16848330
A flexible graphical user interface for performance modeling
We identify three goals for the graphical user interface (GUI) of a network simulation environment: user friendliness, model re-usability, and application extensibility. We address the user friendliness issue by proposing a simple yet efficient approach to setup parameters for the simulation models. We address the application extensibility issue by a two-layer GUI architecture. The two layers are loosely-coupled, and the first layer can be easily replaced (without affecting the other components of the simulation environment). We address the model re-usability issue by subnetworks. Unlike most existing simulation packages where subnetwork is simply a method to group the nodes, the subnetwork construct in our approach is an integral part of the simulation environment (i.e., all operations for a basic node also apply to a subnetwork). The port concept is used to explicitly define the I/O relationship between a subnetwork and the outside world. Parameter dialog boxes are used to set up the parameters for a subnetwork conveniently. Finally, a simple stack mechanism is proposed to measure subnetwork-wide output statistics.<<ETX>>
15619003
A Graphical User Interface Design for Network Simulation
Abstract This article describes a prototyping effort of a flexible graphical user interface (GUI) for a simulation tool called COPS. The GUI is designed to allow parameter setup for all modules in simulation model, and can be easily replaced by new GUIs implemented in different languages/graphical tools. This article provides design guidelines and implementation details of the flexible GUI.
10913965
A study of time warp rollback mechanisms
The Time Warp “optimistic” approach is one of the most important parallel simulation protocols. Time Warp synchronizes processes via rollback. The original rollback mechanism called lazy cancellation has aroused great interest. This paper studies these rollback mechanisms. The general tradeoffs between aggressive and lazy cancellation are discussed, and by a conservitive-optimal simulation is defined for comparitive purposes. Within the framework of aggressive cancellation, we offer some observations and analyze the rollback behavior of tandom systems. The lazy cancellation mechanism iss examined using a metric called the sensitivity of output message. Both aggressive and lazy cancellation are shown to work well for a process with a small simulated load intensity. Finally, an analytical model is given to analyze message preemtion, an important factor that affects the performance of rollback mechanisms. Results indicate that message preemtion has a significant effect on performance when (1) the processor is highly utilized, (2) the execution times of messages have high varience, and (3) rollbacks occur frequently.
5110930
A comparison study of the two-tier and the single-tier personal communications services systems
A two-tier PCS system integrates the high tier PCS system and the low tier PCS systems into a single system to provide the advantages of both tiers. Such a system is expected to provide better service (more available and more cost effective to the users) at the expense of the extra tier switching management. We compare the performance of the two-tier PCS system and the single low tier system in two aspects: the registration traffic and the service availability. Because of the tier management, the two-tier system generates more registration traffic than the single low tier system. Under the range of the input parameters in our study, we show that the two-tier system generates less than 10% extra registration traffic than the single low tier system in most cases and generates less than 20% registration traffic in the worst cases. It is clear that for the service availability, the two-tier system is better than the single one tier system. We also study the probability that a call is forced terminated in the single low tier system because the low tier becomes unavailable during the call (such a call can be continued in the two-tier system).
1571256
Parallelism analyzers for parallel discrete event simulation
Discrete event simulation is usually time consuming. Recently, there has been a great deal of interest in using parallel computers to speed up the simulation process. Before the parallel simulation approach is applied, it is important to understand the inherent parallelism of simulation applications. A simple technique called critical path analysis was proposed to study paralllelism of simulation applications. This paper describes three critical path analysis algorithms based on different event-scheduling (process scheduling) policies. These algorithms are much simpler than a previous approach, where the events must be recorded in a trace and an extra pass is required to process the event trace. In our approach, the critical path analysis algorithms are integrated with the sequential simulation. At the end of the sequential simulation, the optimal parallel execution time is also computed. Livny proposed an algorithm similar to our approach (His, however, was designed for a specific language). Our algorithms can be integrated with sequential simulation programs written by users or be integrated with simulation languages. Another advantage of our algorithms over previous approaches is that ours can be used to study load balancing under different event-scheduling policies. Since our algorithms can be easily inserted in sequential simulation programs, critical path analysis can be applied to existing sequential programs without difficulty. The results can then be used to predict the performance of parallel simulation on similar applications. An example is given to show how useful information can be obtained from our algorithms.
