Fixed and mobile telecom operators, enterprise network operators and cloud providers strive to face the challenging demands coming from the evolution of IP networks (e.g. huge bandwidth requirements, integration of billions of devices and millions of services in the cloud). Proposed in the early 2010s, Segment Routing (SR) architecture helps face these challenging demands, and it is currently being adopted and deployed. SR architecture is based on the concept of source routing and has interesting scalability properties, as it dramatically reduces the amount of state information to be configured in the core nodes to support complex services. SR architecture was first implemented with the MPLS dataplane and then, quite recently, with the IPv6 dataplane (SRv6). IPv6 SR architecture (SRv6) has been extended from the simple steering of packets across nodes to a general network programming approach, making it very suitable for use cases such as Service Function Chaining and Network Function Virtualization. In this paper we present a tutorial and a comprehensive survey on SR technology, analyzing standardization efforts, patents, research activities and implementation results. We start with an introduction on the motivations for Segment Routing and an overview of its evolution and standardization. Then, we provide a tutorial on Segment Routing technology, with a focus on the novel SRv6 solution. We discuss the standardization efforts and the patents providing details on the most important documents and mentioning other ongoing activities. We then thoroughly analyze research activities according to a taxonomy. We have identified main categories during our analysis of the current state of play: Monitoring, Traffic Engineering, Failure Recovery, Centrally Controlled Architectures, Path Encoding, Network Programming, Performance Evaluation and Miscellaneous. We report the current status of SR deployments in production networks and of SR implementations (including several open source projects). Finally, we report our experience from this survey work and we identify a set of future research directions related to Segment Routing.

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.

Decreasing the soaring energy cost is imperative in large data centers. Meanwhile, limited computational resources need to be fairly allocated among different organizations. Latency is another major concern for resource management. Nevertheless, energy cost, resource allocation fairness, and latency are important but often contradicting metrics on scheduling data center workloads. Moreover, with the ever-increasing power density, data center operation must be judiciously optimized to prevent server overheating. In this paper, we explore the benefit of electricity price variations across time and locations. We study the problem of scheduling batch jobs to multiple geographically-distributed data centers. We propose a provably-efficient online scheduling algorithm - GreFar - which optimizes the energy cost and fairness among different organizations subject to queueing delay constraints, while satisfying the maximum server inlet temperature constraints. GreFar does not require any statistical information of workload arrivals or electricity prices. We prove that it can minimize the cost arbitrarily close to that of the optimal offline algorithm with future information. Moreover, we compare the performance of GreFar with ones of a similar algorithm, referred to as T-unaware, that is not able to consider the server inlet temperature in the scheduling process. We prove that GreFar is able to save up to 16 percent of energy-fairness cost with respect to T-unaware.

Today, backbone networks of telecom operators deploy a large number of devices and links. This is mainly due to both redundancy purposes for network service reliability and resource overdimensioning for maintaining quality of service during rush hours. Unfortunately, current network devices do not have power management primitives, and have constant energy consumption independent of their actual workloads. Starting from these considerations, we propose a viable approach to introduce and support standby modes in backbone network devices. This approach can be effectively used to almost halve the energy requirements of the whole telecom core network. Our main idea consists of periodically reconfiguring nodes and links to meet incoming traffic volumes and operational constraints of real-world networks, such as reliability, stability, quality of service, and reconvergence times. To this purpose, the approach we propose directly exploits the main features of both backbone device architectures and the network protocol stack.

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.

Nowadays, the rapid growth of Cloud computing services is stressing the network communication infrastructure in terms of resiliency and programmability. This evolution reveals missing blocks of the current Internet Protocol architecture, in particular in terms of virtual machine mobility management for addressing and locator-identifier mapping. In this paper, we propose some changes to the Locator/Identifier Separation Protocol (LISP) to cope with this gap. We define novel control-plane functions and evaluate them exhaustively in the worldwide public LISP testbed, involving five LISP sites distant from a few hundred kilometers to many thousands kilometers. Our results show that we can guarantee service downtime upon live virtual machine migration lower than a second across American, Asian and European LISP sites, and down to 300 ms within Europe, outperforming standard LISP and legacy triangular routing approaches in terms of service downtime, as a function of datacenter-datacenter and client-datacenter distances.