Ece Yaprak

Improvement in reliability of the token ring network by reversal of token in case of a single component failure

The inherent functional property of the unidirectional token movement in a token ring network, is modified in this paper and an algorithm is presented that enables the continuity of operation, in case of a single link component failure, thereby improving the system reliability of a basic conventional token ring network. This phase of operation is temporary until the maintenance restores the normal ring operation. Also the partition of network in case of multi-failure is proposed for single link token ring. The disadvantage of asymmetric time-wait is discussed at the end.<<ETX>>

Dynamic buffer allocation in an ATM switch

Efficient and fair use of buffer space in an Asynchronous Transfer Mode (ATM) switch is essential to gain high throughput and low cell loss performance from the network. In this paper a shared buffer architecture associated with threshold-based virtual partition among output ports is proposed. Thresholds are updated based on traffic characteristics on each outgoing link, so as to adapt to traffic loads. The system behavior under varying traffic patterns is investigated via simulation; cell loss rate is the quality of service (QoS) measure used in this study. Our study shows that the threshold based dynamic buffer allocation scheme ensures a fair share of the buffer space even under bursty loading conditions.

Use of local-area networks as alternating sequential-parallel systems

Abstract An Alternating Sequential-Parallel system is described. It is shown that it can be implemented on a LAN and programmed in Ada. A modification of the binary search algorithm shows a reasonable speedup. ASP also provides good fault detection and availability features. The additional costs of changing a LAN to an ASP are negligible.

Design architectures for 3g and IEEE 802.11 WLAN integration

Wireless LAN access networks show a strong potential in providing a broadband complement to Third Generation cellular systems. 3G networks provide a wider service area, and ubiquitous connectivity with low-speed data rates. WLAN networks offer higher data rate but cover smaller areas. Integrating 3G and WLAN networks can offer subscribers high-speed wireless data services as well as ubiquitous connectivity. The key issue involved in achieving these objectives is the development of integration architectures of WLAN and 3G technologies. The choice of the integration point depends on a number of factors including handoff latency, mobility support, cost-performance benefit, security, authentication, accounting and billing mechanisms. We review 3G-WLAN integration architectures and investigate two such architectures in the case when the UMTS network is connected to a WLAN network at different integration points, namely the SGSN and the GGSN. The evaluation of these integration architectures were conducted through experimental simulation tests using OPNET.

An efficient ATM network switch scheduling

The problem of allocating network resources to application sessions backlogged at an individual switch has a great impact on the end-to-end delay and throughput guarantees offered by the network. There exists a class of algorithms based on weighted fair queueing (WFQ) for scheduling packets which are work-conserving and they guarantee fairness to the backlogged sessions. These algorithms also apply to ATM networks with a packet equal to a single cell or an ATM block (of fixed size). Bursts are groups of varying numbers of cells. We generalize WFQ to schedule bursts. Our motivation is to derive an adaptive algorithm which generalizes the (fixed size) packet level to a varying size packet level. The new algorithm enhances the performance of the switch service for many important applications. The proposed scheme maintains the work-conserving property, and also provides throughput and fairness guarantees. The worst-case delay bound is also given. We use simulation to study the performance characteristics of our algorithm. Our results demonstrate the efficiency of the new algorithm.

Adaptive buffer threshold updating for an ATM switch

Efficient and fair use of buffer space in ATM switches is essential to gain high throughput and low cell-loss performance from the network. A shared buffer architecture associated with threshold based virtual partition among output ports is proposed. Thresholds are updated based on traffic characteristics on each outgoing link, so as to adapt to traffic loads. System behavior under varying traffic patterns is investigated via simulation. Cell loss rate is the quality of service (QoS) measure that is used in this paper. The study shows that the threshold based adaptive buffer allocation scheme ensures fair share of the buffer space even under bursty loading conditions.

Timed neural Petri nets

This paper proposes the concept of timed neural Petri nets, which are isomorphic to neural net architecture. The timed neural Petri net concept combines the new orientation of the neural net with the modeling capabilities of the Petri Net. A big advantage to the utilization of Petri nets for modeling (especially in the neural case) is the proper representation of concurrent or parallel events. The neural net architecture techniques are applied to the Petri net, and the neural Petri net concept extends the basic Petri net definition. The paper is divided into four parts: introduction to neuron concept, timed neural Petri net (TNPN) development, analysis and example of the TNPN, and conclusions.<<ETX>>

An Urn Occupancy Approach for Modeling the Energy Consumption of Distributed Beaconing

In past years, ultrawideband technology has attracted great attention from academia and industry for wireless personal area networks and wireless sensor networks. Maintenance of connectivity and exchange of data require an efficient way to manage the devices. Distributed beaconing defined by ECMA-368 is used to manage the network in fully distributed fashion. All the devices must acquire a unique beacon slot, with the beacon period accessed using a slotted Aloha scheme. In this paper, we study the efficiency of distributed beaconing in the presence of k newcomer devices forming a closed system. Efficiency is measured in terms of energy consumption and network setup delay. ECMA-368 defines two distinct phases: extension and contraction. Both phases are analyzed with particular emphasis on the extension phase by means of an absorbing Markov chain model. The main contributions of this paper are: 1) a systematic approach to model distributed beaconing by formulating two equivalent urn occupancy problems of the extension and contraction phases; 2) the use of exponential generating functions to obtain closed-form expressions of the transition probabilities of the absorbing Markov chain; and 3) comparison to computer simulations based on Opnet modeling and with the preexisting literature.

A cell burst scheduling for ATM networking. I. Theory

Fair queueing is a useful queueing discipline for packet switching systems. It was developed in last decade and was aimed at the general packet switching systems with varying packet length. However it is not suitable for use in the ATM networking, because the ATM cell length is very small and fixed, and so the scheduling scheme on a per cell basis is not practical. We introduce the burst and quality unit concepts in the scheduling algorithm and we make some significant modification on the fair queueing and adapt it to ATM networking to meet QoS requirements. Under the work-conserving assumption, we show that the burst based non-preemptive and preemptive algorithms provide throughput and fairness guarantees.

An efficient network-switch scheduling for real-time applications

Bursts consist of a varying number of asynchronous transfer mode cells corresponding to a datagram. Here, we generalized weighted fair queueing to a burst-based algorithm with preemption. The new algorithm enhances the performance of the switch service for real-time applications, and it preserves the quality of service guarantees. We study this algorithm theoretically and via simulations.