MobFogSim: Simulation of mobility and migration for fog computing

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Abstract

Fog computing is an extension of the cloud towards the network edge that brings resources and services of computing in closer proximity to end users. This proximity provides several benefits such as reduced latency that improves user experience. However, user mobility may limit such benefits in practice, as the distance to a fog service may vary as a user moves from one location to another. Migration of a fog service may be one possible mitigation strategy, enabling the service to always be close enough to a user. Although many simulators exist for evaluating application behaviour and performance within a fog computing environment, none allows evaluation of service migration solutions to support mobility. MobFogSim is presented in this work to overcome this limitation. It extends iFogSim to enable modelling of device mobility and service migration in fog computing. MobFogSim is validated by comparing simulation results with those obtained from a real testbed where fog services are implemented as containers. Additional experiments are carried out in MobFogSim taking account of various mobility patterns of a user, derived from Luxembourg SUMO Traffic (LuST). We use an experiment-based approach to study the impact of user mobility on container migration in fog computing.

Introduction

The Internet has become the largest and most popular mechanism for communication among people, corporations, and governments around the world. Furthermore, a number of devices are connected to the Internet, consuming and generating data as well as offering a variety of computing services. Such devices can be fixed or mobile, for example carried by their users or attached to a vehicle. Nowadays, many applications and services running on fixed or mobile devices rely on remote services, as in cloud computing servers [1], [2], to store data and/or perform data processing. One of the limitations of using remote devices for storage and computing is the potentially large latency experienced by users. In general, data centres can be far away from the end device running the application, causing increased delays to access data and higher turnaround times for processing.

Fog computing [3] was proposed to overcome these limitations. Fog computing extends the cloud towards the network edge, distributing resources and services of computing as close as the user’s access point, thus only one hop away from end devices. It is worth highlighting that fog computing does not replace the cloud but rather complements it. Fog computing therefore does not only reduce network delays but also: (i) lowers bandwidth consumption; (ii) improves security and privacy; (iii) provides better context awareness; and (iv) enables uninterrupted services in case of intermittent connectivity to the cloud [4]. Devices hosting fog computing services are known as fog nodes, cloudlets, or micro data-centres (MDC).

User mobility may impair fog computing performance. This is because mobility causes a change of the access points, which may increase the delay to the fog service hosted in the original cloudlet/MDC [5]. When a mobile user changes access point, ideally their data and current applications being processed should migrate to the cloudlet at the new access point to minimise access delay. To accomplish this, we assume that the user has a virtual machine (VM) or a container, similarly to cloud computing services, that contains her/his processes and data. Understanding where each application (or its components) should run and where data should be kept involves a multi-layered infrastructure with heterogeneous devices and networks as well as applications that have heterogeneous requirements and can move along the infrastructure. Simulation can be a time- and cost-effective way to evaluate VM/container migration solutions in fog computing environments with mobile users.

In a previous work [6], we introduced mobility concepts to iFogSim in a preliminary support for mobility. In this paper, we present MobFogSim, an open-source3 simulator that extends the preliminary work from [6] to model more generalised aspects related to device mobility and VM/container migration in the fog, e.g., user position and speed, connection handoff, migration policies and strategies, to name a few. The contribution of this paper is threefold:

  • We discuss the design considerations and the implementation details of MobFogSim, highlighting aspects required to model device mobility and VM/container migration in fog computing;

  • We validate MobFogSim by comparing its container migration results with those obtained from a real testbed;

  • We study the impact of user mobility on container migration in fog computing. This is achieved by running simulations in MobFogSim where users move with different mobility patterns taken from Luxembourg SUMO Traffic (LuST). The approach can be generalised to other (similar) mobility patterns.

The rest of the paper is organised as follows. Section 2 provides a general background on VM/container migration in fog computing and describes the events that occur during connection handoff and VM/container migration. Section 3 briefly outlines the features available in iFogSim and describes the design considerations for VM/container migration modelling in MobFogSim. In Section 4 we provide implementation details of MobFogSim, comparing it with iFogSim. Section 5 describes the experiments that we carried out over a real testbed to obtain seed values for supporting simulation in MobFogSim. Results of container migration over the testbed are also described in this section. In Section 6 we validate MobFogSim by comparing its results against those from the testbed. Section 7 reviews existing fog computing simulators, describing difference with MobFogSim. Finally, Section 8 provides the key conclusions we can draw from the simulations.

Section snippets

Basic concepts

In this section, we briefly introduce fog computing, virtualisation and migration concepts as well as the migration model considered in the proposed simulator.

Design considerations

MobFogSim is a simulator that extends iFogSim to model aspects related to device mobility and VM/container migration in fog computing. We had already incorporated new features into iFogSim in a previous work [6]. In this paper, we extend that preliminary version to cover a wider set of parameters as well as to support mobility by integrating our simulator with the mobility tool Simulation of Urban Mobility (SUMO) [9]. These modifications, which allow more generalised mobility simulations in fog

Implementation details

In this section, we discuss the most noteworthy aspects relative to the implementation of MobFogSim. In Section 4.1, we report the main Java classes that make MobFogSim an extension of iFogSim with support to device mobility and VM/container migration. Then, in Section 4.2, we focus on the simulation events and their flow within the migration and handoff procedure. Finally, Section 4.3 illustrates how we extended the preliminary version of MobFogSim to support realistic user’s mobility patterns.

Simulator calibration and container migration over a real testbed

The objective of this section is twofold. Firstly, in Sections 5.1–5.3, we describe the experiments that we carried out over a real testbed to calibrate MobFogSim (i.e., to obtain realistic input values for the next simulations). Such a testbed, which is depicted in Fig. 14 and is detailed in the following sections, is the same that was used in [13] to evaluate container migration techniques in fog computing. Secondly, in Section 5.4, we report from [13] the main container migration results

MobFogSim evaluation

In this section, we evaluate MobFogSim. Specifically, Section 6.1 validates our simulator by comparing its results of container migration with those from the real testbed. Then, in Section 6.2, we employ MobFogSim to assess how user’s mobility impacts on container migration in the fog. To this purpose, we run simulations where users move with different realistic mobility patterns taken from urban buses of Luxembourg.

Related work

In this section, we review the state-of-the-art simulators for fog computing environments and highlight the comprehensiveness and novelty of MobFogSim. Table 4 summarises the main characteristics of these simulators, with a focus on mobility support.

VirtFogSim [21] does not model aspects such as VM/container migration, energy consumption, or pricing. However, it dynamically tracks the energy-delay application performance against abrupt changes due to failures or device mobility, e.g.,

Conclusions

The need to support VM/container migration in fog computing (particularly for mobile users) has been outlined in this paper. Migration can take account of geographical location of cloudlets with reference to the user, the direction and speed of travel of the user, and the network characteristics between the user and the cloudlet. The migration process has been described as a set of events (identified in a number of different scenarios), taking account of both migration and handoff strategies.

Acknowledgments

The authors would like to thank the following agencies for partially supporting this research: Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); the São Paulo Research Foundation (FAPESP), grant #2015/16332-8; the INCT of the Future Internet for Smart Cities funded byCNPq proc. 465446/2014-0, Coordenação de Aperfeiçoamento de Pessoal de NÃvel Superior - Brasil (CAPES) - Finance Code 001, FAPESP proc. 14/50937-1, and FAPESP proc. 15/24485-9; the Italian Ministry of Education

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    1

    Carlo Puliafito and Diogo Gonçalves share the first author role in this paper.

    2

    Part of this research was conducted while Carlo Puliafito was also affiliated to the University of Florence (DINFO), Italy, and visiting student at Cardiff University, UK.

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