Daouda Ahmat
email: daouda.ahmat@gmail.com

Mahamat Barka
email: mahamat.barka@gmail.com

Damien Magoni
email: magoni@labri.fr

SEMOS: A Middleware for Providing Secure and Mobility-aware Sessions over a P2P Overlay Network

Keywords: connectivity, mobility, overlay, P2P, VPN, security

Mobility and security are major features for both current and future network infrastructures. Nevertheless, the integration of mobility in traditional virtual private networks is difficult due to the costs of re-establishing broken secure tunnels and restarting broken connections. Besides session recovery costs, renegotiation steps also present inherent vulnerabilities. In order to address these issues, we propose a new distributed mobile VPN system called SEcured MObile Session (SEMOS). Based upon our CLOAK peer-to-peer overlay architecture, SEMOS provides security services to the application layer connections of mobile users. Secure and resilient sessions allow user connections to survive network failures as opposed to regular transport layer secured connections used by traditional VPN protocols.

Introduction

Mobile devices and wireless networks have progressively provided increased connectivity for users. However, such extended connectivity often comes at the expense of vulnerabilities to attacks such as eavesdropping. Malicious users can infiltrate public open networks and attack legitimate traffic. Virtual Private Networks (VPN) are offering high security to the network traffic [START_REF] Berger | Analysis of current vpn technologies[END_REF]. Traditionally, these systems allow the user to securely and remotely communicate with its Intranet through insecure public networks such as the Internet. Security services provided by these infrastructures are robust against malicious users attacks. However, traditional VPNs fail to support users' mobility. Indeed, network failures automatically break-up secure tunnels and involve a subsequent renegotiation that is then necessary to re-establish broken tunnels. This renegotiation requires expensive computational operations in order to restore tunnels as well as transport-layer and application-layer connections. This phase of negotiation causes not only significant latency but also presents risks of Man-In-The-Middle (MITM) attacks. Traditional VPNs can not therefore effectively operate in dynamic and mobile environments. In addition, lack of means, disruptedenvironments and unsteady networks, due to both poor-quality devices and technical skills deficiency, are pervasive in developing countries, particularly in Africa. In these areas, secured resilient sessions are needed to overcome both security and performance issues inherent to connection disruptions.

In this paper, we propose a new mobile VPN-like system called SEcured MObile Session (SEMOS). This system is designed to support both the mobility and the security of SEMOS entities. We have implemented a prototype and have tested and evaluated it by running experiments upon an emulated mobile network. We have compared its features and performances to three other existing solutions namely HIP, N2N and MOBIKE that propose open source implementations. Results show that our solution provides more features and exhibits better connection resumption performances.

This paper is an extended version of our previous work presented at Wireless Days 2012 in Dublin [START_REF] Ahmat | Muses: Mobile user secured session[END_REF]. This new version includes an exhaustive state of the art, a more detailed description of the SEMOS underlying P2P overlay network called CLOAK and a comparative evaluation of three existing similar and open source solutions (i.e., HIP, MOBIKE and N2N), with respect to features and latency performances. In addition, we have extended MUSeS properties by adding several useful design features. In order to avoid name conflicts, we have also changed the name of our solution from MUSeS in [START_REF] Ahmat | Muses: Mobile user secured session[END_REF] to SEMOS in this paper.

Related work

Up to now, several mobile VPN solutions have been proposed in various research papers. In this section, we study some interesting existing solutions that address the design of mobile VPNs. Mobile VPN systems based on both IPsec [START_REF] Kent | Security Architecture for the Internet Protocol[END_REF] and Mobile IP [START_REF] Perkins | IP Mobility Support for IPv4[END_REF] have been proposed several times such as in [START_REF] Binkley | An Integrated IPsec and Mobile-IP for FreeBSD[END_REF], [START_REF] Braun | Secure mobile IP communication[END_REF], [START_REF] Choi | Mobile multi-layered ipsec[END_REF] and [START_REF] Ruppelt | Building ALL-IP Based Virtual Private Networks in Mobile Environment[END_REF], in order to attempt to overcome the inherent mobility drawbacks of traditional VPNs.

Nevertheless, as explained in [START_REF] Adrangi | Problem Statement: Mobile IPv4 Traversal of Virtual Private Network Gateways[END_REF], many problems arise from the combination between IPsec and MobileIP. In order to overcome these problems, a model has been proposed which is based on the use of two HAs (internal HA and external HA) and two FAs (internal FA and external FA) by Vaarala et al. in [START_REF] Vaarala | Mobile IPv4 Traversal across IPsec-Based VPN Gateways[END_REF]. However, this model imposes the use of three imbricated tunnels({x-MIP{GW{i-MIP{original packet}}}}).

In addition, an IPsec-based mobile VPN requires n tunnels (n security layers) when there are n IPsec hops between the source and destination entities. Therefore, the imbricated tunnels in such VPN systems have a negative impact on their network performances (i.e., throughput, overhead, etc).

In order to address IPsec mobility inherent issues, several improved schemes based on the IPsec architecture have been proposed by Eronen et al. in [START_REF] Eronen | IKEv2 Mobility and Multihoming Protocol (MOBIKE)[END_REF], [START_REF] Devarapalli | Secure Connectivity and Mobility Using Mobile IPv4 and IKEv2 Mobility and Multihoming (MOBIKE)[END_REF], or [START_REF] Karbasioun | Securing mobile IP communications using MOBIKE protocol[END_REF]. Based on security extensions to MOBIKE [START_REF] Eronen | IKEv2 Mobility and Multihoming Protocol (MOBIKE)[END_REF], the solution described in [START_REF] Karbasioun | Securing mobile IP communications using MOBIKE protocol[END_REF] combines secure connectivity and Mobile IPv4. This approach resolves considerably the issues notified in [START_REF] Adrangi | Problem Statement: Mobile IPv4 Traversal of Virtual Private Network Gateways[END_REF] such as overhead, NAT traversal or mobility problems due to the combination of IPsec and Mobile IPv4. These solutions are however not free of scalability issues and network overhead that they inherit from IPsec and Mobile IP.

The dynamic VPN approach proposed in [START_REF] Ishimura | Dynamic IP-VPN architecture with secure IPsec tunnels[END_REF] enables to use alternately IPsec in Full-Mesh mode or in Hub mode with a centralized IPsec Gateway. The first mode is only used when routing problems occur. This architecture extends MO-BIKE in order to support dynamic tunnels. However, this model is not designed to support mobility.

Another proposal leveraging MOBIKE is presented by Migault in [START_REF] Migault | E2e: An optimized ipsec architecture for secure and fast offload[END_REF], where they propose an alternative End-to-End security (E2E) architecture based on their own MOBIKEX protocol, which extends the MOBIKE mobility and multihoming features to multiple interfaces and to the transport mode of IPsec. Based on a topology organized in communities, peer-to-peer (P2P) mobile VPN systems have also been proposed such as ELA [START_REF] Aoyagi | ELA: A Fully Distributed VPN System over Peer-to-Peer Network[END_REF] or N2N [START_REF] Deri | N2N: A Layer Two Peer-to-Peer VPN[END_REF].

