Nicolas Tixier

CUTTING THE CITY IN HALF: AMBIENCES, TRANSECTS AND PROJECTS

INTRODUCTION

The term 'transect' is defined by geography as "a field observation device -or the "representation" of a given space, along a linear path and based on the vertical dimensionaimed at highlighting superpositions, spatial successions or associations between phenomena" [START_REF] Robic | [END_REF]. Transect is a practice whose elements were suggested at the early 20 th century, mainly by Scottish urban-botanist Patrick Geddes, in order to be applied to the development of a given territory. Patrick Geddes insisted on the "synoptic" potential of the section, i.e., on its ability to give visibility to reports arising from long historical periods that can still be observed in present days, that link collective forms of human life to the structures of physical geography. 1 Geddes' use of this graphic projection also aimed at bringing together different disciplinary perspectives in a single visual representation. This factor certainly explains why, from that time on, the merge of graphic and cultural conventions of architectural section with those of the transect, which were practiced in the fields of human geography and biological sciences, was outlined. The resumption of the famous Valley Section by Team 10 2 -which had been envisioned by Patrick Geddes fifty years earlier and resulted from the geographic works by Humboldtopened room for the hybridization of the two genres at the service of the architectural and urban design that, until then, remained undeveloped.

Nowadays, the transect is often revisited, both as representation technique and field practice. In the opinion of the present authors, it is a hybrid device between technical section and sensitive path: it is built through drawings, photos, measurements, texts or videos, as it is practiced in situ, as well as by perceptions, speeches, wanderings and, overall, through walks and crossings. 3 The transect aims to be a tool to both question and express sensitive spaces and experienced practices by rehabilitating the atmospheric dimension in urban representations and by enabling the inclusion of local narratives in specialized debates between disciplines.

Transect understanding and analysis processes follow the development of a method based on sampling, selection and assembly procedures; such a method can become a projective device supported by its repeatability and differences from other devices. Next, topics that would configure this device in the future are introduced; they show (as well as 1. Patrick Geddes' first publications, his famous valley sections, date back to 1925. For an archeology of this idea, see [START_REF] Ferretti | Aux origines de l'aménagement régional: le schéma de la Valley Section de Patrick Geddes[END_REF]. 2. See the famous "Doorn Manifesto", by Peter Smithson (1954). 3. This article repeats and develops two articles by Nicolas [START_REF] Tixier | Le transect urbain. Pour une écriture corrélée des ambiances et de l'environnement[END_REF][START_REF] Tixier | Le transect: un opérateur abductif[END_REF]. suggest) the gestures, experiences and likely transformations, both in the act of living and in flows of people, activities, vegetation, ambience, among others.

Transect is not a unidisciplinary tool, it is an open support to knowledge and to representations of all disciplines that, therefore, can dialogue in a multipolar way. Its ability to identify and collect both unique and paradigmatic situations is based on the practice of inventorying. Its ability to compare things and situations is also associated with the concept of album. However, it remains open like Aby Warburg's Atlas Mnémosyne. 4 There is no need of having a formatted framework or a unit of representation modes. One can go from one scale to another, from one document to another. One can add and remove elements to the transect, whenever necessary. It is literally a work plan (a table, a wall, in the digital or physical environment) that can be shared and changed, since documents placed side by side, based on their association with a given context, produce meaning along the section line.

The transect enables a unique space and a non-hierarchical temporality, since it allows the emergence of different projects or experiences to be discussed and conducted.

