A. Athan and D. Duchamp, "Agent-Mediated Message Passing for Constrained Environments, " Usenix symposium on Mobile and Location-Independent Computing, 1993.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....there and then returns to the original node (home node) bearing a result. Therefore, the mobile agent can utilize the bandwidth of the network more efficiently than one accessing the distributed database using a direct connection, especially when data transmission is the bottleneck of the task [2, 5, 15, 22]. Consequently, mobile agents can reduce network traffic, overcome network latencies and enhance robustness and fault tolerant capabilities of distributed applications [1, 11, 14, 24] It is important that mobile agents perceive the condition of the network. The status of the network is ....

A. Athan and D. Duchamp. Agent-mediated message passing for constrained environments. In USENIX Mobile and Location-Independent Computing Symposium, 1993.

....Thus, the mobile agent can utilize the bandwidth of the network much more efficiently than can be achieved by accessing the distributed database remotely using a direct connection. The total computation time taken can be shortened, especially when data transmission is the bottleneck of the task [2][3] 11] 16] In this domain, information is spread over several hosts and it is now common for these hosts to be geographically separated [9] 10] Should the mobile agents be ordered to retrieve information in an information retrieval system, all the pertinent nodes have to be specified, and these ....

A. Athan and D. Duchamp. Agent-mediated message passing for constrained environments. In USENIX Mobile and Location-Independent Computing Symposium, 1993.

....on the fly when the mobile moves away from its home network. 8.4 Use of Agents and Proxies Use of agents or intermediaries for protocols and applications based on the client server model is not a new concept. For mobile environments, an agent based model for message passing was suggested in [4]. In addition, the indirect approach where the intermediary (or a set of intermediaries) exists at the application layer for supporting the execution of distributed algorithms over mobile hosts, has been investigated by Badrinath et al. 8] Thekkath et al. 88] advocated the use of a server clerk ....

A. Athan and D. Duchamp. Agent-mediated message passing for constrained environments. In Proc. of the USENIX Symposium on Mobile and LocationIndependent Computing, August 1993.

....Application Application Middle (b) Middle process executed on the mobile device. Figure 1. The middle process model. The second parameter in this model concerns the position for the execution of the middle process. A number of approaches propose the fixed network to execute the middle process [4, 24, 8]. This approach is depicted in figure 1(a) The exact position of the middle process at the fixed network depends on its role. Placing it at the fringe of the fixed network makes it easier to gather information about wireless link characteristics. Moreover, special network protocols can be used ....

.... can be performed 1) by applying lossy compression on data [8, 18] or by filtering information embedded on protocols [24] to reduce the amount of traffic on the wireless link; 2) by reordering message delivery to place important data ahead of less important data [14] and or 3) by batching requests [4]. Managing weak connectivity is also achieved by caching and prefetching data on (or near) the mobile computer. Indeed, some middle processes store frequently used data and are responsible for maintaining their consistency which can be done with [5] or without [17] applications assistance. On the ....

A. Athan and D. Duchamp. Agent-Mediated Message Passing for Constrained Environments. In Proc. of the Usenix Symposium on Mobile and Location-Independent Computing, 1993.

....clients development work both at the server and at the client site. It suffices a different pair of agents per application type E. Pitoura Summer School on Mobile Computing, Jyvaskyla, 1998 10 The Pair of Agents Model Proxy pairs have been gaining attention [35, 8] Extensions to RPC [12, 5, 3], e.g. asynchronous queued RPC [12] The RPC is stored in a local stable log at a client side agent and control is immediately returned to the application. When connected, the log is drained in the background Queueing RPCs leaves space for performing various optimizations on the log. ....

....with disconnections and weak connectivity a server side intercept agent on the mobile host as well. Application Server Mobile Host Agent Server Side Agent Application Server side agent at the mobile host posses special features: e.g. a mechanism to automatically start applications on demand [3]. E. Pitoura Summer School on Mobile Computing, Jyvaskyla, 1998 12 Mobile Agents Besides the functional components, organization of data. As a collection of objects: the units of information exchange among mobile and static hosts. Objects encapsulate not only pure data but also ....

