E1AR0002@SMUVM1.BITNET (03/12/86)
Naomi Schulman Publications COMPUTER SYSTEMS LABORATORY STANFORD UNIVERSITY Stanford, CA 94305 RECENT REPORTS & NOTES LIST #6 MARCH, 1986 ABSTRACTS ------------------------------------------------------------------------------- CSL T.R. 85-272 Bibliography of the Computer Systems Laboratory: 1968-1985 Edited by Naomi Schulman March 1985 52 pages.....$5.00 This report lists, in chronological order, all technical reports and notes published by the Computer Systems Laboratory (formerly named Digital Systems Laboratory) of Stanford University, from l968 to date. Information regarding availability, prices, and alternative sources is included. ------------------------------------------------------------------------------- CSL T.R. 85-273 Theoretical Results on Distributed Processing with Limited Computing Resources by Hemant Kanakia and Fouad A. Tobagi March 1985 43 pages.....$3.55 A task is a set of related operations which can be performed on some input data. An algorithm is a collection of tasks with an underlying structure defined in terms of precedence relationships among the tasks. Two models of processing systems are considered. A distributed processing system consists of separate processors, each one dedicated to perform a single task, and permits pipelined processing of consecutive requests, as well as concurrent processing of tasks for a given request. A centralized processing system consists of a single processor which performs all the tasks for a given request sequentially, and services the requests sequentially without pipelining. The performance of these two systems is compared in terms of average execution times, under the constraint that the capacity of the processor in the centralized system is equal to the sum of the capacities of individual processors in the distributed system. ------------------------------------------------------------------------------- CSL T.R. 85-274 Conditions for Product Form Solutions in Multihop Packet Radio Network Models by Jose M. Brazio and Fouad A. Tobagi April, 1985 35 pages.....$3.25 Consider multihop packet radio networks operating under a general class of channel access protocols. For the purpose of throughput analysis, analytical models are considered which describe the joint activity of the transmitters in the network, under the assumptions of heavy traffic and zero propagation and processing delays. The problem addressed in this paper is that of finding conditions for the existence of product form solutions for the steady-state probabilities of these models. The main result states that a necessary and sufficient condition for a given network topology, channel access protocol, and traffic pattern, to lead to a product form solution is that the blocking between each pair of used links, as specified by the access protocol, be symmetric. This result assumes Poisson scheduling point processes associated with the links of the network. The proof is given in two steps: first, for systems where all packet length distributions are exponential, giving rise to Markovian processes; and second, for general packet length distributions (subject to the restriction of possessing a positive density almost everywhere), giving rise to Generalized Semi-Markov Processes. It is also shown that a product form solution does not exist whenever any of the scheduling point processes in the network is not Poisson. In addition, it is proven that the computation of the normalization factor appearing in the expression of the product form solution is an NP-hard problem. ------------------------------------------------------------------------------- CSL T.R. 85-275 Packet Voice on a Local Area Network with Round Robin Service by Michael Fine and Fouad A. Tobagi April, 1985 52 pages.....$3.80 In this paper, we propose a combined voice/data protocol suitable for multiple access broadcast networks that provide round robin service to the stations. Such networks are well suited to the integration of voice and data since they guarantee bounded delay and provide high utilization of the channel even at high bandwidths. Using one such network proposal --- namely Expressnet --- as a representative scheme, we examine the characteristics of the service that voice traffic experiences under the voice/data protocol. We show that the access protocol is able to utilize the channel efficiently to support a large population of voice sources while maintaining low packet delay and guaranteeing some prespecified minimum bandwidth for data traffic. In addition, we show the advantages of silence suppression, i.e., discarding speech that constitutes silent periods, and we examine the cost of overloading the network in terms of the amount of speech discarded. ------------------------------------------------------------------------------- CSL T.R. 85-276 Fred Terman, The Father of Silicon Valley by Carolyn E. Tajnai May 1985 20 pages.....