Recently, polling has been included as a resource sharing mechanism in the medium access control (MAC) protocol of several communication systems, such as the IEEE 802.11 wireless local area network, primarily to support real-time traffic. Furthermore, to allow these communication systems to support multimedia traffic, the polling scheme often coexists with other MAC schemes such as random access. Motivated by these systems, we develop a model for a polling system with vacations, where the vacations represent the time periods in which the resource sharing mechanism used is a non-polling mode. The real-time traffic served by the polling mode in our study is telephony. We use an on-off Markov modulated fluid (MMF) model to characterize telephony sources. Our analytical study and a counterpart validating simulation study show the following. Since voice codec rates are much smaller than link transmission rates, the queueing delay that arises from waiting for a poll dominates the total delay experienced by a voice packet. To keep delays low, the number of telephone calls that can be admitted must be chosen carefully according to delay tolerance, loss tolerance, codec rates, protocol overheads and the amount of bandwidth allocated to the polling mode. The effect of statistical multiplexing gain obtained by exploiting the on-off characteristics of telephony traffic is more noticeable when the impact of polling overhead is small

Fixed mobile convergence is a topic that is receiving significant attention from the research community as well as telecom equipment vendors around the world. The paper surveys standardization activities and proposes an end-to-end architecture that will support this architecture. The role of traffic management IP-based quality of service is recognized as a vital component for the success of a multiservice, IP-based and converged network

Spatial reuse protocol (SRP) is a media access control (MAC)-layer protocol that operates over a double counter-rotating ring network topology. SRP is designed to enhance the SONET network so that it can handle data traffic more efficiently. We study the all-terminal reliability of an SRP ring implementing intelligent protection switch (IPS) and enhanced intelligent protection switch (E-IPS). We calculate reliability for all scenarios under which all-terminal connectivity is maintained. By summing up the results arising from individual mutually exclusive events, all-terminal reliabilities for IPS and E-IPS are obtained. By further assuming constant and time-dependent component failure rates, mean time to failure (MTTF) and mean time to failure improvement factor (MTIF) measures are calculated. Results show that MTTF/MTIF vary as functions of network size, component reliability and coverage factor. The advantage of E-IPS over IPS is more obvious when network size is big and concentrator failure rate is small. Our analysis could be helpful to network designers who wish to determine whether the additional cost/complexity added by the E-IPS scheme is justified.

We propose a dial-up optical access architecture that allows an end host dynamically to request and receive a high-speed circuit for connection to its Internet service provider's router. We carry out an analytical comparison of the current leased-line architecture and our proposed dial-up architecture for access networks. It shows significant capacity savings, for example, savings of 39% at 50% traffic load for a call blocking probability of 0.5% assuming 3000 hosts share the optical link. With a call queueing model, we demonstrate that even if the circuit is held for long durations in the dial-up architecture, bandwidth savings are possible over the leased-line architecture.

In this paper we describe an efficient algorithm for the constrained shortest path problem which is defined as follows. Given a directed graph with two weights on each link e, a cost l/sub e/, and a delay t/sub e/, find the cheapest path from a source to all destinations such that the delay of each path is no more than a given threshold. The constrained shortest path problem arises in quality-of-service-sensitive routing in data networks and is of particular importance in real time services. The problem formulation and the algorithmic framework presented are quite general; they apply to IP, ATM, and optical networks. Unlike previous algorithms, our algorithm generates paths from one source to all destinations. Our algorithm is strongly polynomial, and is asymptotically faster than earlier algorithms. We corroborate our analysis by a preliminary simulation study.

We characterize the time-dependent behavior of a typical queuing system that arise in ATM networks under the presence of overloads. The transient queue length distribution and transient cell loss probability are obtained numerically and transient characteristics such as maximum overshoot and relaxation time are used to quantify the effects of congestion periods. A new measure, expected excess loss in overload (EELO) is defined to quantify the effects of overload when compared with the system behavior in the steady-state regime. The basic modeling technology that we use is an extended form of stochastic Petri nets and a software tool called the stochastic Petri net package (SPNP).

Derives expressions for the time-dependent state probabilities and the time-averaged state-probabilities for the leaky bucket rate control scheme. The model is based on the theory of Markov regenerative processes. The results specialize to those obtained by Sidi et al. (1993) for the steady-state behavior of the leaky bucket. The present results are more general, however, in that they apply to the transient regime and to more general arrival processes.>

The inherently weak reliability behavior of the ring architecture has led network designers to consider various design choices to improve network reliability. We assess the impact of provisions such as node bypass, secondary ring and concentrator trees on network reliability. For this reason, we develop closed-form expressions for the reliability and the mean time-to-failure of the double counter-rotating ring architecture. For our comparisons we adopt the 2-terminal, and the all-terminal reliability criteria. Our network reliability expressions are valid for any time-to-failure distributions of links and nodes.>

Five different attachment schemes proposed for the FDDI (fiber distributed data interface) token ring are compared in terms of reliability. For this purpose, the topologies are first studied in isolation (reliability of the path to the backbone) and subsequently end-to-end user reliabilities are computed by combining backbone reliability with the reliability of the path to the backbone.>

The paper develops reliability models and derives closed-form results for network reliability and network mean time to failure, including both node and link failures, for a very popular high speed LAN, the FDDI (fiber distributed data interface). It then extends the results to composite measures of performance and reliability.>