Michael Paterakis

A simple window random access algorithm with advantageous properties

A simple full-feedback-sensing window random access algorithm is proposed and analyzed. The throughput of the algorithm is 0.429; its delay and resistance to feedback channel errors are better than those induced by J.I. Capetanakiss (ibid., vol.IT-25, p.505-15, Sept. 1979) window algorithm. In addition, the simple operations of the algorithm allow for the analytical evaluation of the output-traffic interdeparture distribution. >

Disk scheduling for mixed-media workloads in a multimedia server

Most multimedia applications require storage and retrieval of large amounts of continuous and discrete data at very high rates. Disk drives should be servicing such mixed workloads achieving low response times for discrete requests, while guaranteeing the uninterrupted delivery of continuous data. Disk scheduling algorithms for mixed workloads, although they play a central role in this task, have been overlooked by related multimedia research efforts, which so far have mostly concentrated on the scheduling of continuous requests only. The focus of this paper is on efficient disk I/O scheduling algorithms for mixed workloads in a multimedia storage server. We propose novel algorithms, a taxonomy of relevant algorithms, and study their performance through experimentation. Our results show that our proposed algorithms offer drastic improvements in discrete request average response times, low response-time variability, while serving continuous requests without interruptions.

An investigation of reservation random access algorithms for voice-data integration in microcellular wireless environments

We present the results of a simulation study that explores the performance of two promising reservation random access (RRA) protocols for transmitting voice packets over a common radio broadcast channel in a microcellular radio environment. We examine two inherently stable RRA voice protocols, RRA three cell and RRA two cell, with respect to voice transmissions under ideal and adverse channel conditions. In addition, we investigate the ability of both protocols to support efficient voice-data integration within the system. The RRA two-cell and RRA three-cell algorithms clearly mark the end of the voice contention period, thereby enabling all of the terminals within the microcell to differentiate between available voice and available data slots. Separating the two distinct types of transmissions and resolving the contending voice packets first thus enforces the priority of the voice traffic. In addition, each protocol can be combined with efficient, easy to implement, collision resolution random access protocols for transmitting data packets. Such a voice-data integration mechanism eliminates the potential voice degradation caused by competition between voice and data terminals for available slots. Our results show that the protocols provide stable and robust performance under adverse channel conditions and that they can be employed to sustain voice-data integration under heavy system loading.

On the voice‐data integration in third generation wireless access communication networks

Mobile wireless communications, which includes cellular telephones, land mobile radio, and personal communication systems, have experienced enormous growth over the last decade. Data services represent a critical component of future wireless communications, but have received little attention. While some attention has been given to specialized mobile data networks, less has been directed at the ongoing design of data services in evolving digital cellular networks. In this paper we report on the results of a simulation study which explores voice-data integration performance in third generation wireless communication networks. These networks are designed to provide access to broadband ISDN networks for large numbers of mobile voice and data users. The primary goal of the paper is the development of multiple access transmission protocols that will enable the voice and data terminals to efficiently share the terminal to base station wireless channel. Reservation Random Access (RRA) protocols are used for voice traffic, and multiple random access contention protocols are used for data traffic. The RRA protocols used enable the data terminals to precisely determine the end of voice packet contention periods, therefore providing a natural separation between voice and data contention. Such voice data integration mechanisms allow the voice contending terminals to resolve their contention without any interference from the data terminals. Data contention resolution does not degrade the voice performance, since it follows the voice contention resolution. The above approach is a promising alternative to other existing proposals due to its superior data packet throughput-delay performance under steady state, and voice performance under transient conditions. Our results show that dispersed voice and data terminals can efficiently share a wireless channel.

Design and performance evaluation of an RRA scheme for voice-data channel access in outdoor microcellular environments

In PCS networks, the multiple access problem is characterized by spatially dispersed mobile source terminals sharing a radio channel connected to a fixed base station. In this paper, we design and evaluate a reservation random access (RRA) scheme that multiplexes voice traffic at the talkspurt level to efficiently integrate voice and data traffic in outdoor microcellular environments. The scheme involves partitioning the time frame into two request intervals (voice and data) and an information interval. Thus, any potential performance degradation caused by voice and data terminals competing for channel access is eliminated. We consider three random access algorithms for the transmission of voice request packets and one for the transmission of data request packets. We formulate an approximate Markov model and present analytical results for the steady state voice packet dropping probability, mean voice access delay and voice throughput. Simulations are used to investigate the steady state voice packet dropping distribution per talkspurt, and to illustrate preliminary voice-data integration considerations.

