R.E. Bryant. Simulation of packet communication architecture computer systems. Technical report, Computer Science Laboratory, Massachusetts Institute of Technologies, Cambridge, Massachusetts, 1977.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....order, it is sufficient, though not always necessary, that each logical process finds and executes the earliest future event. The advent of PDES was marked by the invention of conservative protocols, the first of which was the null message protocol, or so called Chandy Misra Bryant protocol [16, 12], developed back in 1979. In most cases, conservative protocols require each logical process to broadcast to its neighbors, in the form of null mes sages, a lower bound on the timestamp of events that it will send to other logical processes. This bound is often called Earliest Output Time (EOT) ....

....events in non decreasing timestamp order. Therefore, to preserve the causality order, it is sufficient, though not always necessary, that each component finds and executes the future event with the smallest timestamp. Research on PDES has been largely dominated by the studies of conserva tive [12, 16] and optimistic protocols [35] and of their performance. Unfortunately, both types of protocols have their strengths and weaknesses. Efficiency of con servative protocols in parallel execution is limited by the amount of lookahead in individual components, which is equal to the difference ....

R. E. Bryant. Simulation of packet communications architecture computer systems. Technical report, Massachusetts Institute of Technology, 1979.

....new concepts, such as lookback, impact time, which may bring new insights into the PDES research. CONSERVATIVE AND OPTIMISTIC The advent of PDES was marked by the invention of conservative protocols, the first of which was the null message protocol, also known as the Chandy Misra Bryant protocol [2,3], developed in 1979. Conservative protocols require each logical process to broadcast to its neighbors, in the form of null messages, a lower bound on the timestamp of events it will send to other logical processes, or Earliest Output Time (EOT) By listening to the null messages from all ....

Bryant, R.E., Simulation of Packet Communications Architecture Computer Systems. 1977, Technical Report MIT-LCS-TR-188, Massachusetts Institute of Technology.

....kernel must be able to support memory management, which is sensitive to simulation time advancement. The rst conservative parallel simulation protocol, which is also the rst parallel simulation protocol, is called CMB algorithm, proposed independently by Chandy and Misra [22] and Bryant [15]. A simulation model can be partitioned into logical processes (LPs) where events on one LP can only be allowed to a ect the state of that LP. State modi cation of other LPs can only be achieved by delivering events (sometimes called messages) to those LPs. Partitioning application into logical ....

R. E. Bryant. Simulation of packet communication architecture computer systems. Technical Report MIT-LCS-TR-188, M.I.T., 1977. 66

....is to determine when it is safe to process an event, i.e. when can one guarantee no event containing a smaller time stamp will be later received by this LP. An LP cannot process an event until it has been guaranteed to be safe. 3.1. 1 First Generation Algorithms The algorithms described in (Bryant 1977; Chandy and Misra 1978) were perhaps the first synchronization algorithms to be developed. They assume the topology indicating which LPs send messages to which others is fixed and known prior to execution. It is assumed each LP sends messages with non decreasing time stamps, and the communication ....

Bryant, R. E. (1977). Simulation of Packet Communication Architecture Computer Systems. Computer Science Laboratory. Cambridge, Massachusetts, Massachusetts Institute of Technology.

....i.e. each LP processes incoming messages in non decreasing timestamp order, guarantees causality correctness [12] There are two main approaches in implementing the virtual time paradigm: conservative and optimistic. The conservative approach was proposed by Chandy and Misra [4] and Bryant [3], and is often referred to as the Chandy Misra Bryant approach. The optimistic approach was proposed by Jefferson and Sowizral [17, 18] The conservative approach does not permit causality error. Each LP in the simulation processes incoming messages only when the underlying synchronization ....

....executed. If the safety condition cannot be ensured, the LP will be blocked. The main problem in the conservative approach is that blocked LPs may cause deadlock. Take the scenario depicted in figure 1 as an example. As LP 2 does not have the timestamp information Event Timestamp A[1,2] 5 D[2,3] 8 A[3,2] not available Pending Events for LP 2 Pending Events for LP 3 Event Timestamp D[3,4] 9 A[2,3] not available D[3,2] 6 A: arrival event : waiting for arrival D: departure event LP LP 2 LP LP 1 3 4 Figure 1: A Deadlock Example for the arrival event A[3,2] it cannot ....

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R.E. Bryant, "Simulation of Packet Communications Architecture Computer Systems", MIT-LCSTR -188, Massachusetts Institute of Technology, 1977.

....and maintenance, not on simulation speed. When speed is discussed, their HDL modeling performance guidelines address serial simulators. Nevertheless, they are good starting points for model developers and are highly recommended reading. Parallel simulation research began more than 20 years ago [7, 8] as a means of improving simulation execution times. Due to the importance of this problem area, significant interest has focused on this area, with numerous algorithms and implementations developed to achieve faster simulations. Electronic design automation represents one of the areas of primary ....

