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Byline: Lixin Wang (1), Mounir Hamdi (2) Keywords: multiple access protocols; multimedia wireless networks; performance evaluation Abstract: This paper proposes a new medium access protocol (MAC) protocol for futurewireless multimedia personal communication systems, denoted hybrid andadaptive multiple access control (HAMAC) protocol. The HAMAC protocolintegrates fixed assignment TDMA protocol, reservation-based protocols, andcontention-based protocols into a single wireless network so as tosimultaneously and efficiently support various classes of traffic such asconstant-bit-rate (CBR), variable-bit-rate (VBR), and available-bit-rate (ABR)traffic. In particular, the HAMAC protocol uses a novel preservationslot technique to overcome the packet contention overhead in packetreservation multiple access (PRMA) like protocols, while keeping mostisochronous service features of TDMA protocols to serve voice and CBR trafficstreams. A preservation slot is a very short slot which is used torepresent a CBR connection when the traffic in the CBR connection is in asilent period in which there is no meaningful data to transmit. Due to thevery short length of the preservation slot, it only takes minimalportion of the bandwidth pre-allocated to the CBR connection, so that theremaining bandwidth can be freed for other connections to use. When the CBRsource becomes active again, the preservation slot is replaced bynormal data slots without any reservation operation, extra delay, orsignificant bandwidth loss. Consequently, the guaranteed service andsimplified signaling features of TDMA protocols, together with the adaptivebandwidth allocation features of PRMA-like protocols, are both realized in theHAMAC protocol. We have analyzed the performance of the HAMAC protocol usingextensive simulations. The results show that the HAMAC protocol can achievevery low loss rates for various multimedia traffic with stringent quality ofservice (QoS) requirements and outperforms state-of-the-art PRMA-likeprotocols. As a result, the HAMAC protocol appears to be a good candidate forfuture generation multimedia personal communication systems. Author Affiliation: (1) The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (2) The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong E-mail Article History: Registration Date: 24/09/2004

The throughput performance of a wireless media access protocol taking into account the effect of correlated channel fading, capture, and propagation delay is analyzed. For efficient access on the uplink (mobile-to-base-station link), the protocol makes use of the uplink channel status information which is conveyed to the mobiles through a busy/idle flag broadcast on the downlink (base-station-to-mobile link). A first-order Markov model is used to describe the correlation in the packet success/failure process on a Rayleigh-fading channel. The analytical results obtained through the first-order Markov approximation of the channel are compared to those obtained from an independent and identically distributed (i.i.d.) channel model. The Markovian-fading channel model is shown to provide better performance results than the i.i.d. channel model. Simulations show that a first-order Markov approximation of the Rayleigh-fading process is quite accurate. An enhanced version of the access protocol to take advantage of the memory in the fading channel behavior is proposed and analyzed. The effect of retransmission of erroneous data packets and propagation delay on the throughput is also analyzed. It is shown that the access protocol with an error detect (ED) feature is efficient in slow fading (e.g., pedestrian user speeds), whereas a retransmission protocol is more efficient in fast fading (e.g., vehicular user speeds). Index Terms - Capture, correlated fading, Markov channel, retransmission, wireless access.

The Totem multiple-ring protocol provides reliable totally ordered delivery of messages across multiple local-area networks interconnected by gateways. This consistent message order is maintained in the presence of network partitioning […]

Byline: F. Arani (1), W. He (1), B. Honary (1) Keywords: Error control coding speech coding; combined source and channel coding. Abstract: A novel speech transmission technique over noisy channel condition based on combined ARS and channel coding schemes is described. The proposed scheme is suitable for time varying channels with some form of ARQ facilities. It is shown that under an AWGN channel condition, up to 3.8 dB gain relative to a conventional 32 kbits/s transmission can be provided using the combined technique. Author Affiliation: (1) Lancaster Communications Research Centre, Engineering Department, Lancaster University, Lancaster, LA1 4YR, UK Article History: Registration Date: 28/09/2004

A Connectionless, Lightweight, and Multiway (CLAM) communications environment was designed and developed. It offers an efficient and scalable multiprotocol backing for distributed applications using multimodal data. Effective scheduling algorithms for simultaneous support of multiple, threads-based user-space protocols are described, one of which is readily portable for shared-memory multiprocessors, allowing two or more protocols to coexist in an OS process.

With reference to road transport information (RTI) applications, such as cooperative driving, short-range intervehicle communications in a highway environment are investigated in this paper. The research in this field indicates the suitability of the 60-64-GHz band. Due to the distributed nature of the intervehicle communication system, an R-ALOHA protocol is considered; multihop (MH) and single-hop (SH) strategies are compared. Network performance is assessed by considering the joint impact of random access, interference, thermal noise, propagation, and packet capture effect. Several figures of merit are analyzed and discussed: packet success probability (PSP), system stabilization time (SST), first success time (FST), and deadline failure probability (DFP). Network performance is evaluated either by an analytical approach or by a software tool able to simulate a one-lane highway scenario. Both steady-state and transition situations are considered. System performance in terms of PSP (in the presence of two-ray Rice fading, noise, and interference with antenna diversity and selection combining) is analytically evaluated to validate the simulation tool and to prove the suitability of an MH network strategy. The simulation approach allows the evaluation of the impact of protocol parameters on network performance, with reference to nonsteady-state situations. Index Terms - Highway, intervehicle, millimeter waves, multihop.