Integrated wireless access for videoconference from MPEG-4 and H.263 video coders with voice, E-mail, and web traffic

In this paper, a new medium access control protocol for wireless communications, named Multimedia Integration Multiple Access Control (MI-MAC), is presented and investigated. We explore, via an extensive simulation study, the performance of MI-MAC when integrating voice, e-mail data, and web packet traffic with either MPEG-4 or H.263 videoconference streams over a noisy wireless channel of high capacity. Our scheme, one of the first in the literature that considers the integration of MPEG-4 or H.263 streams with other types of packet traffic over wireless networks, achieves high aggregate channel throughput in all cases of traffic load, while preserving the quality of service (QoS) requirements of each traffic type.

Highly efficient voice-data integration over medium and high capacity wireless TDMA channels

A new medium access control (MAC) protocol for mobile wireless communications is presented and investigated. We explore, via an extensive simulation study, the performance of the protocol when integrating voice and data traffic over two wireless channels, one of medium capacity (referring mostly to outdoor microcellular environments) and one of high capacity (referring to an indoor microcellular environment). Data message arrivals are assumed to occur according to a Poisson process and to vary in length according to a geometric distribution. We evaluate the voice packet dropping probability and access delay, as well as the data packet access and data message transmission delays for various voice and data load conditions. By combining two novel ideas of ours with two useful ideas which have been proposed in other MAC schemes, we are able to remarkably improve the efficiency of a previously proposed MAC scheme [5], and obtain very high voice sources multiplexing results along with most satisfactory voice and data performance and quality of service (QoS) requirements servicing. Our two novel ideas are the sharing of certain request slots among voice and data terminals with priority given to voice, and the use of a fully dynamic low-voice-load mechanism.

On multiple traffic type integration over wireless TDMA channels with adjustable request bandwidth

A new medium access control (MAC) protocol for mobile wireless communications is presented and investigated. We explore, via an extensive simulation study, the performance of the protocol when integrating voice, video and data packet traffic over a wireless channel of high capacity (referring to an indoor microcellular environment). Depending on the number of video users admitted into the system, our protocol varies: a) the request bandwidth dedicated to resolving the voice users contention, and b) the probability with which the base station grants information slots to voice users, in order to preserve full priority for video traffic. We evaluate the maximum voice capacity and mean access delay, as well as the aggregate channel throughput, for various voice and video load conditions, and the maximum voice capacity, aggregate channel throughput and average data message delays, for various video, voice and data load conditions. As proven by the comparison with a recently introduced efficient MAC scheme (DPRMA), when integrating voice and video traffic our scheme obtains higher voice capacity and aggregate channel throughput. When integrating all three traffic types, our scheme achieves high aggregate channel throughput in all cases of traffic load.

Call-admission-control and traffic-policing mechanisms for the transmission of videoconference traffic from MPEG-4 and H.263 video coders in wireless ATM networks

In this paper, we explore, via an extensive simulation study, the performance of a call-admission-control (CAC) and traffic-policing mechanisms proposed for transmitting multiple quality encoded videoconference movies over a wireless asynchronous transfer mode channel of high capacity, depending on the users needs and requests. Both the CAC algorithm and the traffic-policing mechanism are novel mechanisms proposed for the first time in this paper. For their implementation, we use an estimation of the equivalent bandwidth of the movies, which has been introduced in the past. We focus on both MPEG-4 and H.263 coded movies, as the integration of such video streams has not been studied in the relevant literature. In the case of H.263 movies, our scheme achieves high aggregate channel throughput, while preserving the very strict quality-of-service requirements of the video traffic.

High performance data broadcasting systems

Data broadcasting as a means of efficient data dissemination is a key technology facilitating ubiquitous computing. For this reason, broadcast scheduling algorithms have received a lot of attention. However, all existing algorithms make the core assumption that the data items to be broadcast are immediately available in the transmitters queue, ignoring the key role that the disk subsystem and the cache management play in the overall broadcast system performance. With this paper we contribute a comprehensive systems perspective towards the development of high performance broadcast systems, taking into account how broadcast scheduling, disk scheduling, and cache management algorithms affect the overall performance. We contribute novel techniques that ensure an efficient interplay between broadcast scheduling, cache management, and disk scheduling. We study comprehensively the performance of the broadcast server, as it consists of the broadcast scheduling, the disk scheduling, the cache management algorithms, and the transmitter. Our results show that the contributed algorithms yield considerably higher performance. Furthermore, one of our algorithms is shown to enjoy considerably higher performance, under all values of the problem and system parameters. A key contribution is the result that broadcast scheduling algorithms have only a small effect on the overall system performance, which necessitates the definition of different focal points for efforts towards high performance data broadcasting.