L. MOREAU. DISTRIBUTED DIRECTORY SERVICE AND MESSAGE ROUTING FOR MOBILE AGENTS. Science of Computer Programming, 39(2--3):249--272, 2001.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....comparison, but see [Sew00] There is a large body of semantic work on concurrent and distributed algorithms. Crudely, it can be subdivided into work taking an automata theoretic approach and work on encodings of high level primitives. The former includes [AP98, JNW98] addressing Mobile IP, and [Mor99] which studies an infrastructure providing a similar abstraction to that of this paper. All involve more or less idealised models of algorithms rather than directly executable code. The latter includes encodings of choice [NP96] # join communication [FG96] and authenticated communication ....

Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Technical Report ECSTR M99/3, University of Southampton, 1999.

....achieve this, remote communication is required. 2.3. 2 Remote Communication An Extended Service A variety of mobile agent addressing strategies can be explored to achieve remote communication, including centralised indexes, forwarding pointers, home agents and other agent tracking strategies [11]. However, there is no explicit support for such strategies in the core. Instead, the DIET system provides multiple forms of remote communication through ARC and application layer extensions, exploiting a variety of strategies to suit different applications and scenarios. These forms of remote ....

Moreau, L. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2-3):249272, 2001.

....mobile agents, tracking, agent name, security. 1 Introduction Early research on mobile agent systems concentrated on how to migrate mobile agents. Many agent systems exist today and there is a notable shift towards research in how to best support transparent communication between mobile agents [20, 16, 10, 11]. Transparent means that agents need not be aware of the actual location of agents with which they wish to communicate. Two general problems must be solved in order to achieve transparent communication: first, the peer agent must be located, for instance by means of a tracking service that maps ....

....of a tracking service that maps an agent s location invariant name onto its current whereabouts. Second, messages must be routed to the peer. This can become difficult since mobile agents might run away from messages. Guaranteed delivery is addressed for instance by Murphy, Picco, and Moreau [11, 10]. In this article we address the problem of establishing a public global tracking service for mobile agents, which scales to the Internet and accounts for the particularities of mobile agents (frequent changes in locations) Public means that lookups of agent locations are not restricted in ....

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Luc Moreau. Distributed directory service and message routing for mobile agents. Technical Report ECSTR M99/3, Department of Electronics and Computer Science, University of Southampton, November 1999.

....mobile agents, name server, agent name. 1 Introduction Early research on mobile agent systems concentrated on how to migrate mobile agents. Manifold agent systems exist today and there is a notable shift towards research in how to best support transparent communication between mobile agents [18, 15, 9, 10]. Transparent means that agents need not be aware of the actual location of agents with which they wish to communicate. Two problems must be solved in order to achieve transparent communication: The peer agent must be located, for instance by means of a name service that maps an agent s ....

....by means of a name service that maps an agent s location invariant name onto its current whereabouts. Messages must be routed to the peer. This can become difficult since mobile agents might run away from messages. Guaranteed delivery is addressed for instance by Murphy, Picco, and Moreau [10, 9]. In this article we address the problem of how to locate agents. Our goal is to provide adequate global name services for mobile agents, which scale to the Internet and account for the particularities of mobile agents (frequent changes in locations) Establishing name services for mobile agents ....

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Luc Moreau. Distributed directory service and message routing for mobile agents. Technical Report ECSTR M99/3, Department of Electronics and Computer Science, University of Southampton, November 1999.

....pointer the server will send the message to its parent. Discussion Certain optimisations are plausible, e.g. if an agent migrates very often within some sub tree, only the root of the sub tree would contain the current location of the agent (the cost of a move operation would be cheaper) In [Mor99] Moreau describes an algorithm for routing messages to migrating agents which is also based on distributed directory service. A proposition of Globe uses a hierarchical location service for worldwide distributed objects [vSHBT98] The Hierarchical Location Directory scales better than Forwarding ....

Luc Moreau. Distributed directory service and message router for mobile agents. Technical Report ECSTR M99/3, University of Southampton, 1999. 23

....by means of a name service that maps an agent s location invariant name onto its current whereabouts. Messages must be routed to the peer. This can become dicult since mobile agents might run away from messages. Guaranteed delivery is addressed for instance by Murphy, Picco, and Moreau [10, 9]. In this article we address the problem of how to locate agents. Our goal is to provide adequate global name services for mobile agents, which scale to the Internet and account for the particularities of mobile agents (frequent changes in locations) Establishing name services for mobile agents ....

