Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ucbvax!smu.CSNET!leff From: leff@smu.CSNET.UUCP Newsgroups: comp.doc.techreports Subject: stanford7 Message-ID: <8707100604.AA08873@ucbvax.Berkeley.EDU> Date: Thu, 9-Jul-87 19:19:12 EDT Article-I.D.: ucbvax.8707100604.AA08873 Posted: Thu Jul 9 19:19:12 1987 Date-Received: Sun, 12-Jul-87 08:56:45 EDT Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 417 Approved: techreports@smu.csnet Naomi Schulman Publications COMPUTER SYSTEMS LABORATORY STANFORD UNIVERSITY Stanford, CA 94305 RECENT REPORTS & NOTES LIST #10 JANUARY 1987 To order reports, see end of this announcement. ABSTRACTS CSL-TR-87-313 A Macroscopic Profile of Program Compilation and Linking M.A. Linton and R.W. Quong January 1987 15 pages.....$3.25 To profile the changes made to programs during development and maintenance, we have instrumented the make utility that is used to compile and link programs. With minor modifications, we have used make to find out how much time programmers spend waiting for compiling and linking, how many modules are compiled each time a program is linked, and the change in size of the compiled modules. Our measurements show that most programs are relinked after only one or two modules are recompiled, and that over 90% of all recompilations yield object code that is less than 100 bytes larger in size. We are using these results to guide the design of an incremental programming environment, particularly with respect to an incremental linker. ------------------------------------------------------------------------------- CSL-TR-87-314 Post-Game Analysis An Initial Experiment for Heuristic-based Resource Management in Concurrent Systems Jerry C Yan February 1987 18 pages.....$3.40 In concurrent systems, a major responsibility of the resource management system is to decide how the application program is to be mapped onto the multi-processor. Instead of using abstract program and machine models, a generate-and-test framework known as "post-game analysis" that based on data gathered during program execution is proposed. Each iteration consists of (i) (a simulation of) an execution of the program; (ii) analysis of the data gathered; and (iii) the proposal of a new mapping that would have a smaller execution time. These heuristics are applied to predict execution time changes in response to small perturbations applied to the current mapping. An initial experiment was carried out using simple strategies on "pipeline-like" applications. The results obtained from four simple strategies demonstrated that for this kind of application, even simple strategies can produce acceptable speed-up with a small number of iterations. ------------------------------------------------------------------------------- CSL-TR-97-315 also numbered STAN-CS-87-1149 Proceedings from the Nineteenth Annual Meeting of the Stanford Computer Forum Edited by: Katie Mac Millen, Ann Diaz-Barriga Carolyn Tajnai February 1987 246 pages.....$15.00 } Operating for almost two decades, the Stanford Computer Forum is a cooperative venture of the Computer Science Department and the Computer Systems Laboratory (a laboratory operated jointly by the Computer Science and Electrical Engineering Departments. CSD and CSL are internationally recognized for their excellence; their faculty members, research staff, and students are widely known for leadership in developing new ideas and trends in the organization, design and use of computers. They are in the forefront of applying research results to a wide range of applications. The Forum holds an annual meeting in February to which three representatives of each member company are invited. The meeting lasts two days and features technical sessions at which timely computer research at Stanford is described by advanced graduate students and faculty members. There are opportunities for informal discussions to complement the presentations. This report includes information on the Forum, the program, abstracts of the talks and viewgraphs used in the presentations. ------------------------------------------------------------------------------- CSL-TR-87-316 PERFORMANCE OF DEMAND ASSIGNMENT MULTIPLE ACCESS SCHEMES IN BROADCAST BUS NETWORKS Michael Fine March 1987 248 pages.....$14.90 Local area communications networks based on packet switching techniques provide simple architectures and efficient and flexible operation. Various ring systems and CSMA contention bus systems have been in operation for several years. More recently, a number of demand assignment multiple access (DAMA) schemes suitable for broadcast bus networks have emerged which provide conflict-free broadcast communications by means of various distributed round-robin scheduling algorithms. In some of these schemes, explicit tokens, i.e., control messages, are used to provide the required scheduling. Other schemes use implicit tokens whereby stations in the network rely on information deduced from the activity on the bus to schedule their transmissions. In this work, three basic access mechanisms, according to which these implicit-token DANA schemes can be classified, are identified. We describe these three mechanisms and the various service disciplines achieved by them together with their network topologies. We present some representative schemes for each class, discussing their performance and other important attributes. We show that these schemes overcome some of the performance limitations of existing random access schemes, making them particularly suited to the high bandwidth requirements of an integrated-services digital local network. For a more extensive and detailed evaluation of the performance of these DAMA schemes, we examine two of them, Expressnet and Fasnet, operating under various service disciplines. Throughput and delay characteristics over a range of operating conditions are presented and discussed. Lastly we propose a combined voice/data protocol suitable for DAMA broadcast networks. 