Traffic placement policies for a multi-band network

Recently protocols were introduced that enable the integration of synchronous traffic (voice or video) and asynchronous traffic (data) and extend the size of local area networks without loss in speed or capacity. One of these is DRAMA, a multiband protocol based on broadband technology. It provides dynamic allocation of bandwidth among clusters of nodes in the total network. A number of traffic placement policies for such networks are proposed and evaluated. Metrics used for performance evaluation include average network access delay, degree of fairness of access among the nodes, and network throughput. The feasibility of the DRAMA protocol is established through simulation studies. DRAMA provides effective integration of synchronous and asychronous traffic due to its ability to separate traffic types. Under the suggested traffic placement policies, the DRAMA protocol is shown to handle diverse loads, mixes of traffic types, and numbers of nodes, as well as modifications to the network structure and momentary traffic overloads

CSMA/RN: A universal protocol for gigabit networks

Networks must provide intelligent access for nodes to share the communications resources. In the range of 100 Mbps to 1 Gbps, the demand access class of protocols were studied extensively. Many use some form of slot or reservation system and many the concept of attempt and defer to determine the presence or absence of incoming information. The random access class of protocols like shared channel systems (Ethernet), also use the concept of attempt and defer in the form of carrier sensing to alleviate the damaging effects of collisions. In CSMA/CD, the sensing of interference is on a global basis. All systems discussed above have one aspect in common, they examine activity on the network either locally or globally and react in an attempt and whatever mechanism. Of the attempt + mechanisms discussed, one is obviously missing; that is attempt and truncate. Attempt and truncate was studied in a ring configuration called the Carrier Sensed Multiple Access Ring Network (CSMA/RN). The system features of CSMA/RN are described including a discussion of the node operations for inserting and removing messages and for handling integrated traffic. The performance and operational features based on analytical and simulation studies which indicate that CSMA/RN is a useful and adaptable protocol over a wide range of network conditions are discussed. Finally, the research and development activities necessary to demonstrate and realize the potential of CSMA/RN as a universal, gigabit network protocol is outlined

Extremely high data-rate, reliable network systems research

Significant progress was made over the year in the four focus areas of this research group: gigabit protocols, extensions of metropolitan protocols, parallel protocols, and distributed simulations. Two activities, a network management tool and the Carrier Sensed Multiple Access Collision Detection (CSMA/CD) protocol, have developed to the point that a patent is being applied for in the next year; a tool set for distributed simulation using the language SIMSCRIPT also has commercial potential and is to be further refined. The year's results for each of these areas are summarized and next year's activities are described

SIMULATION MODEL MANAGEMENT: RESOLVING THE TECHNOLOGICAL GAPS

Model management poses requirements and responsibilities that extend throughout the life cycle of a simulation model. Recent publications have identified major problems in cost and time overruns, which are traceable to deficiencies in project and sponsor management. Beginning with the division of the simulation model life cycle into seven phases, we define "model management" and develop the requirements for a Model Management System (MMS). The functional description of a MMS focuses on those phases that jointly characterize the model development effort. Recent research in simulation model development is described, and particular emphasis is given to the approach taken with the Conical Methodology

Distributed simulation, no special tools required

A tool kit of C language functions that can be linked with SIMSCRIPT programs to provide the data communication primitives necessary for distributed simulation is presented. A test case is discussed and some timing data are presented. Additionally some metrics, developed to determine the applicability of the server model decomposition for particular simulations, are discussed

Distributed simulation of network protocols

Simulations of high speed network protocols are very CPU intensive operations requiring very long run times. Very high speed network protocols (Gigabit/sec rates) require longer simulation runs in order to reach a steady state, while at the same time requiring additional CPU processing for each unit of time because of the data rates for the traffic being simulated. As protocol development proceeds and simulations provide insights into any problems associated with the protocol, the simulation model often must be changed to generate additional or finer statistical performance information. Iterating on this process is very time consuming due to the required run times for the simulation models. The results of the efforts to distribute a high speed ring network protocol, Carrier Sensed Multiple Access/Ring Network (CSMA/RN), are presented

A SPECIFICATION LANGUAGE TO ASSIST IN ANALYSIS OF DISCRETE EVENT SIMULATION MODELS

The use of effective development environments for discrete event simulation models should reduce development costs and improve model performance. A model specification language to be used in a model development environment is defined. This approach is intended to reduce modeli ng costs by interposing an intermediate form between a conceptual model (the model as it exists in the mind of the modeler) and an executable representation of that model. As a model specification is being constructed, the incomplete specification can be analyzed to detect some types of errors and to provide some types of model documentation. The primitives to be used in this specification language, called a Condition Specification, are carefully defined. A specification for the classical patrolling repairman model is used as an example to illustrate this language. Some types of diagnostics which are possible based on such a representation are summarized, as well as some model specification properties which are untestable

GRAPH-BASED DIAGNOSIS OF DISCRETE EVENT MODEL SPECIFICATIONS

Several diagnostics which assist in the construction of specifications for discrete event simulation models are defined. The model specifications to be analyzed must be in a particular form called a Condition Specification. The diagnostics are based on analysis of graphs easily derived from a Condition Specification. Most of the diagnostics are intended to be applied as a Condition Specification is being developed. Th ree categories for the classification of diagnostics of model specifications are defined. Two examples illustrate the graphical forms derivable from a Condition Specification

Diagnostic Assistance Using Digraph Representation of Discrete Event Simulation Model Specifications

Automated diagnosis of digraph representations of discrete event simulation models is illustrated as an effective model verification technique, applicable prior to coding the model in an executable language. The Condition Specification is shown to provide an effective representation, from which automated analysis can initiate with a digraph extraction. Subsequent diagnostic simplification techniques are applied to the digraph, either automatically or in concert with the modeler

A carrier sensed multiple access protocol for high data base rate ring networks

The results of the study of a simple but effective media access protocol for high data rate networks are presented. The protocol is based on the fact that at high data rates networks can contain multiple messages simultaneously over their span, and that in a ring, nodes used to detect the presence of a message arriving from the immediate upstream neighbor. When an incoming signal is detected, the node must either abort or truncate a message it is presently sending. Thus, the protocol with local carrier sensing and multiple access is designated CSMA/RN. The performance of CSMA/RN with TTattempt and truncate is studied using analytic and simulation models. Three performance factors, wait or access time, service time and response or end-to-end travel time are presented. The service time is basically a function of the network rate, it changes by a factor of 1 between no load and full load. Wait time, which is zero for no load, remains small for load factors up to 70 percent of full load. Response time, which adds travel time while on the network to wait and service time, is mainly a function of network length, especially for longer distance networks. Simulation results are shown for CSMA/RN where messages are removed at the destination. A wide range of local and metropolitan area network parameters including variations in message size, network length, and node count are studied. Finally, a scaling factor based upon the ratio of message to network length demonstrates that the results, and hence, the CSMA/RN protocol, are applicable to wide area networks