$2.65 Silicon Valley, located on the San Francisco, California, peninsula, radiates outward from Stanford University. It is contained by the San Francisco Bay on the east, the Santa Cruz Mountains on the west, and the Coast Range to the southeast. At the turn of the century, when fruit orchards predominated, the area was known as the Valley of Heart's Delight. Today, semiconductor chips, made of silicon, are the principal product of the local high-tech industries. It has been said that an institution is but the lengthened shadow of one great man. Inasmuch as Silicon Valley is an institution, Fred Terman was such a man. ------------------------------------------------------------------------------- CSL T.R. 85-277 Throughput Performance of a Direct Sequence CDMA Packet Radio Network by J. S. Storey & F. A. Tobagi June 1985 99 pages.....$5.45 A Code Division Multiple Access (CDMA) spread spectrum pack radio network model is presented. The topology is single-hop fully connected network with identical users. The network model allows the performance of the radio links to be specified in detail. A model of a BPSK Direct Sequence (DS) CDMA radio channel with convolutional Forward Error Correction (FEC) coding is used. A refinement of the network model takes into account the restriction that hald-duplex radios cannot transmit and receive simultaneously. Single hop throughput and probability of successful first transmission are derived. The effects on throughput of the received signal strength E /N , the number of b o chips per bit N and the number of users M are shown. A channel load sense access protocol is introduced in which radios are blocked from transmitting when the channel is heavily loaded. The increase in throughput due to this protocol is shown for zero and for non-zero propagation delay. ------------------------------------------------------------------------------- CSL T.R. 85-278 Performance Evaluation of Channel Access Schemes in Multi-Hop Packet Radio Networks with Regular Structure by Simulation by F. A. Tobagi and D. H. Shur June 1985 72 pages.....$4.55 In this report, the performance of various channel access schemes in multi-hop packet radio networks with a regular structure is studied by means of simulation. The channel access schemes considered are: ALOHA (pure and slotted), Carrier Sense Multiple Access (CSMA), Busy Tone Multiple Access (BTMA), Code Division Multiple Access (CDMA), and a new hypothetical scheme introduced here for comparison purposes referred to as Coded Activity Signalling Multiple Access (CASMA). Network throughput and packet delay are evaluated, as well as the effects on performance of the nodal transmission scheduling rate, the propagation delay among nodes, and to some extent the input flow control. In this study, we consider networks in which both the topology and the traffic pattern are symmetric. This renders all nodes in the network statistically identical, and thus helps reduce the complexity of the simulation task considerably without jeopardizing the objective. The performance of CSMA in such networks is shown to be rather poor as compared with its performance in fully connected networks, while relatively high performance is achieved by the CASMA scheme, the various BTMA protocols, as well as the CDMA scheme, as compared with CSMA and the ALOHA schemes. ------------------------------------------------------------------------------- CSL T.R. 85-279 Multi-Level Logic Array Synthesis by Chris Rowen July 1985 169 pages.....$7.90 Automatic synthesis of VLSI circuits from function descriptions creates the opportunity for vastly reduced design cost, but presents formidable challenges. This silicon compilation can be accomplished by a four step translation: 1) writing the function in terms of available logic components, 2) minimization of this logic representation, 3) mapping of logic into the target technology's circuit primitives and 4) selection of a detailed layout configuration. Multi-level logic and Weinberger arrays serve as ideal partners in synthesis of large circuit structures. Deeply nested logic expressions can save area, power, and circuit delay compared to their more common sum-of-products equivalents, and Weinberger arrays can directly implement the arbitrary interconnections required by these complex logic functions. The Stanford Weinberger Array Minimizer and Implementor (SWAMI) system explores two phases of this compilation with special care, heuristic minimization of multi-level logic expressions, and gate placement in Weinberger arrays. SWAMI's logical optimization phase adopts heuristic methods to reduce the circuit area and delay for each logic function. Three transformations, decomposition, composition and local rewriting, change the depth of the logic representation and capitalize on commonly used subexpressions. The topological optimization phase presents new algorithms for linear ordering placement in one-dimensional Weinberger arrays, and introduces a new topology for two-dimensional logic arrays. SWAMI tunes nMOS and CMOS layouts for area and performance according to designer specifications, and produces VLSI logic blocks that are often smaller or faster that equivalent PLA-based implementations. ------------------------------------------------------------------------------- CSL T.R. 85-280 Host Groups: A Multicast Extension for Datagram Internetworks by D.R. Cheriton & S.E. Deering July 1985 8 pages.....