexity of application scenarios due to dynamicity leads to complex requirements that can not be fulfilled continuously by a single overlay mechanism and system configuration, even less when certain cost limitations are to be satisfied. In order to deal with this problem, existing overlay approaches have to be extended to allow for an adaption of the deployed overlay mechanism at runtime. This adaption, thereby, either can be done by :

• Adjusting the parameter configuration of the deployed overlay mechanism to optimize its performance and cost, or by
• Executing a transition to another overlay mechanism that allows for a better performance and cost under the given environmental conditions.

Motivated by the concept of overlays as well as the concept of adaption the goal of the Adaptive Overlay Communications group (AOC) at the Multimedia Communications Lab is the research and design of new models, mechanisms, and methodologies for an adaptive and context–aware overlay communication. 

The group’s research results should lead to a paradigm shift in the design, implementation, deployment, and maintenance of overlay mechanisms. Future overlay mechanisms will be able to adapt their functionality dynamically at runtime without the knowledge or interference of the user, thereby transparently reacting to changes in the environmental conditions.