Carl H. Hauser

Epidemic algorithms for replicated database maintenance

Whru a dilt~lhSC is replicated at, many sites2 maintaining mutual consistrnry among t,he sites iu the fac:e of updat,es is a signitirant problem. This paper descrikrs several randomized algorit,hms for dist,rihut.ing updates and driving t,he replicas toward consist,c>nc,y. The algorit Inns are very simple and require few guarant,ees from the underlying conllllunicat.ioll system, yc+ they rnsutc t.hat. the off(~c~t, of (‘very update is evcnt,uwlly rf+irt-ted in a11 rq1ica.s. The cost, and parformancc of t,hr algorithms arc tuned I>? c%oosing appropriat,c dist,rilMions in t,hc randoinizat,ioii step. TIN> idgoritlmls ilr(’ c*los~*ly analogoIls t,o epidemics, and t,he epidcWliolog)litc\ratiirc, ilitlh iii Illld~~rsti4lldill~ tlicir bc*liavior. One of tlW i

Smart Generation and Transmission With Coherent, Real-Time Data

,oritlims 11&S brc>n implrmcWrd in the Clraringhousr sprv(brs of thr Xerox C’orporat~c~ Iiitcrnc4, solviiig long-standing prol>lf~lns of high traffic and tlatirl>ilsr inconsistcllcp.

The portable common runtime approach to interoperability

In recent years, much of the discussion involving “smart grids” has implicitly involved only the distribution side, notably advanced metering. However, todays electric systems have many challenges that also involve the rest of the system. An enabling technology for improving the power system, which has emerged in recent years, is the ability to measure coherent, real-time data. In this paper, we describe major challenges facing electrical generation and transmission today that availability of these measurements can help address. We overview applications using coherent, real-time measurements that are in use today or proposed by researchers. Specifically, we describe, normalize, and then quantitatively compare key factors for these power applications that influence how the delivery system should be planned, implemented, and managed. These factors include whether a person or computer is in the loop and (for both inputs and outputs) latency, rate, criticality, quantity, and geographic scope. From this, we abstract the baseline communications requirements of a data delivery system supporting these applications and suggest implementation guidelines to achieve them. Finally, we overview the state of the art in the supporting computer science areas of overlay networking and distributed computing (including middleware) and analyze gaps in commercial middleware products, utility standards, and issues that limit low-level network protocols from meeting these requirements when used in isolation.

GridStat: A Flexible QoS-Managed Data Dissemination Framework for the Power Grid

Operating system abstractions do not always reach high enough for direct use by a language or applications designer. The gap is filled by language-specific runtime environments, which become more complex for richer languages (CommonLisp needs more than C+ +, which needs more than C). But language-specific environments inhibit integrated multi-lingual programming, and also make porting hard (for instance, because of operating system dependencies). To help solve these problems, we have built the Portable Common Runtime (PCR), a language-independent and operating-system-independent base for modern languages. PCR offers four interrelated facilities: storage management (including universal garbage collection), symbol binding (including static and dynamic linking and loading), threads (lightweight processes), and low-level I/O (including network sockets). PCR is “common” because these facilities simultaneously support programs in several languages. PCR supports C. Cedar, Scheme, and CommonLisp intercalling and runs pre-existing C and CommonLisp (Kyoto) binaries. PCR is “portable” because it uses only a small set of operating system features. The PCR source code is available for use by other researchers and developers.

Security, trust, and QoS in next-generation control and communication for large power systems

With the increase in the monitoring of operational data at very high rates in high voltage substations and the ability to time synchronize these data with global positioning systems, there is a growing need for transmitting this data for monitoring, operation, protection, and control needs. The sets of data that need to be transferred and the speed at which they need to be transferred depend on the application-for example, slow for postevent analysis, near real time for monitoring and as close to real time as possible for control or protection. In this paper, we describe GridStat, a novel middleware framework we have developed to provide flexible, robust, and secure data communications for the power grids operations. Test results demonstrate that such a flexible framework can also guarantee latency that is suitable for fast wide-area protection and control.

