A Survey on Mobility-Induced Service Migration in the Fog, Edge, and Related Computing Paradigms <s> • Green energy: <s> In order to overcome the scalability problem of the traditional Internet of Things architecture (i.e., data streams generated from distributed IoT devices are transmitted to the remote cloud via the Internet for further analysis), this article proposes a novel approach to mobile edge computing for the IoT architecture, edgeIoT, to handle the data streams at the mobile edge. Specifically, each BS is connected to a fog node, which provides computing resources locally. On the top of the fog nodes, the SDN-based cellular core is designed to facilitate packet forwarding among fog nodes. Meanwhile, we propose a hierarchical fog computing architecture in each fog node to provide flexible IoT services while maintaining user privacy: each user's IoT devices are associated with a proxy VM (located in a fog node), which collects, classifies, and analyzes the devices' raw data streams, converts them into metadata, and transmits the metadata to the corresponding application VMs (which are owned by IoT service providers). Each application VM receives the corresponding metadata from different proxy VMs and provides its service to users. In addition, a novel proxy VM migration scheme is proposed to minimize the traffic in the SDNbased core. <s> BIB001 </s> A Survey on Mobility-Induced Service Migration in the Fog, Edge, and Related Computing Paradigms <s> • Green energy: <s> Fully utilizing green energy can remarkably decrease the operational cost of cloudlet providers in provisioning green cloudlet networks (GCNs), which are powered by both green and brown energy. Owing to the spatial and temporal dynamics of energy demands and green energy generation, migrating Avatars (i.e., virtual machines) from green energy deprived cloudlets into green energy over-provisioned cloudlets can reduce the total on-grid energy consumption of GCN. However, Avatar migration itself consumes non-negligible energy consumption. In this letter, we propose the Energy driven AvataR migration (EARN) scheme to reduce the total on-grid energy consumption of GCN by considering the energy consumption of Avatar migrations. The performance of EARN is demonstrated by extensive simulations. <s> BIB002 </s> A Survey on Mobility-Induced Service Migration in the Fog, Edge, and Related Computing Paradigms <s> • Green energy: <s> The Internet of Things (IoT) conceives a world where everyday objects are able to join the Internet and exchange data as well as process, store, collect them from the surrounding environment, and actively intervene on it. An unprecedented number of services may be envisioned by exploiting the Internet of Things. Fog Computing, which is also known as Edge Computing, was proposed in 2012 as the ideal paradigm to support the resource-constrained IoT devices in data processing and information delivery. Indeed, the Fog, which does not replace the centralized Cloud but cooperates with it, distributes Cloud Computing technologies and principles anywhere along the Cloud-to-Things continuum and particularly at the network edge. The Fog proximity to the IoT devices allows for several advantages that must be continuously guaranteed, also when end devices move from one place to another. In this paper, we aim at examining in depth what it means to provide mobility support in a Fog environment and at investigating what are the main challenges to be faced. Besides, in order to highlight the importance of this topic in everyday life, we provide the reader with three scenarios where there is an integration between the IoT and Fog Computing, and in which mobility support is essential. We finally point out the main research directions in the field. <s> BIB003 </s> A Survey on Mobility-Induced Service Migration in the Fog, Edge, and Related Computing Paradigms <s> • Green energy: <s> Recently, Mobile Edge Computing (MEC) is proposed to deploy with cellular base stations (BSs) to reduce the offloading delay and to provide computational resources and storage to nearby mobile users. However, the deployment of MEC with a BS introduces special challenges to mobility management. First, a MEC can only be accessed within the coverage area of its BS. Therefore, a user needs to perform both a radio handoff (HO) and a service migration when moving out of the cell coverage range. Second, as MECs have limited computational resource and storage, the target MEC may not have sufficient available resources to support new users. Therefore, a user with computation task may be forced to perform a radio HO to a different target BS in order to successfully migrate the service. These cause unnecessary HOs in cellular networks, especially when MECs are deployed with small cells, e.g., femtocells. These unnecessary HOs and service migrations incur a large signaling and migration cost. In this paper, we first propose a novel architecture, SharedMEC, to support user mobility. In addition, we propose a service HO decision algorithm and an analytical model to analyze the total cost which considers the total HO signaling cost, total migration signaling cost, and total migration cost. Simulation results show that our proposed architecture and service HO decision algorithm can significantly reduce the total cost. To the best of our knowledge, this is the first work that considers HO and migration issues together and analyzes the total cost in MEC systems. <s> BIB004 </s> A Survey on Mobility-Induced Service Migration in the Fog, Edge, and Related Computing Paradigms <s> • Green energy: <s> Mobile edge computing platforms, such as cloudlets, bring computation resources closer to mobile users, as compared to the cloud, which decreases the end-to-end network latency. This benefit enables a myriad of real-time mobile applications, especially augmented reality (AR), that require low latency and high