Rendezvous Mechanism Research Articles

Energy-aware spectrum coordination with intelligent frequency-hopping for software defined networks

Software-defined Cognitive radio (CR) networking is considered a promising communication paradigm that can deliver huge spectrum opportunities for enabling massive deployment for wireless Internet-of-Things (IoT) applications and services. An important challenge in this domain is how to provide effective energy-efficient distributed spectrum coordination mechanisms (known as Spectrum Rendezvous), through which the CR IoT users can opportunistically coordinate their transmissions over the idle licensed frequency channels without relying on the existence of a dedicated common control channel (CCC). This paper proposes a novel frequency hopping (FH) distributed rendezvous mechanism for CR-capable IoT (CR-IoT) networks using grid-based quorum systems, referred to as adaptive grid-based quorum channel-hopping scheme. The proposed quorum-based scheme divides the time into equidistant cycle segments, referred to as quorum-based FH intervals. Each quorum interval consists of equal-duration beaconing intervals, each associated with a licensed channel. According to the proposed algorithm, each CR-IoT device randomly selects awake-sleep schedules based on the adopted quorum system structure. Any two devices can exchange their control information over the assigned channels of their common awake beaconing intervals. The proposed algorithm provides probabilistic guarantees on the successful rendezvous (RDV) between any two CR-IoT users within a single quorum-based FH interval (cycle) and dynamically adjusts the adopted QS structure based on the time-varying traffic load in the CR-IoT network such that the RDV probability and the expected average time to rendezvous improve with the least possible energy consumption. Compared to reference design schemes, the simulation results demonstrate that the proposed algorithm significantly increases the RDV probability, reduces the average rendezvous time, and reduces the energy consumption per successful RDV.

On Cooperative Channel Rendezvous in Cognitive Radio Networks

In cognitive radio (CR) networks, establishing communication sessions requires the communicating pairs to meet each other on a common channel via a “rendezvous” process. Designing distributed rendezvous protocols without common control channels is a challenging problem due to the dynamic and opportunistic spectrum access paradigm. The existing protocols, mainly based on channel hopping, suffer from the rendezvous difficulty due to asymmetric channel perceptions and significant rendezvous delay when the system scales. In this paper, we exploit a long-neglected opportunity for enabling rendezvous in CR networks-the cooperation among cognitive users. We develop a novel cooperative rendezvous mechanism by introducing the cooperative cognitive nodes serving as “bridges” between communicating pairs to facilitate their rendezvous process. We establish a mathematics framework to study the rendezvous delay and robustness and derive the performance limit in asymptotic scenarios. Our analytical results are further confirmed by the simulation results showing the performance improvement of the developed cooperative rendezvous protocol with only small overhead.

A Rendezvous Mechanism for Energy Balance and Link Quality in WSNs

Quorum System is a good method to assist the design of sensors of the wake-up scheduling mechanism. However, there are some problems about idle rendezvous and poor link quality when the sensor performs a sensing task according to the Quorum System. In order to improve the efficiency of the sensors and reduce energy consumption, a new rendezvous mechanism is proposed. The use of energy and the link quality between sensors are considered from a global perspective. It can not only ensure the rendezvous opportunity among sensors, but also balance the residual energy of the sensors, so it can improve the energy-saving efficiency of traditional Quorum System. According to the simulation, compared with the traditional Quorum System scheduling mechanism, the rendezvous mechanism proposed in this paper can effectively reduce the number of time-slots when the sensor is idle. Moreover, it also realizes the balance of the residual energy of the sensor and the link quality, which prolongs the life cycle of the wireless sensor network and improves the communication quality.

Probabilistic vs. Sequence-Based Rendezvous in Channel-Hopping Cognitive Networks

Rendezvous in cognitive networks refers to the ability of cognitive nodes to find each other and form a network, or to find and join an already operating cognitive network. Two main approached to rendezvous have emerged: sequence-based mechanism that guarantees maximum time-to-rendezvous and blind random hopping resilient to unpredictable primary user activity. In this paper we develop analytical models for time to rendezvous in the presence of primary user activity for the orthogonal sequence-based mechanism and a blind rendezvous mechanism integrated with a transmission tax-based MAC protocol with cooperative sensing. Our analysis shows that the blind mechanism performs better under random primary user activity, the difference being more pronounced when the number of channels is high and/or primary user activity is more intense. In addition, the probabilistic mechanism allows rendezvous with either an emergent or a fully operational CH-CPAN piconet without any interruption, unlike the sequence-based mechanism which precludes any data exchange during the rendezvous process.