....the agent. Though the chain of references can be reduced in length e.g. by successively eliminating the middle host in a chain of three hosts. Strategies based on forward references and dynamic forshortening of reference chains are frequently proposed, e.g. by Wojciechowski, Sewell, and Moreau [15, 9]; they are used in Mole for the purpose of orphan detection [2] The four models di er in terms of which parties are active when agents shall be located, and which host acts as the principal name server. The di erences between the four discussed models are summarized below: Model Active Name ....

Luc Moreau. Distributed directory service and message routing for mobile agents. Technical Report ECSTR M99/3, Department of Electronics and Computer Science, University of Southampton, November 1999.

....comparison, but see [Sew00] There is a large body of semantic work on concurrent and distributed algorithms. Crudely, it can be subdivided into work taking an automata theoretic approach and work on encodings of high level primitives. The former includes [AP98, JNW98] addressing Mobile IP, and [Mor99] which studies an infrastructure providing a similar abstraction to that of this paper. All involve more or less idealised models of algorithms rather than directly executable code. The latter includes encodings of choice [NP96] join communication [FG96] and authenticated communication ....

Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Technical Report ECSTR M99/3, University of Southampton, 1999.

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Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2-3):249-272, 2001.

....to call the migrate primitive again. Such successive migrations create a sequence of nested remote groups, reminiscent of forwarding pointers left by mobile agents. There is an opportunity to shortcut such sequences of remote groups using a mechanism similar to the collapsing of chains of pointers [8]. The rationale for requiring a single thread in a group g before allowing migration to proceed is the following. After migration, g acts as a handle for the remote group : exhaustion of g implies that g is exhausted; if more energy is transferred to g , it is passed on to g . ....

Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2--3):249--272, 2001.

.... applications would run in the user s vicinity, making use of the local infrastructure; iii) even if the local network is not connected to the Internet, local services could be accessed; iv) Shadows and applications can communicate reliably using transparent routing of messages to mobile agents [8, 9]. When a user moves to a new location, their mobile device interacting with the infrastructure will request the user s Shadow to migrate to a new location. However, this may fail when the user s local network is not connected with the user s previous location. In order to support services in the ....

....Shadow spawns new applications as requested by the device and forwards messages to and from them; in essence, the Shadow acts as a router of messages to the applications. Communications between Shadow and applications are robust to the migration of Shadows, based on a transparent routing algorithm [8, 9]; on the other hand, communications between device and Shadow may fail as the device changes location. If the migration of all Shadows fails, a new Shadow is spawned locally, and the device keeps a log of all created Shadows. When several Shadows are requested to migrate to a speci c destination, ....

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Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2-3):249-272, 2001.

.... objects and to collapse the distributed state, whenever possible according to connectivity (or even according to locality [21] However, we adopted a modular approach: rst, we investigated the collapse of state for non mobile objects [20, 24] then we studied the requirements for mobile objects [22]. The needs di er substantially and a bene t of our approach is that it helps us to understand the interactions between the di erent algorithm components. In addition, our solution does not introduce any synchronisation with the mutator, and keeps the number of messages to be exchanged low, by ....

....reduces the number of third party dependencies. Shapiro, Dickman and Plainfoss e [30, 29] address the problem of distributed garbage collection for mobile objects. Our approach separates distributed reference counting from the problem of object migration, for which we devised a speci c algorithm [22]. Our comparison therefore focuses on non mobile objects. They introduce the notion of SSP (stub scion pair) chains, which essentially is their representation of di usion trees. They allow tree rerooting, which they call chain short cutting , through a method similar to Dickman s rst technique, ....

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Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2-3):249-272, 2001.

....to call the migrate primitive again. Such successive migrations create a sequence of nested remote groups, reminiscent of forwarding pointers left by mobile agents. There is an opportunity to shortcut such sequences of remote groups using a mechanism similar to the collapsing of chains of pointers [8]. The rationale for requiring a single thread in a group g before allowing migration to proceed is the following. After migration, g acts as a handle for the remote group g : exhaustion implies that g is exhausted; if more energy is transferred to g , it is passed on to g . ....

Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2--3):249--272, 2001.

....code. No support is provided to bootstrap or initialise new hosts at run time into a cluster in any of these libraries. Additional work is needed to enable mobile agents to be deployed within the Computational Grid, and ranges from support for managing forwarders during service migration [25], maintaining state consistency after migration, checkpointing the complete execution state, selective data migration after service migration, and mechanisms to deal with security, related both to the host receiving the mobile code, and the integrity of the mobile agent itself. All of these ....

Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, Accepted for publication.

....To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and or a fee. SAC 2002, Madrid, Spain 2002 ACM 1 58113 445 2 02 03 . 5. 00 have previously investigated a communication layer for mobile agents based on forwarding pointers [16, 10]. In such an approach, when mobile agents migrate, they leave forwarding pointers that are used to route messages. A point of concern is to avoid cyclic routing when agents migrate to previously visited sites; additionally, lazy updates and piggy backing of information on messages can be used to ....

