Showing papers on "Asynchronous communication published in 1996"

Distributed algorithms

Abstract: In Distributed Algorithms, Nancy Lynch provides a blueprint for designing, implementing, and analyzing distributed algorithms. She directs her book at a wide audience, including students, programmers, system designers, and researchers. Distributed Algorithms contains the most significant algorithms and impossibility results in the area, all in a simple automata-theoretic setting. The algorithms are proved correct, and their complexity is analyzed according to precisely defined complexity measures. The problems covered include resource allocation, communication, consensus among distributed processes, data consistency, deadlock detection, leader election, global snapshots, and many others. The material is organized according to the system model-first by the timing model and then by the interprocess communication mechanism. The material on system models is isolated in separate chapters for easy reference. The presentation is completely rigorous, yet is intuitive enough for immediate comprehension. This book familiarizes readers with important problems, algorithms, and impossibility results in the area: readers can then recognize the problems when they arise in practice, apply the algorithms to solve them, and use the impossibility results to determine whether problems are unsolvable. The book also provides readers with the basic mathematical tools for designing new algorithms and proving new impossibility results. In addition, it teaches readers how to reason carefully about distributed algorithms-to model them formally, devise precise specifications for their required behavior, prove their correctness, and evaluate their performance with realistic measures. Table of Contents 1 Introduction 2 Modelling I; Synchronous Network Model 3 Leader Election in a Synchronous Ring 4 Algorithms in General Synchronous Networks 5 Distributed Consensus with Link Failures 6 Distributed Consensus with Process Failures 7 More Consensus Problems 8 Modelling II: Asynchronous System Model 9 Modelling III: Asynchronous Shared Memory Model 10 Mutual Exclusion 11 Resource Allocation 12 Consensus 13 Atomic Objects 14 Modelling IV: Asynchronous Network Model 15 Basic Asynchronous Network Algorithms 16 Synchronizers 17 Shared Memory versus Networks 18 Logical Time 19 Global Snapshots and Stable Properties 20 Network Resource Allocation 21 Asynchronous Networks with Process Failures 22 Data Link Protocols 23 Partially Synchronous System Models 24 Mutual Exclusion with Partial Synchrony 25 Consensus with Partial Synchrony

Computer Networks as Social Networks: Collaborative Work, Telework, and Virtual Community

Abstract: When computer networks link people as well as machines, they become social networks. Such computer-supported social networks (CSSNs) are becoming important bases of virtual communities, computer-supported cooperative work, and telework. Computer-mediated communication such as electronic mail and computerized conferencing is usually text-based and asynchronous. It has limited social presence, and on-line communications are often more uninhibited, creative, and blunt than in-person communication. Nevertheless, CSSNs sustain strong, intermediate, and weak ties that provide information and social support in both specialized and broadly based relationships. CSSNs foster virtual communities that are usually partial and narrowly focused, although some do become encompassing and broadly based. CSSNs accomplish a wide variety of cooperative work, connecting workers within and between organizations who are often physically dispersed. CSSNs also link teleworkers from their homes or remote work centers to main organi...

The weakest failure detector for solving consensus

Abstract: We determine what information about failures is necessary and sufficient to solve Consensus in asynchronous distributed systems subject to crash failures. In Chandra and Toueg [1996], it is shown that W, a failure detector that provides surprisingly little information about which processes have crashed, is sufficient to solve Consensus in asynchronous systems with a majority of correct processes. In this paper, we prove that to solve Consensus, any failure detector has to provide at least as much information as W. Thus, W is indeed the weakest failure detector for solving Consensus in asynchronous systems with a majority of correct processes.

Multimedia collaboration system with separate data network and A/V network controlled by information transmitting on the data network

Abstract: A multimedia collaboration system that integrates separate real-time and asynchronous networks--the former for real-time audio and video, and the latter for control signals and textual, graphical and other data--in a manner that is interoperable across different computer and network operating system platforms and which closely approximates the experience of face-to-face collaboration, while liberating the participants from the limitations of time and distance. These capabilities are achieved by exploiting a variety of hardware, software and networking technologies in a manner that preserves the quality and integrity of audio/video/data and other multimedia information, even after wide area transmission, and at a significantly reduced networking cost as compared to what would be required by presently known approaches. The system architecture is readily scalable to the largest enterprise network environments. It accommodates differing levels of collaborative capabilities available to individual users and permits high-quality audio and video capabilities to be readily superimposed onto existing personal computers and workstations and their interconnecting LANs and WANs. In a particular preferred embodiment, a plurality of geographically dispersed multimedia LANs are interconnected by a WAN. The demands made on the WAN are significantly reduced by employing multi-hopping techniques, including dynamically avoiding the unnecessary decompression of data at intermediate hops, and exploiting video mosaicing, cut-and-paste and audio mixing technologies so that significantly fewer wide area transmission paths are required while maintaining the high quality of the transmitted audio/video.

Call control in video conferencing allowing acceptance and identification of participants in a new incoming call during an active teleconference

Abstract: A multimedia collaboration system that integrates separate real-time and asynchronous networks--the former for real-time audio and video, and the latter for control signals and textual, graphical and other data--in a manner that is interoperable across different computer and network operating system platforms and which closely approximates the experience of face-to-face collaboration, while liberating the participants from the limitations of time and distance. These capabilities are achieved by exploiting a variety of hardware, software and networking technologies in a manner that preserves the quality and integrity of audio/video/data and other multimedia information, even after wide area transmission, and at a significantly reduced networking cost as compared to what would be required by presently known approaches. The system architecture is readily scalable to the largest enterprise network environments. It accommodates differing levels of collaborative capabilities available to individual users and permits high-quality audio and video capabilities to be readily superimposed onto existing personal computers and workstations and their interconnecting LANs and WANs. In a particular preferred embodiment, a plurality of geographically dispersed multimedia LANs are interconnected by a WAN. The demands made on the WAN are significantly reduced by employing multi-hopping techniques, including dynamically avoiding the unnecessary decompression of data at intermediate hops, and exploiting video mosaicing, cut-and-paste and audio mixing technologies so that significantly fewer wide area transmission paths are required while maintaining the high quality of the transmitted audio/video.

