Mudumbai Ranganathan

Sumatra: A Language for Resource-Aware Mobile Programs

Programs that use mobility as a mechanism to adapt to resource changes have three requirements that are not shared with other mobile programs. First, they need to monitor the level and quality of resources in their operating environment. Second, they need to be able to react to changes in resource availability. Third, they need to be able to control the way in which resources are used on their behalf (by libraries and other support code). In this chapter, we describe the design and implementation of Sumatra, an extension of Java that supports resource-aware mobile programs. We also describe the design and implementation of a distributed resource monitor that provides the information required by Sumatra progams. changes.

A Reliable Message Delivery Protocol for Mobile Agents

The abstractions and protocol mechanisms that form the basis for inter-agent communications can significantly impact the overall design and effectiveness of Mobile Agent systems. We present the design and performance analysis of a reliable communication mechanism for Mobile Agent systems. Our protocols are presented in the context of a Mobile Agent system called AGNI . We have developed AGNI communication mechanisms that offer reliable peer-to-peer communications, and that are integrated with our agent location tracking infrastructure to enable efficient, failure-resistant networking among highly mobile systems. We have analyzed the design parameters of our protocols using an in-situ simulation approach with validation through measurement of our prototype implementation in real distributed systems. Our system assumptions are simple and general enough to make our results applicable to other Agent systems that may adopt our protocols and/or design principles.

Mobile Streams: a middleware for reconfigurable distributed scripting

A large class of distributed applications follow an event-driven or reactive paradigm. Such applications can benefit from mobile agent technology by making it easy to add reconfigurability, extensibility and failure resilience features at an application level. We present the design of middleware for building reactive, extensible, reconfigurable distributed systems, based upon an abstraction which we call Mobile Streams. Using our system, a distributed, event-driven application can be scripted from a single point of control and dynamically extended and reconfigured while it is executing. Our system is suitable for building a wide variety of applications; for example, distributed testing, conferencing and control-oriented applications. We illustrate the use of our system by presenting example applications.

Real-time centralized spectrum monitoring: Feasibility, architecture, and latency

This paper describes the implementation and evaluation of a real-time, centralized spectrum monitoring and alert system. Such a system can be used to support emerging spectrum sharing solutions that use a centralized controller to mediate tiered access to spectrum. These controllers rely on realtime awareness of spectrum activity. In addition to describing the architecture and prototype implementation of this real-time monitoring system, we propose a test method to measure the latency of detecting a spectrum occupancy event. This latency is measured as the time from when the event (e.g., a signal transmission) begins to when an alert of that event is delivered to a subscribed client. We used this test method to measure the latency of two different sensor implementations in conjunction with our spectrum occupancy server and found the 95th percentile of latency to be under 80 ms in both cases, plus the network transmission delays of any wide area network involved.

Testing SIP call flows using XML protocol templates

A Session Initiation Protocol (SIP) Call Flow is a causal sequence of messages that is exchanged between interacting SIP entities. We present a novel test system for SIP based on the notion of XML Protocol Templates, of SIP call flows. These templates can be pattern matched against incoming messages and augmented with general purpose code to implement specific protocol responses. This architecture allows test systems to be easily scripted, modified and composed. We describe these techniques in the construction of a SIP web-based interoperability tester (SIP-WIT) and comment on their potential more general use for scripting SIP services.

A mobile debugger for mobile programs

Mobile programs can move computation from one site to another during execution. This flexibility has many potential advantages [3]. It, however, comes at a cost. Mobile programs are hard to debug. Debugging distributed programs is hard even without mobility; adding mobility makes it harder. Our experience with implementing and using mobile languages [l, 41 indicates that suitable debugging support is critical if mobile programs are to fulfill their potential. We briefly describe the design and implementation of Asbestos, a debugger for mobile programs written using the AGNI framework [4]. Asbestos allows position-independent debugging of AGNI programs. It allows users to monitor and control the execution of multiple communicating mobile programs. It provides local and global singlestepping, local and global break-points, and local and global watch-points. AGNI programs are organized around Mobile Streams [4]. A Mobile Stream (ME&ream) is a named communication end-point that can move from machine to machine while maintaining a well-defined ordering guarantee. Multiple message-handlers may be dynamically attached to (and detached from) an MStream and are independently and concurrently invoked for each message. Handlers operate in an atomic fashion changes in the state of the MStream (location, set of handlers etc.) are allowed only in between messages. An MStream has a globally unique name. AGNI is implemented using Tel. An AGNI program consists of a set of MStreams and the associated message-handlers (written in Tel). Asbestos is built on top of the Tel debugger [2] and uses it, for all local debugging. Asbestos glues together multiple debuggers to provide global debugging (global break-points, watchpoints and synchronized single-stepping). In addition, it keeps track of the state of individual debuggers. When an MStream moves, Asbestos detaches the local debugger(s), captures its (their) state and ships the debugger statca along with the MStream data and handlers. At the University of California Santa Barbara, CA 93106

Providing disruption QoS in an OFDM system using Residual Idle Time Based opportunistic spectrum access

Dynamic spectrum access (DSA) is emerging as a promising technology to mitigate spectrum scarcity caused by static frequency allocation. Among the different models proposed for DSA, opportunistic spectrum access (OSA) is a promising class of solutions. In any DSA system, it is important to make sure that the performance of primary users (PUs) does not degrade significantly as a result of dynamic use of spectrum by secondary users (SUs). One of the main reasons for slow commercial adoption of OSA technology is the lack of system implementations which can demonstrate bounding interference to PUs below a given threshold. In this paper, we report a preliminary implementation of an OSA scheme which can ensure that the interference to the PU is bounded. We present our experience and challenges in building this system using the open source software toolkit GNU Radio on a software defined radio (SDR) implemented with a Universal Software Radio Peripheral (USRP).

Programmable Active Services for SIP

SIP-based IP telephony offers the promise of rapid service creation and dynamic deployment. SIP services are fragments of code that are triggered by SIP messages and can perform actions on behalf of registered users. We present programmable active services for SIP (PASS), a technique that uses Java security and Java bytecode re-writing to allow un-trusted services to run on SIP signaling servers. Our technique allows users to write and upload services as Java classes with no a priori constraints on the structure or content of the programs. This generality permits users to leverage the extensive Java libraries and to program new SIP services in familiar environments. We define an extended, SIP specific, Java security model that restricts the behavior of the executing SIP service and that constrains the computational resources that it consumes

Emergency telecommunication support for IP telephony

As universal high speed internet access becomes a reality, phone calls are increasingly being made over the Internet rather than the conventional PSTN. The danger to this trend is the un-availability of priority mechanisms for communication between emergency response personnel during times of disaster. We define a proposed architecture to enable ETS support for SIP-based VOIP systems.

Re-configurable distributed scripting

Several distributed testing, control and collaborative applications are reactive or event driven in nature. Such applications can be structured as a set of handlers that react to events and that in turn can trigger other events. We have developed an application building toolkit that facilitates development of such applications. Our system is based on the concept of Mobile Streams. Applications developed in our system are dynamically extensible and re-configurable and our system provides the application designer a mechanism to control extension and re-configuration. We describe our system model and give examples of its use.