16744149
Performance Analysis for Dual Band PCS Networks
In a dual band personal communications services (PCS) network, heavy traffic areas are covered by microcells which overlay macrocells. In such a network, microcells and macrocells utilize different frequency bands. We propose an analytic model to study the performance of a dual band PCS architecture. Our model assumes that a PCS subscriber has a general residence time distribution in a microcell and the macrocell residence time distribution is derived from the microcell residence time distribution. An iterative algorithm is used to compute the overflow traffic from a microcell to its overlaid macrocell. Then, the call incompletion probability is computed by a macrocell model based on the overflow traffic. Our study indicates that the variance of the microcell residence time distribution and the number of microcells covered by a macrocell have significant effects on the call incompletion probability.
27728163
Hybrid routing
A general-purpose routing algorithm for very-large-scale integrated (VLSI) circuits and printed circuit board (PCB) designs is proposed. Ideas behind the maze-running algorithm and the hierarchical routing algorithm are combined into a powerful algorithm called hybrid routing. The new algorithm demonstrates a speed compatible to a hierarchical router and produces routings with quality equivalent to that obtained by a maze router. Hybrid routing is based on the maze-running method with a third search dimension added. The extra search space is built by recursively constructing a hierarchy of coarser grid meshes. By means of a parameter-controlled expansion into the coarser meshes, the hybrid router is able to find the preferred search region very quickly and will not miss local information as a hierarchical router does. A user-given parameter can turn the algorithm into a pure maze router, a pure hierarchical router, or a wide spectrum of hybrid routers with different speed/quality characteristics between the extremes. The algorithm has been implemented and integrated into a global router that can handle large-scale routing, such as that encountered in the sea-of-gates layout. >
13450793
On IEEE 802.14 medium access control protocol
In this article we present a comprehensive survey on the architecture, protocol issues, and standard of the hybrid fiber coaxial (HFC) networks which are evolving from the existing residential CATV networks. We first describe the HFC architecture and discuss the problems in providing two-way communication. Then, we identify three important medium access control (MAC) issues in designing the IEEE 802.14 standard; namely, synchronization, upstream channel access modes, and collision resolution. Resolutions adopted by the IEEE 802.14 Committee are illustrated after giving a protocol overview. Key resolutions include compensating round trip correction (RTC), interleaving minislots of data and request concurrently, and resolving collisions by multiple collision resolution engines, using the n-ary tree plus p-persistence algorithm with a first transmission rule. A comparative summary of some draft proposals that lead to the standard is given. Finally, we pinpoint two headend algorithms, minislot allocation and request scheduling, which are left open in the standard. They do not affect interoperability but may have a critical impact on performance.
27186635
Register minimization beyond sharing among variables
Traditionally, it is assumed that every variable in the input HDL (hardware description language) behavioral description needs to be held in a register; a register can be shared by multiple variables if they have mutually disjointed lifetime intervals. This approach has been shown effective for signal-flow-like computations such as various DSP algorithms. However, the same is not true for the synthesis of control-dominated circuits, which usually have variables of different bit-width as well as very long lifetime. To go beyond register minimization by lifetime-analysis-based sharing, we propose holding some variables in the state registers, some signal nets, some unclocked sequential networks or a combination of above. We identify the conditions in which the substitution is feasible. We have implemented the proposed method in a software program called VReg. Experimental results have demonstrated that VReg minimizes the number of registers more effectively than the lifetime-analysis-based approach does. Better register area minimization also generally leads to faster designs.
15077607
A transformation-based method for loop folding
We propose a transformation-based scheduling algorithm for the problem given a loop construct, a target initiation interval and a set of resource constraints, schedule the loop in a pipelined fashion such that the iteration time of executing an iteration of the loop is minimized. The iteration time is an important quality measure of a data path design because it affects both storage and control costs. Our algorithm first performs an As Soon As Possible Pipelined (ASAPp) scheduling regardless the resource constraint. It then resolves resource constraint violations by rescheduling some operations. The software system implementing the proposed algorithm, called Theda.Fold, can deal with behavioral loop descriptions that contain chained, multicycle and/or structural pipelined operations as well as those having data dependencies across iteration boundaries. Experiment on a number of benchmarks is reported. >
19539329
Induction and Deduction for Autonomous Networks
The key issues in network management are the representation and sharing of management information and the automatic management mechanisms based on the underlying information infrastructure. The authors propose a framework, which operates on the standard management information base (MIB) and common management information protocol (CMIP), for a network management system with learning and inference as its management engines. In addition to the general domain knowledge, patterns related to the managed network are learned to enhance the understanding of the network and refine the knowledge base. Facts in object-oriented databases or queries from management applications trigger the inference process on logical rules which are either prespecified knowledge or learned network patterns. Forward inference drives prediction and control, while backward inference directs diagnosis and supports view abstraction. A case study on ATM network topology tuning is presented. >