Modeling and analysis of temporal constraints in communication protocols

Reachability analysis is the most popular and the most used method in protocol validation. It consists in constructing a graph called reachability graph, describing the communication of communicating machines exchanging messages through fifa channels. The states and structure of this graph are then analysed according to given properties to validate the corresponding communication protocol. In this paper, we go from the communicating machines used in the classical reachability analysis, to design temporal communicating machines allowing to specify quantitative temporal aspects of communication protocols. A temporal reachability graph describing the global behaviour of temporal communicating machines is then defined. After that, we show how this graph can be used to analyse general properties of communication protocols submitted to temporal constraints and we establish several complexity results dealing with this approach.     

Deadlock detection in communicating finite state machines by even reachability analysis

A network of communicating finite state machines (CFSM) consists of a set of finite state machines which communicate asynchronously with each other over (potentially) unbounded FIFO channels by sending and receiving typed messages. As a concurrency model, CFSMs has been widely used to specify and validate communications protocols. CFSMs is also powerful and suitable for modeling mobile communication systems – a CFSM can naturally model a mobile station in a wireless communication system. The unbounded FIFO channels are ideal for modeling the communication behavior among mobile stations. Fair reachability is a very useful technique in detecting errors of deadlocks and unspecified receptions in networks of (CFSMs) consisting of two machines. The paper extends the classical fair reachability technique, which is only applicable to the class of two-machine CFSMs, to the general class of CFSMs. For bounded CFSMs, the extended fair reachability technique reduces by more than one half the total number of reachable global states that have to be searched in verifying freedom from deadlocks. The usefulness of the new reachability technique, called even reachability, is demonstrated through two examples. This revised version was published online in June 2006 with corrections to the Cover Date.     

Lossy Communicating Finite State Machines

A network of communicating finite state machines (CFSM) consists of a set of finite state machines that communicate asynchronously with each other over (potentially) unbounded FIFO channels by sending and receiving typed messages. As a concurrency model, CFSMs has been widely used to specify and validate communications protocols. In this paper we propose to extend the classical CFSM model by introducing a new type of actions – the deletion action. The resulted model is called lossy communicating finite state machines (LCFSMs). The LCFSM model remedies two weaknesses in classical CFSM model. We show that the LCFSM model allows specification and verification of unreliable communication channels with no need of extra CFSMs. The LCFSM model enables more succinct specification and verification of communication protocols that use unreliable communication channels. LCFSM paradigm can also be used to concisely model communication errors such as dropping datagrams in UDP due to lack of local buffers.     

一个基于知识的通信有限状态机生成器

通信有限状态机(CFSM)是一种直观、易懂且描述能力较强的形式描述工具。它被广泛地用来描述通信协议等。但是,由于描述对象的复杂性和缺少适当的支援工具,通信有限状态机的生成一般依靠手工完成。这除了效率低外,也使得所产生的CFSM的性能取决于描述人员的习惯、经验、能力等。本文描述一个基于知识的CFSM半自动生成器。该生成器用专家系统开发语言OPS83构成,能交互地生成两个不含常见逻辑错误的互相传递消息的CFSM。另外,该生成器还以友好的用户接口:(图形、颜色、文字等方式)向用户展示CFSM的生成过程和生成结果。     

Modeling robust asynchronous communication protocols withfinite-state machines

A.V. Aho et al. (Comput. Math. Applic., vol.8, p.205-14, 1982) used communicating finite-state machines to model synchronous protocols for reliable communication across unreliable channels. Their ideas are extended to modeling asynchronous protocols for communication across unreliable channels using finite-state machines communicating via an unreliable shared memory. Lower bounds on the size of machines and the number of symbols in the transmission alphabet required to achieve reliable communication are established. Two types of finite-state machines and two fault models for the shared memory are considered. In each case it is shown that there are robust protocols for deletion and insertion errors. It is also shown that there are no robust protocols for mutation errors. In contrast, in the synchronous case, robust protocols exist for all of these types of errors     