Exploiting the potential of DTN for energy-efficient internetworking

Since its original conception as a space-oriented communications architecture, Delay Tolerant Networking (DTN) has been generalized to address issues in terrestrial networks as well. In this work we employ DTN to form an internetworking overlay that exploits the surplus capacity of last hop wireless channels in order to prolong battery life for mobile networking devices. We propose a novel rendezvous mechanism and show experimentally that the DTN overlay can shape traffic, allowing the wireless interface of the mobile device to switch to the sleep state during idle intervals without degrading performance. The simulation experiments are based on a comprehensive DTN agent that incorporates the rendezvous mechanism and facilitates quantifying energy conservation. The DTN agent, implemented in ns-2, enables the study of additional Bundle Protocol design issues, such as route selection, bundle sizing, retransmission strategies, and highlights the need for cross-layer interaction between DTN and the underlying transport protocol.

Distributed WiFi detection and integration in dense urban mobile Peer-to-Peer networks

Running Peer-to-Peer applications—such as multimedia streaming or file sharing—on mobile devices significantly increases the congestion in 3G access networks. Offloading traffic from 3G to WiFi domains is promising in such scenarios, since communication is possible without generating any load in the WiFi’s uplink or in the Internet, given that peers are located in the same WiFi domain. However, in today’s urban areas devices are commonly in range of dozens of infrastructure-based WiFi domains, a fact that calls for an efficient rendezvous mechanism. In this article, we propose a rendezvous mechanism that efficiently enables physically close mobile devices running an arbitrary P2P application to peer with each other in a common WiFi domain. The mechanism builds upon tree-based collection, aggregation, and distribution of WiFi information. Using a stochastic model, we estimate the overhead of the mechanism based on WiFi density statistics from real world urban areas. We further show how to reduce this overhead on the expense of a reduced rendezvous success probability by applying Bloom Filters. Simulations of a tree-based Peer-to-Peer media streaming application demonstrate that the mechanism can in fact support effective offloading of P2P traffic to WiFi domains.

Characteristics of multiprocessing MCNP5 on small personal computer clusters

The feasibility and efficiency of performing MCNP5 calculations with a small, heterogeneous computing cluster built from Microsoft® WindowsTM personal computers (PC) are explored. The performance increases that may be expected with such clusters are estimated for cases that typify general radiation-shielding calculations. Our results show that the speed increase from additional slave PCs is nearly linear up to 10 processors. Guidance is given as to the specific advantages of changing various parameters present in the system. Implementing load balancing, and reducing the overhead from the MCNP rendezvous mechanism add to heterogeneous cluster efficiency. Hyper-threading technology and matching the total number of slave processes to the total number of logical processors also yield modest speed increases in the range below 7 processors. Because of the ease of acquisition of heterogeneous desktop computers, and the peak in efficiency at the level of a few physical processors, a strong case is made for the use of small clusters as a tool for producing MCNP5 calculations rapidly, and detailed instructions for constructing such clusters are provided.

Rendezvous point relocation in protocol independent multicast - sparse mode

Protocol independent multicast - sparse mode is the most widely used multicast routing architecture. It builds a shared distribution tree centered at a rendezvous point and then builds source-specific trees for those sources whose data rate warrants it. Current implementations of the protocol decide on the rendezvous point administratively, which leads to congestion and delays. An attractive solution would be dynamic relocation of the rendezvous point depending on the members of the multicast group. We present a rendezvous point calculation and relocation mechanism for protocol independent multicast -sparse mode. Simulation of the proposed mechanisms is used to demonstrate the effectiveness of the proposals.

Implementation of communicating reactive processes

Communicating reactive processes (CRP) is a new paradigm that unifies capabilities of synchronous and asynchronous approaches to parallel programming; Esterel and Statecharts are two important languages following the synchronous approach while the asynchronous approach is followed by languages like ADA, CSP and Occam. CRP is designed for complex applications like process/robot control requiring both forms of concurrency. A CRP program consists of independent reactive Esterel nodes that communicate via CSP like rendezvous mechanism. CRP has capabilities of both the classes of languages: nondeterminism, rendezvous, instantaneous reaction, preemption as well as new features like watchdogs over asynchronous communication. This paper discusses an implementation of the rendezvous mechanism of CRP. The implementation is nontrivial due to the following constraints: (1) there has to be a mutual agreement between the participating processes over the selection of rendezvous and 2. the implementation is to be distributed with no process having instantaneous global knowledge. It has been shown earlier that no fully distributed implementation that allows complete autonomy to Esterel nodes is possible. So any implementation has to weaken one of these assumptions. Here we have proposed an implementation of CRP by weakening the assumption of complete autonomy of Esterel nodes. A detailed description of this solution along with a formal proof of correctness has been given in the paper.