In opposition to most dynamic VPN systems, these systems have the advantage to be fairly scalable and to have ability to communicate across NAT and firewalls. Decentralized P2P VPN are flexible and self-organizing infrastructures that enable users to create their own secure networks upon an untrusted network. N2N and ELA topologies are very similar despite the fact that N2N is based on the OSI layer two whereas ELA is based on the OSI layer three. However the use of super nodes in N2N limits its full scalability as these nodes have a more important role than the other nodes and thus they can weaken the overall strength of the N2N network and may even break its connectivity if they fail. Freelan [START_REF] Kauffmann | The freelan secure channel protocol[END_REF] is a multi-platform and open-source peer-to-peer VPN that abstracts a LAN over the Internet.

The Host Identity Protocol (HIP) [START_REF] Moskowitz | Host identity protocol (hip) architecture[END_REF][START_REF] Gurtov | Host Identity Protocol (HIP): Towards the Secure Mobile Internet[END_REF] is an architecture that provides both mobility and multihoming services. HIP introduces a new name space that enables the separation between the host identity, called Host Identity Tag or HIT, and the host location.

3 System description

Design

As shown in Figure 1, SEMOS is a communication layer directly used by the applications. SEMOS is using another communication layer called CLOAK which enables the creation and management of a P2P overlay network above any IP network [START_REF] Tiendrebeogo | Virtual connections in p2p overlays with dht-based name to address resolution[END_REF]. This system is designed to provide traffic security and session continuity. Applications produce data and send it to the SEMOS middleware. Data is then sliced in packets that are encrypted and authenticated. Unlike IPsec or TLS which rely on IP addresses to define the identity of the communication entities, SEMOS relies on permanent device identifiers called names provided by CLOAK. SEMOS can keep a user session active despite a connection disruption and can resume an interrupted secure session.

Overlay

CLOAK is an architecture for building P2P overlay networks which are autonomous and dynamic. A new peer can join any peer already inside the overlay usually by setting up a transport layer connection such as TCP with this peer. The new peer is then offered an overlay address which is unique and dependent on its location in the overlay. These virtual addresses or coordinates are taken from hyperbolic planeand used by a greedy routing algorithm for forwarding the data inside the overlay.

SEMOS session

CLOAK P2P Overlay

Mobile & secure connection Fig. 2. Routing through the P2P overlay network.

CLOAK was originally defined in our paper [START_REF] Tiendrebeogo | Virtual connections in p2p overlays with dht-based name to address resolution[END_REF], which presented the protocols and modules of the architecture with details and reported simulation results upon static and dynamic networks concerning routing success ratio, path length and stretch, as well as DHT performances. The DHT scheme defined by CLOAK is fully explained in our paper [START_REF] Tiendrebeogo | Reliable and scalable distributed hash tables harnessing hyperbolic coordinates[END_REF]. The Figure 2 shows how a packet is routed over CLOAK.

Permanent identifiers details

The CLOAK system provides a lookup service based upon distributed tables that consist of pairs defined as < ID CLOAK , @ overlay >.

Figure 3 describes the mobility mechanism provided by CLOAK. When a CLOAK node joins the network, it stores the pair < ID CLOAK , @ overlay > into the DHT, where ID CLOAK is its permanent identifier and @ overlay is its virtual temporary address. Thus, after moving within the network or leaving the network, when the node reconnects to the network, it will update the pair < ID CLOAK , @ overlay > by replacing its old address @ overlay by its new address that determines its current location. Only ID CLOAK , which is a permanent identifier, is used to identify the endpoints of a session in order to keep sessions active despite connection disruptions.

Architecture

As shown in figure 4, the SEMOS system is based on four main components:

-The Session Security Module (SSM) manages security services such as confidentiality, integrity and protection against replay attacks;

-The Session Reliability Module (SRM) is designed to provide fault-tolerant secure user sessions; In a nutshell, SRM offers user session continuity service that survives despite connection disruptions caused by lower layers failures; -The Local Connection Manager (LCM) handles multiple local TCP connections in order to support several simultaneous user applications; -The Port Forwarder (PF) enables to forward destination ports into local ports in order to intercept and process traffic and finally to send it. Interruption detection: When a connection fails, SRM has the ability to detect and handle it (see Figure 5). The destination's unreachability detection is made possible by an acknowledgment mechanism that is based on the exchange of request-reply messages.

When there is a packet loss, detected by a lack of acknowledgment or a wait timeout, the communication will be temporarily suspended. Each peer concerned by an interrupted session attempts to reestablish the connection with the corresponding peer. It sends Re-Hello packets (see Figure 7 that describes Re-Hello packet structure) at regular time intervals to attempt to restart the disrupted session.

Session Identifier: When a mobile SEMOS entity wishes to communicate with a remote corresponding node, these two peers compute together, in the handshake phase, a unique value in order to singly identify each session following the same principle as with a socket connection. When Alice sends a Hello message (see Figure 6 that describes the Hello packet structure) to Bob to start the communication (handshake phase), Alice generates a partial session ID (pSessIDa) and sends it to Bob. After receiving pSessID-a, Bob also generates a partial The communication, identified by a SessID, can be therefore started between the two actors. Precisely, a partial session ID (pSessID) is essentially computed by a combination between a source port number (psN) and a peer ID (pID): pSessID = psN pID.

Secure Mobility: In our model, the concept of secure mobility is a way to allow mobile users to keep an established secure session active when the underlying system connection fails until a subsequent new connection is started. In other words, when a user changes its location as shown in Figure 8 or when its connections are disrupted by network failures, the user session survives as long as necessary to resume the communication.

Experiment

In order to assess those four VPN technologies in a mobility scenario, we have used a tool called Network Emulator For Mobile Universes (NEmu), developed by Vincent Autefage [START_REF] Autefage | Network emulator: a network virtualization testbed for overlay experimentations[END_REF]. Furthermore, NEmu is an emulator that enables the creation of virtualized roaming or mobile devices which is needed in our scenario. The virtual machines run on top of QEMU using the Debian OS. QEMU virtual hosts are interconnected by virtual switches emulated by the Virtual Network Device (VND) software. In order to emulate roaming or mobile devices, NEmu uses the Network Mobilizer (nemo) software module. We have used a minimal FTP-like application based on the OpenBSD version of nc in order to experiment on the four different mobile VPN solutions presented. Table 1 provides the average results of ten experiments for each of the four systems. Location change duration showed in the second column is the same for all systems, it is defined as a parameter in NEmu. The third column shows the average latency for each system over ten rounds of experiments. These results show that SEMOS has the smallest average and maximum values for the latency due to communication resumption. Besides, failures do not cause any packet loss despite the long duration of disruption.

Conclusion

In this paper, we have presented a new solution called SEMOS for the simultaneous security and mobility of end-to-end connections. SEMOS is based on our P2P overlay system called CLOAK which provides dynamic naming, addressing and routing services. SEMOS builds upon CLOAK to provide secure and resilient sessions to the applications run by mobile users. In other words, user sessions can be paused for any period of time and can be restarted without the cost of renegotiating security parameters. In addition, SEMOS makes disruptions at lower layers completely transparent to the user applications and to their remote corresponding peers. The secured mobility and roaming of SEMOS user communications is thus ensured. The SEMOS middleware is designed to support several user applications simultaneously.