Distributed multimedia and QOS: a survey

Quality of service (QOS) is increasingly important for all components within distributed multimedia systems, as this survey reveals. We discuss the QOS parameters found in communication protocols, operating systems, multimedia databases and file servers, as well as those directly affecting the human user     

Applying generic timing tests for distributed multimedia software systems

With recent advances in network technologies and computing power, multimedia systems have become a popular means for information delivery. However, testing of these systems is difficult. Due to incomplete control of their runtime and communication environment, precise temporal properties of multimedia systems are nonreproducible. Traditional software testing, which mainly deals with functional correctness, cannot be directly applied to testing temporal properties. Furthermore, time points are hard to be measured exactly, and in this sense are nondeterministic and nonreproducible. To address this problem, we propose a framework for testing the generic temporal properties of media objects in distributed multimedia software systems (DMSS). The timing properties are based on Allen's basic binary temporal relations between two objects, which can be extended to cover multiple objects. We have developed techniques for test case generation, and test result analysis based on a distributed tester architecture. Test templates are used in test case generation to reduce the possibility of human error, and the entire testing procedure can be automated. A prototype system has been built to test a DEC HPAS multimedia presentation system, which is a multimedia system supporting W3C's SMIL standard. Detailed discussions on practical issues illustrated with a number of actual tests are given. Experimental results have shown that our framework is effective in detecting errors in temporal properties. Furthermore, ways to reduce the test effort have been discussed, and guidelines for coming up with criteria for verdict computation based on the real-time requirements of the applications have been suggested.     

Multimedia communication

Multimedia communication deals with the transfer, protocols, services, and mechanisms of discrete media data (such as text and graphics) and continuous media data (like audio and video) in/over digital networks. Such a communication requires all involved components to be capable of handling a well-defined quality of service (QoS). The most important QoS parameters are used to request: (1) the required capacities of the involved resources, (2) compliance to end-to-end delay and jitter as timing restrictions, and (3) restriction of the loss characteristics. In this paper, we describe the necessary issues and study the ability of current networks and communication systems to support distributed multimedia applications. Further, we discuss upcoming approaches and systems that promise to provide the necessary mechanisms and consider which issues are missing for a complete multimedia communication infrastructure     

A QoS Routing Protocol with Bandwidth Allocation in Multichannel Ad Hoc Networks

Mobile multimedia applications have recently generated much interest in mobile ad hoc networks (MANETs) supporting quality-of-service (QoS) communications. Multiple non-interfering channels are available in 802.11 and 802.15 based wireless networks. Capacity of such channels can be combined to achieve higher QoS performance than for single channel networks. The capacity of MANETs can be substantially increased by equipping each network node with multiple interfaces that can operate on multiple non-overlapping channels. However, new scheduling, channel assignment, and routing protocols are required to utilize the increased bandwidth in multichannel MANETs. In this paper, we propose an on-demand routing protocol M-QoS-AODV in multichannel MANETs that incorporates a distributed channel assignment scheme and routing discovery process to support multimedia communication and to satisfy QoS bandwidth requirement. The proposed channel assignment scheme can efficiently express the channel usage and interference information within a certain range, which reduces interference and enhances channel reuse rate. This cross-layer design approach can significantly improve the performance of multichannel MANETs over existing routing algorithms. Simulation results show that the proposed M-QoS-AODV protocol can effectively increase throughput and reduce delay, as compared to AODV and M-AODV-R protocols.     

An architecture for real-time multimedia communication systems

A multimedia communication system includes both the communication protocols used to transport the real-time data and the distributed computing system (DCS) within which any applications using the protocols must execute. The architecture presented attempts to integrate these communications protocols with the DCS in a smooth fashion in order to ease the writing of multimedia applications. Two issues are identified as being essential to the success of this integration: the synchronization of related real-time data streams, and the management of heterogeneous multimedia hardware. The synchronization problem is tackled by defining explicit synchronization properties at the presentation level and by providing control and synchronization operations within the DCS which operate in terms of these properties. The heterogeneity problems are addressed by separating the data transport semantics (protocols themselves) from the control semantics (protocol interfaces)     