Byline: N. Movahhedinia (1), G. Stamatelos (1), R.H.M. Hafez (1) Keywords: Wireless multimedia; ATM; bandwidth allocation; polling. Abstract: The rapid development of wireless in-building communication systems, has widened the scope of supported applications. Remote terminals may be capable of producing broadband real-time traffic such as variable bit-rate (VBR) video or bursty data transfers. Consequently one of the important issues in indoor broadband wireless networks (IBWN) is employment of an efficient bandwidth management protocol. In such a protocol, both the effects of radio channel behavior and the traffic heterogeneity have to be considered. In this paper we present a bandwidth allocation scheme based on the interplay of the radio channel characteristics and the traffic parameters and requirements. In the proposed scheme the base station visits the terminals in a non-uniform cyclic fashion. The inter-visit interval and the amount of service which is provided to each user during a visit, is determined using the channel and traffic parameters based on an analytical approach. This system is evaluated by simulations and is found to provide improved performance in fulfilling the requirements of multimedia services in IBWN. Author Affiliation: (1) Department of System and Computer Engineering, Carleton University, Ottawa, K1S 5B6 Article History: Registration Date: 28/09/2004

High performance, distributed data acquisition and control systems based on the CAMAC Serial Highway have been used extensively in the nuclear science field for 20 years. The need for higher I/O system throughput and the increased use of VXIbus-based instrumentation has led to the development of a new highway interconnect. This interconnect supports CAMAC crates, VXI chassis or a mixture of CAMAC and VXI on a high-speed fiber-optic highway. A typical highway interconnect system consists of a VMEbus or PCI bus host interface card, a fiber-optic ring configuration, CAMAC crate controllers and/or VXI Slot-0 controllers. The development of a VME-based I/O controller is being considered. Various throughput benchmarks and initial field experience are discussed. The crate controller supports the FASTCAMAC protocol being proposed to the NIM Committee. The maximum I/O throughput in FAST-CAMAC mode is 10 megabytes/s.

Erasure-generation techniques are investigated in conjunction with symbol interleaving as methods to improve the performance of meteor-burst communication systems. Erasure generation via Viterbi's ratio-threshold test (RTT) and a Bayesian scheme are both considered. It is found that a system using fixed-rate coding, interleaving, and erasure generation can significantly outperform more complex variable-rate coding schemes which do not use erasures. Index Terms - Meteor-burst communications, Reed-Solomon codes, variable-rate codes.

Packet-switched technology has been demonstrated as effective in cellular radio systems with short propagation delay, not only for data, but also for voice transmission. In fact, packet voice can efficiently exploit speech on-off activity to improve bandwidth utilization over time division multiple access (TDMA). Such an approach has been first suggested in the packet reservation multiple-access (PRMA) technique, an adaptation of the reservation ALOHA protocol to the cellular environment. However, being PRMA-based on a fixed frame scheme, it cannot thoroughly take advantage of the very short propagation delays encountered in microcellular systems that allow, for instance, the immediate retransmission of packets lost because of the interference noise from adjacent cells. In this paper, we present the centralized PRMA, a natural enhancement of PRMA, in which the base station (BS) plays a central role in scheduling the transmissions of mobile stations (MS's). As a consequence, the transmission scheduling is very flexible and can account for the different traffic rate and delay constraints that emerge from voice and data integration. Packet retransmission policy to recover corrupted packets can be implemented and operated efficiently to provide an acceptable grade of service, even in a very noisy environment. The simulation results presented in this paper show the quantitative improvements of the centralized packet reservation multiple-access (C-PRMA) performance with respect to PRMA. Index Terms - Local wireless communications, multiple access, packet voice.

Replicated data management protocols have been proposed that exploit a logically structured set of copies. These protocols have the advantage that they provide limited fault-tolerance at low communication cost. The proposed protocols can be viewed as analogues of the read-one write-all protocol in the context of logical structures. In this paper, we start by generalizing these protocols in two ways for logical structures. First, the quorum based approach is applied to develop protocols that use structured read and write quorums, thus attaining a high degree of data availability for both read and write operations. Next, the reconfiguration or views approach is developed for these structures resulting in protocols that attain high degrees of availability at significantly low communication cost for read operations. In this sense, the proposed protocols have the advantages of the read-one write-all protocol for low cost read operations as well as the majority quorum protocol for high data availability. Finally, we generalize the reconfiguration approach to allow for the dynamic reconfiguration of the database system from one replica management protocol to another. This allows database systems to adapt to an evolving and dynamic application environment. Index Terms - Distributed databases, fault-tolerance, reconfiguration, replicated data.

The performance of several replica control protocols was evaluated via a comparison of their average case message overhead in the presence of node failures. The comparison also considered the trade-off between system availability and communication overhead of the majority voting, tree, grid, hierarchical quorum consensus and RST protocols. The implications of the results for designing replicated databases were also discussed.

This work presents a new protocol, VELOS, for tolerating partitionings in distributed systems with replicated data. Our primary goals were influenced by efficiency and availability constraints. The proposed protocol achieves optimal availability, according to a well known metric, while ensuring one-copy serializability. In addition, however, VELOS is designed to reduce the cost involved in achieving high availability. We have developed mechanisms through which transactions, in the absence of failures, can access replicated data objects and observe shorter delays than related protocols, and impose smaller loads on the network and the servers. Furthermore, VELOS offers high availability without relying on system transactions that must execute to restore availability when failures and recoveries occur. Such system transactions typically access all (replicas of all) data objects and thus introduce significant delays to user transactions and consume large quantities of resources such as network bandwidth and CPU cycles. Thus, we offer our protocol as a proof that high availability can be achieved inexpensively. Index Terms - Availability, concurrency control, distributed computing, partitionings, recovery, replication, transactions.