In 5G, network slicing is considered as an important enabler to support various verticals simultaneously, by providing dedicated and isolated slice services over a common infrastructure. Many verticals have specific Service Level Agreement (SLA), which should be guaranteed by mechanisms like service assurance (SA). In 5G, SA is required to collaborate with orchestration and management to automate the slice provisioning process. In this paper, we first propose a hierarchical, distributive, and modular SA architecture to assure the entire slice services from end to end (E2E), based on distributed modules assuring underlying services, functions, and resources. Secondly, a closed loop is formed between assurance and orchestration to enable automation by cooperation between monitoring, analytics, and orchestration. In addition, correlation across layers (infrastructure, network function, network service and E2E slice) is considered to form a closed loop through all layers to further improve efficiency. The joint approach also allows to optimize the tradeoff between the cost and the performance of SA. Simulation results illustratively demonstrate the benefit of the proposed approach.

The fifth generation (5G) of cellular networks promises to be a major step in the evolution of wireless technology. 5G is planned to be used in a very broad set of application scenarios. These scenarios have strict heterogeneous requirements that will be accomplished by enhancements on the radio access network and a collection of innovative wireless technologies. Softwarization technologies, such as Software‐Defined Networking (SDN) and Network Function Virtualization (NFV), will play a key role in integrating these different technologies. Network slicing emerges as a cost‐efficient solution for the implementation of the diverse 5G requirements and verticals. The 5G radio access and core networks will be based on a SDN/NFV infrastructure, which will be able to orchestrate the resources and control the network in order to efficiently and flexibly and with scalability provide network services. In this paper, we present the up‐to‐date status of the software‐defined 5G radio access and core networks and a broad range of future research challenges on the orchestration and control aspects.

Software-Defined Networking (SDN) is a new paradigm that promises to enhance network flexibility and innovation. However, operators need to thoroughly assess its advantages and threats before they can implement it. Robustness and fault tolerance are among the main criteria to be considered in such assessment. The currently available SDN controllers offer different fault tolerance mechanisms, but there are still many open issues, especially regarding the trade-off between consistency and performance in a fault- tolerant SDN platform. In this paper, we describe existing fault-tolerant SDN controller solutions, and propose a mechanism to design a consistent and fault-tolerant Master-Slave SDN controller that is able to balance consistency and performance. The main objective of this paper is to bring the performance of an SDN Master-Slave controller as close as possible to the one offered by a single controller. This is obtained by introducing a simple replication scheme, combined with a consistency check and a correction mechanism, that influence the performance only during the few intervals when it is needed, instead of being active during the entire operation time.

Network Function Virtualization (NFV) promises to transform the way telecom providers design and operate networks and network services. Virtualized Evolved Packet Core (vEPC) is one of the NFV use cases that has got most attention, where dependability is a major concern. In the traditional EPC, functions are deployed in proprietary network elements with proven characteristics, e.g., a defined availability, and corresponding guarantees. Hence, network operators have a firm basis for the design of a robust mobile core network. On the other hand, in the vEPC, network operators face a more challenging environment, where functions, subsystems and requirements are interrelated in a more complex manner. Hence, the assessment of the network robustness, and the design to meet dependability requirements become hard. In order to address this challenge, we provide initial guidelines to model system availability in vEPC scenarios, we propose a stochastic activity networks dependability model to assess it, and finally, we identify the most relevant factors to be considered by providers to fulfill the demanding dependability requirements of the mobile core.

The dependability of ICT systems is vital for today's society. However, operational systems are not fault free. Providers and customers have to define clear availability requirements and penalties on the delivered services by using SLAs. Fulfilling the stipulated availability may be expensive. The lack of mechanisms that allow a fine control of the SLA risk may lead to over-dimension the provided resources. Therefore, a relevant question for ICT service providers is: How to guarantee the SLA availability in a cost efficient way? This paper studies how to combine different fault tolerant techniques with different costs and properties, in order to economically fulfill a given SLA requirement. GEARSHIFT is a mechanism that enables ICT providers to set the fault tolerance technique (gear ratio) needed, depending on the current service conditions and requirements. We illustrate how to use the proposed model in a backbone network scenario, using measurements from a production national network. Finally, we show that the total costs of delivering an ICT service follow a simple convex function, which allows an easy selection of the optimal risk by tuning properly the combination of fault tolerant techniques.

Failures are undesirable events that should be always prevented. This paper agrees with this concept, but it is also aware that failures are unavoidable events. The main objective of this paper is to show how the failure handling through clever fault management mechanisms produces a direct positive impact on energy efficient cloud computing deployment. We address the virtual machine consolidation problem, and its associated bin packing problem. In spite of being studied for several years, it is, to the authors knowledge, the first time that this is studied under the presence of server failures that force the migration of some virtual machines at unexpected random times. We found that the extra dynamics generated by the compulsory reallocation of virtual machines produces a reduction in the number of servers needed, allowing some servers to be switched off, and hence having a more energy efficient cloud operation. Through some case studies, we show the amount of energy saved by the effect of random servers failures. Finally, we show that under some conditions, the optimal number of active servers may be reached.

SLAs are common means to define specifications and requirements of cloud computing services, where the guaranteed availability is one of the most important parameters. Fulfilling the stipulated availability may be expensive, due to the cost of failure recovery software, and the amount of physical equipment needed to deploy the cloud services. Therefore, a relevant question for cloud providers is: How to guarantee the SLA availability in a cost efficient way? This paper studies different fault tolerance techniques available in the market, and it proposes the use of an hybrid management to have full control over the SLA risk, using only the necessary resources in order to keep a cost efficient operation. This paper shows how to model the probability distribution of the accumulated downtime, and how this can be used in the design of hybrid policies. Using specific case studies, this paper illustrates how to implement the proposed hybrid policies, and it shows the obtained cost saving by using them. This paper takes advantage of the cloud computing flexibility, and it opens the door to the use of dynamic management policies to reach specific performance objectives in ICT systems.

SLAs are common means to define specifications and requirements of cloud computing services in business relationships. The terms that define the guaranteed availability for a given period are fundamental to these contracts. In this context, a natural question for cloud providers is: How to guarantee the availability promised? This paper studies the level of availability offered to a virtual machine during an SLA period in clouds with different: size, redundancy, and fault tolerance techniques. Finally, this paper proposes the use of the SLA -budget for the implementation of smart policies in: i) the assignment of spare servers when virtual machines are restored. ii) the dynamic use of different fault tolerance licenses. Using such policies results in a considerable reduction of the probability of breaching the SLA guarantee, by making an efficient use of the cloud resources available. This paper is a first step in the design of SLA-aware cloud architectures.

Dependencies between failures in operational networks may have a huge impact on their reliability and availability. In this paper we analyze failure logs to identify simultaneous and potentially correlated failures in routers and links of an IP backbone network. We show that the actual behavior of failure processes does not support the independence assumption commonly used in theoretical studies. Scatter plots are presented to visualize the failure processes, and it is seen that geographical adjacency has a pronounced effect. The existence of high correlation coefficients and high autocorrelation in some failure processes was observed. A formal analysis confirms this. The consequences of these dependencies on the provisioning of guaranteed availability are briefly discussed.