Random access protocols for high-speed interprocessor communicationbased on an optical passive star topology

A multiple-instruction multiple-data (MIMD) distributed memory parallel computer system environment is considered. Media access control protocols that maintain good performance with high capacity optical channels are investigated. Three examples of star-coupled structures are introduced, one of which exhibits optical self-routing. Self-routing single-step optically interconnected communication structures can be designed through the incorporation of agile laser diode sources and wavelength tunable optical filters in a wavelength-division multiple-access environment. Intermediary latencies typical of MIMD distributed memory systems are eliminated. The degree and diameter of the resulting structures are dramatically reduced, and the complexity of the communication subsystem is reduced since intermediate buffering and routing of packets are eliminated     

Temporal Partitioning Data Flow Graphs for Dynamically Reconfigurable Computing

FPGA-based configurable computing machines are evolving rapidly in large signal processing applications due to flexibility and high performance. In this paper, given a reconfigurable processing unit (RPU) with a logic capacity of A_RPU and a computational task represented by a data flow graph G = (V, E, W), we propose a network flow-based multiway task partitioning algorithm to minimize communication costs for temporal partitioning. The proposed algorithm obtains an optimal solution with minimum interconnection under area constraints. The optimal solution is a cut set. In our approach, two techniques are applied. In the initial partition, any feasible min-cut is produced by the proposed network flow-based algorithm, so a set of feasible min-cuts is obtained. From the feasible solutions, the scheduling technique selects an optimal global solution.     

Quality-based evaluation of multimedia synchronization protocolsfor distributed multimedia information systems

Distributed, networked multimedia information systems will be a critical component of technology-based information infrastructures in the future. We present an infrastructure for supporting multimedia applications. We discuss various characteristics of multimedia data and the effect of the network on the required quality of presentation for multimedia data. We present a suite of synchronization protocols to support the quality of presentation. The crux of these protocols is the scheduling of multimedia information for synchronized delivery, over broadband networks with limited resources, and is identified as an NP-hard problem. We introduce two parameters which can be used to measure the performance of end-to-end synchronization protocols in a network supporting distributed multimedia applications. We propose and implement several heuristic scheduling algorithms, and compare their performance. We deduce the appropriateness of these algorithms in different types of distributed multimedia environments     

多媒体中的几个关键技术

本文概要地分析介绍了多媒体技术中若干关键技术，包括多媒体信息系统模型，多媒体信息融合理论和实现，多媒体信息的表示，多媒体通信有关的实现方案，多媒体系统的服务质量要求。这些问题的探讨及解决，在极大程度上影响着多媒体系统的性能提高，甚至影响着新一代多媒体信息处理的发展方向。     

Wireless multimedia sensor networks: A survey

In recent years, the growing interest in the wireless sensor network (WSN) has resulted in thousands of peer-reviewed publications. Most of this research is concerned with scalar sensor networks that measure physical phenomena, such as temperature, pressure, humidity, or location of objects that can be conveyed through low-bandwidth and delay-tolerant data streams. Recently, the focus is shifting toward research aimed at revisiting the sensor network paradigm to enable delivery of multimedia content, such as audio and video streams and still images, as well as scalar data. This effort will result in distributed, networked systems, referred to in this paper as wireless multimedia sensor networks (WMSNs). This article discusses the state of the art and the major research challenges in architectures, algorithms, and protocols for wireless multimedia sensor networks. Existing solutions at the physical, link, network, transport, and application layers of the communication protocol stack are investigated. Finally, fundamental open research issues are discussed, and future research trends in this area are outlined.     