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 Expressnet as a representative scheme, we examine the characteristics of the service that the voice traffic experiences under this 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 look at the effects of overloading the network. ------------------------------------------------------------------------------- CSL-TR-87-317 COMPARATIVE PERFORMANCE OF BROADCAST BUS LOCAL AREA NETWORKS WITH VOICE AND DATA TRAFFIC Timothy A. Gonsalves March 1987 216 pages.....$13.30 Recently, local area networks have come into widespread use for computer communications. Together with the trend towards digital transmission of telephone signals, this has sparked interest in the use of computer networks for the transmission of integrated voice/data traffic. This work addresses two related aspects of local area network performance, a detailed characterization of the performance of Carrier Sense Multiple Access with Collision Detection (CSMA/CD), and the comparative performance of several broadcast bus networks with voice/data traffic. While prior analysis of CSMA/CD has shown that the protocol achieves good performance with data traffic over a range of conditions, the widely used IEEE 802.3 (Ethernet) implementation of the protocol has several aspects that are not easily amenable to mathematical analysis. These include the binary-exponential back-off algorithm used upon collision, the number of buffers per station, and the physical distribution of stations. Performance measurements on operational 3 and 10 Mb/s networks are presented. These demonstrate that the protocol achieves high throughput with data traffic when the packet transmission time is long compared to the propagation delay, as predicted by analysis. However, at 10 Mb/s, with short packets on the order of 64 bytes, performance is poorer. The inflexibility of measurement leads to the use of simulation to further study the behaviour of the Ethernet. It is shown that, with large numbers of stations, while the throughput of the standard Ethernet is poor, a simple modification to the retransmission algorithm enables near-optimal throughput to be achieved. The effects of the number of buffers and of various distributions of stations are quantified. It is shown that stations near the ends of the network and isolated stations achieve lower than average performance. The second focus of this research is the performance of broadcast bus networks with integrated voice/data traffic. The networks considered are the contention-based Ethernet and two contention-free round-robin schemes, Expressnet and the IEEE 802.4 Token Bus. To accommodate voice traffic on such networks, a new variable-length voice packetization scheme is proposed which achieves high efficiency at high loads. While several studies of voice/data traffic on local area networks have appeared in the literature, the differing assumptions and performance metrics used render comparisons with one another difficult. For consistency, a network-independent framework for evaluation of voice/data networks is formulated. Using simulation, a systematic evaluation is undertaken to determine the regions of good performance of the networks under consideration. Interactions between the traffic types and protocol features are studied. It is shown that the deterministic schemes almost always perform better than the contention scheme. Two priority mechanisms for voice/data traffic on round-robin networks are investigated. These are alternating round mechanism and the token rotation times mechanism which restricts access rights based on the time taken for a token to make one round. An important aspect of this work is the accurate characterization of performance over a wide region of the design space of voice/data networks. ------------------------------------------------------------------------------- CSL-TR-87-318 CAPACITY ANALYSIS OF MULTIHOP PACKET RADIO NETWORKS UNDER A GENERAL CLASS OF CHANNEL ACCESS PROTOCOLS AND CAPTURE MODELS Jose Manuel Rego Lourenco Brazio March 1987 295 pages.....$17.25 A packet radio network is a collection of geographically distributed packet radio units communicating over a shared broadcast channel. Usually not all radio units are within hearing range of each other, and thus multihop operation is required. These networks represent the natural extension of point-to-point packet-switched data networks when mobile operation is desired. An important difference exists, however, with respect to the latter: due to the multiaccess nature of the radio channel, the success of a packet at a destination depends on the activity, during the transmission of the packet, of the neighbors of the destination, and on system parameters such as the type of signaling and received power levels. The conditions under which a packet is successfully received in the presence of interfering packets are designated as the {\sl capture mode. Due to the existence of multiuser interference, some form of coordination among the users is required when accessing the channel. This purpose is accomplished by the {\sl channel access protocol.