Institute for Systems Research Technical Reports

Permanent URI for this collectionhttp://hdl.handle.net/1903/4376

This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.

Browse

Author: search.filters.author.Ephremides, AnthonySubject: search.filters.subject.Communication

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Efficient Simulation of DEDS by Means of Standard Clock Techniques: Queueing and Integrated Radio Network Examples
    (1993) Wieselthier, Jeffrey E.; Barnhart, Craig M.; Ephremides, Anthony; ISR; CSHCN
    Simulation is an important tool in the study of communication networks manufacturing systems, and other complicated man-made systems. Many systems of this type are examples of discrete- event dynamic systems (DEDS) for which analytical models have not yet been developed; thus simulation is the primary method for their performance evaluation and control. Although in many cases simulation can provide a good estimate of system performance, it can also be extremely time consuming, and therefore expensive. This is especially true when it is necessary to evaluate system performance for a large number of values of one or more parameters or for different control policies.
  • Thumbnail Image
    Item
    Admission Control Schemes for Spot-Beam Satellite Networks
    (1993) Ramseier, S.; Ephremides, Anthony; ISR; CSHCN
    In this report, we consider communication networks with a satellite with multiple spot beams. We describe the structure and features of these networks, and we consider admission control schemes which optimize the network revenue if several services types with different revenues are present. We show that in some cases the blocking of some calls even if capacity is available can considerably increase the network revenue. We will point out, however, that complete sharing, i.e., accepting calls on a first- come, first-served basis, is optimum for systems with similar traffic types.
  • Thumbnail Image
    Item
    Stability Properties of Constrained Queueing Systems and Scheduling Policies for Maximum Throughput in Multihop Radio Networks
    (1992) Tassiulas, L.; Ephremides, Anthony; ISR; CSHCN
    The stability of a queueing network with interdependent servers is considered. The dependency of servers is described by the definition of their subsets that can be activated simultaneously. Multihop packet radio networks (PRN's) provide a motivation for the consideration of this system. We study the problem of scheduling the server activation under the constraints imposed by the dependency among them. The performance criterion of a scheduling policy p is its throughput that is characterized by its stability region Cp, that is, the set of vectors of arrival rates for which the system is stable. A policy po is obtained which is optimal in the sense that its stability region Cpo is a superset of the stability region of every other scheduling policy. The stability region Cpo is characterized. Finally, we study the behavior of the network for arrival rates that lie outside the stability region. Implications of the results in certain types of concurrent database and parallel processing systems are discussed.
  • Thumbnail Image
    Item
    Dynamic Server Allocation to Parallel Queues with Randomly Varying Connectivity
    (1992) Tassiulas, L.; Ephremides, Anthony; ISR; CSHCN
    Consider N parallel queues competing for the attention of a single server. At each time slot each queue may be connected to the server or not depending on the value of a binary random variable, the connectivity variable. The server is allocated to one of the connected queues at each slot; the allocation decision is based on the connectivity information and on the lengths of the connected queues only. At the end of each slot, service may be completed with a given fixed probability. Such a queueing model is appropriate for some communication networks with changing topology (radio networks with mobile users, or networks with variable links such as meteor-burst communication channels). In the case of infinite buffers, necessary and sufficient conditions are obtained for stabilizability of the system in terms of the different system parameters. The allocation policy that serves the longest connected queue stabilizes the system when the stabilizability conditions hold. The same policy minimizes the delay for the special case of symmetric queue (i.e., queues with equal arrival, service, and connectivity statistics) is provided. In a system with a single buffer per queue, an allocation policy is obtained that maximizes the throughput and minimizes the delay when the arrival and service statistics of different queues are identical.