John R. Heath

Traffic overflow in loss systems with selective trunk reservation

Abstract We consider two traffic streams competing for service at an n -server queuing system. Jobs from stream 1, the protected stream, are blocked only if all n servers are busy. Jobs from stream 2, the best effort stream, are blocked if n − r , r ≥1, servers are busy. Blocked customers are diverted to a secondary group of c − n servers with, possibly, a different service rate. For the case r =1, we calculate the joint probabilities of the number of primary and secondary busy servers. For r >1, we describe a procedure for deriving the joint probabilities. These probabilities allow for the calculation of various performance measures including the overflow probabilities of the primary server and secondary server group. Our model is applicable to traffic control in communication networks that use the selective trunk reservation method.

Analysis of gateway congestion in interconnected high-speed local networks

The effects of congestion on performance in interconnected high-speed local networks are investigated. The system studied uses network adapters as gateways to connect distributed local networks through a high-performance network link. Throughput measurements were determined by simulations of various combinations of link speeds, gateway buffering capacities, and local network traffic loads. The performance effects of several high-speed, local-network, bus-access protocols are investigated. Simulation model parameters are based on measurements of HYPERchannel networks. >

Coherency Hub Design for Multisocket Sun Servers with CoolThreads Technology

To bring the benefits of CMT to larger workloads, these systems had to scale beyond a single socket. Because CMT requires massive memory bandwidth to achieve adequate throughput performance, the challenge was to develop a coherency link and fabric that would allow performance to scale along with thread count in a multinode (that is, multisocket) system. In this article CoHubs coherency scheme, ASIC design, and transtransaction flows, and discussion of the engineering challenges created by 800-MHz operation and a six-stage pipeline budget is presented. The basic principles embodied in the multinode coherency protocol and CoHub design will be important building blocks for future multinode CMT systems with higher node counts.

Traffic overflow in closed queueing models

We consider a generalized birth death process that represents a multiserver (closed or open) overflow queueing system with n primary servers and c-n secondary servers. An arrival to the system joins a server of the primary group, if available, otherwise it overflows to the secondary group. If all servers are busy, arrivals are queued, provided the queue buffer is not full, and served as servers become free. Arrivals that find the queue buffer full are lost. Our overflow model differs from models in the open literature in that it combines state dependent arrival rates with group dependent service rates. We present a general formulation that allows a simple derivation of the joint stationary probabilities of i busy primary servers and j busy secondary severs. This main result easily lends itself to an efficient iterative algorithm to evaluate the joint probabilities. We apply our basic theorem to produce new results for several overflow models. A distinctive feature of our approach is that it uses transform-free analysis.

A model of channel allocation in multichannel local networks

Abstract We consider a queueing model with preferentially ordered parallel servers that models a demand assignment channel allocation scheme used in multichannel local networks. We devise a method for reducing the number of system states to construct a tractable model from which we derive, for each n , the probability distribution that k of the first n ordered servers are busy. From these distributions, utilizations of individual servers are derived. Then assuming Poisson arrivals and exponential service time distributions, we develop analytic expressions for server utilizations. For the finite population model, where analytic expressions cannot be derived, we develop an efficient polynomial algorithm to compute server utilizations. Simple expressions for calculating upper bounds on finite population model server utilizations are also derived.