} This thesis deals with the problem of the capacity analysis of a multihop packet radio network; namely, given a network specified by its topology, traffic pattern, channel access protocol, and capture mode, finding the maximum feasible link traffics compatible with the given traffic pattern. In this thesis we start by examining the capture behavior obtained from different signaling methods, and the question of the feasibility of implementation of different protocols under different signaling methods. The signaling schemes that form the basis of the discussion are narrowband and direct-sequence spread-spectrum. We then formulate a Markovian model that, through the appropriate setting of its parameters, allows the representation of the capture behavior of the different signaling methods, and the representation of the actions of the protocols in a general class that includes some of the main protocols of interest for packet radio applications. Examples of protocols in this class are Carrier Sense Multiple Access (CSMA), Busy Tone protocols, Disciplined-ALOHA, and ALOHA. From this model we derive throughput measures, and develop algorithms for finding the network capacity under a given traffic pattern. We then apply the analytical framework developed to the study of the relative performance of a number of channel access protocols in some simple topologies, and of the influence on this performance of system parameters such as the type of signaling, the bit durations and, for spread spectrum systems, the type of code assignment. ------------------------------------------------------------------------------- CSL-TR-87-319 THROUGHPUT PERFORMANCE OF SPREAD SPECTRUM MULTIPLE ACCESS PACKET RADIO NETWORKS James Scott Storey March 1987 219 pages.....$13.35 In this dissertation, an integrated model of an unslotted spread spectrum multiple access (SSMA) packet radio network is developed. The model combines a detailed model of the radio channel, accounting for the effect of multi-user interference, with a network model that traces the evolution of the number of interfering transmissons and accounts for the half-duplex nature of the radios. A new analysis of the performance of a Viterbi decoder in a packet radio environment allows the model to be used for a system with convolutional forward error correction (FEC) coding. The synchronization process is also analyzed and incorporated into the integrated model. The model makes use of several approximations for tractability. A discrete event simulation is used to validate these approximations. The integrated model leads to numerical results which show the throughput and the probability of success for a packet as a function of the channel level and network level parameters. Specifically, for the radio channel, these parameter include the modulation format, the received signal power, the spread spectrum bandwidth expansion, and the presence or absence of FEC coding. Also, the throughput is found as a function of the synchronization parameters, such as the detection thresholds and correlation times, for several different synchronization circuits and preamble structures. At the network level, the parameters are the traffic rate and the network size. The random access protocols considered include unslotted ALOHA and channel load sensing, which is an extension of carrier sensing to an SSMA network. The results indicate the effects on the throughput of receiver availability, channel errors, and the synchronization process. For each of these effects, regions are found where the effect is the primary factor limiting performance. REsults for the network with a channel load sensing protocol showed little improvement over the results for the network with the simpler ALOHA protocol. Results for the FEC coded and uncoded systems are compared, and it is seen that the systems with FEC coding outperform the uncoded systems. A further finding is that by using a two stage acquisition circuit, the performance can be very close to the performance achieved with an ideal synchronization process. ------------------------------------------------------------------------------- CSL-TR-87-320 PERFORMANCE EVALUATION OF MULTIHOP PACKET RADIO NETWORKS BY SIMULATION David Hilton Shur March 1987 218 pages.....$13.40 Packet switched networks provide an efficient and flexible method for interconnecting geographically distributed users for the purpose of digital data transmission. In packet radio networks, nodes transmit packets over multiple-access broadcast radio channels instead of wire, cable or fiber optics links. If the destination node of a packet is not within the power range of its source node, intermediate nodes are needed to deliver the packet in a store-and-forward fashion. Therefore, multihop packet radio networks have both the multiple-access feature typical of broadcast networks and the store-and-forward feature of point-to-point networks. Since only under restrictive assumptions is performance analysis tractable, simulation techniques must be used. The basic behavior of various existing channel access schemes, namely, ALOHA, CSMA, CDMA, and BTMA, and a new scheme referred to as Coded Activity Signalling Multiple Access (CASMA) is investigated. In networks with a regular structure and balanced traffic flow, the effects of transmission scheduling rate, the ratio of propagation delay to packet transmission time, store-and-forward buffer size, and to some extent network access flow control on throughput and delay performance are examined. We show that contrary to the case of single-hop, fully connected networks, the performance of CSMA is not only substantially degraded due to hidden nodes, but it is also affected to a much lesser extent by propagation delay. BTMA and CASMA on the other hand are observed to achieve a relatively high capacity, and to be more sensitive to propagation delay. The performance of a number of variants of a well known buffer management scheme, the Structured Buffer Pool (SBP) is also studied. The effect of the number of buffers per repeater differs according to the channel access scheme employed. The performance of ALOHA and CSMA is not very sensitive to the buffer size, while BTMA and CASMA exhibit up to a 50\% degradation in capacity in certain examples. In more general networks, we show that the CSMA access scheme may exhibit a high degree of variance in the achievable capacity among different PRUs and links, as compared with the other access schemes. Simple sub-optimal transmission scheduling algorithms are introduced to treat the problem of large-scale realistic networks, and are shown to perform well in a `real-world' example. ------------------------------------------------------------------------------- CSL-TR-87-321 CONCURRENT COMMUNICATION AMONG MULTI-TRANSCEIVER STATIONS OVER SHARED MEDIA Yitzhak Birk March 1987 222 pages.....