A. Athan and D. Duchamp. Agent-Mediated Message Passing for Constrained Environments. In Proceedings USENIX Symposium on Mobile and Location-Independent Computing, pages 103--1070, Cambridge, Massachusetts, August 1993.

....the intermediary can act not only as a filter, but also as an agent; i.e. as a permanent representative for a mobile host that might not always be powered up or connected to the Internet. Such an indirect approach has been advocated before for dealing with resource constrained mobile systems [3, 6, 8, 28, 41, 52, 64, 82]. In general, the intermediary implements an extra level of indirection, permitting run time adjustment of design time decisions about the nature and amount of client server traffic. Some of these advantages can be achieved without the use of proxies. However, without a proxy in most cases both ....

A. Athan and D. Duchamp. Agent-Mediated Message Passing for Constrained Environments. In Proc. Mobile and Location-Independent Computing Symposium, pages 103--107. USENIX, August 1993.

....The Xerox PARC work [Adams, 1993] the BNU project [Watson, 1993] and Mobile IP [Perkins, 1993] all use routing techniques to overcome the problems of intermittent connectivity and changing network topology. OSF 1 AD s mobile sockets [Zajcew, 1993] and Columbia s agent mediated messaging [Athan, 1993] use surrogates to overcome limitations in their local environments. The Xerox PARC work is similar to the original X work. PARCTabs are small PDAs that use infra red communication inside a building to transmit display information from an application to the PDA. Location messages from the PARCTab ....

Athan, A. et al.; Agent-Mediated Message Passing for Constrained Environments; Proceedings of the Mobile and Location-Independent Computing Symposium, pgs 103-108, August 1993.

....A second area of research is the design of higher level strategies to deal with the high error rates that may be found on wireless links. Examples are linklevel retransmission, transparent protocol translators, and proxies inside the network that modify the behavior of the higher level protocols [6,7,3 5,32,9,8]. Our proposed adaptive error correction strategy may have a direct impact on these efforts. Our results suggest that local error correction or avoidance on the wireless link may in some cases reduce the error rates to the point that an unmodified transport level protocol can be used. In other ....

Duchamp, D. and Athan, A. Agent-mediated Message Passing for Constrained Environments. in: Proceedings of the USENIX Mobile and Location-Independent Computing Symposium. USENIX Association, 1993, pp. 103-- 107.

....problems to be solved. There has not been any work that directly addresses the problems involved in making a complex, heterogeneous computational system accessible from mobile platforms. However, there are several interesting projects, some ongoing, which are related to this task. Duchamp et al. [45, 1] have proposed the notion of introducing a proxy between the mobile client and the servers on the wired network, which delays writing out all but the most important data. In [38] they show its use in creating a lazy replicated file service. However, their system is based on Mach. Similar ideas, ....

A. Athan and D. Duchamp, Agent-Mediated Message Passing for Constrained Environments, Proc. Mobile and Location-Independent Computing (Cambridge, MA), USENIX, August 1993, pp. 103--107.

....networks that will commonly be used by mobile computers. New network architectures and protocols must therefore be devised to deal with these changed conditions. One approach to dealing with mobility that seems to be gaining popularity is to have a proxy [Watson 1993] or agent [Adams 1993] [Athan 1993] for each mobile computer. This proxy resides at a fixed network address and is responsible for keeping track of the whereabouts of the mobile host. The mobile host is known to other hosts on the network only by its proxy s address and so all messages intended for it are sent to its proxy which ....

A. Athan and D. Duchamp (1993) Agent-mediated Message Passing for Constrained Environments, USENIX Mobile and Location-Independent Computing Symposium, Aug. 1993, Cambridge, MA, pp.