Totality is initially no longer a project defined by the classic game of scales (territory reading, masterplan definition, architectural design, details' production) or limited to the application of technical solutions; it is not a project that would be only imposed by its designers or that, conversely, would only arise from users' practice. It is, above all, an intermediate space for dialogue and negotiation, where all actors in the territory (from residents to designers, from politicians to managers) can find the project material in compliance with their scale, areas of expertise and practices. Building spaces based on this encounter (between disciplines, between actors, which are herein understood as having their own language) requires asking translation-related or, more precisely, translators' questions, as a third party between two unknown languages that also do not understand one another, but a third party that does not disappear, that remains present. As things are not translated from one language to another in our work field, it is necessary creating conditions to enable reading and understanding different languages and modes of representation adopted by different actors. It is also necessary creating devices that, 4. The Atlas Mnémosyne by Aby Warburg is a large (flat) montage of photographic reproductions capable of "replacing the transmission issue with the matter of its exposure [thus, organizing] a network of tensions and anachronisms between images". Based on the vertical juxtaposition of synoptic panels, and without the intervention of the verbal register, "the Warburg's Atlas presents, on each plate, a multiplicity of images, so that the comparisons become multipolar". "Warburg's Atlas multiplies the framework and the scales". The atlas based on Warburg was not designed as a book, but as a worktable open to the reading and manipulation of new images. "Atlases are capable of creating heterotopias by operating across divisions and sets of domains that are often separate from one another" [START_REF] Michaud | et l'image en mouvement[END_REF][START_REF]L'album de l'art à l'époque du musée imaginaire[END_REF]. according to Paul [START_REF] Ricoeur | Sur la traduction[END_REF], are capable of welcoming any language, of showing "linguistic hospitality" and of organizing contents in order to pass them on and to make them dialogue with other contents. This third-party role should be a wish, rather than an obligation -as Ricoeur has already said -to help "improving one's own language".

The transect potentially appears as a framing power because it does not belong to the previously defined categories of mobilized elements and due to exchanges it is restricted to. It may even seem like an implicit criticism of urban zoning and of its regulations, which enables bringing local singularities and residents' practices back to the core of discussions in order to work on the future of things for and with their environment in different ways.

APPROACHING URBAN DAILY LIFE BASED ON AMBIENCES

The theoretical interest on the transect is mainly explained by the fact that it is used as a means of approaching a plural representation of aspects observed at the heart of any urban situation: the unity and uniqueness of a given place, its daily life and its ambiences.

There is no evidence enough to describe what would make the urban aspect something banal, part of the daily routine of dwelling. Moreover, it is even harder to take it into account in the logic of a project. And yet, we pay attention, and sometimes we are even "caught" by the perceived ambience at the time we arrive to a certain place: we are attentive to excellent lighting, to a particular sound, to how we are energized by a lively public space or otherwise calmed by it, to how we are led to contemplation in a place steeped in calm… Often singular and irreducible, the ambience of a given place can change depending on the day, time, climate, public and on our actions. However, despite these variations, it often presents features that give the place an identity that enables acknowledging it.

We experience and are tested by ambiences on a daily basis. Although we can easily feel and share our sensitive experiences, paradoxically, the concept of ambience escapes any significantly-strict formal definition. It lies on what is singular, it is a whole whose parts do not separate from one another before our sensory channels, actions, perceptions and representations. However, we only know how to analyze it by dissecting it in a plural way, sense by sense, topic by topic. Thus, the more our knowledge about ambiences' composition and form of constitution gets more accurate -they are enriched by sound, light, thermal, tactile ... as well as by spatial and social analysis -the more we risk losing what makes its unit, this always unique relationship lived in the place. "A fleeting singular, a dispersed plural", according to Jean-François Augoyard (2007). 5

TRANSECT, THE CONTEXTUALIZED DIALOGUE OF SEIZED ELEMENTS

Studies about ambiences are based on the cross-checking of different data such as spatial typology; acoustic measurements; aero-hygro-thermal fluids; sunlight and lighting; direct observation of uses; collection of statements by users, inhabitants and local actors; history of the construction and environmental conditions, among others. Reporting this data and crossing them in a meaningful way is not so obvious: some data are graphical, whereas others are metric, temporal, textual, photographic, or even video-or sound-based. In addition, each record presents significant variations in data nature and status. The transect appears as one of the possibilities of literally putting data deriving from different records side by side. These data interact with each other, based on their locations and distances. They respond to, complete, blend to, contradict, resonate and ignore each other, among others. They are not just organized in front of each other; they initially present an extremely specific thread, since they are always in line with the cutting edge, with the transect layout. It is a major difference from Aby Warburg's atlas, which does not presuppose any context on the worktable before depositing the elements. This association between data and cutting edge can be located in a very accurate way (through direct association with a given location) or in a more globalized manner, based on the likely distance one can cover to place the element upwards (the sky) or downwards (the ground).  new data can always complete the transect; thus, they can reinforce or influence the stories and deposited elements; and  the future of the place is not registered, but it takes shape among the profile, data and stories of the place, thus enabling the link among past, present and future.