Impossibility of Synchronization in the Presence of Preemption

This paper is concerned with implementation of Communicating Reactive Processes(CRP), a new paradigm unifying capabilities of synchronous and asynchronous approaches to parallel programming. Synchronous languages like Esterel, Statecharts have features like instantaneous broadcasts, logical concurrency and determinism. Asynchronous languages, like ADA and CSP, allow physical concurrency and rendezvous communication mechanisms. CRP is designed for complex real-time process control applications requiring both forms of concurrency. CRP programs can be compiled into reactive nodes that communicate using rendezvous mechanism. Implementation of rendezvous is non trivial as the following constraints are to be satisfied: 1) mutual agreement over selection of a rendezvous required between the concerned processes, 2) the implementation has to be distributed with no single process knowing instantaneously global state. This problem has been solved for Hoare's CSP, but none of these solutions can be extended to CRP. The reason is that in CRP, an enabled rendezvous can be preempted by a local reaction. In this paper, we establish that there can not exist fully distributed implementation of CRP that allows complete autonomy to reactive nodes.

A rendezvous with Linda

The Ada 9X revision found the rendezvous mechanism too complex to implement as the communication mechanism in a distributed system. In this paper another distributed programming model, Linda, is related to the rendezvous mechanism. Linda can be used to allow tasks to communicate in a rendezvous like manner. Sequences of Linda operations that roughly corresponds to different rendezvous operations are given and a small extension of Linda is presented in order to handle more of the rendezvous constructs. Linda can be used to communicate across partitions as well as within partitions.

Dynamic models of parallel computations for macropipelined programs

We have considered dynamic models of parallel computations and transformation algorithms for macropipelined programs that increase the internal exchange asynchronism of the parallel components. The models generalize the well-known CSP synchronous exchange paradigm (the rendezvous mechanism) [18] and provide a theoretical justification for the development of a whole range of interconnected semantic models of asynchronous computation with increasing degree of exchange asynchronism. Some publications ensure asynchronous exchange only by buffering [15, 16]. The dynamic model approach developed in this study combines buffering and analysis of data dependences of the exchange operators. It not only reduces losses associated with synchronization of communicating parallel processes, but also ensures automatic resolution of some classes of data exchange deadlocks. Experience with dynamic models as a means of increasing the efficiency of macropipelined programs and multilevel memory in multiprocessor systems [12, 17] can be applied in other programming systems and parallel program design systems of both compiling (S1, S2) and interpreting (S3) type.

An algorithm for speculative parallel execution of rendezvous-synchronized simulation

This paper presents an approach for speculative parallel execution of rendezvous-synchronized simulations. Rendezvous-synchronized simulation is based on the notions of processes and gates and on the rendezvous mechanism defined in the basic process algebra of LOTOS—a standard formal specification language for temporal ordering [2] . Time is introduced via a mechanism similar to the delay behaviour annotation provided by the TOPO toolset [4-6] . The algorithm allows speculative gate activations. This increases the available parallelism while ensuring correct execution of the computation. The model is used to describe closed stochastic queueing network simulations. Analysis of their execution results suggests that the model makes available a promising degree of parallelism.

Inside a trader in global trading

As defined by the APM 1, a trader provides a ‘rendezvous mechanism for dynamic binding of clients to some well-known or published services’. Information becomes more involved and inaccessible between clients and servers when the environment grows into a very large-scale networked community. The functions to manage the dynamics of trading become so sophisticated and complicated compared to the simple client/ server concept that they require some special system module to provide such services to both the clients and servers. Standard trading policy also must be established to enable diverse clients and servers to participate in this general trading facility. This paper discusses the increasing prominence of traders and the different stages of growth of the environment in which the traders perform. It examines various standards related to trading. It provides a practicable technical approach, and suggests an implementable architecture leading to the development of a standard-compliant trader that can perform at various stages as the environment matures.