....20, 21] These studies are essential to improving our understanding of the constraints governing the absolute performance of a simulation The U.S. Air Force Institute of Technology (AFIT) 22] has developed an asynchronous, conservative PDS simulator following the Bryant Chandy Misra algorithm [7]. AFIT s research focuses on optimization of null messages and partitioning algorithms to effectively use Intel hypercubes such as the iPSC 2 hypercubes and Paragon architectures. The Auriga compiler, involving Carnegie Mellon University [23] The University of Minnesota [24] IBM [25] and FTL ....

Bryant, R.E. "Simulation of Packet Communication Architecture Computer Systems." Tech Report MIT/LCS/TR-188, Laboratory for Computer Science, MIT, Cambridge, MA, 1977.

....the next event, this form of simulation is called event driven. The algorithm for sequential event driven simulation can not be easily adapted for concurrent execution on a number of processors, since the event list cannot be effectively partitioned for such executions. Distributed simulation [4, 5, 2] offers a radically different approach to simulation. Shared data objects of a sequential simulation, namely the clock and the event list, are discarded: no shared variables are considered in this algorithm. In the algorithm proposed in [10] one machine may simulate a single physical process; ....

R. E. Bryant. Simulation of Packet Communication Architecture Computer Systems. Technical report, Massachusetts Institute of Technology, Cambridge, 1977.

....to date may be found in [Righ89] Fuji90] Fuji92] Fuji93] Fers94] and [Nico94] the following sections provide a short presentation of the most influential of them. 3.7. 1 Conservative Techniques Conservative techniques were originally proposed by Chandy and Misra [Chan79a] and Bryant 12 [Brya77]. These techniques allow a logical process to accept and process an event only if it is absolutely safe to do so, thus strictly avoiding the 11 Reynolds has introduced an alternative, more detailed taxonomy [Reyn88] Reyn89] However, within the scope of this thesis, the conventional taxonomy ....

Bryant, R. E., "Simulation of Packet Communication Architecture Computer Systems", Technical Report MIT-LCS-TR-188, Laboratory for Computer Science, Massachusetts Institute of Technology, USA, 1977.

....design principle espouses a common, global model representation, ALSP makes no such provision in terms of TFM implementation. Rather than appealing to a centralized event list, time flow is regulated using a variant of the Chandy MisraBryant (CMB) parallel discrete event simulation (PDES) protocol [Bryant 1977; Chandy and Misra 1979; 1981] 6 A null message scheme is used for deadlock avoidance, and the standard CMB requirement for lookahead applies. Note that in a fixed time environment, such as the Joint Training Confederation (see Section 2.4) an actor, a, with timestep, d, has lookahead, l 5 d ....

BRYANT, R. E. 1977. Simulation of packet communications architecture computer systems. Tech. Rep. MIT-LCS-TR-188, Massachusetts Institute of Technology.

....principle espouses a common, global model representation, ALSP makes no such provision in terms of TFM implementation. Rather than appealing to a centralized event list, time flow is regulated using a variant of the Chandy Misra Bryant (CMB) parallel discrete event simulation (PDES) protocol [Bryant 1977; Chandy and Misra 1979; Chandy and Misra 1981] 6 A nullmessage scheme is used for deadlock avoidance, and the standard CMB requirement for lookahead applies. Note that in a fixed time environment, such as the Joint Training Confederation (see Section 2.4) an actor, a; with timestep, ffi; has ....

Bryant, R. E. 1977. Simulation of packet communications architecture computer systems. Technical Report MIT-LCS-TR-188, Massachusetts Institute of Technology.

....Terms: Algorithms, Theory Additional Key Words and Phrases: Activity scanning; Aggregate Level Simulation Protocol; conceptual frameworks; High Level Architecture; time flow mechanisms. 1 Introduction Conservative synchronization mechanisms for parallel discrete event simulation (PDES) date to [4, 6, 7]. These mechanisms are inherently prone to deadlock. The most common implementations of conservative synchronization avoid deadlock through the use of null messages and a quantity known as lookahead. This type of conservative synchronization with deadlock avoidance has been implemented within the ....

Bryant, R.E. (1977). "Simulation of Packet Communications Architecture Computer Systems," Technical Report MIT-LCS-TR-188, Massachusetts Institute of Technology.

....executing in parallel, a thread is allocated for each processor and if possible each thread is bound to an individual processor. 2. 1 TasKit TasKit is a simulation kernel that implements the Critical Channel Traversing (CCT) algorithm [12] CCT is an extension of the Chandy Misra Bryant (CMB) 3][2] algorithm that incorporates scheduling decisions into the conservative causality maintenance calculations. It uses a simple dynamic load balancing scheme that has been shown to work well when used with computer network simulations with irregular workloads [10] TasKit uses the logical process ....

