Dynamic Bandwidth Allocation in ATM Networks

Today's new applications such as World Wide Web, video conferencing and multimedia have introduced a large amount of traffic into the network. Additionally new applications are also heading towards real time process. Instant access to the network, greater level of performances and higher degree of satisfaction has become the main concerns of users using these new applications. Although current transmission mediums have advanced in capacity through means such as optical fiber and Gigabit Ethernet, future and unknown new services tend to consume up the available bandwidth. ATM network is the new technology used to support a wide variety of services including data, voice, video and most possibly other future applications. Its flexibility, efficiency and high throughput have gained popularity but with greater complexity due to different approaches in handling different type of services.A high-speed network such as ATM networks must have an effective traffic management scheme in order to gain high data throughput with the least cost of operation. Thus, simulation and modeling are the effective methods used to design the trade-off between network parameters and their performances. Effective sharing of network resources such as bandwidth and buffer are studied through the dynamic allocation method. Static allocation scheme has been proven inefficient to provide high resources utilization as can be seen in STM networks compared to A TM networks. However, ATM networks should provide different dynamic allocation methods according to its different services and traffic characteristics. Four dynamic allocation strategies have been designed, evaluated and compared for their performances. They are called Static Bandwidth Allocation, Bandwidth Allocated Proportional to Expected Queue Length, Bandwidth Allocated Proportional to Expected Queue Length with Threshold Value and Bandwidth Allocated with Threshold Interrupt. Bandwidth Allocated with Threshold Interrupt is proven to be the most effective strategy as it could response to congestion immediately

Comparing the Efficiency of IP and ATM Telephony

Circuit switching, suited to providing real-time services due to the low and fixed switching delay, is not cost effective for building integrated services networks bursty data traffic because it is based on static allocation of resources which is not efficient with bursty data traffic. Moreover, since current circuit switching technologies handle flows at rates which are integer multiples of 64 kb/s, low bit rate voice encoding cannot be taken advantage of without aggregating multiple phone calls on a single channel. This work explores the real-time efficiency of IP telephony, i.e. the volume of voice traffic with deterministically guaranteed quality related to the amount of network resources used. IP and ATM are taken into consideration as packet switching technology for carrying compressed voice and it is compared to circuit switching carrying PCM (64 Kb/s) encoded voice. ADPCM32 is the voice encoding scheme used throughout most of the paper. The impact of several network parameters, among which the number of hops traversed by a call, on the real-time efficiency is studie

Up-link performance of the DQRUMA MAC protocol in a realistic indoor environment for W-ATM networks

This paper evaluates by simulation the performance of the distributed queuing request update multiple access (DQRUMA) MAC protocol in a realistic indoor environment. This protocol has been simulated in conjunction with a type-II hybrid-ARQ protocol based on punctured R-S codes for the LLC layer. The analysis was carried out for a multicarrier modulation scheme (OFDM) with QPSK modulation on each carrier. The hidden Markov model (HMM) is used for modelling the physical layer of the system. The performance of the protocol in terms of throughput, mean delay, CLR and p.d.f. of the delay is presented. The pseudo-Bayesian algorithm as well as harmonic back-off are applied to calculate the retransmission probability for the backlogged users.Peer ReviewedPostprint (published version

Efficient memory management in VOD disk array servers usingPer-Storage-Device buffering

We present a buffering technique that reduces video-on-demand server memory requirements in more than one order of magnitude. This technique, Per-Storage-Device Buffering (PSDB), is based on the allocation of a fixed number of buffers per storage device, as opposed to existing solutions based on per-stream buffering allocation. The combination of this technique with disk array servers is studied in detail, as well as the influence of Variable Bit Streams. We also present an interleaved data placement strategy, Constant Time Length Declustering, that results in optimal performance in the service of VBR streams. PSDB is evaluated by extensive simulation of a disk array server model that incorporates a simulation based admission test.This research was supported in part by the National R&D Program of Spain, Project Number TIC97-0438.Publicad

Apparatus and method for congestion control in high speed networks

An adjustable bit rate (ABR) feedback control scheme is provided where the effects of multiloop delays and high priority traffic transmission are built into the control model. The data traffic is filtered by a low pass filter. Then, the low frequency bandwidth of the filtered traffic is measured and compared to a predetermined threshold. If the measured value exceeds the threshold, the ABR traffic flow is reduced. If the measured value is less than the threshold, the ABR traffic flow is increased. In addition, a General Prediction Control (GPC) method may be applied to the control model for optimal performance. An object of the invention is to minimize the unused link capacity subject to no congestion, where the ABR traffic is adapted to the low frequency variation of high priority traffic flow for high efficiency.Board of Regents, University of Texas Syste

Performance evaluation of MPEG-4 video streaming over UMTS networks using an integrated tool environment

Universal Mobile Telecommunications System (UMTS) is a third-generation mobile communications system that supports wireless wideband multimedia applications. This paper investigates the video quality attained in streaming MPEG-4 video over UMTS networks using an integrated tool environment, which comprises an MPEG-4 encoder/decoder, a network simulator and video quality evaluation tools. The benefit of such an integrated tool environment is that it allows the evaluation of real video sources compressed using an MPEG-4 encoder. Simulation results show that UMTS Radio Link Control (RLC) outperforms the unacknowledged mode. The latter mode provides timely delivery but no error recovery. The acknowledged mode can deliver excellent perceived video quality for RLC block error rates up to 30% utilizing a playback buffer at the streaming client. Based on the analysis of the performance results, a self-adaptive RLC acknowledged mode protocol is proposed

Energy Converter with Inside Two, Three, and Five Connected H2/Air Swirling Combustor Chambers: Solar and Combustion Mode Investigations

This work reports the performance of an energy converter characterized by an emitting parallelepiped element with inside two, three, or five swirling connected combustion chambers. In particular, the idea is to adopt the heat released by H2/air combustion, occurring in the connected swirling chambers, to heat up the emitting surfaces of the thermally-conductive emitting parallelepiped brick. The final goal consists in obtaining the highest emitting surface temperature and the highest power delivered to the ambient environment, with the simultaneous fulfillment of four design constraints: dimension of the emitting surface fixed to 30 30 mm2, solar mode thermal efficiency greater than 20%, emitting surface peak temperature T > 1000 K, and its relative DT 99.9%, and high peak temperature, but the emitting surface DT is strongly sensitive to the geometrical configuration. The present work is related to the “EU-FP7-HRC-Power” project, aiming at developing micro-meso hybrid sources of power, compatible with a thermal/electrical conversion by thermo-photovoltaic cells