Network function virtualization foresees the virtualization of service functions and their execution on virtual machines. Any service is represented by a service function chain (SFC) that is a set of VNFs to be executed according to a given order. The running of VNFs needs the instantiation of VNF Instances (VNFIs) that in general are software modules executed on virtual machines. The virtualization challenges include: 1) where to instantiate VNFIs; ii) how many resources to allocate to each VNFI; iii) how to route SFC requests to the appropriate VNFIs in the right sequence; and iv) when and how to migrate VNFIs in response to changes to SFC request intensity and location. We develop an approach that uses three algorithms that are used back-to-back resulting in VNFI placement, SFC routing, and VNFI migration in response to changing workload. The objective is to first minimize the rejection of SFC bandwidth and second to consolidate VNFIs in as few servers as possible so as to reduce the energy consumed. The proposed consolidation algorithm is based on a migration policy of VNFIs that considers the revenue loss due to QoS degradation that a user suffers due to information loss occurring during the migrations. The objective is to minimize the total cost given by the energy consumption and the revenue loss due to QoS degradation. We evaluate our suite of algorithms on a test network and show performance gains that can be achieved over using other alternative naive algorithms.

In this paper we analyze the challenging problem of energy saving in IP networks. A novel network-level strategy based on a modification of current link-state routing protocols, such as OSPF, is proposed; according to this strategy, IP routers are able to power off some network links during low traffic periods. The proposed solution is a three-phases algorithm: in the first phase some routers are elected as "exporter" of their own Shortest Path Trees (SPTs); in the second one the neighbors of these routers perform a modified Dijkstra algorithm to detect links to power off; in the last one new network paths on a modified network topology are computed. Performance study shows that, in an actual IP network, even more than the 60% of links can be switched off.

Network function virtualization (NFV) is a new network architecture framework that implements network functions in software running on a pool of shared commodity servers. NFV can provide the infrastructure flexibility and agility needed to successfully compete in today's evolving communications landscape. Any service is represented by a service function chain (SFC) that is a set of VNFs to be executed according to a given order. The running of VNFs needs the instantiation of VNF instances (VNFIs) that are software modules executed on virtual machines. This paper deals with the migration problem of the VNFIs needed in the low traffic periods to turn OFF servers and consequently to save energy consumption. Though the consolidation allows for energy saving, it has also negative effects as the quality of service degradation or the energy consumption needed for moving the memories associated to the VNFI to be migrated. We focus on cold migration in which virtual machines are redundant and suspended before performing migration. We propose a migration policy that determines when and where to migrate VNFI in response to changes to SFC request intensity. The objective is to minimize the total energy consumption given by the sum of the consolidation and migration energies. We formulate the energy aware VNFI migration problem and after proving that it is NP-hard, we propose a heuristic based on the Viterbi algorithm able to determine the migration policy with low computational complexity. The results obtained by the proposed heuristic show how the introduced policy allows for a reduction of the migration energy and consequently lower total energy consumption with respect to the traditional policies. The energy saving can be on the order of 40% with respect to a policy in which migration is not performed.

We propose an architecture for a bufferless packet optical switch employing the wavelength dimension for contention resolution. The optical packet switch is equipped with tunable wavelength converters shared among the input lines. An analytical model Is proposed in order to determine the number of converters needed to satisfy prefixed packet loss probability constraints. This analytical model very accurately fits with simulations results. A sensitivity analysis of the required number of converters as a function of the main system parameters (number of input and output lines, number of wavelengths, ...) and traffic parameters has been carried out. Making use of the introduced dimensioning procedure we have observed that the proposed architecture allows a saving in terms of employed number of converters with respect to the other architectures proposed in literature. Such a saving can reach about 95% of the number of converters.

This article reports a review of the most significant issues related to network architectures and technologies which will enable the realization of future optical Internet networks. The design of such networks has to take into consideration the peculiar characteristics of Internet traffic. Several architectures have been proposed to provide optical networking solutions, based on wavelength-division multiplexing and compatible with the IP world. These architectures are presented briefly, and the main advantages and drawbacks are discussed. Furthermore, advanced network architectures are reported. In particular, two network paradigms are illustrated and discussed: the optical transparent packet network and optical burst switching. Finally, the key technologies are illustrated

This paper deals with a strategy to save energy in an IP network during low traffic hours allowing a subset of IP router interfaces to be put in sleep mode by means of an Energy Aware Routing (EAR) strategy. The EAR is fully compatible with OSPF and is based on the “Shortest Path Tree (SPT) exportation” mechanism, consisting in sharing the SPTs among couple of routers. The EAR strategy is able to control the set of links to be put in sleep mode through the concept of “move”. This approach gives the network operator the possibility to control the network performance and allows a smoothed QoS degradation strategy to be implemented. A formulation of the EAR problem is presented and will be demonstrated that this problem can be traced back to the well-known problem of the maximum clique search in an undirected weighted graph. A heuristics, called Max Compatibility, is presented and, as shown in the performance evaluation study, it allows to save about 30% of network links with a negligible increase of network path lengths and link loads.