We have implemented a prototype of SEMOS as a middleware inserted between user applications and our CLOAK P2P overlay middleware. Currently, applications using the SEMOS API to implement secure and mobile sessions, must be recompiled. Devices running these applications must also run the CLOAK middleware and belong to a CLOAK overlay. SEMOS is implemented in C and can be downloaded at [START_REF] Ahmat | SEcure MObile Session[END_REF].

We have compared its features to three existing similar solutions: HIP, MO-BIKE and N2N. We have also evaluated the performances of SEMOS and the corresponding implementations of the other solutions in an emulated dynamic network environment by using NEmu. We have shown that HIP is the closest solution for providing all the functionalities offered by SEMOS. We have also observed that the latency resumption of SEMOS was the smallest of the four evaluated implementations, which places it as an interesting alternative to existing solutions.

Our future work will consist in completing and improving our current implementation as well as integrating a key management scheme suitable for dynamic networks to provide the users with a means to exchange or generate secret keys in-band. To this end, we have designed a key generation technique based on the Shamir's secret sharing method and using multiple disjoint paths in the overlay, for creating a secret key without requiring certificates such as in Diffie-Hellman [START_REF] Ahmat | End-to-End Key Exchange Through Disjoint Paths in P2P Networks[END_REF]. We are currently evaluating this technique and we plan to insert it in the negotiation phase of a SEMOS connection.

Fig. 1 .

 1 Fig. 1. Architecture overview.

Fig. 3 .

 3 Fig. 3. Mobility scheme based upon the CLOAK DHT.

Fig. 4 .

 4 Fig. 4. Interaction between SEMOS components when receiving data.

Fig. 5 .Fig. 6 .Fig. 7 .

 567 Fig. 5. Failure detection and recovery mechanism. Hello Packet Header Routing Header Src ID = IDCLOAKSrc Dst ID = IDCLOAKDst Additional Header Fields Packet Type = flag 0 RC P = Source port DST P = Destination port IsConnectionOK() = Yes / No Payload % partial session ID PSess ID = uuid() SRC Port

Fig. 8 .

 8 Fig. 8. User mobility with ongoing secure session.

Table 1 .

 1 Experiment results.

	System	Location change	Average latency	Maximum latency
	HIP	20 s	16 s	21 s
	MOBIKE	20 s	13 s	19 s
	N2N	20 s	49 s	92 s
	SEMOS	20 s	4 s	11 s


come   L'archive ouverte pluridisciplinaire

Recension d'ouvrage : Silvia Antosa, Richard Francis Burton: Victorian Explorer and Translator, Bern, Peter Lang, 2013. 219 pages. Cette monographie rédigée par Silvia Antosa, spécialiste des études gaies et lesbiennes, du corps et du genre, est consacrée à la vie et à l'oeuvre de l 'explorateur et traducteur victorien, Richard Francis Burton (1821-1890). L'accent est mis sur les récits de voyage et sur les traductions d'écrits érotiques non occidentaux de cet écrivain controversé, et sur la manière dont ces textes contestent et retravaillent les discours dominants de leur époque sur la race, le genre et la sexualité. L'ouvrage examine aussi les débats que suscitèrent ces écrits dans des disciplines comme l'anthropologie, la sexologie et la médecine. Cette étude montre que Burton entretenait une relation ambiguë avec les institutions coloniales. Il soutint le projet colonial en occupant diverses fonctions officielles en Afrique, en Inde ou dans la péninsule arabique, mais il était aussi un contestataire irrévérent, qui s'insurgeait parfois contre les autorités. Il se situait à la fois dans le système et en dehors de celui-ci. Silvia Antosa explore la manière dont Burton défiait les normes socioculturelles britanniques, en s'appropriant et en important dans son discours et ses écrits les rituels et les langages des sujets coloniaux. Il adoptait en effet les multiples identités masculines des endroits qu'il visitait, en portant par exemple les habits traditionnels des pays dans lesquels il séjournait, ce qui impliquait des processus d'identification et de « dés-indentification ». Ces masques lui permirent de faire des rencontres du même sexe, lesquelles remettaient en question les barrières entre colonisateurs et colonisés. Silvia Antosa place son auteur sous le signe de la mobilité et de l'instabilité, arguant qu'il était conscient de la nature transitoire du monde dans lequel il évoluait et qu'il reflétait lui-même par son nomadisme. Ses voyages lui permettaient de mettre le monde en perspective et de reformuler des idées considérées comme acquises. Cette monographie présente dans un premier temps les principaux débats sociaux, politiques et culturels liés à l'impérialisme et au colonialisme, par exemple les relations entre colonisateur et colonisé, ou les questions de race, de britannicité et de classe. Elle s'intéresse à l'émergence d'un discours orientaliste et à la construction textuelle de l'Empire britannique. Elle étudie ensuit la place de l'écriture de voyage de Burton dans les débats de son époque et la manière dont ces écrits négocient des questions sensibles en contribuant à leur formulation mais aussi en les déconstruisant de manière radicale. Silvia Antosa considère enfin la participation de Richard Burton aux débats de ton époque sur la sexualité, et elle souligne l'influence de ces débats sur ses traductions d'ouvrages érotiques indiens et arabes. Elle étudie en particulier l'impact des activités de Burton le voyageur, anthropologue et traducteur sur sa traduction des Mille et Une Nuits. Elle montre que si son écriture semble à première vue suivre une approche orientaliste en opposant sensualité orientale et moralité victorienne, elle propose en fait un discours alternatif sur le genre et la sexualité, marqué par d'autres systèmes culturels que Burton transposait dans ses livres. Cet ouvrage a le mérite de faire découvrir un auteur complexe et passionnant, à la fois « explorateur, linguiste, ethnologue, anthropologue, archéologue, interprète, poète, écrivain, soldat, homme d'épée, diplomate et conteur » (11) que l'on rencontre ici dans toute sa richesse et ses contradictions. Cette exploration permet aussi de se plonger dans la complexité et les ambivalences de la période victorienne dans laquelle s'inscrit cette oeuvre hors du commun. La monographie de Silvia Antosa se situe à la croisée des études gaies et des recherches sur le récit de voyage, et elle intéressera les spécialistes de ces deux domaines scientifiques. Elle se distingue aussi par son analyse subtile de questions inter-et transculturelles. Son contenu érudit et son style accessible en font un ouvrage agréable à lire et à découvrir.

Nathalie Vanfasse


Daouda Ahmat
email: daouda.ahmat@gmail.com

Mahamat Barka
email: mahamat.barka@gmail.com

Damien Magoni
email: magoni@labri.fr

Mobile VPN Schemes: Technical Analysis and Experiments

Keywords: mobile VPN, resilient session, seamless resumption

A new class of Virtual Private Networks (VPN), which supports both security and mobility, has recently emerged. Called mobile VPN, these systems provide not only secure tunnels but also session continuity mechanisms despite location change or connection disruptions. These mechanisms enable secure sessions to survive in dynamic/mobile environments without requiring a renegotiation of security keys during the session resumption phase. In this paper, we compare four open-source mobile VPNs in terms of functionality and performance.