....on resource allocation. Moreover, it has been noted (see, e.g. 4, 5] that search costs impact on the structuring of distributed algorithms for mobile hosts. To reduce search cost, various location management strategies have been proposed for a variety of mobile network configurations [1, 3, 6, 10, 11, 19, 21]. In this paper, we propose and evaluate a statistical framework for resource discovery in distributed systems with mobile hosts in which the spatial location of resources can change with time. Resource discovery involves (1) identifying the location of a desired resource and (2) making the ....

A. Athan and D. Duchamp, "Agent-mediated message passing for constrained environments," USENIX Symposium on Mobile and Location Independent Computing, pp. 103--107, 1993.

....When this intermediary server is assigned to a particular mobile user, and performs actions on behalf of that mobile user, it is termed a User Agent . The need for an agent inside the fixed network, acting on behalf of a mobile user, has been proposed in several research projects [2] 3] 4][5][6] 7] The Berkeley Infopad project [2] has a pad server which manages and controls access to the mobile terminal. The pad server allocates and manages the bandwidth available to the applications running on the mobile terminal and keeps track of the location of the mobile terminal. When the ....

....provides services to the user. The Teleporting system [6] is another interesting application which adopts the notion of agents. It uses proxy servers, a special type of X server, for making application interfaces (X displays) mobile. These proxy servers are instantiated for each user. 3 In [5], the agent is given the responsibility of storing and filtering messages. The ability to store messages is beneficial when the mobile computer is disconnected from the fixed network or operates in power save mode. Filtering messages helps reduce the amount of data transferred over the wireless ....

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A. Athan and D. Duchamp, "Agent-Mediated Message Passing for Constrained Environments, " Usenix symposium on Mobile and Location-Independent Computing, 1993.

....value added intelligent services on behalf of their subscribers. In this setup, the end device becomes a remote control for the user agent, which in turn serves as a personal server for a subscriber. This makes our notion of user agents more general than the ones typical in mobile computing [16], 17] 18] 19] The design of Pigeon has been completed. A prototype has been implemented and is operational at Bell Laboratories. The current prototype supports a software pager PCS phone simulator and a prototype IS 136 digital cellular phone. The Pigeon servers are implemented using C as ....

A. Athan and D. Duchamp, "Agent-mediated message passing for constrained environment," in Proceedings of Mobile & LocationIndependent Computing, Cambridge, Massachusetts, Aug. 2--3 1993, pp. 103--107.

....system [17] to improve the performance of applications. The Odyssey project on mobile information access plans to provide support for application specific resource monitoring and adaptation. The primary adaptation mechanism under consideration is change in data fidelity [20] Athan and Duchamp [1] propose the use of remote execution for reducing the communication between a mobile machine and the static network. In all these systems, location of the various computation modules is fixed; adaptation is achieved by changing the way in which the network is used. Several systems have been built ....

A. Athan and D. Duchamp. Agent-mediated Message Passing for Constrained Environments. In Proceedings of the USENIXMobile and Location-independent Computing Symposium, pages 103--7, Aug 1993.

.... are considered a major challenge and research groups have considered solutions ranging from the use of Forward Error Correcting (FEC) codes that in effect improve the error rate seen at higher levels[22] to the use of special transport level protocols that treat wireless links in a special way[13, 3, 15, 4, 40]. However, while the error characteristics of wired networks have been well documented, relatively little experimental data is available for wireless LANs. There are some obvious reasons why one would expect wireless connections to have higher error rates than wired connections. Wired connections ....

D. Duchamp and A. Athan. Agent-mediated message passing for constrained environments. In Proceedings of the USENIX Mobile and Location-Independent Computing Symposium, pages 103--107. USENIX Association, August 1993.

.... coupled with modification of the TCP software on the mobile hosts[5] solves only part of the problem because the transmitting host still performs a slow start if more than one segment is lost per window, thus limiting the effective throughput[12] Other proxy based approaches have been suggested[2] for mobile hosts but they do not pertain to the transport layer. 3 Indirect TCP Overview This section gives an overview of indirect TCP and describes the benefits of using indirection at the transport layer. We begin with a brief description of the Indirect Protocol model [4] on which indirect ....

