On the trade-off between element availability and cost in virtualized network infrastructures

Lately network virtualization (technology) is receiving more and more attention. Network virtualization is the sharing of physical resources by subdividing a physical node or link into many virtual nodes or virtual links. This sharing allows to create Virtual Networks (VNs) as servicespecific networks to be embedded onto a physical network in a dynamic way. Further, it is possible to share the same physical network amongst multiple network operators thereby saving on capital and operational expenditures. The calculation of the effective allocation of the physical resources (e.g. bandwidth for the connections or capacity for the servers) among the requested VNs is known as the Virtual Network Embedding (VNE) problem. One concept that uses network virtualization and recently gained a lot of attention from telecom operators and vendors is Network Functions Virtualization (NFV). It promises to virtualize entire classes of network node functions within a data-center and to deliver network services in the form of Virtualized Network Function (VNF) service chains using commercial off-the-shelf hardware and IT virtualization technologies. Since multiple VNs or VNFs can share the physical resources of the underlying physical network (elements) in network virtualization and NFV, even a single failure in the underlying network can affect a large number of the services of the operators. The chances of a catastrophic failure could especially be higher with commercial off-the-shelf data-center hardware than in a traditional non-virtualized network infrastructure. Thus, network reliability, availability and survivability are important features for hosting high-demand services in the virtual network environment. To overcome the physical failure impact on VNs, backup and protection mechanisms are needed. However, different backup or protection mechanisms result in a different cost for the network operators. Therefore, a balance between high availability and cost has to be found. Specifically, mobile network operators require high availability (in the range of ‘five nines’) for offering their services to the customers, however, this also results in high infrastructure and operational costs. Therefore the important question occurs of whether it is possible to use low-cost devices in combination with network virtualization technologies to save cost and still achieve the requested availability for the services to the customers. In light of the above, this dissertation proposes new algorithms for reliable VNE with explicit availability requirements for the services in optical transport networks and virtualized datacenter networks. In the first step, a virtual network embedding algorithm which provides path protection with explicit virtual link availability constraints is developed for the use in the optical fiber wide area network. The algorithm decides when it is necessary to deploy one or more backup paths if one single path is enough to fulfill the requested availability constraint. Further, adding an optimization step results in a more resource efficient embedding. For data-