Abstract — IP-based solutions to accommodate mobile hosts within existing internetworks do not address the distinctive features of wireless mobile computing. IP-based transport protocols thus suffer from poor performance when a mobile host communicates with a host on the fixed network. This is caused by frequent disruptions in network layer connectivity due to — i) mobility and ii) unreliable nature of the wireless link. We describe the design and implementation of I-TCP, which is an indirect transport layer protocol for mobile hosts. I-TCP utilizes the resources of Mobility Support Routers (MSRs) to provide transport layer communication between mobile hosts and hosts on the fixed network. With I-TCP, the problems related to mobility and the unreliability of wireless link are handled entirely within the wireless link; the TCP/IP software on the fixed hosts is not modified. Using I-TCP on our testbed, the throughput between a fixed host and a mobile host improved substantially in comparison to regular TCP. 1

We consider the problem of providing network access to hosts whose physical location changes with time. Such hosts cannot depend on traditional forms of network connectivity and routing because their location, and hence the route to reach them, cannot be deduced from their network address. In this paper, we explore the concept of providing continuous network access to mobile computers, and present a set of IP-based protocols that achieve that goal. They are primarily targeted at supporting a campus environment with mobile computers, but also extend gracefully to accommodate hosts moving between different networks. The key feature is the dependence on ancillary machines, the Mobile Support Stations (MSSs), to track the location of the Mobile Hosts. Using a combination of caching, forwarding pointers, and timeouts, a minimal amount of state is kept in each MSS. The state information is kept in a distributed fashion; the system scales well, reacts quickly to changing topologies, and does ...

Over the past few years, Transmission Control Protocol (TCP) has become the most widely used transport layer protocol on the Internet. TCP performs poorly however, if one of the communicating hosts is a mobile wireless computer [6]. One way to address this performance problem is to modify TCP to make it aware of host mobility. Such an approach

Networking protocols are being modified to handle mobility of hosts. This paper argues that there is a need to make mobility explicit at every level of the OSI model --- even above the network level through user or application level. Further, it is proposed that the mobile host and the first hop (wireless link) of communication be handled differently than the rest of the network. Hence, in networks with mobile hosts, we propose a radical approach of indirect interaction between clients and servers. 1 Introduction The client-server paradigm has served well for structuring applications in distributed systems. The paradigm is implicitly based on two assumptions: 1) the end points of the communication link are fixed and 2) the underlying network infrastructure is to a large extent homogeneous (high bandwidth, reliable, and low latency). However, mobile hosts have different characteristics from fixed hosts. Mobility implies that hosts will connect from different access points and ma...

Mobile Computing is a new emerging computing paradigm of the future. Data Management in this paradigm poses many challenging problems to the database community. In this paper we identify these new challenges and plan to investigate their technical significance. New research problems include management of location dependent data, wireless data broadcasting, disconnection management and energy efficient data access. 1 Introduction The rapidly expanding technology of cellular communications, wireless LAN, wireless data networks, and satellite services will give mobile users capability of accessing information anywhere and anytime. In the near future, tens of millions of users will carry a portable (palmtop, laptop) computer (often called personal digital assistant (PDA) or personal communicator) with wireless connection to a worldwide information network. Coming years will most likely be the decade of mobile or nomadic computing. This vision poses new challenging problems to the databas...

Mobile computing is a new emerging computing paradigm posing many challenging data management problems. We identify these new challenges and investigate their technical significance. New research problems include management of location dependent data, frequent disconnections, structuring distributed algorithms for mobile hosts, wireless data broadcasting, and energy efficient data access. 1 Introduction The rapidly expanding technology of cellular communications, wireless LAN, and satellite services will make it possible for mobile users to access information anywhere and at anytime. In the near future, tens of millions of users will carry a portable computer often called a personal digital assistant or a personal communicator. Various possibilities are shown in Figure 1. Smaller units will run on AA batteries and may be diskless; larger units will run on Ni-Cd packs. These will be powerful laptop computers with large memories and powerful processors. Regardless of size, all mobile co...

this paper, we have used the terms mobile and portable computing interchangeably. However, strictly speaking, we view portable computing as a more restrictive form of mobile computing: though a portable computer may connect to the network from different locations, it essentially connects to the network at any given access point through an individual wired connection and therefore, cannot simultaneously move and maintain its connection to the network. The notion of a "cell" and the associated wireless communication with a broadcast capability, is absent from portable computing.

Mobile internetworking revolves around the premise that a mobile host (MH) will frequently attach to and detach from the Internet, thus changing its address frequently. Location management in mobile internetworking refers to the process of keeping track of the current addresses of MHs in the Internet. Protocols proposed for mobile internetworking rely on a combination of searches and updates for location management. A drawback of these protocols is that they are not uniformly efficient over all possible call-to-mobility ratios (i.e., the relative frequency of searches as compared to updates) . An important issue, therefore, is how the overall costs of location management can be reduced, regardless of the call-to-mobility ratio. The aim of this work is to explore a new and practical scheme for location management, with emphasis on network cost reduction.

As users, services, databases, and computers become increasingly mobile, so fades the era of the fixed network. Modern networks are becoming mobile networks which must accommodate a broad range services with differing mobility characteristics. Consequently, there is an impetus to understand mobility and its effect on communications systems. Of particular interest are the unique stresses imposed by mobile computing and especially mobile computer programs (agents). As an aid to greater understanding, we propose a theoretical framework for the study of mobility tracking based on user/service/host location probability distributions. We show how this methodology, using stochastic ordering and information theory, can enable quantitative comparison of various mobility management schemes as well as insight into the mobility tracking problem over a wide range of mobility characteristics. This general approach should aid both applications and future research. This work supported in part b...

Source messages intended for a mobile host can be routed in one of two ways. Either the source knows the direct route to the mobile host, and is informed of all location changes by the mobile host (informed routing), or the source directs messages to a home agent that forwards messages to the mobile host (triangle routing). When the rate at which the mobile host changes location and the rate at which messages are directed to the mobile host are known and fixed, we show that the optimal routing policy is described by a threshold rule that depends on the normalized differential route cost between triangle and informed routing and the call to mobility ratio (source messaging rate divided by location update rate). Since the call to mobility ratio may not be known a priori or may change slowly with time, we also derive an adaptive policy selection algorithm. The policy is derived from a maximum likelihood estimate of the call to mobility ratio based on observations of message arrivals and l...