Département Informatique

Computer Science Department of Telecom SudParis

New paper “Request relaxation based-on provider constraints for a capability-based NaaS services discovery” at CAISE 2023

Authors: Imen Jerbi, Hayet Brabra, Mohamed Sellami, Walid Gaaloul, Sami Bhiri, Boualem Benatallah, Djamal Zeghlache, and Olivier Tirat


Network as a Service (NaaS) enables cloud customers to connect their distributed services across multiple clouds without relying exclusively on their infrastructures. The discovery of NaaS services remains challenging not only because of their scale and diversity but also because of the hidden constraints that cloud providers impose on these services at the networking layer. NaaS services are usually offered in the form of service bundles containing underlying services and constraints not requested by the customers. This creates undesirable dependencies and constraints that hamper portability, compatibility and interoperability across providers. The problem of service discovery becomes more challenging when these constraints are the main and first cause that prevents a customer’s request from being fulfilled. Without a mechanism that enables customers to identify these constraints and to adjust their requests accordingly, existing service discovery solutions are likely to fall short. We propose to complement existing service discovery solutions by not only identifying unmatched constraints but also recommending relaxing discovery requests to retrieve optimal and compliant services.

New article “Process mining for Artifact-Centric Blockchain Applications” in the SIMPAT journal

Authors: Leyla Moctar M’Baba, Nour Assy, Mohamed Sellami, Walid Gaaloul and Mohamedade Farouk NANNE


Process mining can provide valuable insights into user behavior, performance, and security for blockchain applications. In return, process mining benefits from the trustworthiness of blockchain data. One obstacle to realizing these benefits is that blockchain data is inadequate for process mining. This issue has been previously explored in literature, but mainly with regards to workflow-centric processes, leaving out the more common artifact-centric applications. This article introduces ACEL (Artifact-Centric Event Log), an extension to the OCEL (Object-Centric Event Log) standard, specifically designed for artifact-centric processes. Additionally, we present a method for extracting ACEL logs from the Ethereum blockchain platform and demonstrate its effectiveness and the perspectives of process discovery through two case studies of public Ethereum applications.

Best paper “SmartSPEC: Customizable Smart Space Datasets via Event-Driven Simulations” at PERCOM 2022

Authors: Andrew Chio, Daokun Jiang, Peeyush Gupta, Georgios Bouloukakis, Roberto Yus, Sharad Mehrotra and Nalini Venkatasubramanian

Mark Weiser Best Paper Award (sponsored by Elsevier Pervasive and Mobile Computing)

This paper presents SmartSPEC, an approach to generate customizable smart space datasets using sensorized spaces in which people and events are embedded. Smart space datasets are critical to design, deploy and evaluate robust systems and applications to ensure cost-effective operation and safety/comfort/convenience of the space occupants. Often, real-world data is difficult to obtain due to the lack of fine-grained sensing; privacy/security concerns prevent the release and sharing of individual and spatial data. SmartSPEC is a smart space simulator and data generator that can create a digital representation (twin) of a smart space and its activities. SmartSPEC uses a semantic model and ML-based approaches to characterize and learn attributes in a sensorized space, and applies an event-driven simulation strategy to generate realistic simulated data about the space (events, trajectories, sensor datasets, etc). To evaluate the realism of the data generated by SmartSPEC, we develop a structured methodology and metrics to assess various aspects of smart space datasets, including trajectories of people and occupancy of spaces. Our experimental study looks at two real-world settings/datasets: an instrumented smart campus building and a city-wide GPS dataset. Our results show that the trajectories produced by SmartSPEC are 1.4x to 4.4x more realistic than the best synthetic data baseline when compared to real-world data, depending on the scenario and configuration.

Keywords: smart space, sensor, simulation, trajectory

New paper “Analysis of the Impact of Interaction Patterns and IoT Protocols on Energy Consumption of IoT Consumer Applications” at DAIS 2022

Authors: Rodrigo Canek, Pedro Borges, and Chantal Taconet

DAIS 2022 paper

Nowadays, it is estimated that half the connected devices are related to the Internet of Things (IoT). The IoT paradigm contributes to the increase of the Information Technology energy demand. The energy demand is due on one side to the huge number of IoT devices, and on the other side to the plethora of IoT end user applications consuming
data produced by those devices. However, taking into account energy consumption in the development of such applications, consuming data produced by IoT devices is still challenging. There is a lack of knowledge on what are the best practises to develop green IoT applications. The work presented in this paper aims to raise the awareness of application designers concerning the impact of the choice of IoT protocols and interaction patterns on the energy consumption of the applications. For this purpose, we have experimentally analysed the energy consumption of HTTP and MQTT, which are two of the most popular, mature and stable protocols for IoT consumer applications. For the HTTP protocol, we have studied both the publish-subscribe and the request-reply interaction patterns. For MQTT, we have studied the publish-subscribe interaction pattern with the three available Quality of Services. We also examine the impact of message payload on energy consumption. The results show that the publish/subscribe interaction pattern has lower energy consumption (around 92% less) than the synchronous interaction pattern and HTTP consumes 20% more energy than the MQTT protocol for the publish/subscribe interaction pattern. Finally, we have shown that the payload has a low impact on energy consumption having a 9% overhead on payloads ranging from 24 to 3120 bytes

Keywords: Middleware, Internet of Things applications, IoT protocols Interaction patterns, IoT Platforms, Energy Consumption, Green IT