Introduction

A Virtual Private Network (VPN) provides increased security between two remote entities that exchange data through untrusted networks such as the Internet [START_REF] Berger | Analysis of current vpn technologies[END_REF]. VPN systems prevent against various attacks such eavesdropping or replay. However, traditional VPNs fail to support the mobility of users. Indeed, network failures automatically break-up secure tunnels and involve a subsequent renegotiation that is then necessary to reestablish broken tunnels. Such a negotiation involves expensive computational operations in order to restore tunnels as well as transport and application layers connections. This phase of negotiation causes not only significant latency but also presents risks of Man-In-The-Middle attacks. Traditional VPNs can not therefore effectively operate in dynamic and/or mobile environments.

Mobile devices and dynamic environments become pervasive in the Internet. However, for instance traditional VPN infrastructures do not support session continuity result from location change or network reconfiguration. After each connection disruption, key renegotiation process is needed to restore broken tunnel. In order to address network failures resulting from location changes or network reconfigurations, several solutions were proposed in the literature [START_REF] Deri | N2N[END_REF][START_REF] Moskowitz | Host identity protocol (hip) architecture[END_REF][START_REF] Eronen | IKEv2 Mobility and Multihoming Protocol (MOBIKE)[END_REF][START_REF] Ahmat | Muses: Mobile user secured session[END_REF][START_REF] Gurtov | Host Identity Protocol (HIP): Towards the Secure Mobile Internet[END_REF][START_REF] Binkley | An Integrated IPsec and Mobile-IP for FreeBSD[END_REF] .

Mobile VPN Technologies

Up to now, several mobile VPN solutions have been proposed in various research papers. In this section, we describe some leading examples of mobile VPN systems and technical concepts in this area proposed in litterature.

N2N

In opposition to most dynamic VPN systems, these systems have the advantage to be fairly scalable and to have ability to communicate across NAT and firewalls. Decentralized P2P VPN are flexible and self-organizing infrastructures that enable users to create their own secure networks upon an untrusted network. A layer 2 peer-to-peer VPN (see figure 1), called N2N [START_REF] Deri | N2N[END_REF], and ELA [START_REF] Aoyagi | ELA: A Fully Distributed VPN System over Peer-to-Peer Network[END_REF] topologies are very similar despite the fact that N2N is based on the OSI layer 2 whereas ELA is based on the OSI layer 3. However the use of super nodes in N2N limits its full scalability as these nodes have a more important role than the other nodes and thus they can weaken the overall strength of the N2N network and may even break its connectivity if they fail. Freelan [START_REF] Kauffmann | The freelan secure channel protocol[END_REF] is a multi-platform and open-source peer-to-peer VPN that abstracts a LAN over the Internet. Based over the UDP protocol, the FreeLAN Secure Channel Protocol (FSCP) is designed to be secure and efficient, and it tries to reduce the network overhead. In addition, Freelan systems can be configured to act according to a client/server, peer-to-peer or hybrid model whichever suits best.

IPSec + Mobile IP

Mobile VPN systems based on both IPsec [START_REF] Kent | Security Architecture for the Internet Protocol[END_REF] and Mobile IP [START_REF] Perkins | IP Mobility Support for IPv4[END_REF] have been proposed several times such as in [START_REF] Motorolla | Mobile VPN, Secure Connectivity on the Move[END_REF], [START_REF] Binkley | An Integrated IPsec and Mobile-IP for FreeBSD[END_REF], [START_REF] Braun | Secure mobile IP communication[END_REF], [START_REF] Choi | Mobile multilayered ipsec[END_REF] and [START_REF] Ruppelt | Building ALL-IP Based Virtual Private Networks in Mobile Environment[END_REF], in order to attempt to overcome the inherent mobility drawbacks of traditional VPNs. Nevertheless, as explained in [START_REF] Adrangi | Problem Statement: Mobile IPv4 Traversal of Virtual Private Network Gateways[END_REF], many problems arise from the combination between IPsec and MobileIP. In order to overcome these problems, a model has been proposed which is based on the use of two HAs (Home Agents) -internal HA and external HA -and two FAs (Foreign Agents) -internal FA and external FA -by Vaarala et al. in [START_REF] Vaarala | Mobile IPv4 Traversal across IPsec-Based VPN Gateways[END_REF]. However, this model imposes the use of three imbricated tunnels({x-MIP{GW{i-MIP{original packet}}}}), as shown in figure 2. In addition, a IPsec-based mobile VPN requires n tunnels (n security layers) when there are n IPsec hops between the source and destination entities. Therefore, the imbricated tunnels in such VPN systems have a negative impact on their network performances (i.e., throughput, overhead, etc).

In order to address IPsec mobility inherent issues, several improved schemes based on the IPsec architecture have been proposed by Eronen et al. in [START_REF] Eronen | IKEv2 Mobility and Multihoming Protocol (MOBIKE)[END_REF], [START_REF] Devarapalli | Secure Connectivity and Mobility Using Mobile IPv4 and IKEv2 Mobility and Multihoming (MOBIKE)[END_REF], or [START_REF] Karbasioun | Securing mobile IP communications using MOBIKE protocol[END_REF]. Based on security extensions to MOBIKE [START_REF] Eronen | IKEv2 Mobility and Multihoming Protocol (MOBIKE)[END_REF], the solution described in [START_REF] Karbasioun | Securing mobile IP communications using MOBIKE protocol[END_REF] combines secure connectivity and Mobile IPv4. This approach resolves considerably the issues notified in [START_REF] Adrangi | Problem Statement: Mobile IPv4 Traversal of Virtual Private Network Gateways[END_REF] such as overhead, NAT traversal or mobility problems due to the combination of IPsec and Mobile IPv4. These solutions are however not free of scalability issues and network overhead that they inherit from IPsec and Mobile IP.

Based upon the NEMO architecture [START_REF] Devarapalli | Network Mobility (NEMO) Basic Support Protocol[END_REF], the mobile VPN scheme presented in [START_REF] Petrescu | Mobile VPN and V2V NEMO for public transportation[END_REF] provides secure connectivity between vehicles for public transportation. In other words, this model provides secure vehicle to vehicle (V2V) communications as well as secured communications between passengers in the same (or in a different) vehicle. As the above mobile VPN solutions, this current model is designed to use the best properties of MOBIKE and Mobile IP.

The dynamic VPN approach proposed in [START_REF] Ishimura | Dynamic IP-VPN architecture with secure IPsec tunnels[END_REF] enables to use alternately IPsec in Full-Mesh mode or in Hub mode with a centralized IPsec Gateway. The first mode is only used when routing problems occur. This architecture extends MO-BIKE in order to support dynamic tunnels. However, this model is not designed to support mobility.