R. Bryant. Simulation of Packet Communication Architecture Computer Systems. Technical Report MIT/LCS/TR188, MIT, November 1977.

....and reliability of the various network models can be exploited in the design of an algorithm, which results in improved performance. Methods for time management and event message exchange within a parallel discrete event simulation have been examined for some time. Chandy, Misra[1] and Bryant[2] describe the Null Message Protocol, in which only the smallest available event at each simulation entity is processed. This protocol assumes there is always an event message available from all peers, and uses a null message as a placeholder when no event message is present. Mattern[3] describes a ....

R. E. Bryant, "Simulation of packet communications architecture computer systems," in MIT-LCS-TR-188, 1977.

....must agree on the lower bound time stamp (LBTS) Essentially each simulator must determine that no other simulator can create events at an earlier time before it can be allowed to process its most recent event. A number of protocols exist which allow a group of simulators to agree on the LBTS[3, 4, 12]. Using a good time management runtime library, such as that provided by the Georgia Tech RTIKIT, the main event processing loop of a network simulator can easily be modified to handle events in proper timestamp order. Using RTIKIT each simulator will call the Next Event Request (NER) service of ....

R. E. Bryant. Simulation of packet communications architecture computer systems. In MIT-LCS-TR-188, 1977.

.... simulation as shown in [10] 12] Thus, several customised dynamic load balancing schemes have been proposed for various parallel simulation protocols [7] 8] 10] 12] 18] A CMB SMP protocol, an extension to the conservative asynchronous simulation protocol by Chandy, Misra, and Bryant [1], 2] 3] was proposed in [20] It is an efficient protocol that is customised for shared memory multiprocessor systems. To improve performance, simulation objects were partitioned to form LPs with the objective of achieving load balancing and maximum lookahead (between LPs) These LPs are then ....

....to fulfil the release rate of the A T factory. A detailed discussion on the simulation model can be found in [19] 4. The Load Balancing Schemes 4. 1 The CMB SMP protocol The CMB SMP protocol is an extension to the conservative asynchronous simulation protocol by Chandy, Misra, and Bryant (CMB) [1], 2] 3] It is 2 A task is defined as a collection of logical processes that are highly dependent on each other in [16] 3 specifically designed for shared memory multiprocessor systems. It eliminates the need for sending null messages by using the concept of safetime. Safetime is defined as ....

R.E. Bryant, "Simulation of Packet Communications Architecture Computer Systems", MIT-LCS-TR-188, Massachusetts Institute of Technology, 1977.

....MHz, and Celeron processors at 266 MHz. At the time of PADS 99, Intel was shipping 550 MHz Pentium III and 466 MHz Celeron processors, using essentially the same 100MHz system bus and memory. PDES algorithms are typically divided into two orthogonal categories: optimistic [11] and conservative [2, 4]. Conservative techniques are so called because events can only be executed when they are known to be safe. By comparison, optimistic algorithms execute events aggressively, but must roll back to a previous saved state if a causality error occurs. A third set of adaptive or hybrid algorithms [12] ....

R. E. Bryant, "Simulation of Packet Communications Architecture Computer Systems," Massachusetts Institute of Technology MIT-LCS-TR-188, 1977 1977.

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R.E. Bryant. Simulation of packet communication architecture computer systems. Technical report, Computer Science Laboratory, Massachusetts Institute of Technologies, Cambridge, Massachusetts, 1977.

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R.E. Bryant, Simulation of Packet Communications Architecture Computer Systems, MIT-LCS-TR-188, Massachusetts Institute of Technology, 1977.

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Bryant R.E.: Simulation of Packet Communication Architecture Computer Systems. Technical Report MIT-LCS-TR-188, Massachusetts Institute of Technology, Cambridge 1977.

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R. E. Bryant. Simulation of Packet Communication Architecture Computer Systems. Technical Report MIT-LCS-TR-188, M.I.T, Cambridge, MA, 1977.

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R. E. Bryant. Simulation of Packet Communication Architecture Computer Systems. Technical Report MITLCS -TR-188, M.I.T, Cambridge, MA, 1977.

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R. Bryant. Simulation of Packet Communications Architecture Computer Systems. MIT-LCS-TR-188, Massachusetts Institute of Technology, 1977.

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R. E. Bryant, "Simulation of Packet Communications Architecture Computer Systems," Massachusetts Institute of Technology MIT-LCS-TR-188, 1977.

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R.E. Bryant. "Simulation of packet communications architecture computer systems". Technical Report MIT-LCS-TR-188, Massachusetts Institute of Technology, 1977.

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R. E. Bryant. Simulation of packet communication architecture computer systems. MIT/LCS 188, Massachusetts Institute of Technology, November 1977.

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