It is important going back to an essential point, which is the reason why each transect must be built: the aim of the research matters as much as the raison d'être of a potential project. This initial issue strongly guides, without a doubt, the transect line and data collection. Therefore, in order to meet these goals, we must do more than just "investigate", interpret, associate and then design one or more likelihoods of evolution, rather than a solution, based on specificities of the context, by giving ourselves creative freedom. As in any research, the elements capable of working with the largest possible number of clues for interpretations and future projections derive from a given context. Such interpretations and projections, all together, form narratives capable of explaining the likely outcomes of each situation [START_REF] Tixier | L'ambiance est dans l'air. La dimension atmosphérique des ambiances architecturales et urbaines dans les approches environnementalistes[END_REF][START_REF] Tixier | Le quotidien en projets[END_REF]POUSIN et al., 2014).

Therefore, whenever there is orientation about the type of data to be collected at research implementation time, there is also the selection of data to be kept and deposited in the transect. Thus, it is necessary finding the right amount of data to be selected in this operation (not so little to the point of leading to a poor transect in stories and likely developments; nor too much to the point of hindering visual associations between the taken elements and their context). Working with several (and different) disciplines, both in data collection and transect construction processes, not only helps guiding the selection of such amount, but also accepting what each person wants to highlight and, consequently, to group. The size of the worktable and the scale selected for the transect play an important role in this operation. Once the elements were placed in the transect, they can be brought both into the debate and the design process, as well as be made available to us (researchers and urban planners) and, above all, to local actors. Thus, understanding a given situation involves elements found in residents' speech, a set of localized measurements, the shape of the building or vegetation type, some photos, an element that is part of the story, among others. Therefore, such an understanding is not explicit, it is built by each person at transect-reading time. It refers to our own knowledge, either of disciplinary or experimental nature. It needs to be narrated and shared with others. The implementation of a critical and design discourse takes place naturally and can be registered in the transect, whose representational function becomes, therefore, the matrix support of the project.

TRANSECT EXPLOITATION: TRANSITIONING FROM THE ROUND TO THE LONG TABLE

The long table 6 device consists in effectively having ... a long table where the worked-on urban section is implemented; it includes a minimum number of elements capable of expressing the issues to be addressed, based on the project in progress (residents' and experts' speech, photographs, uses expressed therein, quantitative data, an enlarged section at a specific point, elements that are part of the diagnosis and of problems, project sketches, among others). Thus, it is a matter of summoning actors who live in the place where the issue will be addressed to participate in a debate, based on the aforementioned section, to trigger reactions based on what is already registered, or on what is still missing, as well as to add comments, information or new narratives, based on discussions happening in different places around the table, among others.

Putting both the issues and the actors under debate has the advantage of always keeping the context at the core of changes -due to the presence of the section in front of participants -since the transition to the round table (which is necessary to enable a certain distancing) often places the debate at the level of stating opinions or of taking positions that may deviate from the features of the place. Triggering the first comments is in itself a moderator-like task, since it is necessary listening and encouraging the actors to debate among themselves and with the collectivity participating in the process. Three properties used in prospective diagnosis are applicable to this type of method, namely: speech-generating device, notation-collection device, and device capable of revealing experienced realities. The multiplicity of experiments conducted in different contexts has rapidly enabled identifying some principles contributing to improve device efficiency: 6. Terminology that we have proposed along with Pascal Amphoux.

 After the first long tables were held, it was essential having "thick description" elements (cf. [START_REF] Geertz | The interpretation of cultures[END_REF], although we were not initially looking for a synthesis capable of stopping us from analyzing the density of the situation (through a highly-technical representation) and of experiences (through significantlysimplified narratives).

 Positioning along the transect a set of data that "look at each other" ("two images can form a story, as Jean-Luc Godard used to say) and adhere to the context due to the graphic device, which enables maintaining each element in its own enunciation mode (a text remains a text, an image remains an image, a measure remains a measure, among others). Consequently, we ended up significantly straying away from the logic of the overlapping thematic layers, which are specific to geographic information systems, which, in their turn, overall require codifications such as colors, hatches, values, markers, among others.

 In order to be applied in the best way possible, the previous two points must be subjected as little as possible to codes that require captions to be interpreted. If a given datum requires caption to be contextualized or specified, it becomes clearer at the time it is simply indicated as information on the transect device under data themselves.