Another proposal leveraging MOBIKE is presented by Migault in [START_REF] Migault | E2e: An optimized ipsec architecture for secure and fast offload[END_REF], where they propose an alternative End-to-End security (E2E) architecture based on their own MOBIKEX protocol, which extends the MOBIKE mobility and multihoming features to multiple interfaces and to the transport mode of IPsec. Based on a topology organized in communities, peer-to-peer (P2P) mobile VPN systems have also been proposed such as ELA [START_REF] Aoyagi | ELA: A Fully Distributed VPN System over Peer-to-Peer Network[END_REF] or N2N [START_REF] Deri | N2N: A Layer Two Peer-to-Peer VPN[END_REF].

HIP-based Mobile VPN

The Host Identity Protocol (HIP) [START_REF] Moskowitz | Host identity protocol (hip) architecture[END_REF][START_REF] Gurtov | Host Identity Protocol (HIP): Towards the Secure Mobile Internet[END_REF] is an architecture that provides both mobility and multihoming services. HIP introduces a new name space that enables the separation between the host identity, called Host Identity Tag or HIT, and the host location, as shwon in figure 3. Each HIP host is uniquely identified by the public key of its public/private key pair. When a mobile node changes its point of network attachment, its IP address is then changed and the new IP address will be communicated to its correspondent hosts. However, in addition to remaining at an experiment stage for some years, HIP introduces a new layer between the transport and the network layers in the OSI stack. This implies that the host's operating system must be modified in order to use HIP although a user-space implementation does exist. In order to provide both security and mobility, HIP has been extended in two subsequent proposals: Hi3 [START_REF] Gurtov | Hi3: An efficient and secure networking architecture for mobile hosts[END_REF] and SPEAR [START_REF] Jookos | A secure peer-to-peer services overlay architecture[END_REF]. Previously known as P2P SIP-over-HIP (p2pship), SPEAR was originally designed for SIP-based communication applications (i.e., SIP proxy), allowing users to make peer-to-peer voice / video calls, without the help of a centralized SIP infrastructure. It now supports various protocols and applications. HIP is used as data transport, making the connections secure and enabling features such as mobility and multihoming.

Evaluation

In this section, we present a functional analysis as well as the experiment environment and the results of the evaluation of our approach MUSeS [START_REF] Ahmat | Muses: Mobile user secured session[END_REF] and three state-of-art solutions, namely: N2N, HIP and MOBIKE.

Functional Analysis

Table 1 describes the technical comparison between MOBIKE, N2N, HIP and MUSeS. Indeed, all these systems are based on UDP to exchange information in both handshake and re-handshake steps. The MUSeS middleware has the smallest number of exchanged packets for these two phases of communication. While both HIP and MUSeS proceed through direct connection, MOBIKE is based on indirect secure connection (through an IPSec gateway) and N2N is based on triangular negotiation in both handshake and re-handshake phases. For the two first systems, mobility is limited. This means that only N2N Edge Node and MOBIKE client can be really mobile. OpenHIP [START_REF] Henderson | OpenHIP[END_REF] MUSeS [START_REF] Ahmat | SEcure MObile Session[END_REF] Security Analysis: A Mobile VPN enables, in one hand, to secure communication and to keep open application sessions during location change. In other hand, mobile VPN is free to session key renegotiation in the resumption phase. These two technical properties are needed in secure mobile environments. Despite their interesting properties, the systems that operate in autonomous and mobile environments are constantly subject to some security challenges such as DoS and replay attacks.

To prevent replay attacks, MUSeS packets are built by adding sequence number to their headers. In other words, each packet is separately identified by its sequence number added to its header. Thus, when a packet is replayed, it will be automatically detected and subsequently it will be destroyed.

In the resumption phase, a Re-hello is generated and then sent in order to restore interrupted session without using session key renegotiation mechanism. However, Re-hello packet could be replayed because it does not contain a sequence number in order to detect replay attack. Thus, a malicious user that has infiltrated the network could then send a succession of Re-hello packets with the aim of perpetrating Denial-of-Service (DoS) attacks. In addition, the receiver peer cannot determine which oacket is the last one received among other received packets, otherwise this problem could be solved easily. In concrete terms, on receiving Re-hello, the receiver peer processes it in order to resolve and, the challenge and before finishing, it receives another, again another, etc. Finally, the target peer will be saturated by a flooding of Re-hello requests. Furthermore, HIP could be vulnerable to DoS attacks in the resumption phase as shown in the paper analyzing HIP protocol security [START_REF] Aura | Analysis of the hip base exchange protocol[END_REF].

To address this security issue, MUSeS assigns a timestamp when to each Re-hello packet in order to recognize the freshest request among received requests. In this way, the MUSeS system tries to prevent DoS attacks that use an uninterrupted sequence of Re-hello packets. Due to their mobility, flexibility and autonomy, P2P-based VPN systems are unfortunately not totally invulnerable to intrusion of malicious users. Indeed, in fully decentralized P2P networks, each peer can join and leave the network at any time and usually without any authentication. In our system, authentication is guaranteed by using challenge messages.

Typically, to authenticate a peer over the network, a node encrypts a random challenge message and sends it to its corresponding peer. On receiving this message, the corresponding peer decrypts it and sends the same message to the initiator peer. Thus, the initiator peer ascertains the identity of the corresponding peer.

The HIP protocol is designed to be resistant to Denial of Service (DoS) and Man in the Middle (MitM) attacks, and when used with ESP enabled, it provides DoS and MitM protection to upper layer protocols, such as TCP and UDP.

In N2N and MOBIKE however, there can be no secure tunnels without a N2N-Super-Node or a MOBIKE-GW. In other words, when N2N-Super-Nodes and MOBIKE-GWs are unavailable, any secure communication is then impossible. The HIP protocol and MUSeS do not suffer from these impairments.

Although MUSeS offers a solid security mechanism in remote communication between two peers, there is, however, a security weak point in local applicative connections. Unlike communication between two MUSeS peers, local communication between MUSeS and applications is not secured. This means that an unauthorized user application launched by a malicious user should establish connection with a remote honest MUSeS or eavesdrop exchanged traffic between MUSeS and local applications. This untrusted communication should cause security issues.

On the one hand, to prevent external malicious processes to connect to MUSeS, only local applications are authorized to connect to MUSeS by loopback address. On the other hand, only the root user can catch, by using tcpdump or wireshark, local traffic passed through from local applications to the MUSeS middleware and conversely. Therefore, plain text data exchanged between local applications and MUSeS are protected.

Mobility Analysis: MOBIKE and N2N are both based upon permanent virtual addresses in order to identify separately mobile nodes. However, when N2N-Super-Node and MOBIKE-Gateway (MOBIKE-GW) change their network points of attachment, any mobility would be possible. Thus, these systems have limited mobility. Indeed, MOBIKE authorizes only the mobility for initiators. However, in addition to mobility, MOBIKE supports also multi-homing for initiators. This means that MOBIKE mobile nodes can have several network interfaces and use them in order to support network link breakdown. In opposition to MOBIKE, all two endpoints of a N2N tunnel keep up mobility.

