An important issue to be addressed for the next generation of wirelessly-connected hand-held devices is battery longevity. In this paper we examine this issue from the point of view of the Network Interface (NI). In particular, we measure the power usage of two PDAs, the Apple Newton Messagepad and Sony Magic Link, and four NIs, the Metricom Ricochet Wireless Modem, the AT&T Wavelan operating at 915 MHz and 2.4 GHz, and the IBM Infrared Wireless LAN Adapter. These measurements clearly indicate that the power drained by the network interface constitutes a large fraction of the total power used by the PDA. We also conduct trace-driven simulation experiments and show that by using application-specific policies it is possible to ...

Unlike distributed transactions, mobile transactions do not originate and end at the same site. The implication of the movement of such transactions is that classical atomicity, concurrency and recovery solutions must be revisited to capture the movement behavior. As an effort in this direction, we define a model of mobile transactions by building on the concepts of split transactions and global transactions in a multidatabase environment. Our view of mobile transactions, called Kangaroo Transactions, incorporates the property that transactions in a mobile computing system hop from one base station to another as the mobile unit moves through cells. Our model is the first to capture this movement behavior as well as the data behavior which reflects the access to data located in databases throughout the static network. The mobile behavior is dynamic and is realized in our model via the use of split operations. The data access behavior is captured by using the idea of global and local transactions in a multidatabase system. This research was partially supported by the National Science Foundation under Grant Number INT-9417907 and by a Massive Digital Data System (MDDS) effort sponsored by the Advanced Research and Development Committee of the Community Management Staff. Part of this research was performed while Margaret Dunham (then Margaret Eich) was on sabbatical at the University of Queensland in Brisbane, Australia. y This research was partially supported by Hughes Research Laboratories under Grant Number 906356. 1 1

this paper, we look at the problems associated with delivering multicast messages to mobile hosts. First, we identify how a mobile host's ability to connect to different MSSs at different times, affects delivery of multicast messages and present schemes to deliver multicast messages to MHs from atleast-one location, from atmost-one location, and from exactly-one location. Next, we introduce "multicast groups" of mobile hosts wherein each multicast group is associated with a "host view", a set of MSSs representing the aggregate location information of the group. A host-view membership algorithm is then presented and combined with the multicast scheme for exactly-once delivery. As a result, to deliver a multicast message to a specified group, copies of the message need be propagated only to the MSSs in the group's host-view. 1 Introduction

One of the most important issues affecting host mobility is the location and routing scheme that allows hosts to move seamlessly from one site to another. This paper presents a method that exploits the locality properties of a host's pattern of movement and access history. Two concepts, "local region" and "patron service", are introduced based on the locality features. For each mobile host, the local region is a set of designated subnetworks within which a mobile host often moves, and the patrons are the hosts from which the majority of traffic for the mobile host originated. These are used to confine the effects of a host moving, so location updates are sent only to its local area, and to those source hosts which are most likely to call again. Our scheme has the advantages of limiting location updates, and providing optimal routing, whilst increasing network and host scalability.

Abstract Reliable multicast is a powerful communication primitive for structuring distributed programs in which multiple processes must closely cooperate together. In this paper we propose a protocol for supporting reliable multicast in a distributed system that includes mobile hosts and evaluate the performance of our proposal through simulation. We consider a scenario in which mobile hosts communicate with a wired infrastructure by means of wireless technology. Our proposal provides several novel features. The sender of each multicast may select among three increasingly strong delivery ordering guarantees: FIFO, Causal, Total. Movements do not trigger the transmission of any message in the wired network as no notion of hand-off is used. The set of senders and receivers (group) may be dynamic. Size of data structures at mobile hosts, size of message headers, number of messages in the wired network for each multicast, are all independent on the number of group members. The wireless network is assumed to provide only incomplete spatial coverage and message losses could occur even within cells. Movements are not negotiated and a mobile host that leaves a cell may enter any other cell, perhaps after a potentially long disconnection. The simulation results show that the proposed protocol has good performance and good scalability properties. 1

... This paper presents an operational system model for explicitly incorporating the effects of host mobility with appropriate cost measures. It points out the drawbacks of executing distributed algorithms in this model that are not explicitly designed for mobile hosts. To overcome the resource constraints of mobile hosts, we propose a two tier principle for structuring distributed algorithms for mobile hosts so that the computation and communication requirements of an algorithm is borne by the static hosts to the extent possible. In addition, since location of a mobile host could change after initiating a distributed computation and before receiving the result, location management of mobile participants need to be explicitly integrated with algorithm design.

Integration of mobile computers within existing data networks introduces new issues in the design of distributed algorithms and services. Location of a mobile host changes with time, and so the message count of a distributed algorithm should account for the "search" necessary to locate mobile participants. Further, mobile hosts are faced with resource constraints not commonly encountered by their tethered counterparts, viz. a low-bandwidth connection to the rest of the network, and tight restrictions on power consumption. This dissertation

Much research has been devoted to mobile computing and database query management with the advent of portable computers and wireless communication systems. This paper proposes an architecture based on current mobile models, but with the addition of a mailbox, which serves as a storage area for the mobile hosts. Mobile Hosts (MHs) and Mobile Support Stations (MSSs) are connected over a wireless virtual subnet, and the MSSs are in turn connected to a wired static network. The architecture uses the TCP/IP protocol for communication in a mobile computing environment. Cellular providers (CP), the mobile network, and supporting hardware are defined and then assembled into a detailed example which traces the database query through the architecture. 1 Introduction In the past, computer users would have to disconnect from the network every time they needed to travel, but with the emergence of wireless connections the user is able to maintain a connection to the network during movement. A mobile...

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We consider reliable multicast in distributed systems including mobile hosts (MHs) that communicate with a wired infrastructure by means of wireless links. Nearly all existing proposals are based on hand-off, i.e. whenever a MH switches cell, state information about this host travels across the wired network from the support station of the old cell to that of the new cell. However, we are not aware of any detailed performance analysis for hand-off based reliable multicast protocols: previous research in this area has focused mainly on correctness rather than on performance. We analyze in detail, by simulation, the performance of a proposal by Acharya and Badrinath that is based on hand-off and has been highly influential in the design of later protocols. Then, we compare this proposal with one by us that is based on an entirely different philosophy and is the only existing proposal not based on hand-off. Surprisingly, we found that our proposal outperforms the one by Acharya and Badrinath in all the aspects considered: latency, scalability, bandwidth usage efficiency and quickness in managing cell switches of MHs. Moreover, we found that this performance improvement is not obtained at the expense of increased resource requirements on MHs such as energy or memory. We believe that this performance and cost analysis allows us to gain insights into the design of reliable multicast protocols for distributed mobile systems. 1.