Todd D. Hodes

An architecture for a secure service discovery service

The widespread deployment of inexpensive communications technology, computational resources in the networking infrastructure, and network-enabled end devices poses an interesting problem for end users: how to locate a particular network service or device out of hundreds of thousands of accessible services and devices. This paper presents the architecture and implementation of a secure Service Discovery Service (SDS). Service providers use the SDS to advertise complex descriptions of available or already running services, while clients use the SDS to compose complex queries for locating these services. Service descriptions and queries use the eXtensible Markup Language (XML) to encode such factors as cost, performance, location, and deviceor service-specific capabilities. The SDS provides a highlyavailable, fault-tolerant, incrementally scalable service for locating services in the wide-area. Security is a core component of the SDS and, where necessary, communications are both encrypted and authenticated. Furthermore, the SDS uses an hybrid access control list and capability system to control access to service information.

A network architecture for heterogeneous mobile computing

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.

Composable ad-hoc mobile services for universal interaction

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 aptiotistandardizationof 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 composableobjects. 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.

An architecture for secure wide-area service discovery

The widespread deployment of inexpensive communications technology, computational resources in the networking infrastructure, and network-enabled end devices poses an interesting problem for end users: how to locate a particular network service or device out of hundreds of thousands of accessible services and devices. This paper presents the architecture and implementation of a secure wide-area Service Discovery Service (SDS). Service providers use the SDS to advertise descriptions of available or already running services, while clients use the SDS to compose complex queries for locating these services. Service descriptions and queries use the eXtensible Markup Language (XML) to encode such factors as cost, performance, location, and device- or service-specific capabilities. The SDS provides a fault-tolerant, incrementally scalable service for locating services in the wide-area. Security is a core component of the SDS: communications are both encrypted and authenticated where necessary, and the system uses a hybrid access control list and capability system to control access to service information. Wide-area query routing is also a core component of the SDS: all information in the system is potentially reachable by all clients.

Composable ad hoc location-based services for heterogeneous mobile clients

This paper introduces a comprehensive architecture that supports adapting a client devices 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 make them network‐accessible, (3) building an underlying discovery architecture, and (4) mapping between exported object interfaces and client device controls. We motivate the need for these capabilities 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.

Flexible internetworking of devices and controls

This paper describes the TSpaces approach to integrated control of heterogeneous devices in heterogeneous control networks. The TSpaces system is an application middleware that provides a uniform layer of indirection between components. The system provides gatewaying between legacy network protocols and IP, asynchronous group communication, a shared data schema, component rendezvous and event composition. The authors describe each of these facilities, emphasizing how they enable evolutionary extension of application behaviors, and illustrate with example control applications.

Shared remote control of a video conferencing application: motivation, design, and implementation

Most conferencing systems are focused on facilitating one of two types of meetings: those in a single room, consisting entirely of collocated participants, or those with isolated individuals at different physical locations. Our experiences are of a third style: hybrid meetings consisting of both collocated groups and isolated participants. We illustrate the limitations of using an existing desktop-based tools in the shared meeting room portion of this hybrid meeting style, and propose adding a software control substrate matched to the specifics of the application to address the inadequacies. We derive requirements for the in-room applications, and, as a concrete example from the domain, describe the design and implementation of an application for manipulation of in-room shared video display. Our design employs a user interface split across multiple physical devices paired with a control protocol managing communication between them. The client portion runs on wirelessly-connected portable devices (laptops and 3Com Palm Pilots) and supports per-user input; the server portion handles presentation of shared output on a video monitor. Our design is optimized for meeting room use in three ways: simplified operation to reduce demands on attention, support for remote control, and support for access by multiple simultaneous users.

Dynamically-wiresized Elmore-based routing constructions

We analyze the impact of wiresizing on the performance of Elmore-based routing constructions. Whereas previous wiresizing schemes are static (i.e., they wiresize an existing topology), we introduce a new dynamic wiresizing technique, which uses wiresizing considerations to drive the routing construction itself. Simulations show that dynamic wiresizing affords superior performance over static wiresizing, and also avoids topological degeneracies. Moreover, dynamically-wiresized Elmore-based routing constructions significantly outperform all previous methods (including A-Trees) in term of maximum source-sink signal delay, affording to 73% average SPICE delay improvement over traditional Steiner routing.<<ETX>>

A fixed-point recursive digital oscillator for additive synthesis of audio

This paper summarizes our work adapting a recursive digital resonator for use on sixteen-bit fixed-point hardware. Our modified oscillator is a two-pole filter that maintains frequency precision at a cost of two additional operations per filter sample. The new filters error properties are expressly matched to use in the range of frequencies relevant to additive synthesis of digital audio and sinusoidal modelling of speech in order to minimize the additional computational overhead. We present the algorithm, an error analysis, a performance analysis, and measurements of an implementation on a fixed-point vector microprocessor system.