12052255
Flexible network support for mobility
Fueled by the large number of powerful tight-weight portable computers, the expanding availability of wirel= networks, and the popularity of the Internet, there is an increasing de mand to connect portable computers to the Internet at any time and in any place. However, the dynamic nature of such connectivity requires more flexible network support than has typically been atiable for stationary workstations. ThM paper introducw the following two me~anisms, in the context of Mobile 1P [24], to ensure a mobile host’s convenient and efficient communication with other hosts in a &anging environment. One me&anism supports multiple packet defivery methods (such as regular 1P or Mobile 1P) and adaptively selects the most appropriate one to use Wcordlng to the char=teristim of eti trfic flow. The other medanism enables a mobile host to make use of multiple wtive network interfww simultaneously and to control the selection of the most dwirable network interfaces for both outgoing and incoming pdets for different traffic flows. We demonstrate the usefdnm of these two network layer me&anisms and describe how they are implemented.
18186547
Experiences with a Mobile Testbed
This paper presents results from an eight-day network packet-trace of MosquitoNet. MosquitoNet allows users of laptop computers to switch seamlessly between a metropolitan-area wireless network and a wired network (10 Mbit/s Ethernet) available in offices and on-campus residences. Results include the amount of user mobility between the wired and wireless networks, the amount of mobility within the wireless network, an examination of application end-to-end delays, and an examination of overall packet loss and reordering in the wireless network. We find that the average mobile host switches between the wired and wireless networks 14 times during the trace and moves within the wireless network five times. Round trip latencies in the wireless network are very high, with a minimum of 0.2 seconds. Even higher end-to-end delays, of up to hundreds of seconds, are due to packet loss and reordering. These delays cause users to change their usage patterns when connected to the wireless network. We conclude that latency is a critical problem in the wireless network.
15922787
Supporting Mobility in MosquitoNet
The goal of the MosquitoNet project is to provide continuous Internet connectivity to mobile hosts. Mobile hosts must be able to take advantage of the best network connectivity available in any location, whether wired or wireless. We have implemented a mobile IP system that supports seamless switching between different networks and communication devices. In contrast to previous approaches to mobile IP, we believe mobile hosts should not assume any explicit mobility support from the networks they visit, aside from basic Internet connectivity. This decision places extra responsibilities on the mobile hosts themselves. In this paper, we describe the design and implications of such a system. Measurements of our implementation show that the inherent overhead to switch networks (below 10ms) is insignificant compared to the time required to bring up a new communication device.
33266884
Flexible Network Support for Mobile Hosts
Fueled by the large number of powerful light-weight portable computers, the expanding availability of wireless networks, and the popularity of the Internet, there is an increasing demand to connect portable computers to the Internet at any time and in any place. However, the dynamic nature of a mobile host's connectivity and its use of multiple network interfaces require more flexible network support than has typically been available for stationary workstations.This paper introduces two flow-oriented mechanisms, in the context of Mobile IP , to ensure a mobile host's robust and efficient communication with other hosts in a changing environment. One mechanism supports multiple packet delivery methods (such as regular IP or Mobile IP) and adaptively selects the most appropriate one to use according to the characteristics of each traffic flow. The other mechanism enables a mobile host to make use of multiple network interfaces simultaneously and to control the selection of the most desirable network interfaces for both outgoing and incoming packets for different traffic flows. We demonstrate the usefulness of these two network layer mechanisms and describe their implementation and performance.
7900372
Complexity of the Unique Extension Problem in Default Logic
In this paper we analyze the problem of checking whether a default theory has a single extension. This problem is important for at least three reasons. First, if a theory has a single extension, nonmonotonic inference can be reduced to entailment in propositional logic (which is computationally easier) using the set of consequences of the generating defaults. Second, a theory with many extensions is typically weak i.e., it has few consequences; this indicates that the theory is of little use, and that new information has to be added to it, either as new formulae, or as preferences over defaults. Third, some applications require as few extensions as possible (e.g. diagnosis). We study the complexity of checking whether a default theory has a single extension. We consider the combination of several restrictions of default logics: seminormal, normal, disjunction-free, unary, ordered. Complexity varies from the first to the third level of the polynomial hierarchy. The problem of checking whether a theory has a given number of extensions is also discussed.
13480741
Source authentication in group communication systems
Many group communication systems need to enforce a restriction that limits members are authorized to send messages to the group. Receivers therefore need to authenticate message sources before the received messages are accepted. Source authentication in peer-to-peer systems is trivial: the two communication parties can agree on one pair key and use this key to authenticate each other. However, because the group key is shared by all members in a group system, it is quite challenging to identify the sender and determine its authorization. Furthermore, if the authorization can be changed at run-time, source authentication problem can be even harder. This paper presents a source authentication technique called TTA scheme (Transitive Trust Authentication). TTA supports source authentication as well as dynamic authorization change. In addition, its computation and communication overhead is low.
1639134
Towards the theoretical foundation of choreography
With the growth of interest on the web services, people pay increasinglyattention to the choreography, that is, to describe collaborations ofparticipants in accomplishing a common business goal from a globalviewpoint. In this paper, based on a simple choreography language and arole-oriented process language, we study some fundamental issues relatedto choreography, especially those related to implementation, includingsemantics, projection and natural projection, dominant role in choices anditerations, etc. We propose the concept of dominant role and somenovel languages structures related to it. The study reveals some cluesabout the language, the semantics, the specification and theimplementation of choreography.
6031727
Towards the Formal Model and Verification of Web Service Choreography Description Language
The Web Services Choreography Description Language (WS-CDL) is a W3C specification for the description of peer-to-peer collaborations of participants from a global viewpoint. For the rigorous development and tools support for the language, the formal semantics of WS-CDL is worth investigating. This paper proposes a small language CDL as a formal model of the simplified WSCDL, which includes important concepts related to participant roles and collaborations among them in a choreography. The formal operational semantics of CDL is given. Based on the formal model, we discuss further: 1) project a given choreography to orchestration views, which provides a basis for the implementation of the choreography by code generation; 2) translate WS-CDL to the input language of the model-checker SPIN, which allows us to automatically verify the correctness of a given choreography. An automatic translator has been implemented.
16590593
An approach to hardware/software partitioning for multiple hardware devices model
Computer aided hardware/software partitioning is one of the key challenges in hardware/software co-design. This paper describes a new approach to hardware/software partitioning for multiple hardware-devices model. The partitioning is transformed into a reachability problem of timed automata, and the optimal solution can be obtained by means of an optimal reachability algorithm. To relax the initial condition of partitioning for optimization, two algorithms are designed to explore the dependency relations among processes in the sequential specification. Some experiments are conducted with model checker UPPAAL to show our approach is both effective and efficient.