HIP introduces an interesting scheme of mobility and multi-addressing over IPv4 and IPv6 networks and it is designed to work in a NAT-less environment. Indeed, the HIP hosts do not change identities during location changes; this implies network addresses changes. Each HIP host is identified by its public key that is self-certified, called Host Identity (HI). Thus, when a mobile node changes its IP address, it notifies its currently active peers by sending a control packet containing its new location. When correspondent peers change simultaneous their location, the previous notifying method fails and a deadlock will occur. However, HIP introduces a rendezvous mechanism in order to address this simultaneous mobility issue. Unlike previous mobility methods, MUSeS proposes a new mobility scheme based on identifiers provided by a DHT infrastructure [START_REF] Tiendrebeogo | Virtual connections in p2p overlays with dht-based name to address resolution[END_REF].

Each MUSeS host is identified separately by a name and an address defined as coordinates taken from the hyperbolic plane.

An Interruption Detection mechanism is introduced by MUSeS to detect failures and to subsequently activate the SRM module. SRM is based on keepalive messages which are periodically sent. Thus, when network failures occur within lower layers, communication will be temporarily interrupted and failures will be confined within SRM and hidden to higher layers. Due to these properties, mobility is transparent to both user applications running over MUSeS middleware and all the other MUSeS modules, except the SRM component. Therefore, loopback connections established between MUSeS and local applications survive to networks failures despite network attachment point change events, for instance.

Performance Analysis

In order to assess those four VPN technologies in a mobility scenario, we have used a tool called Network Emulator For Mobile Universes (NEmu), developed by Vincent Autefage and presented in [START_REF] Autefage | Network emulator: a network virtualization testbed for overlay experimentations[END_REF].

An experiment has been carried out with the above implementation in a dynamic environment composed of one mobile node. A mobile node inside this environment has the ability to leave one network (one virtual router) in order to join another one (another virtual router). This event causes a network failure during the move until a possible subsequent reconnection. This disruption is transparent for the application and it does not prevent the MUSeS system from continuing to run despite the fact that the mobile node is disconnected for a moment. Technically, in our experimentation, the node mobility consists in causing an artificial failure on a virtual network interface. We disconnect a virtual wire from a virtual switch and reconnect it on another virtual switch. The MUSeS system hides this network change not only to the user's application but also to the remote corresponding node.

Figures 4 to 7 show the evolution of the throughput between the two corresponding applications over time. For all systems, the network interruption happens at the 40 th second after the start of the experiment and the throughput instantly drops to zero in the time intervals [40s ; 60s[. This means that the disruption duration is 20 seconds. The connectivity is reestablished at the network and CLOAK level at the 60 th second. However, due to latency, the throughput remains at zero after the 60 th second until the effective recovery. This latency varies from one system to another. Indeed, whereas MUSeS middleware has a latency of 3 seconds (see Figure 7), MOBIKE, N2N and HIP protocols have respectively latencies of 12 seconds (see Figure 6), 51 seconds (see Figure 4) and 13 seconds (see Figure 5).

Conclusion

Disrupted networks, due to both poor-quality devices and technical skills deficiency, are pervasive in developing countries, particularly in Africa. In theses areas, secured resilient sessions are needed to overcome both security and performance issues inherent to connection disruptions. In this paper, we have presented four open-source mobile VPN solutions, have provided a detailed technical analysis of those systems and have compared them in terms of functionality and performance. Results show that MUSeS is a competitive solution for providing secure and mobile communications.

Fig. 1 .

 1 Fig. 1. Example of N2N topology.

Fig. 2 .

 2 Fig. 2. IETF Mobile VPN (source: IETF).

Fig. 3 .

 3 Fig. 3. HIP layer within the TCP/IP stack.

Fig. 4 .Fig. 5 .Fig. 6 .Fig. 7 .

 4567 Fig. 4. N2N resumption latency.

Table 1 .

 1 Comparison of the evaluated mobile VPN systems.

	Mobile VPN system	MOBIKE	N2N	HIP	MUSeS
	Handshake packets	8	3	3	2
	Re-handshake packets	6	3	3	2
	Secure connection mode Mobility supported by systems	indirect 1 limited 3	triangular 2 limited c	direct √	direct √
	Implementations	StrongSwan [27]	n2n [2]


Nathalie Vanfasse Nathalie Bantz

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Hardy offre une perspective inédite sur celle-ci. Les nouvelles sont envisagées comme des annonces de romans ou au contraire comme un aboutissement par rapport à des romans écrits précédemment. Elles sont particulièrement intéressantes dans leur traitement de phénomènes de dissonance ou de défamiliarisation, essentiels dans l'ensemble de l'oeuvre de Hardy. Ce livre sera particulièrement apprécié par des lecteurs à la fois férus de l'oeuvre de Thomas Hardy et de narratologie.

  Nathalie Bantz, Les Nouvelles de Thomas Hardy: Stratégies narratives d'une écriture sous contrainte. Paris : Honoré Champion, 2011. 400 pages Recension Nathalie Vanfasse Aix Marseille Univ, LERMA, Aix-en-Provence, France Cet ouvrage traite des nouvelles de Thomas Hardy, un domaine moins exploré que celui de ses romans ou de ses poèmes car souvent considéré comme mineur et secondaire. Il vise, selon son auteure, à établir un trait d'union entre les différents genres explorés par le romancier. Le volume comprend une bibliographie très riche qui sera utile aux amateurs des nouvelles de Hardy. Un index des textes, des personnages et des auteurs rend la consultation du livre plus aisée. Nathalie Bantz a même pris soin de fournir à ses lecteurs un glossaire, une annexe biographique, un classement générique des nouvelles, une fresque chronologique et un classement des recueils et nouvelles. Nathalie Bantz s'intéresse aux stratégies d'écriture à l'oeuvre dans ces nouvelles et elle les compare à celles utilisées par Hardy dans ses romans. Ce qui l'intéresse, c'est la dimension subversive que Hardy introduit subrepticement dans l'écriture de ses nouvelles. Une des modalités de cette subversion des codes établis est le choix de la polyphonie qui permet au romancier de faire entendre plusieurs voix sans qu'aucune d'entre elles ne domine les autres, ce qui remet en question l'usage d'un narrateur omniscient en charge du récit. Nathalie Bantz montre cependant que Hardy n'est pas toujours fidèle à ce choix narratif et que de temps à autre il revient à la norme du narrateur classique, ce qui témoigne d'un tiraillement au sein de son écriture et d'hésitations entre deux conceptions de la narration. L'ouvrage montre comment par de telles stratégies, Hardy parvient à contourner la censure que lui faisaient subir les éditeurs de l'époque ou les critiques qu'adressaient à son encontre les critiques littéraires victoriens. Selon elle, l'apparente conformité des nouvelles dissimule en fait des formes de rébellion et l'adoption de codes dominants n'est en fait qu'une façon de mieux les dénoncer. Nathalie Bantz part d'interprétations contradictoires de l'oeuvre de Hardy tantôt considérée comme conformiste tantôt comme subversive pour étendre cette réflexion aux nouvelles. Son étude se concentre sur les nouvelles écrites par Hardy sans collaboration et destinées à un public adulte. Dans ces nouvelles, Nathalie Bantz se penche sur les schémas narratifs et les structures narratives. La première partie du volume étudie les nouvelles comme le lieu d'une affirmation de la voix narrative mais aussi de son effacement et elle en montre toutes les modalités. La deuxième partie du livre se penche sur la manière dont l'apparent conformisme de Hardy dans ses nouvelles s'avère souvent une manière de contourner les normes de son temps. La contestation se traduit au sein d'un texte conservateur par des détails typographiques, des titres ou des images. Nathalie Bantz souligne cependant l'ambivalence, l'ambiguïté d'une écriture qui finalement refuse de prendre parti et présente le réel dans toute sa complexité. Cette étude a le mérite de souligner l'importance des nouvelles dans l'oeuvre de Hardy. Les microlectures très fines et très nombreuses permettent d'en découvrir toute la richesse. Nathalie Bantz en explore le fonctionnement et situe ce décryptage dans le cadre de l'oeuvre de Hardy dans son ensemble. Elle démontre que l'écriture de ces nouvelles se place entre la forme plus contrainte des romans et la facture plus libre des poèmes, mais que Hardy ne se sentait pas pour autant enfermé dans un carcan quand il écrivait ses nouvelles, car il savait négocier les conventions de ce genre littéraire. Des romans à la poésie en passant par les nouvelles, Nathalie Bantz voit une gradation de l'écriture de Hardy vers une liberté croissante. Elle souligne la complexité de la figure de l'auteur qui se confond parfois avec le narrateur mais cherche à se distinguer de la personne réelle de Hardy. Cette figure tantôt présente, tantôt absente est insaisissable et elle s'identifie par moments aux opprimés de la société victorienne. Les nouvelles, selon Nathalie Bantz, offrent une variété de situations énonciatives beaucoup plus large que celle des romans, ce qui constitue autant de terrains d'expérimentation narrative différents. Ce travail sur les nouvelles de Hardy situé dans le contexte de l'oeuvre de