The analysis taking place during the long table is refined through exchanges among actors participating in it. It results from consensus or, on the contrary, it expresses strong local controversies and often focuses on project sketches at all scales (from residents' intervention to urban orientation) in order to consolidate or change the situation (either built, social or sensitive). It is a plural way of putting the everyday life into debate and in projects.

TRANSECT AND PROJECT(S)

If the transect enables the transition to the project at different times of its construction or when it works as mediation between actors, is it possible building projects as transects?

From the formal viewpoint, any project focused on creating or renewing a line that crosses an existing line can be seen as a transect. However, the transect's ability to read a However, these lines and sections in the physical environment sometimes take on more common, although not less powerful, aspects in the practice of, and perception about, the city enabled by them, due to spatial, social and historical densities that make us feel. After the 19 th century passageways -which were appreciated by Walter Benjamin and Charles Baudelaire (for whom every passerby is a flâneur) -, would the "transect" lines be the passageways of the 21 st century (where every passerby is an operator without a camera) (cf. PACI; BONNARD, 2014)?

There are also projects presenting a more symbolic aspect that resemble transversal projects due to their academic construction. An example of this type of recent project, which is particularly exciting for us, lies on The Newtown Creek Nature Walk, in It was designed to evoke the rich and continuous environmental, industrial and cultural stories surrounding Newtown Creek". Far from being just a place for the body and sensations -as Catherine [START_REF] Grout | Paysage et art contemporain[END_REF] has shown very well in one of the rare studies carried out about this project -, we see it as a thread from which everything can be implanted: history, geography and society. Based on this solid and thought-provoking project, it is possible identifying tools and concepts such as section, tracks, stratum, atlas, urban miniature, tasckape, among others. It is so, to the point that this project appears to us as the paradigm of a transect project at public space scale.

But it is, above all, from the structural viewpoint of how to understand a given territory that the transect consolidates its potential by revealing unique spaces and nonhierarchical temporalities for a whole set of projects. The whole is no longer mainly a project defined by the classic game of scales, or a project that is only imposed by its designers or, conversely, that arises from users' practice. It is, above all, a space for negotiation, where all actors in the territory can find the project material in compliance with their own scale practices.

USING THE TRANSECT

How do we proceed when we consider these elements as clues? First, we associate data and, then, we compare situations. Clearly, there is deduction and induction whenever one tries to generalize, establish rules or check consequences; but unique contexts are always the ones that quickly resist to any explanatory rule. Each place is a unique composition that must be understood based on its spatial arrangements. Thus, abduction, which is herein mainly understood as the formulation of hypotheses into the narratives integrating the clues, is often carried out around the long table. It is done through the development of a new link between two elements that were not previously connected, through the introduction of new elements by actors participating in the long table, through the implementation of a new arrangement associated with a logic that applies to elements of other nature (analogy), but also through the introduction of a novelty capable of catalyzing a given situation and of overruling previous interpretations. First of all, the long table is a fertile and abductive time to enunciate narratives, to experience, the very narrative of the place in terms of what is literally placed on the table and, then, to implement, change or reinforce such a narrative in order to test its validity by enunciating it to others. The interpretation of a given situation always requires outlining its future. The novelty of a given narrative or proposition comes before the establishment of new relationship between elements that already exist, in order to set relationships between elements that would be composed in an original way, based on the singularity of each place. In other words, innovation no longer lies just on the novelty field, either it is technical or aesthetic; it lies on the always unique hybridization of different challenges specific to each existing situation; it is, above all, a matter of bringing things up (AMPHOUX, 2009, p. 22-23).

It rests on the (pragmatist) idea that every urban situation is a "public thing", that it is a permanent construction. Once the elements have been placed in the transect, they can work as clues to develop possibilities for the future or to tell a story about the past, to give meaning to the present. Thus, it seems to us that all the work on the future of a given place one wants to build, based on the knowledge about what already exists, goes through an abduction phase. Therefore, as Dewey would say, relevant clues necessary to manifest a given situation often give room to a set of possibilities and help attracting the public. This process enables a local validity that a group of actors, or even public policies, must be able to count on, even from top to bottom.

5.

