Abstract not found

Due to the availability of a wide variety of wireless access technologies, a mobile host can potentially have subscriptions and access to more than one wireless network at a given time. In this paper, we consider such a multi-homed mobile host, and address the problem of achieving bandwidth aggregation by striping data across the multiple interfaces of the mobile host. We show that both link layer striping approaches and application layer techniques that stripe data across multiple TCP sockets do not achieve the optimal bandwidth aggregation due to a variety of factors specific to wireless networks. We propose an end-to-end transport layer approach called pTCP that effectively performs bandwidth aggregation on multi-homed mobile hosts. We show through simulations that pTCP achieves the desired goals under a variety of network conditions.

"Access is the killer app" [3] is the vision of the Daedalus project at U.C. Berkeley. Being able to be connected seamlessly anytime anywhere to the best network still remains an unfulfilled goal. Often, even determining the "best" network is a challenging task because of the widespread deployment of overlapping wireless networks. In this paper, we describe a policy-enabled handoff system that allows users to express policies on what is the "best" wireless system at any moment, and make tradeoffs among network characteristics and dynamics such as cost, performance and power consumption. We designed a performance reporting scheme estimating current network conditions, which serves as input to the policy specification. A primary goal of this work is to make it possible to balance the bandwidth load across networks with comparable performance. To avoid the problem of handoff instability, i.e., many mobile hosts making the same handoff decision at essentially the same time, we designed r...

This paper introduces the notion of “universal interaction,” allowing a device to adapt its functionality to exploit services it discovers as it moves into a new environment. Users wish to invoke services — such as controlling the lights, printing locally, or reconfiguring the location of DNS servers — from their mobile devices. But aprioristandardization of interfaces and methods for service invocation is infeasible. Thus,the challenge is to develop a new service architecture that supports heterogeneity in client devices and controlled objects, and which makes minimal assumptions about standard interfaces and control protocols. There are five components to a comprehensive solution to this problem: 1) allowing device mobility, 2) augmenting controllable objects to make them network-accessible, 3) building an underlying discovery architecture, 4) mapping between exported object interfaces and client device controls, and 5) building complex behaviors from underlying composable objects. We motivate the need for these components by using an example scenario to derive the design requirements for our mobile services architecture. We then present a prototype implementation of elements of the architecture and some example services using it, including controls to audio/visual equipment, extensible mapping, server autoconfiguration, location tracking, and local printer access.

many axes, including screen size, color depth, effective bandwidth, processing power, and ability to handle specific data encodings, e.g., GIF, PostScript, or MPEG. As shown in tables 1 and 2, each type of variation often spans orders of magnitude. High-volume devices such as smart phones [12] and smart two-way pagers will soon constitute an increasing fraction of Internet clients, making the variation even more pronounced. These conditions make it difficult for servers to provide a level of service that is appropriate for every client. Application-level adaptation is required to provide a meaningful Internet experience across the range of client capabilities. Despite continuing improvements in client computing power and connectivity, we expect the high end to advance roughly in parallel with the low end, effectively maintaining a gap between the two and therefore the need for application-level adaptation. Platform SPEC92/ Screen Bits/ Memory Size pixel

This article summarizes the results of the BARWAN project, which focused on enabling truly useful mobile networking across an extremely wide variety of real-world networks and mobile devices. We present the overall architecture, summarize key results, and discuss four broad lessons learned along the way. The architecture enables seamless roaming in a single logical overlay network composed of many heterogeneous (mostly wireless) physical networks, and provides significantly better TCP performance for these networks. It also provides complex scalable and highly available services to enable powerful capabilities across a very wide range of mobile devices, and mechanisms for automated discovery and configuration of localized services. Four broad themes arose from the project: 1) the power of dynamic adaptation as a generic solution to heterogeneity, 2) the importance of cross-layer information, such as the exploitation of TCP semantics in the link layer, 3) the use of agents in the infrastructure to enable new abilities and to hide new problems from legacy servers and protocol stacks, and 4) the importance of soft state for such agents for simplicity, ease of fault recovery, and scalability.

Wireless links have intrinsic characteristics that affect the performance of transport protocols; these include variable bandwidth, corruption, channel allocation delays, and asymmetry. In this paper we review simulation models for cellular, WLAN and satellite links used in the design of transport protocols, and consider the interplay between wireless links and transport. We argue that the design and evaluation of transport protocols can be improved by providing easily available models of wireless links that strike a balance between realism, generality, and detail.

Numerous transport protocols have been proposed in related work for use by mobile hosts over wireless environments. A common theme among the design of such protocols is that they specifically address the distinct characteristics of the last-hop wireless link, such as random wireless errors, round-trip time variations, blackouts, handoffs, etc. In this paper, we argue that due to the defining role played by the wireless link on a connection’s performance, locating the intelligence of a transport protocol at the mobile host that is adjacent to the wireless link can result in distinct performance advantages. To this end, we present a receiver-centric transport protocol called RCP (Reception Control Protocol) that is a TCP clone in its general behavior, but allows for better congestion control, loss recovery, and power management mechanisms compared to sender-centric approaches. More importantly, in the context of recent trends where mobile hosts are increasingly being equipped with multiple interfaces providing access to heterogeneous wireless networks, we show that a receiver-centric protocol such as RCP can enable a powerful and comprehensive transport layer solution for such multi-homed hosts. Specifically, we describe how RCP can be used to provide: (i) a scalable solution to support interface specific congestion control for a single active connection; (ii) seamless server migration capability during handoffs; and (iii) effective bandwidth aggregation when receiving data through multiple interfaces, either from one server, or from multiple replicated servers. We use both packet level simulations, and real Internet experiments to evaluate the proposed protocol.

This paper introduces a comprehensive architecture that supports adapting a client device's functionality to new services it discovers as it moves into a new environment. Users wish to invoke services --- such as controlling the lights, printing locally, gaining access to application-specific proxies, or reconfiguring the location of DNS servers --- from their mobile devices. But a priori standardization of interfaces and methods for service invocation is infeasible. Thus, the challenge is to develop a new service architecture that supports heterogeneity in client devices and controlled objects while making minimal assumptions about standard interfaces and control protocols. Four capabilities are needed for a comprehensive solution to this problem: 1) allowing device mobility, 2) augmenting controllable objects to makethem network-accessible, 3) building an underlying discovery architecture, and 4) mapping between exported object interfaces and client device controls. We motivate the n...

Hot swapping technology combined with pervasive heterogeneous networks empowers mobile laptop users to select the best network device for their current environment. Unfortunately, the majority of systemsoftware remains "customized"for a particular network configuration, and assumes that many characteristics associated with the network environment remain invariant over the runtime of the software. Mobility causes changes in the environment and nullifies many of these assumptions. This leads to severe loss in system functionality when resources are lost, and failure to benefit when resources are gained. This paper describes Physical Media Independence (PMI), an architecture for dynamically diverse network interface management. PMI addresses three issuesconcerningdynamicnetwork configuration. First, a model for device availability is proposed to accurately determine when a network device is operational. Second, a structured methodology is used to construct adapters that reconfigure the s...