computation power. However, when mobile users move away from the attached cloudlet, the offloaded services have to be migrated or rebuilt on a new nearby cloudlet. However, this service rebuilding process takes a lot of time and may deteriorate user experience. In this paper, we propose a smart service rebuilding scheme which seamlessly restores the offloading services on the target cloudlet while the mobile user is moving. The service rebuilding process includes the radio handoff stage and service handoff stage. A seamless service rebuilding process is achieved via predicting user's target cloudlet before being triggered a radio handoff, by leveraging extracted features from the captured frames of the mobile user's camera. Furthermore, based on the proposed service rebuilding scheme, we design a feature mapping algorithm to achieve a high prediction precision and a short prediction latency. We implement our scheme on a testbed and conduct experiments using real world AR applications. The experimental results show that our proposed scheme decreases the service rebuilding latency by around 65.8%, as compared to the conventional rebuilding process. In addition, we conduct extensive simulations to evaluate the performance of our proposed feature mapping algorithm. Simulation confirms that our algorithm is robust and can predict users' target cloudlet with high precision and low latency. <s> BIB005 </s> A Survey on Mobility-Induced Service Migration in the Fog, Edge, and Related Computing Paradigms <s> • Green energy: <s> Mobile Edge Computing (MEC) will play a key role in next-generation mobile networks to extend the range of supported delay-sensitive applications. Furthermore, an increasing attention is paid to provide user-centric services, to better address the strict requirements of novel immersive applications. In this scenario, MEC solutions need to efficiently cope with user mobility, which requires fast relocation of service instances to guarantee the desired Quality of Experience. However, service migration is still an open issue, especially for resource-constrained edge nodes interconnected by high-latency and low-bandwidth links. In this paper, by leveraging the potential of lightweight container-based virtualization techniques, we investigate a novel approach to support service provisioning in dynamic MEC environments. In particular, we present a framework where proactive service replication for stateless applications is exploited to drastically reduce the time of service migration between different cloudlets and to meet the latency requirements. The performance evaluation shows promising results of our approach with respect to classic reactive service migration. <s> BIB006
In line with what has been presented in BIB002 and BIB001 , including green energy efficiency in the migration decision criteria would be beneficial to achieve a reduced on-grid energy consumption, thus resulting in increased sustainability. • Federation: The problem of performing migrations across federated fog domains has not been explicitly addressed in the literature, and most of the reviewed works implicitly consider a scenario of a single provider. However, if migration across federated domains run by different providers is to be considered, several challenges have to be addressed, mostly related with SLA enforcement mechanisms, as suggested in BIB003 . This involves not only user-provider agreements but also agreements among different providers with potentially conflicting interests. To this end, deriving solutions inspired from roaming in the telecommunications industry may be envisioned as a starting point for facilitating migrations across multiprovider fog domains. • Joint radio handover-service migration optimization: Joint radio handover-service migration decision optimization could be further investigated in situations where this is relevant, especially with the advent of 5G. This could not only enhance the user's service performance but also is likely to result in a more efficient usage of the network and the edge computing infrastructure. So far, only a few contributions, such as BIB004 and BIB005 , have addressed these aspects in a joint manner. • Mobile user-mobile FN scenario: Even though the mobile user-mobile FN scenario is likely to occur frequently in the context of fog computing, especially with the advent of smart vehicles that can act as fog nodes, this scenario has not been explored much in the literature, as pointed out in Section 3. In fact, even the works that deal with mobile vehicles as VM hosts do not explicitly specify whether the clients, which are being served by those vehicles, are also mobile or not. Further optimizations in this regard can be made considering both clients' and vehicles' mobility patterns, especially when dealing with specific types of vehicles (e.g., buses) having relatively stable routes. • Standardization and implementations: As stated in BIB006 , the ETSI MEC specification provides guidelines for application relocation between Mobile Edge Hosts (MEHs) in MEC. Such a specification can be found in [61] , where a set of requirements, use cases, and issues pertaining to mobility in MEC have been outlined. However, no such guidelines have been reported in the context of fog computing by the OpenFog consortium (OFC) [67] . In fact, the OFC reference architecture emphasizes that application migration across nodes spanning different levels of a fog deployment should be supported, but no additional details regarding this were provided. On the technology level, since the use of the container technology is increasingly gaining in popularity for different service implementations, efforts toward implementing efficient live container migration techniques, such as the efforts done in the P. Haul project [73] , should be further reinforced. This will substantially reduce the migration time for timecritical edge applications.