  With respect to the principles of debate about the definition and effectiveness of the concept of ambiences, we herein refer to some references in chronological order, starting with the number organized by Luc Adolphe, "Ambiances architecturales et urbaines", in Les cahiersde la recherche architecturale et urbaine , N. 42-43, 3 rd trim. 1998. Marseille, Éditions Parenthèses; then, the collective work organized by Pascal Amphoux, Jean-Paul Thibaud, Grégoire Chelkoff (eds), Ambiances en débat, Bernin, ed. A la Croisée, 2004 ; the work by Jean-Paul Thibaud Enquête d'ambiances. Éprouver la ville en passant, Genève, Éd. MetisPresses, 2015. And, most recently, studies by Gernot Böhme, Tonino Griffero, Jean-Paul Thibaud, Juhani Pallasmaa, Architecture and Atmosphere, ed., by P. Tidwell, Tapio Wirkkala-Rut Bryk Foundation, Espoo, 2014; by Gernot Böhme, The Aesthetics of Atmospheres, ed. by Jean-Paul Thibaud, London, coll. Ambiances, Atmospheres and Sensory Experiences of Spaces, Routledge, 2016; and by Tonino Griffero, Quasi-Things. The Paradigm of Atmospheres, Albany, Suny Press, 2017. The set of arranged elements generates a triple-open urban narrative, in the sense that:  the transect reader is the one who decides what he/she is going to read and in what order he/she is going to do it, what he/she is going to connect with, what he/she is going to keep as important, among others;

  crossed context and to reproduce a reciprocal change is what defines its strength. Thus, projects comprising an old railroad such as the High Line in New York (launched in 2009), or the Promenade Plantée in Paris (launched place twenty years earlier, in 1988), are wellknown and consolidated examples of built devices that literally work as transects.

  Greenpoint, Brooklyn. It was launched in 2007 by artist George Trakas and landscaper Quenell Rothschild & Partners. Based on our viewpoint, this project manifests what we could call "transect". It is described as follows at the time it was introduced to the public: "It is a linear walkway by the sea and an entrance garden at the access point of the street.


Samir Medjiah
email: medjiah@laas.fr

Christophe Chassot
email: chassot@laas.fr

On the enhancement of non-functional requirements for cloud-assisted middleware-based IoT and other applications

Keywords: Cloud-assisted, middleware, micro-service, service oriented, QoS management, IoT, autonomic computing, dynamic (re)configuration, dematerialized network function, scalability, NFV, SDN, model-driven

The Internet of objects (IoT) will have to meet the non-functional needs (QoS, security, etc.) of new business applications supported by the cloud. To do this, the interactions between the underlying application software and the communicating objects will rely on networks and communication middleware with configurable, programmable and dynamically deployable capabilities. These capabilities will be available both on pre-existing entities but also on virtual entities, i.e. that will be dynamically created in the Cloud according to the need. In this new ecosystem, meeting the end-to-end QoS needs of these future applications is a major challenge. This challenge has particularly to be tackled both at the level of the Middleware intermediary entities and at the level of the networks interconnecting these entities. In this context, this paper presents our approach for a self-adaptive QoS management at the middleware level for IoT applications. This approach is aimed at: 1) taking advantage of the technological opportunities offered by the Cloud, the dynamic deployment of processing functions and the autonomic computing paradigm, 2) taking into account the heterogeneity of the solutions that will coexist in this landscape, and 3) ensuring the consistency of the (re) configuration choices thanks to appropriate theoretical tools.

Introduction

Context

The future Internet, including not only usual terminals but more generally any form of communicating objects, will have to meet non-functional needs (security and quality of service -QoS in particular) of new business applications, taking advantage of Cloud in various domains such as remote supervision, personal assistance, and urban transport.

To do this, the interactions between the application software and these objects will be based on communication networks and "middleware" layer allowing both to abstract applications from the complexity of underlying technologies (networks and connected objects), but also to avoid "vertical" fragmentation of IoT solutions. In this new ecosystem, several challenges already addressed in the "classical" Internet are to be (re)considered in particular the performance of the whole communication system (i.e. including network layers and middleware) in response to the expressed Application-level QoS requirements, for instance, in terms of high service availability or bounded response time. From 2010, a major standardization effort has been conducted at the Middleware level, notably via ETSI and the oneM2M consortium [START_REF]Machine-to-Machine communications (M2M); Functional architecture[END_REF] [START_REF]oneM2M functional architecture[END_REF]. However, the proposed solutions remain a point of fragility in front of the expected performances. Some works begin to address the QoS problem at the IoT Middleware level by proposing mechanisms for managing application level traffic (for example, delaying less priority requests in case of congestion) and / or allocated resources of the underlying machines [START_REF] Banouar | QoS Management Mechanisms for Enhanced Living Environments in IoT[END_REF].