Istiven Appavoo
email: istiven.appavoo@sattgc.com

Anicet Marionneau
email: anicet.marionneau@hotmail.com

Michel Berducat
email: michel.berducat@irstea.fr

Benoit Merckx
email: benoit.merckx@sattgc.com

Natacha Olivier
email: natacha.olivier@sattgc.com

Loïc Cotten
email: loic.cotten@alliancefb.fr

Facing complex outdoor challenges by inter-disciplinary research"

Keywords: forest, plantation, RTK-GPS, precision, yield

The labor shortage, the need to increase the forest density and the great increase in surface for planting trees has led to a reflection in R&D. This article discusses the abilities of a tree planting machine which works automatically. The need to design this type of machine was due to the massive exploitation of forests done by the wood industry and subsistence farming. The device which is hitched up to a tractor can plant in the presence of tree stump and vegetable wreckage. Several hydraulic actuators work in parallel to enable the plantation of one tree per second (a machine with two planting organs). The planting organ has been designed to plant trees without stopping the tractor.

INTRODUCTION

The tree planting volume has considerably increased during the last decades due to the massive destruction and massive exploitation of forests. This massive exploitation was mainly caused by the increase in population and by the growing wood needs. The massive destruction was caused by storms.

Tree plantation is realized manually for most of the time. 80% of the trees are planted by hand in France. This type of plantation is difficult, fastidious, slow and the cost of labor is constantly increasing due to labor shortages.

The labour recruitment process had never been efficient. The weaknesses have been attributed to a lack of dedication of the workers resulting in extremely high turnover of manpower. One option to alleviate the labour shortage is increased mechanization. However mechanized plantation in forests is extremely limited due to the maladjustment of the existing planting machines. These issues have led us to a new reflection in R&D.

PLANT AND SOIL TYPES

A study of the soils and the plants is primordial to design an efficient machine. Three forestry cooperatives have helped us gathering information about the plant and soil types: "Alliance Forêt Bois", "Forêts et Bois de l'Est" and "COFORET". These three cooperatives have different types of soil and plant trees for various industries. Our quest was to design a machine that satisfies the needs of all these cooperatives.

The plants

Forest industries plant trees for three main reasons: for biomass, furniture and construction. We can see in the table below, the tree species for each field. Short rotation coppice (SRC) provides a recognised sources of biomass. This woody solid biomass can be used in applications such as district heating, electric power generating stations, alone or in combination with other fuels.

Trees can be conditioned in three forms (see table 2). The volume occupied by these types of conditioning must be closely analysed to be able to make an optimised machine.

Soil types

The design of the machine depends on the characteristics of the soil. There are three types of soil: clay soil, loamy soil and sandy soil. Soils with large clay content are renowned for their ability to shrink and crack compared to the structure of free draining sands and gravels. Clay soil is sticky and must be removed from the moving parts of the machine.

EXISTING TREE PLANTING MACHINES AND INSTRUMENTS

A technology surveillance approach has allowed us to identify the existing machines around the world. Even though several machines have been developed during the 70s, there is actually few forest planting machines that are running. These devices help to plant 20% of the forest in France. We will present below two types of existing machines and one instrument used to plant trees in their different conditionings.

Bracke planter

The carrying capacity of this planter (figure 1) is 80 plants and thus must be refill about every 32 minutes. The average productivity is 150plants/h. The main advantage of this planter is that it can plant trees on forestland after clear-cutting with the presence of tree stumps. But the planting capacity of 150plants/h is too low for the plantation of SRC according to "Alliance forêts Bois". The carrying capacity is also insufficient. This planter can only plant trees in clods.

Double disc planting machine

There are several planting machines that use a double disc system to open the furrow where the operator can insert a plant. Two wheels (figure 2) are used to close the furrow. This type of machine can adapt itself to the planting speed of the operator. The maximum speed is about 1800 plants/h (one tree each 2 seconds).

Figure 2: A double disc planting machine hitched up to a tractor.

The main advantage of this machine is its plantation speed. But that type of machine can't plant in forestry condition. It only works on well prepared ground. This planter can plant trees in their three different conditionings.

Plantation cane (stick)

This plantation cane is widely used by operators to plant on difficult ground conditions. This instrument weight about 4kg and helps the workers to plant at a relatively high speed compare to the use of a shovel.

The plantation speed depends mainly on the ability of the person using it.

Figure 3: Three operators using plantation canes

The main advantage of this instrument is that it avoids the operators to frequently bend over. But the weight of the cane and of the trees makes this type of plantation very fastidious. That is why there are fewer workers who are willing to continue this type of job. Our technology surveillance has allowed us to notice that there is actually any planting machine or instrument that enables to plant trees precisely in forestry condition at a high speed.

DESIGN OF THE PLANTING MACHINE

A planting machine has been designed to resolve the issues seen on existing machines. The device has initially been designed to plant wood energy parcels in forestry conditions, but it can be used to develop agroforestry, to regenerate forests destroyed by storms and to plant trees at road edges. The innovation in this machine is that the plantation is made at constant speed and in the presence of tree stump and vegetable wreckage. An RTK GPS system helps the machine to plant with a precision up to 5cm at a rate of one tree per second (a machine with two planting organs). A patent has been deposited on December 2015.

