Analyzing Cross-layer Interaction in Overlay Networks

Overlay networks have recently gained popularity as a viable alternative to overcome functionality limitations of the Internet (e.g., lack of QoS, multicast routing). They offer enhanced functionality to end-users by forming an independent and customizable virtual network over the native network. Furthermore, they are being widely promoted as a potential architecture of the future Internet in the form of network virtualization, where multiple heterogeneous virtual networks may co-exist on top of a shared native network. The prominent characteristic in either context is that routing at the overlay layer operates independent of that at the underlying native layer. There are several potential problems with this approach because overlay networks are selfish entities that are chiefly concerned with achieving the routing objective of their own users. This leads to complex cross-layer interactions between the native and overlay layers, and often tends to degrade the achieved performance for both layers. As overlay applications proliferate and the amount of selfish overlay traffic surges, there is a clear need for understanding the complex interactions and for strategies to manage them appropriately. Our work addresses these issues in the context of service overlay networks, which represent virtual networks formed of persistent nodes that collaborate to offer improved services to actual end-systems. Typically, service overlays alter the route between the overlay nodes in a dynamic manner in order to satisfy a selfish objective. The objective of this thesis is to improve the stability and performance of overlay routing in this multi-layer environment. We investigate the common problems of functionality overlap, lack of cross-layer awareness, mismatch or misalignment in routing objectives and the contention for native resources between the two layers. These problems often lead to deterioration in performance for the end-users. This thesis presents an analysis of the cross-layer interaction during fault recovery, inter-domain policy enforcement and traffic engineering in the multi-layer context. Based on our characterization of the interaction, we propose effective strategies that improve overall routing performance, with minimal side-effects on other traffic. These strategies typically (1) increase the layer-awareness (awareness of information about the other layer) at each layer, (2) introduce better control over routing dynamics and (3) offer improved overlay node placement options. Our results demonstrate how applying these strategies lead to better management of the cross-layer interaction, which in turn leads to improved routing performance for end-users.