In this context, the advent of the so-called "virtualization" technologies initially linked to the Cloud, makes it now possible to consider the deployment of these mechanisms not only on dedicated equipment (typically a Gateway in the world of IoT) but in private or public data centers with hypervisors offering the required functional capabilities. The concept of "virtual network function" -VNF ("virtual" is not necessarily in the sense of "implemented" on dedicated equipment) has been defined by the ETSI as part of its work on standardization of the NFV technology [START_REF] Etsi | Network Functions Virtualisation ; Virtual Network Functions Architecture[END_REF]. This concept is today to be considered in a wider framework involving the deployment of such functions on any node that can host and execute the corresponding program, whether it has a hypervisor or not (i.e. serverless paradigm [START_REF] Namiot | On micro-services architecture[END_REF]). It is for example possible to deploy and launch an executable applicative program on a simple PC without interrupting the execution of its operating system. It is also possible to deploy an application module and integrate it dynamically within an application code whose design is based on a component or micro services-oriented approach. This analysis leads us to (re)-define the concept of "network function" (NF) (cf. Figure 1), which basically consists in a given processing of packets of any level (Application, Transport, Network, ...). In our vision, the concept of NF integrates and extends the concept of ETSI VNF which appears as a special case of what we call a "dematerialized" (DNF) network function, i.e. deployed outside of its original environment (as opposed to the "physical" network functions). A DNF can then be defined either as a VNF or as an application network function (ANF) consisting in an executable applicative program or an application module.

Problem statement

Let us then consider a vision of an IoT underpinned by a generic IT infrastructure including not only dedicated middleware and network entities (typically gateway / server and routers) but also private and public data centers, and also simple machines on which it is possible to deploy code in the form of an executable application and / or an application module. It should be noted that this code can be applied at the Application level (in the OSI sense of the term), but also at the Transport level (i.e. TCP level of the Internet stack) if the latter is built according to a component-based design [6][7]. In front of the performance problems, the global issue we consider in this positioning article is to define how to take advantage of the characteristics (opportunities and constraints) of the available IT infrastructure with the aim to implement a dynamic management approach of QoS-oriented mechanisms meeting the application requirements, at different levels of the communication system, typically Middleware, Transport and/or Network levels.

Approach

Our approach consists in designing, developing and testing generic architecture models for a self-adaptive management of QoS-oriented network functions (in the NF sense) at the different levels of the communication system:

• taking advantage of the technological opportunities associated with the dynamic deployment of network functions, but also of software-driven networks (in the SDN sense), • taking into account the factual heterogeneity of the solutions being deployed,

• ensuring the consistency of the configuration and reconfiguration choices made for each level through appropriate theoretical tools.

In our work, the autonomy management is based on the autonomic computing paradigm (IBM). In this paper, we mainly focus on the Middleware level.

The rest of this paper is structured as follows. We first detail in section II the notion of middleware-based IoT application; we also position the Cloud and its opportunities. Our approach for a dynamic and autonomous management of network functions (here QoS oriented) is presented in Section III. The key challenges associated with this approach are detailed in Section IV. The conclusions and perspectives of the paper are finally presented in Section V.

Definition and motivation of "cloud-assisted middleware-based applications"