Characteristics of the GC-planter

This machine named "GC-planter" has been designed to plant clod plants automatically, but it can plants semi-automatically, trees with exposed roots and cuttings.

Area of use:

 The GC-planter is made of two planting organs.  The planting organs are separated by a distance of 3m to 4,5m (inter row gap)  The intra row gap is between 0,5m to 10m

The chaotic environment in forests (tree stump, rock, branches, etc.) has obliged us to put a closer attention to all mechanical parts in contact with this environment. The plantation is made using a beak which penetrates the soil and opens to liberate the plant (see figure. 4).

Protecting the planter against the topological soil variability

A security measure along the Z axis (figure. 4) has been made to interrupt the planting cycle if the beak meets an obstacle. The beak moves up if it can't penetrate the soil due to a hard objet. It stays at 60cm above the ground for 1 second and the cycle continues after hopefully crossing the obstacle. This system minimizes the contact of the planting organ with the ground, allowing to plant between rocks and tree stumps.

Other security devices have also been designed along the X and the Y axis to protect the plantation organ. These devices use springs that allow the plantation organ to rotate along the Y axis if it meets an obstacle along the X axis and to rotate along the X axis if it meets an obstacle along the Y axis. The planting organ is therefore protected against obstacles such as rocks and tree stump in all directions.

Plantation organ

Two compacting arms have been designed to compress the soil with a force of about 800N around the plant after plantation (see figure . 4). These arms have also been places on both sides of the beak to remove sticky soil (clay soil). Hydraulic actuators which can work at a pressure of 180 bars are used to make these different movements.

We have got some encouraging plantation results during the first test of this machine. We have however placed overs on the slides to prevent the penetration of dust and soil.

P a g e | 4

RTK GPS

Maintenance tools hitched up to a tractor must be able to travel in straight line between planted trees. Thus, trees must be planted at regular distances in both directions. This planter has the ability to plant in rectangle with a +/-5cm precision on both sides. The distance between each tree can be 4m on the row and 2m between the rows for example. The GCplanter uses an RTK-GPS to determine the plantation spot.

RTK is a highly precise technique that results in +/-2 cm pass-to-pass and year-to-year accuracy. RTK GPS requires two specialized GPS receivers and two radios. One GPS receiver is set up as a base station within a 9.6 km radius of the field where the tractor is places so it can send the correction message to the roving receiver. Both receivers collect extra data from the GPS satellites known as L2 Band, which enables this better precision.

Figure.6. RTK configuration

Automation

The wood energy field needs a plantation density greater than that of a classic forest. The storage system for one plantation organ consists of a mobile part which has about 1250 plants and a fixed part with 1250 plants. The storage capacity of the whole machine is around 5000 plants during the plantation.

An automated system moves the plants from the mobile storage system to the planting organ.

The two planting organs are fixed on both sides of a telescopic beam. The telescopic beam enables the GC-planter to have a width under 3,5m during road transportation. Hydraulic cylinders are used to adjust the distance separating the planting organs. The distance between the plantation lines can be modified from 3m to 4,5m. This distance between them is constant during the plantation. These hydraulic cylinders allow the planting organs to move in parallel and thus to plant in straight line by using the kinematic RTK-GPS system.

The GC-planter is driven hydraulically and each movement can be modified by a programmable logic controller. The control panel which is present in the tractor's cabin allows to start and to stop the plantation, to record the geo-tracking of each plant and to record the characteristics linked to the plantation.

Kinematics of the GC-planter

The planting organ is made of two deformable parallelograms that are oriented using hydraulic actuators. The parallelogram which is fixed to the frame of the planting machine (figure 7) helps to move the beak according to the Z axis and the other parallelogram allow the beak to move according to the X axis. The figure 7 illustrates the movement of the planting organ during one complete cycle. The planting organ goes back to the 1 st position after the 4 th position.

RESULTS OF THE TESTS

"Alliance Forêts Bois" is actually testing the GCplanter in real condition. This company is financing the construction of the prototype. The planting organ is being tested and the programs are being adjusted.

The machine is actually fixed on the three point hitch of a category three tractor.

We have noticed that during the plantation, the machine needs to be stabilized by adding wheels. Two wheels systems are being added to the GCplanter to increase its stability. The wheels will also help to position the planting organ at a constant height above the ground.

CONCLUSIONS

We faced a lot of challenges during the design of this disruptive planting solution. We noticed that the most difficult part was to be able to secure the mechanical parts in this chaotic forestry environment. These security measures guaranties however the efficiency of the planting machine.

Thanks to this machine, we hope to be able to face the reforestation difficulties and the labor shortage.

ACKNOWLEDGEMENTS

The financial support of "Alliance Forêt Bois", "SATT Grand Centre" and "Irstea" is gratefully acknowledged. The authors wish to thank Fabrice Barral, Dimitri Berard-Chavier, Jean Louis Sanz, Benjamin Sanz and Dominique Ganter for their valuable contributions to this work.

Figure 1 :

 1 Figure 1: A Bracke planter mounted on an excavator.

  MCG 2016 -5 th International Conference on Machine Control & Guidance "Facing complex outdoor challenges by inter-disciplinary research" Vichy, France, October 5-6 th , 2016 P a g e | 3

  Figure.4. the planting organAutomatic settings enable the GC-planter to plant vertically on a 25% inclination and a 25% declination ground. This avoids the trees to be bent. Bending trees can't be used for construction. The trees in the figure5below were planted perpendicularly to the slopes.

Figure

  Figure.5. non vertical trees

  Figure.7. kinematics of the GC-planter

Back

  Tomas Ersson, Urbans Bergsten, 2013. Reloading mechanized tree planting devices faster using a seedling tray carousel, pp.5 Back Tomas Ersson, 2014. Concepts for Mechanized Tree Planting in Southern Sweden, pp.59 Erwin ULRICH, 2014. RDV techniques N°43, Nouveaux besoins de plantation en forêt, pp.9 Winfridus Overbeck, June 2012. An overview of industriel tree plantation in the global South, Ejolt report no.

Table 1 :

 1 Type of plantation

		Short rotation	Furniture/
		coppice (biomass)	construction
		Poplar, eucalyptus,	maritime pine,
	Tree species	willow, black locust	Douglas fir,
			black locust
	Stem diameter	< 7 cm	10cm to 15cm
	Density (stem/ha)	6000 to 15000	2000 to 3000
	Exploitation age	< 5 years	7 to 10 years

P a g e | 2

Disc Wheel

Table 2 :

 2 Plant conditioning

	Exposed roots	Plants in clods	Cutting
	H min: 10 cm	The volume of	Length of 20 to
	H max: 80 cm	the clods is	30cm and
	P max: 20/30 cm	bewteen 100 to	diaméter of 1 to
		400cm 3	3cm
	Black locust	maritime pine,	Willow, poplar
		eucalyptus