New paper “Conformance checking for autonomous multi-cloud SLA management and adaptation” at Journal of Supercomputing

Authors: Jeremy Mechouche, Roua Touihri, Mohamed Sellami and Walid Gaaloul

Link: https://link.springer.com/article/10.1007/s11227-022-04363-0


Satisfying cloud customers’ requirements, i.e., respecting an agreed-on service level agreement (SLA), is not a trivial task in a multi-cloud context. This is mainly due to divergent SLA objectives among the involved cloud service providers and hence divergent reconfiguration strategies to enforce them. In this paper, we propose a hierarchical representation of multi-cloud SLAs: sub-SLAs associated with a system’s components deployed on distinct cloud service providers and global-SLA associated with the whole system. We also enrich these SLA representations with state machines reflecting reconfiguration strategies defined by cloud customers. Then, we propose an autonomous multi-cloud resource orchestrator based on the MAPE-K adaptation control loop to enforce them and to avoid SLA violations. Finally, in order to check the conformity of this enforcement with defined multi-cloud SLA, we propose an approach for multi-cloud SLA reporting inspired by conformance checking techniques. An implementation of the approach is presented in the paper and illustrates the approach feasibility.

New paper “Why Globally Re-shuffle? Revisiting Data Shuffling in Large Scale Deep Learning” to be presented at IPDPS’22.

New paper “Why Globally Re-shuffle? Revisiting Data Shuffling in Large Scale Deep Learning” to be presented at IPDPS’22.

Available online: https://hal.archives-ouvertes.fr/hal-03599740/document


Stochastic gradient descent (SGD) is the most prevalent algorithm for training Deep Neural Networks (DNN). SGD iterates the input data set in each training epoch processing data samples in a random access fashion. Because this puts enormous pressure on the I/O subsystem, the most common approach to distributed SGD in HPC environments is to replicate the entire dataset to node local SSDs. However, due to rapidly growing data set sizes this approach has become increasingly infeasible. Surprisingly, the questions of why and to what extent random access is required have not received a lot of attention in the literature from an empirical standpoint.

In this paper, we revisit data shuffling in DL workloads to investigate the viability of partitioning the dataset among workers and performing only a partial distributed exchange of samples in each training epoch. Through extensive experiments on up to 2,048 GPUs of ABCI and 4,096 compute nodes of Fugaku, we demonstrate that in practice validation accuracy of global shuffling can be maintained when carefully tuning the partial distributed exchange. We provide a solution implemented in PyTorch that enables users to control the proposed data exchange scheme.

New paper “Blockchain logging for process mining: a systematic review” at HICSS’2022

Authors: Leyla Moctar M’Baba, Mohamed Sellami, Walid Gaaloul and Mohamedade Farouk NANNE


Considerable progress was forcasted for collaborative business processes with the rise of blockchain programmable platforms. One of the saliant promises was auditable traces of business process execution, but practically it has posed challenges specially with regard to blockchain logs’ structure who turned out to be inadequate for process mining techniques. Approaches to answer this issue have started to emerge in the literature; some focusing on the creation process of event logs, and others dealing with their retrieval from the blockchain. This work outlines the generic steps required to solve these challenges and analyzes findings in these approaches with a consideration for efficiency and future research directions.

New paper “Towards higher-level description of SLA-aware reconfiguration strategies based on state-machine” at ICEBE’2021

Authors: Jeremy Mechouche, Roua Touihri, Mohamed Sellami and Walid Gaaloul


High number of European projects and international initiatives show an increased interest in the multi-cloud paradigm. One key need identified in these studies is an SLA-driven service model for multi-cloud environment. While offering a multi-cloud application, cloud consumer define reconfiguration strategies to avoid violating SLAs established with their customers. In this context, this paper presents an approach for enriching multi-cloud SLA representations with reconfiguration strategies. Advantages of this approach are twofold: (i) simplify SLA administration and (ii) limit SLA violations caused by reconfiguration strategies. We represent reconfiguration strategies based on state-machine formalism. Furthermore, we define thresholds to guarantee their compliance with multi-cloud SLAs and anticipate SLA violations. An implementation of the approach is presented in the paper and illustrates how these thresholds are computed.

New paper “Runtime models and evolution graphs for the version management of microservice architectures” at APSEC 2021

Authors: Yuwei Wang, Denis Conan, Sophie Chabridon, Kavoos Bojnourdi, Jingxuan Ma.

APSEC 2021, https://hal.archives-ouvertes.fr/hal-03419462

Microservice architectures focus on developing modular and independent functional units, which can be automatically deployed, enabling agile DevOps. One major challenge is to manage the rapid evolutionary changes in microservices and perform continuous redeployment without interrupting the application execution. The existing solutions provide limited capacities to help software architects model, plan, and perform version management activities. The architects lack a representation of a microservice architecture with versions tracking. In this paper, we propose runtime models that distinguishes the type model from the instance model, and we build up an evolution graph of configuration snapshots of types and instances to allow the traceability of microservice versions and their deployment. We demonstrate our solution with an illustrative application that involves synchronous (RPC calls) and asynchronous (publish-subscribe) interaction within information systems.

New paper “J-NVM: Off-heap Persistent Objects in Java” to be presented at SOSP’21

New paper “J-NVM: Off-heap Persistent Objects in Java” to be presented at SOSP’21. Congrats to Anatole, Yohan, Kwabena, Pierre and Gaël!