Following the classic deployment of IoT solutions where we have smart objects such a sensors or actuators connected to application servers through one or multiple gateways, communications' management can be very tricky. Indeed, despite the required huge number of connected things to fulfill the application objectives, these devices often use different networking technologies, communication protocols and data formats, making the overall communication between the application logic and the physical objects difficult to achieve. In this context, an application can greatly benefit from the services of software middleware that abstract the application from the underlying networking specifics. Thus, through an IoT middleware, the application logic uses simple APIs that most often follow a RESTful model and use universal protocols such as HTTP or CoAP to interact with the physical objects in order to query sensed data or to trigger object's commands. In this case, the application developer is not required to implement or even to learn specific IoT protocols such as ZigBee, Z-Wave, Bluetooth, etc. in order to communicate with the physical objects. For applications' backend, Cloud based deployment has allowed to tackle the nonfunctional requirements (on particular QoS requirements) through the offered elasticity of resources (storage & compute) being made available to the applications' backend. For example, a virtual machine hosting a MW entity can see its memory (RAM) dynamically resized and scaled up (Vertical Scalability) in order to meet the increasing processing load (e.g. Increase in number of messages routed through this MW entity). Another typical example of the cloudification benefits is the increase in the number of VMs hosting the same MW entity with a load balancing mechanism in order to respond to a sudden load increase.

Cloud based deployment can also allow to tackle functional requirements for example through the dynamic deployment of data/packets processing functions that are implemented in software and previously packaged in virtualization containers (VMs or system-level containers: LXC, Docker, etc.). For example, an application may need its data format to be translated from a text format (e.g. JSON) to a binary format (e.g. BSON) before being exchanged by the MW in order to optimize the data transfer, and translated back again to be received by the final destination. Another example is the deployment of message aggregation function between the application and the MW in order to adapt the MW communications to the underlying networks (e.g. Satellite networks with big data frames).

Enhancement approach

In this section, we present the typical deployment infrastructure of a Cloud-assisted and middleware-based IoT solution (cf. Figure 2). In this context, the IoT application is accessed using a user terminal such as computers or smartphones. An IoT middleware is linking this application to the physical sensors and actuators. The application backend as well as some MW entities are being deployed in public or private Cloud. Some MW entities may be deployed within the Service Provider private infrastructure using dedicated nodes (typically for IoT gateways) or generic deployment nodes such as COTS hardware. In this context, we consider the following actions strategies:

1. Vertical Scalability: as illustrated earlier, this strategy aims to dynamically scale a virtualization container's resources such as memory, storage or compute resource, whether this CV is deployed on a public or private Cloud. ▪ Transcoder: a function for translating the payload of packets from one format to another for transfer optimization or interoperability purposes. For example, JSON from/to BSON (optimization), XML from/to JSON (interoperability), etc. ▪ (De)Compressor: a function for compressing/decompressing the data packets payloads in order to optimize the data transfer especially in constrained networks.

▪ …

Relying on these three action strategies, the system is offered a large panel of mechanisms which are different in behavior, requirements and results. Therefore, system reconfiguration can be achieved through the use of one or a combination of all the possible mechanisms. It is then up to the pacification process to choose the appropriate set of mechanisms and their orchestration in order to meet the targeted non-functional requirements and in particular QoS requirements. Since, these mechanisms are inherently dynamic, autonomous behavior that is based on these mechanisms can be achieved through the implementation of an autonomic manager. In our approach, we have considered the autonomic computing paradigm proposed by IBM [START_REF] Kephart | The vision of autonomic computing[END_REF].

Key challenges

Several challenges have to be addressed in order to carry out the proposed approach. We present in this section the main challenge we have considered.

Design of the management system architecture.

The first challenge is to design the structural and behavioral architecture of the management system leading to the dynamic and autonomous deployment of QoS-oriented network functions. Three areas of research are particularly relevant.

• The first one deals with the OSI level of actions to consider, in our case: Middleware, Transport and Network levels. For each level, knowing the available functional and non-functional constraints and capabilities is a necessary prerequisite. Beyond this, for a multi-level management, the coherence of the adaptation choices is a major issue to avoid overreactions in case of QoS degradation. At the Transport level, the actions consist in adapting the protocol architecture in terms of mechanisms to be implemented in order, on the one hand, to meet the services required by the application, and on the other hand, to be the most appropriate with regards to the features of the underlying network. At the Network level, the SDN technology opens the possibility of configuring the network, for example in dynamically establishing secure and / or QoS-oriented tunnels between two edge routers. • The second research issue is related to the spectrum covered by the targeted autonomous management. In a distributed middleware context, for instance, the design of an autonomous manager acting on all the servers and gateways involved on the data path is a first possibility. However, due to the number of metrics to be processed but also the communication latency between the managed entities and their manager, it is conceivable that such a solution has scalability limitations. The choice of an architecture based on hierarchical policies is conceivable to meet this limit. For a distributed middleware, we can for example imagine two levels of autonomous management, one local to each middleware entity leading to the adaptation of the behavior and / or resources of each of these entities, a higher level global one to define the QoS objectives to be reached by each local manager. • The third challenge is related to the implementation choice of the autonomic manager that can be centralized or distributed. Another implementation choice comes from the use (or not) of the virtually infinite resources of the Cloud with the aim to avoid that the manager becomes itself a bottleneck with respect to QoS.