$2.50 The extensive use of local networks is beginning to drive requirements for internetwork facilities that connect these local networks. In particular, the availability of multicast addressing in many local networks and its use by sophisticated distributed applications motivates providing multicast across internetworks. In this paper, we propose a model of service for multicast in an internetwork, describe how this service can be used, and describe aspects of its implementation including how it would fit into one existing internetwork architecture, namely the US DoD internet Architecture. ------------------------------------------------------------------------------- CSL T.R. 85-281 Prolog Memory-Referencing Behavior by Evan Tick September 1985 This report describes Prolog data and instruction memory-referencing characteristics. Prolog exhibits unconventional referencing behavior of backtracking; the saving and subsequent restoration of a program state. Backtracking introduces memory bandwidth requirements above those of procedural languages. The significance of this and other characteristics was measured by emulating a Prolog architecture running three benchmark programs and simulating various memory models. The results indicate that so-called determinate programs require substantial memory bandwidth because of a limited form of backtracking (shallow). However, this referencing behavior exhibits spatial locality enabling small memory buffers to reduce the bandwidth requirement. A modification to the Prolog architecture having the advantage of further increasing locality is described. ------------------------------------------------------------------------------- CSL T.R. 85-282 Partitioning of Function in a Distributed Graphics System by William I. Nowicki March 1985 Although recent advances in graphics workstations promise much computing power for the future needs of researchers, traditional approaches to software organization waste much of this power. Most systems treat the workstation as either a fixed-function terminal or a self-contained personal computer; these roles have limitations that can be overcome by considering the workstation a multi-function component of a distributed system. Traditional standard graphics packages and object-oriented window systems offer important functionality, but a third approach, virtual terminal management systems, is more appropriate for a distributed operating system. The Stanford Distributed Systems Group has implemented such a distributed system for graphics workstations, organized as a collection of servers providing services to clients. Major issues are how to partition functions between the server and its clients, and physically partition the server. In particular, the service that displays graphical objects is called the Virtual Graphics Terminal Service (VGTS). The VGTS architecture is described, as well as a prototype implementation. This thesis discusses the trade-offs involved in partitioning of function in a distributed graphics system. Performance is one important property traded for advanced functionality or decreased cost. To provide adequate performance in a distributed system, communication costs should be kept low, as well as the frequency of the communication. By providing modeling as well as viewing facilities, the VGTS reduces the communication required between applications and the service. Measurements verify that performance is insensitive to network bandwidth, but depends heavily on CPU speed and protocol characteristics. Using structure provides important speed improvements in some cases, but other basic factors such as inner loop optimization and proper batching of requests make even larger differences. Finally, conclusions are drawn regarding the partitioning approaches taken in the VGTS. The VGTS is suitable for a large class of applications that perform graphics as an aid to user interface, and is portable to a wide range of powerful workstations. Moreover, the VGTS can be used as a basis for further research on many open questions in distributed systems. ------------------------------------------------------------------------------- Publications COMPUTER SYSTEMS LABORATORY Stanford University Stanford, CA 94305 ORDER FORM To Order Reports: Print or type your name and address in the space provided. If your address differs from our mailing label, please indicate that it is new or corrected. Check the report(s) you wish to purchase, whether hardcopy or microfiche. All orders must be PREPAID. California residents must add 7% sales tax. Return this order form with your check or money order made payable to Stanford University. Foreign orders must be paid with an international money order or a check payable in dollars through a U.S. bank. Please type or print your name and complete address: Report # Hardcopy Microfiche Report # Hardcopy Microfiche T.R. 272 $5.00 $2.00 T.R. 277 $5.45 $3.00 T.R. 273 $3.55 $2.00 T.R. 278 $4.55 $2.00 T.R. 274 $3.25 $2.00 T.R. 279 $7.90 $3.00 T.R. 275 $3.30 $2.00 T.R. 280 $2.50 $2.00 T.R. 276 $2.65 $2.00 T.R. 281 $4.10 $2.00 Subtotal CA 7% Tax Total -------