Framework For Real-time Communication Research Articles

A Framework for Real Time Communication on Web using with WebRTC

A Framework for Real Time Communication on Web using with WebRTC

The Ach Library: A New Framework for Real-Time Communication

Correct real-time software is vital for robots in safety-critical roles such as service and disaster response. These systems depend on software for locomotion, navigation, manipulation, and even seemingly innocuous tasks such as safely regulating battery voltage. A multiprocess software design increases robustness by isolating errors to a single process, allowing the rest of the system to continue operation. This approach also assists with modularity and concurrency. For real-time tasks, such as dynamic balance and force control of manipulators, it is critical to communicate the latest data sample with minimum latency. There are many communication approaches intended for both general-purpose and real-time needs [9], [13], [15], [17], [19]. Typical methods focus on reliable communication or network transparency and accept a tradeoff of increased message latency or the potential to discard newer data. By focusing instead on the specific case of real-time communication on a single host, we reduce communication latency and guarantee access to the latest sample. We present a new interprocess communication (IPC) library, Ach which addresses this need, and discuss its application for real-time multiprocess control on three humanoid robots (Figure 1). (Ach is available at http://www.golems.org/projects/ach.html. The name Ach comes from the common abbreviation for the motor neurotransmitter Acetylcholine and the computer networking term ACK.)

Queueing systems with hard delay constraints: a framework for real-time communication over unreliable wireless channels

We provide an account of recent work that formulates and addresses problems that arise when employing wireless networks to serve clients that generate real-time flows. From a queueing systems perspective, these problems can be described as single-server problems where there are several customer classes. Customers balk when their delay exceeds a threshold. There are a range of issues that are of interest. One of the first such issues is to determine what throughput rate vectors are feasible, and to determine the server's schedule. Another is to maximize a utility function of the departure rates of the customer classes. Real-time flows have a delay bound for each of their packets. It is particularly challenging to provide delay guarantees for real-time flows in wireless networks since wireless transmissions are unreliable. We propose a model that jointly considers the delay bounds of packets, the unreliable wireless channels, and the throughput requirements of clients. We then determine the necessary and sufficient condition for feasibility of the client requirements. The analysis and condition are interesting since this problem gives rise to some new features concerning unavoidable idle times in a system. We further derive an efficient, nearly linear time algorithm for admission control, which precisely determines whether it is feasible to fulfill the requirements of all clients in the system. We also propose two on-line scheduling policies and prove that they can fulfill the requirements of all clients whenever that is feasible. We next turn to the scenario where the throughput requirements of clients are elastic, but with hard delay bounds. We formulate this as a utility maximization problem, where client utilities are based on their throughputs. We decompose this problem into two subproblems, and show that this decomposition can be naturally implemented as a bidding game among all clients and the access point, which plays the role of a centralized scheduler. In the bidding game, the strategy of each client is to carry out a simple selfish optimization. We show that the strategy of the access point can be implemented by a simple on-line scheduling policy. A surprising result is that the channel reliabilities need not be known a priori.

Survey of Real-Time Communication in CSMA-Based Networks

The purpose of this paper is to survey the state-of-the-art on real-time (RT) communication in CSMA-based networks and to identify the most suitable approaches to deal with the requirements imposed by next generation communication environments. A special emphasis is given to wired and wireless networks that operate in shared broadcast environments, according to the CSMA medium access protocol. RT communication solutions are classified according to two classification axes. The first axis is related to how collision are dealt with. A second classification axis is related to the compatibility degree achieved by each of the proposed approaches. Finally, a RT communication framework that is adequate to support RT communication in shared environments is briefly discussed.