Models to drive the different steps of the autonomous process

Several paradigms can be envisaged to implement the logic of the autonomous manager, among them the autonomic computing (AC) model proposed by IBM [START_REF] Kephart | The vision of autonomic computing[END_REF]. In addition to its four objectives, which are self-configuration, self-optimization, self-repair and self-protection, the AC relies on the implementation of a four-step loop dealing with: (1) the Monitoring of the resources and / or the performance of the managed system in order to raise symptoms representing for instance a QoS degradation, (2) the Analysis of the causes explaining the identified failures, (3) the Planning of the adaptation actions to be undertaken, and finally (4) the Execution of these actions by the managed system. The implementation of this so-called MAPE-K loop is based on a Knowledge base including the relevant elements (model information, etc.).

Two main approaches can be envisaged to carry out the Monitoring, Analysis and Planning steps: either by working on the managed system itself (for example a middleware entity) including the traffic to be transferred, or on the basis of models, for example of the managed entities and or the incoming traffic. The first approach is costly in terms of resources and / or overhead. The second approach reduces this extra cost at the possible price of an approximation related to the manipulation of models rather than real elements. It has also as advantage to facilitate both a proactive and a reactive adaptation approach. It is also very useful (and sometimes necessary) to tackle the complexity associated to a multi-level management and to deal with the heterogeneity of the current IT infrastructures in terms of usable technologies. Let us finally note that this e-second approach also allows to ensuring the verification of required properties, such the respect of a given structural functioning schema [START_REF] Bouassida Rodriguez | A rule-driven approach for architectural self-adaptation in collaborative activities using graph grammars[END_REF]. The elaboration of such models to drive the different steps of the autonomous process is a challenge in itself that may be addressed thanks to several formalisms and theories such as graphs, queuing theory, etc.

Conclusion and future work

Within the future virtualized Internet of Things, meeting the end-to-end QoS needs of new cloud-based and other applications is a major challenge. This challenge has particularly to be tackled both at the level of the Middleware intermediary entities and at the level of the networks interconnecting these entities. This paper has presented our approach for a self-adaptive QoS management at the middleware (and other) levels for IoT applications within this new ecosystem. The key challenges associated with this approach have been introduced. Our current and future works deal with the proposal of architectural and model-based solutions towards the identified issues.

Fig. 1 .

 1 Fig. 1. Network function concept.

Fig. 2 .

 2 Fig. 2. Typical deployment infrastructure of Cloud-assisted middleware-based IoT solutions.

2 .

 2 Horizontal Scalability: this strategy can be implemented through multiple ways: a. Activation of backup MW entities already deployed within dedicated nodes in order to achieve redundancy. b. Deployment of new instances of CVs hosting MW entities within generic nodes; COTS nodes or private/public Cloud. 3. Dynamic Function Deployment: with this strategy, processing function of data/packets at different levels (application, transport or network) can be deployed in specific locations in order to perform message-oriented QoS adaptation actions. Such processing can be deployed through: a. an application module (ANF) to change/augment the behavior of a MW entity. b. A CV hosting different functions within generic nodes or data centers (public or private) These functions can be classified into data-oriented and packet-oriented functions: o Packet-oriented functions: ▪ Classifier: a function responsible for identifying packet's class in order to achieve differentiated processing. ▪ Marker: a function closely related to the classifier function that is responsible for marking the packets with the appropriate class/category. ▪ Scheduler: a function responsible for packets reordering based on specific scheduling algorithm. This function can rely on the Classier/Marker functions in order to schedule the marked packets based on their marking. ▪ Discarder: a function for dropping marked packets or based on a discarding algorithm ▪ Delayer: a function for delaying marked packets for delaying or based on a specific algorithm. ▪ … o Data-oriented functions, examples include: