Specificity vs. flexibility: On the embedding cost of a virtual network

Abstract

Abstract-The virtualization trend in today's Internet decouples services from the constraints of the underlying physical infrastructure. This decoupling facilitates more flexible and efficient resource allocations: the service can be realized at any place in the substrate network which fulfills the service specification requirements.This paper studies such flexibilities in the context of virtual network (VNet) embeddings. The network virtualization paradigm envisions an Internet where users can request arbitrary VNets from a substrate provider (e.g., an ISP). A VNet describes a set of virtual nodes which are connected by virtual links; both nodes and links provide certain QoS or resource guarantees. While some parts of the VNet may be fully specified (e.g., the node and link locations or technologies), other parts may be flexible or left open entirely.We analyze how flexible specifications can be exploited to improve the embedding of virtual networks. We define a measure for specificity and introduce the notion of the Price of Specificity (PoS) which captures the resource cost of the embedding under a given specification. We identify parameters on which the Price of Specificity depends, and evaluate its magnitude in different scenarios.For example, we find that the PoS can be large even in small settings, and depends both on the substrate size as well as-to a larger extent-the load of the substrate. Moreover, while skewed distributions of resources can yield better allocations, they entail the risks of a high PoS if the demand does not perfectly match. We also provide a formal analysis of the impact of migration, and show that the option to migrate can sometimes increase resource costs.