Erratum to: Development Tools and Techniques for Mobile Telecommunications

The original version of this article unfortunately contained a mistake. Dr. Gabriel A. Wainer is missing as one of the coeditors. His Biography is also added. Gabriel Wainer (SMIEEE, SMSCS) received the M.Sc. (1993) and Ph.D. degrees (1998, with highest honors) in Computer Science from the Universidad de Buenos Aires (Argentina) and IUSPIM (now Polytech de Marseille), Universite Paul Cezanne, AixMarseille III (France). In July 2000, he joined the Department of Systems and Computer Engineering, Carleton University (Ottawa, ON, Canada), where he is now an Associate Professor. Previously he was Assistant Professor in the Computer Sciences Department of the Universidad de Buenos Aires, and he held visiting positions in numerous places, including the Arizona Center of Integrated Modelling and Simulation (ACIMS, University of Arizona), Laboratory of Systems Sciences of Marseille (LSIS-CNRS), University of Nice, Polytech de Marseille, INRIA SophiaAntipolis (France). Prof. Wainer is the Vice-President Publications, and was a member of the Board of Directors of the The Society for Computer Simulation International (SCS) (1998–2000; 2004– 2006). He is Special Issues Editor of the Transactions of the Society for Computer Simulation International (SCS), member of the Editorial Board of Wireless Networks (Elsevier), Journal of Defense Modeling and Simulation (Sage), and the International Journal of Simulation and Process Modelling Inderscience). He is the author of three books and over 200 articles in different venues. He has collaborated in the organization of over 100 conferences in the area (including the co-founding of the SIMUTools Conferences). He is head of the Advanced Real-Time Simulation lab, located at Carleton University’s Centre for advanced Simulation and Visualization (V-Sim). He has been the recipient of various awards, including the IBM Eclipse Innovation Award, a Leadership award by the Society for Modeling and Simulation International, various Best Paper awards. He has been awarded Carleton University’s Research Achievement Award (2005–2006) and the First Bernard P. Zeigler DEVS Modeling and Simulation Award. The online version of the original article can be found at http://dx.doi. org/10.1007/s11036-009-0218-x.

Development Tools and Techniques for Mobile Telecommunications

A vast majority of the current research on telecommunication networks relies on computational tools and computerbased experiments, among which the simulation techniques and tools take a prominent place. This special issue aims at presenting a selected number of papers that illustrate and emphasize this importance of such software tools and techniques. This is also an invitation for the readers to shift focus from the research results to the research process itself. Indeed, telecom research extensively relies on experimental techniques and tools. Therefore, and despite its strong theoretical foundations, this research should also be considered as a highly experimental exercise. As such, and similar to other “older” experimental sciences, we believe that particular attention should be paid also to the experimental process, and to the techniques and tools used to produce research results. Therefore, we are pleased to present this special issue featuring three papers describing new methodologies and tools relevant to the development of Mobile Network technologies. These papers are extensions of the best papers presented at the SIMUTools conference held in Marseille in 2008. SIMUTools is an international conference that brings together researchers and practitioners to address the latest developments in simulation research, methodology, models and practice. The first paper, “Automated Development of Cooperative MAC Protocols: A Complier-Assisted Approach”, Hermann S. Lichte et al., describes new software tools for code generation, and complier-based implementation of cooperative MAC protocols. The authors present a protocol specification language and, through compiler techniques, provide the means for automated validation and performance analysis. Additionally, the compiler is used to translate the specified protocols into program code for simulation and also into code for prototype development. The tools described in the paper present a largely automated development process for generating a practical implementation of cooperative MAC protocols. In the second paper, “Simulation of Ad Hoc Routing Protocols using OMNeT++, A Case Study for the DYMO Protocol”, Christoph Sommer et al. discuss the application of OMNet++ for simulation and performance evaluation of mobile ad hoc network(MANET) routing protocols. More specifically, the authors present guidelines for simulating ad hoc routing protocols using OMNeT++, describing set up procedures, control techniques, appropriate metrics, and evaluation procedures. Application of the guidelines are demonstrated with a simulation model, using OMNet++, and performance evaluation of a specific ad hoc routing network protocol, DYMO. Model calibration and validation “best practice” methods are also demonstrated through their application in this case study. In the third, and final, paper, “An Efficient Mechanism of UMTS Multicast Routing”, Antonios Alexiou et al. present a new multicast packet transmission scheme for Universal Mobile Telecommunication System (UMTS) networks. The authors explain the performance benefits of J. R. Heath (*) Computer Research Group & Department of Computer Science, University of Southern Maine, 93 Falmouth Street, Portland, ME 04104, USA e-mail: heath@usm.maine.rr.com URL: http://www.cs.usm.maine.ed/∼heath/