$13.60 Presently, most local-area networks employ a single broadcast bus to interconnect single-transceiver stations. In order to increase a network's throughput beyond a single bus's data rate without using dedicated switching nodes, multiple buses and multi-transceiver stations are required. We explore the design space of single-hop interconnections among such stations; i.e., interconnections that provide a passive transmission path between any two stations. For example, we present interconnections whose throughput can grow {\sl quadratically} with the number of transmitters and receivers per station. They consist of a collection of buses, each of which interconnects only a proper subset of the stations using one of their transceivers. Yet, for any two stations, there is at least one bus to which they are both connected. We refer to these as selective-broadcast interconnections, or \sbis's. The use of unidirectional media significantly enriches the design space of \sbis's since, unlike with bidirectional media, the sets of receivers that hear two transmissions need not be identical or disjoint. A graph-theoretic criterion for determining whether or not transmissions over a specified pair of paths would interfere with each other is established. It is then used in studying the performance of various \sbis's. Implementation-related issues, such as power budget in fiber optic implementations, are discussed in the context of local-area networks. Lastly, the concept of \sbis's is shown to also apply to memory-processor interconnection, as well as to additional domains. A spread-spectrum channel can accommodate several concurrent successful transmissions, and a single-transceiver node can thus utilize only a small fraction of the channel's capacity. In order to allocate the appropriate fraction of capacity to a ``busy'' node, we propose to equip it with several transmitters and receivers, thereby turning it into a ``supernode''. Several architectures and operation policies for supernodes are suggested and compared; it is shown that a supernode can significantly outperform a collection of independent conventional nodes with the same total numbers of transmitters and receivers. Packet-radio networks with half-duplex nodes, as well as networks with full-duplex nodes, are considered. ------------------------------------------------------------------------------- CSL-TR-87-322 CHANNEL ACCESS SCHEMES AND FIBER OPTIC CONFIGURATIONS FOR INTEGRATED- SERVICES LOCAL AREA NETWORKS M. Mehdi Nassehi March 1987 165 pages.....$10.75 Local Area Networks have been in common use for data communications for several years and have enjoyed great success. More recently, there has been a growing interest in using a single network to support many applications (e.g., speech, high-resolution graphics, facsimile, video, etc.) in addition to traditional data traffic. This leads to so-called Integrated Services Local Area Networks. These additional applications introduce new requirements in terms of volume of traffic and real-time delivery of data which are not met by existing networks. To satisfy these requirements, one needs a high-bandwidth transmission medium, such as fiber optics, and a distributed channel access scheme for the efficient sharing of the bandwidth among the various applications. As far as the throughput-delay requirements of the various applications are concerned, a network structure along with a distributed channel access scheme are proposed which incorporate appropriate scheduling policies for the transmission of outstanding messages on the network. The proposed solution is developed in two steps. First, considering each message to be assigned a delay-cost function based on the application to which it belongs, and assuming perfect knowledge of all outstanding messages, a dynamic scheduling policy is devised which outperforms all existing policies in terms of minimizing the expected cost per message. Secondly, as required for the distributed implementation of the scheduling policy, a broadcast mechanism is devised for the efficient dissemination of all relevant information. The broadcast mechanism is based on unidirectional network structures which provide ordering among the stations. As far as the high-bandwidth transmission medium is concerned, fiber optic technology is considered in this work. The physical ordering among stations which is required by the above access scheme may be achieved either by an active configuration, such as a ring, or by a passive configuration, such as unidirectional bus. In rings, the use of fiber optics does not introduce any new technical problems, since there exist only point-to-point links between neighboring stations. However, in the multi-tapped linear bus, the reciprocity and excess loss of optical couplers along with the low impedance of optical detectors severely limit the number of stations that can be accommodated. A number of alternative passive configurations are proposed which overcome this limitation. Also presented is a unified method for selecting coupler coefficients to minimize the maximum path loss. This method is used to compute the maximum number of stations that a configuration can support. ------------------------------------------------------------------------------- Publications COMPUTER SYSTEMS LABORATORY Stanford University Stanford, CA 94305 415-723-1430 (Hours: M-Th, 8-1) ORDER FORM To Order Reports: Print or type your name and address in the space provided. Check or circle the report(s) you wish to purchase, whether hardcopy or microfiche. All orders must be PREPAID. CALIFORNIA RESIDENTS must add sales tax of their local county. 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 drawn on a U.S. bank, payable in dollars. 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