A generic platform for scalable access to multimedia-on-demandsystems

Access to multimedia servers is commonly done according to a client/server model where the end user at the client host retrieves multimedia objects from a multimedia server. In a distributed environment, a number of end users may need to access a number of multimedia servers through one or several communication networks. Such a scenario reveals the requirement for a distributed access platform. In addition, the demand for multimedia information is increasing beyond the capabilities of high performance storage devices. Therefore, load distribution and scalability issues must be addressed while designing and implementing the distributed access platform. This paper introduces a scalable access platform (SAP) for managing user access to multimedia-on-demand systems while optimizing resource utilization. The platform is generic and capable of integrating heterogeneous multimedia servers. SAP operation combines static replication and dynamic load distribution policies. It provides run time redirecting of client requests to multimedia servers according to the workload information dynamically collected in the system. To support multimedia-on-demand systems with differing quality-of-service (QoS) requirements, the platform also takes into account, as part of the access process, user QoS requirements and cost constraints. This paper also presents an application of the generic platform implementing a scalable movie-on-demand system, called SMoD. Performance evaluation based on simulation shows that in many cases SMoD can reduce the blocking probability of user requests, and thus can support more users than classical video-on-demand (VoD) systems. It also shows that the load is better distributed across the video servers of the system     

Towards a new generation of transport services adapted to multimedia applications

A partial order and partial reliable connection (POC) is an end-to-end transport connection authorized to deliver objects in an order that can differ from the transmitted one. The service provided by such a connection is also authorized to lose some objects in a controlled manner. The POC approach establishes a conceptual link between connectionless best-effort (CL) and connection-oriented reliable (co) protocols. POC is motivated by heterogeneous CL networks such as Internet which are plagued by unordered delivery of packets and losses, which in turn tax the performances of current protocols. Moreover, it has been shown, that out of order delivery is able to economize the use of network resources such as memory and bandwidth, and reduces end-to-end transit delay. To take advantage of POC’S benefits, applications must be able to relax some transport constraints. In this paper a temporal extension of POC, called TPOC (for temporal POC), is introduced. TPOC offers a conceptual framework, which allows the Qos of distributed multimedia applications to be taken into account. The architecture for offering a TPOC transport service is introduced and evaluated for the transport of MPEG video streams. We demonstrate that POC connections fill not only the conceptual gap between CL protocols (such as UDP) and CO protocols (such as TCP) but also provides demonstrable performances improvements for the transport of multimedia streams such as MPEG video.     

The time-triggered architecture

The time-triggered architecture (TTA) provides a computing infrastructure for the design and implementation of dependable distributed embedded systems. A large real-time application is decomposed into nearly autonomous clusters and nodes, and a fault-tolerant global time base of known precision is generated at every node. In the TTA, this global time is used to precisely specify the interfaces among the nodes, to simplify the communication and agreement protocols, to perform prompt error detection, and to guarantee the timeliness of real-time applications. The TTA supports a two-phased design methodology, architecture design, and component design. During the architecture design phase, the interactions among the distributed components and the interfaces of the components are fully specified in the value domain and in the temporal domain. In the succeeding component implementation phase, the components are built, taking these interface specifications as constraints. This two-phased design methodology is a prerequisite for the composability of applications implemented in the TTA and for the reuse of prevalidated components within the TTA. This paper presents the architecture model of the TTA, explains the design rationale, discusses the time-triggered communication protocols TTP/C and TTP/A, and illustrates how transparent fault tolerance can be implemented in the TTA.     

W-CDMA无线多媒体通信系统设计考虑

为了研究和开发第三代移动通信系统,进行Ｗ－ＣＤＭＡ 无线多媒体通信系统和技术的研究十分必要。针对我们个人通信与扩频实验室正在研究开发国家８６３ 高技术通信主题Ｗ－ＣＤＭＡ无线多媒体通信技术的实验系统,我们提出了Ｗ－ＣＤＭＡ无线多媒体通信系统的系统结构,系统信道配置和功能安排,Ｗ－ＣＤＭＡ通信方式,分析了信号调制解调的性能,提出信号功率控制方法。     

On "A Simple Protocol Whose Proof Isńt": The State Machine Approach

We discuss how to model a synchronous protocol (due to Aho, Ullman, and Yannakakis) using communicating finite state machines, and present a proof for its safety and liveness properties. Our proof is based on constructing a labeled finite reachability graph for the protocol. This reachability graph can be viewed as a sequential program whose safety and liveness properties can be stated and verified in a straightforward fashion.