Logically instantaneous message passing in asynchronous distributed systems

Asynchrony (due to unknown message transmission delay) complicates the design of protocols for distributed systems. To simplify the protocol design task therefore, the authors propose an interprocess (point-to-point) communication mechanism that has the characteristic of instantaneous message passing. They first establish a hierarchy among synchronization properties, which shows that to ensure the logically instantaneous message passing property it is not always necessary to use a rendezvous mechanism. Next, they propose a solution to the logically instantaneous message passing problem that is more efficient than R. Bagrodia's (1989) rendezvous and K.J. Goldman's (1991) logically synchronous multicast in the point-to-point (single-cast) setting. This algorithm has the following properties: it is applicable without deadlock to the partner model in which each process acts as both client and server; it requires three control messages to send an application message, which is shown to be quasioptimum message complexity; and its worst-case response time from a send request to the occurrence of the corresponding send event is 2k/spl Delta/ (sec.), where k is the maximum number of interfering send requests and /spl Delta/ (sec.) is an assumed upper bound on interprocess communication delay. Furthermore, two modified algorithms are proposed: one for reducing the number of control messages required for an application message, and the other for attaining a shorter average response time by using a randomization technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rapid prototyping of protocols from LOTOS specifications

AbstractA new tool for generating implementation prototypes of communication protocols and concurrent systems specified using the ISO LOTOS language is presented in this paper. A brief introduction to LOTOS and a discussion of the main problems related to the efficient execution of specifications written in LOTOS are presented first. The design and implementation of the tool are then considered: LOTOS specifications are analysed and translated into C functions which are executed by co‐operating processes in the Unix environment. The set of LOTOS process definitions is first translated into a suitable number of extended finite‐state machines (EFSMs). The method proposed allows the problem of deriving unbounded EFSMs to be circumvented and a sort of control on the process number/size trade‐off to be obtained at the same time.The problem of implementing the LOTOS multi‐way rendezvous mechanism for process synchronization is solved by using an algorithm based on message‐passing techniques. An example of prototype derivation is also described, showing the form of C code generated by translating a simple specification. Finally, some performance figures are presented.

ESTIM: an integrated environment for the simulation and verification of OSI protocols specified in Estelle

Abstract Formal Description Techniques (FDTs) are an efficient support for protocol engineering, as they permit early detection of design errors through a validation of the protocol formal specification against the expected service. This paper describes the use and design of ESTIM, a tool for the validation of protocols specified using the Estelle∗ FDT which enhances ISO Estelle with a powerful rendezvous mechanism. The original point is that ESTIM combines interactive simulation functionalities for a first debugging level together with a verification approach that allows the automaton characterizing the service provided by a protocol to be derived automatically, starting from the formal specification of that protocol in Estelle∗. The ESTIM tool was prototyped in Standard ML to implement Estelle semantics. It is currently available on SUN Sparc workstations and has successfully been applied to several non-trivial protocols.

A protocol for multirendezvous of LOTOS processes

It is noted that the implementation of the multiway rendezvous mechanism of the International Standards Organization (ISO) LOTOS specification language for protocols is very important in the development of tools for the execution of LOTOS. It involves problems such as global knowledge in a distributed environment and distributed agreement. The authors propose a novel algorithm which fully implements the multiway rendezvous of LOTOS within a distributed execution model based on a number of parallel processes. The processes are organized in a hierarchical topology and communicate with each other only by message transfers. The performance of the proposed algorithm is evaluated and is shown to be better than that achieved by other algorithms proposed in the literature. A formal specification of the algorithm in LOTOS is provided. >

Comments on "Critical races in Ada programs

Comments are made on the above named work by G.M. Karam, C.M. Stanczyk, and G.W. Bond (see ibid., vol.15, no.11, p.1471-80, 1989), in which the semantics of the Ada rendezvous mechanism are discussed in terms of the critical race problem and a method is proposed for designing critical race-free programs. It is noted that this problem has been well described and numerous solutions have been presented in the literature during the past ten years (1980-90).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Inter-processor communication and Ada in distributed real-time systems

This paper describes inter-processor communication schemes that can be used for real-time distributed systems implemented in Ada. A general discussion is included for low-level communication primitives, message passing, and remote procedure calls (RPC). The Ada rendezvous mechanism for task communication and synchronization is examined with regard to local and remote information exchange. A detailed treatment is included for the implementation of an RPC mechanism in Ada. The design is illustrated with Ada code examples.