Using threads in interactive systems: a case study

The present communication architecture supporting control of the electric power grid makes it difficult to use the wealth of data collected at high rates in substations, retarding their use in new applications for controlling the grid. A flexible, real-time data network would make it possible to use these data for many more control and protection applications, potentially increasing the grids reliability and increasing its operating efficiency. Applications that could use these data include: decentralised load frequency control; closed-loop voltage control; transient and small-signal stabilisation; and special protection schemes using data gathered over a wide area. Such applications and the flexibility of the underlying communication network imply greater data sharing between utilities, leading to new performance, availability and reliability requirements. This paper examines the security, trust and Quality of Service (QoS) requirements imposed by these applications and shows how they are met by mechanisms included in the GridStat middleware framework that we are developing.

Intelligent Design" Real-Time Simulation for Smart Grid Control and Communications Design

We describe the results of examining two large research and commercial systems for the ways that they use threads. We used three methods: analysis of macroscopic thread statistics, analysis the microsecond spacing between thread events, and reading the implementation code. We identify ten different paradigms of thread usage: defer work, general pumps, slack processes, sleepers, one-shots, deadlock avoidance, rejuvenation, serializers, encapsulated fork and exploiting parallelism. While some, like defer work, are well known, others have not been previously described. Most of the paradigms cause few problems for programmers and help keep the resulting system implementation understandable. The slack process paradigm is both particularly effective in improving system performance and particularly difficult to make work well. We observe that thread priorities are difficult to use and may interfere in unanticipated ways with other thread primitives and paradigms. Finally, we glean from the practices in this code several possible future research topics in the area of thread abstractions.

Experiences creating a portable cedar

IT IS GENERALLY RECOGNIZED THAT A HIGH-BANDWIDTH and highly available networked communication system should overlay the transmission system topology in order to enable the control and protection envisaged today to make the grid more efficient and more reliable. The specifications for such a communication system have been difficult to develop, however, because it needs to support a great variety of applications, many of which have not yet been developed. Organizations such as the North American SynchroPhasor Initiative (NASPI) are trying to build on this vision of a communication system that can utilize phasor measurement data to initiate fast controllers, including flexible alternating current transmission system (FACTS) devices.

Distributing Time-Synchronous Phasor Measurement Data Using the GridStat Communication Infrastructure

Cedar is the name for both a language and an environment in use in the Computer Science Laboratory at Xerox PARC since 1980. The Cedar language is a superset of Mesa, the major additions being garbage collection and runtime types. Neither the language nor the environment was originally intended to be portable, and for many years ran only on D-machines at PARC and a few other locations in Xerox. We recently re-implemented the language to make it portable across many different architectures. Our strategy was, first, to use machine-dependent C code as an intermediate language, second, to create a language-independent layer known as the Portable Common Runtime, and third, to write a relatively large amount of Cedar-specific runtime code in a subset of Cedar itself. By treating C as an intermediate code we are able to achieve reasonably fast compilation, very good eventual machine code, and all with relatively small programmer effort. Because Cedar is a much richer language than C, there were numerous issues to resolve in performing an efficient translation and in providing reasonable debugging. These strategies will be of use to many other porters of high-level languages who may wish to use C as an assembler language without giving up either ease of debugging or high performance. We present a brief description of the Cedar language, our portability strategy for the compiler and runtime, our manner of making connections to other languages and the Unix* operating system, and some measures of the performance of our “Portable Cedar”.

Delivery Requirements and Implementation Guidelines for the NASPInet Data Bus

The emergence of phasor measurement units (PMUs) coupled with GPS time devices makes it feasible to directly compare timestamped measurements collected at different locations without needing to account for clock drift. GridStat is a flexible publish-subscribe status dissemination middleware framework with capabilities that include rate-filtered multicast for each subscription. In this paper we explore GridStats ability to hide the complexities of distributed systems from application developers while efficiently providing time-synchronous groups of PMU data from physically disparate locations.