A. Athan and D. Duchamp. Agent-mediated message passing for constrained environments. In USENIX Symposium on Mobile and Location-dependent Computing, August 1993.

....also been explored in [15] for a digital cellular telephone network. A scheme for installing filters at the MSRs under MH control is described in [30] In addition, the indirect approach where the intermediary (or a set of intermediaries) exists at higher protocol layers has been investigated by [2, 3]. Link layer retransmissions can be used on errorprone wireless links to bring their error rate on par with that on the wired networks but such an approach interferes with the end to end retransmissions of TCP and thus may not result in improved performance [8] Fast retransmissions coupled with ....

A. Athan and D. Duchamp. Agent-mediated message passing for constrained environments. In USENIX Symposium on Mobile and LocationIndependent Computing, August 1993.

.... stations over the internet [5, 9, 17, 37] Spreitzer and Theimer have considered architectures for location information with special emphasis on scalability and privacy [32] Several agent based schemes have been proposed in the literature for message passing and routing; among all, we recall [1, 12, 27]. The goal of search is not to replace these location management schemes, but rather to complement them. As noted by Rose [28] paging strategies based on broadcast throughout the region of a location area are inefficient because they do not take specific account of user mobility characteristics. ....

A. Athan and D. Duchamp, "Agent-mediated message passing for constrained environments," USENIX Symposium on Mobile and Location Independent Computing, pp. 103--107, 1993.

....system [22] to improve the performance of applications. The Odyssey project on mobile information access plans to provide support for application specific resource monitoring and adaptation. The primary adaptation mechanism under consideration is change in data fidelity [23] Athan and Duchamp [4] propose the use of remote execution for reducing the communication between a mobile machine and the static network. In all these systems, location of the various computation modules is fixed; adaptation is achieved by changing the way in which the network is used. Two other recent Java based ....

A. Athan and D. Duchamp. Agent-mediated Message Passing for Constrained Environments. In Proceedings of the USENIX Mobile and Location-independent Computing Symposium, pages 103--7, Aug 1993.

....building mobile applications. Rover [12] uses queued RPC and Relocatable Dynamic Objects to maximise use of the wireless communications medium at an application partitioning level. WitII [18] uses intelligent caching and pre fetching based on hyper object information. Work at Columbia University [1, 7] proposes the creation of Proxy Servers (on the edge of the wired network) and the placement of message filters at these proxies. Messages sent to a Mobile Terminal are passed through these filters before they are dispatched over the hostile wireless connection to the mobile. A currently ....

Athan A. and D. Duchamp, Agent-Mediated Message Passing for Constrained Environments. In Proceedings of the Mobile and LocationIndependent Computing Symposium, August 1993.

....infrastructure in CORBA specifications [26] also behave as agents mapping client requests to servers. Agent based manyto many RPC described in [35] allows integration of results from multiple servers and callbacks. For mobile environments, an agent based model for message passing was suggested in [3]. Schemes for adaptive presentation of data to mobile clients have been presented recently in [37] and [25] The need for subject based naming and binding in dissemination oriented protocols was emphasised in [14] 6 Conclusion and Future Work We have presented in this paper a Remote Procedure ....

A. Athan and D. Duchamp, "Agent-mediated message passing for constrained environments", Proc. of the USENIX Symposium on Mobile and Location-Independent Computing, August 1993.

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A. Athan and D. Duchamp, "Agent-Mediated Message Passing for Constrained Environments, " Usenix symposium on Mobile and Location-Independent Computing, 1993.

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A. Athan and D. Duchamp. Agent-mediated Message Passing for Constrained Environments. In Proceedings of the USENIX Mobile and Location-independent Computing Symposium, pages 103#7, Aug 1993.

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