....space. This discussion shows that reliable delivery of messages to mobile agents without using static locations to route messages is essential, even if peer to peer communications are not adopted as the high level interaction paradigm between agents. Previous work has focused on formalisation [10] and implementation [16] of forwarding pointers, but solutions were not fault tolerant. We summarise such an approach in Section 3 before extending it with support for failures in Section 4. 3. SUMMARY OF DIRECTORY SERVICE In this section, we summarise the principles of a communication layer ....

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Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2-3):249-272, 2001.

....to the RMI technique, a notion of client side stub, called startpoint, is used to communicate transparently with a server side stub, called endpoint. Objects and associated endpoints are allowed to migrate. Our approach takes care of routing method calls using an algorithm that we studied in [22]. The purpose of this paper is to present and evaluate the implementation of this algorithm in Java. In particular, two different strategies for routing method invocations are investigated, namely call forwarding and referrals. The result of our experimentation shows that the latter can be more ....

.... Free from any compatibility constraint, we adopted an algorithm to route messages to mobile agents that does not require any static location: the theoretical definition of this algorithm based on forwarding pointers and the proof of its correctness have been investigated in a previous publication [22]. The purpose of this paper is to present Mobile Objects in Java, an implementation of the algorithm, which offers transparent method invocation and distributed garbage collection for mobile objects. By transparent, we mean that mobile and non mobile objects present a same interface, which is ....

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Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2-- 3):249--272, 2001.

....mobile agents rely on a new distributed algorithm that does not assume the existence of any xed or centralised control. We believe that such an approach makes sofar an ideal candidate for an agent based pervasive environment. The algorithm has been extensively studied in a previous publication [20], including its formalisation and its proof of correctness. We present here the essence of the algorithm and its integration in sofar. Our assumption is that the algorithm is used at the application level (or more precisely at the agent level) we therefore require message delivery to be ....

....several acknowledgement messages arriving at a same platform; the receiver of a message updates its local knowledge if the local timestamp is smaller than the received timestamp. Timestamps are an essential requirement of this algorithm because they prevent the formation of cycles in tables [20]. This simple algorithm, combining agent migration, acknowledgement and timestamps, maintains enough information about the successive locations of mobile agents to be able to route messages to them; however, this approach leaves a trail of forwarding pointers that increases the cost of ....

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Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Technical Report ECSTR M99/3, University of Southampton, 1999.

....distributed management using this framework, we concentrate here on future work related to the framework itself. First, mobility and ontologies for related concepts are to be made part of the framework. Our approach is based on an algorithm that transparently routes messages between mobile agents [34]. The communication model based on startpoints and endpoints will remain the same, but endpoints will be allowed to migrate with their associated agents. In addition, a model of distributed resources [37] will be integrated with sofar so that (mobile) agents are given the opportunity to reason ....

Luc Moreau. Distributed directory service and message router for mobile agents. Technical Report ECSTR M99/3, University of Southampton, 1999.

....its liveness guarantees that agent location information eventually gets propagated. Similar safety and liveness properties are established for the message router. The proofs of these properties have been carried out using the proof assistant Coq [4] complete proofs may be downloaded from [22]. This paper is organised as follows. In Section 2, we informally present the algorithms for the distributed directory service and the message router. A preliminary version of these algorithms was previously sketched [21] but no attempt was made to formalise them at that time. Then, each ....

....the message router that may reuse the distributed directory service. Following previous work [23] we formalise the algorithm by an abstract machine, whose state space is displayed in Figure 7. The presentation very closely follows our encoding of the abstract machine in the proof assistant Coq [22]. The algorithm assumes that agents are referred to by their name; the role of the directory service is to map an agent name to its location. For the sake of modelling and proof simplicity, we formalise the algorithm for a single agent; it is straightforward to generalise it to the case of ....

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Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents: the Constructive Proof in COQ. Available from http://www.staff.ecs.soton.ac.uk/lavm/coq/mobility/, October 1999.

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L. MOREAU. DISTRIBUTED DIRECTORY SERVICE AND MESSAGE ROUTING FOR MOBILE AGENTS. Science of Computer Programming, 39(2--3):249--272, 2001.

No context found.

L. Moreau. Distributed Directory Service and Message Router for Mobile Agents. Science of Computer Programming, 39(2-3):249--272, 2001.

No context found.

Luc Moreau. Distributed Directory Service and Message Router for Mobile Agents. Technical Report ECSTR M99/3, University of Southampton, ECSTR M99/3, 1999.

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