Propagation delay estimation in asynchronous direct-sequence code-division multiple access systems

Abstract: In an asynchronous direct-sequence code-division multiple access (DS-CDMA) communication system, the parameter estimation problem, i.e., estimating the propagation delay, attenuation and phase shift of each user's transmitted signal, may be complicated by the so-called near-far problem. The near-far problem occurs when the amplitudes of the users received signals are very dissimilar, as the case might be in many important applications. In particular, the standard method for estimating the propagation delays will fail in a near-far situation. Several new estimators, the maximum likelihood, an approximative maximum likelihood and a subspace-based estimator, are therefore proposed and are shown to be robust against the near-far problem. No knowledge of the transmitted bits is assumed, and the proposed estimators can thus be used for both acquisition and tracking. In addition, the Cramer-Rao bound is derived for the parameter estimation problem.

Reactive modules

Abstract: We present a formal model for concurrent systems. The model represents synchronous and asynchronous components in a uniform framework that supports compositional (assume-guarantee) and hierarchical (stepwise refinement) reasoning. While synchronous models are based on a notion of atomic computation step, and asynchronous models remove that notion by introducing stuttering, our model is based on a flexible notion of what constitutes a computation step: by applying an abstraction operator to a system, arbitrarily many consecutive steps can be collapsed into a single step. The abstraction operator, which may turn an asynchronous system into a synchronous one, allows us to describe systems at various levels of temporal detail. For describing systems at various levels of spatial detail, we use a hiding operator that may turn a synchronous system into an asynchronous one. We illustrate the model with diverse examples from synchronous circuits, asynchronous shared-memory programs, and synchronous message passing.

System for teleconferencing in which collaboration types and participants by names or icons are selected by a participant of the teleconference

Abstract: A multimedia collaboration system that integrates separate real-time and asynchronous networks--the former for real-time audio and video, and the latter for control signals and textual, graphical and other data--in a manner that is interoperable across different computer and network operating system platforms and which closely approximates the experience of face-to-face collaboration, while liberating the participants from the limitations of time and distance. These capabilities are achieved by exploiting a variety of hardware, software and networking technologies in a manner that preserves the quality and integrity of audio/video/data and other multimedia information, even after wide area transmission, and at a significantly reduced networking cost as compared to what would be required by presently known approaches. The system architecture is readily scalable to the largest enterprise network environments. It accommodates differing levels of collaborative capabilities available to individual users and permits high-quality audio and video capabilities to be readily superimposed onto existing personal computers and workstations and their interconnecting LANs and WANs. In a particular preferred embodiment, a plurality of geographically dispersed multimedia LANs are interconnected by a WAN. The demands made on the WAN are significantly reduced by employing multi-hopping techniques, including dynamically avoiding the unnecessary decompression of data at intermediate hops, and exploiting video mosaicing, cut-and-paste and audio mixing technologies so that significantly fewer wide area transmission paths are required while maintaining the high quality of the transmitted audio/video.

On the impossibility of group membership

Abstract: We prove that the primary-partition group membership problem cannot be solved in asynchronous systems with crash failures, even if one allows the removal or killing of non-faulty processes that are erroneously suspected to have crashed.

System for providing a directory of AV devices and capabilities and call processing such that each participant participates to the extent of capabilities available

Abstract: A multimedia collaboration system that integrates separate real-time and asynchronous networks--the former for real-time audio and video, and the latter for control signals and textual, graphical and other data--in a manner that is interoperable across different computer and network operating system platforms and which closely approximates the experience of face-to-face collaboration, while liberating the participants from the limitations of time and distance. These capabilities are achieved by exploiting a variety of hardware, software and networking technologies in a manner that preserves the quality and integrity of audio/video/data and other multimedia information, even after wide area transmission, and at a significantly reduced networking cost as compared to what would be required by presently known approaches. The system architecture is readily scalable to the largest enterprise network environments. It accommodates differing levels of collaborative capabilities available to individual users and permits high-quality audio and video capabilities to be readily superimposed onto existing personal computers and workstations and their interconnecting LANs and WANs. In a particular preferred embodiment, a plurality of geographically dispersed multimedia LANs are interconnected by a WAN. The demands made on the WAN are significantly reduced by employing multi-hopping techniques, including dynamically avoiding the unnecessary decompression of data at intermediate hops, and exploiting video mosaicing, cut-and-paste and audio mixing technologies so that significantly fewer wide area transmission paths are required while maintaining the high quality of the transmitted audio/video.

Madefast: collaborative engineering over the Internet

Abstract: olitical, economic, and technological forces are changing the landscape of engineering. As the world’s economies become more interconnected and more competitive, there is an increasing need for organizations to form joint design and manufacturing teams that collaborate for the life of a project and then disperse. For example, a new electromechanical product may involve a mechanical design group in Boston working closely with a control systems subcontractor in California and an OEM partner in Singapore. Similar challenges face defense contractors who need to respond rapidly to new requirements. The ARPA Manufacturing Automation and Design Engineering (MADE) program has been developing Internet-based tools, services, protocols, and design methodologies that will allow contractors to compose teams of specialists from different locations and organizations as project needs arise. As a practical test of what the MADE program has achieved, members of the MADE community undertook an ambitious exercise in Madefast: Collaborative Engineering over the Internet

Bandwidth management processes and systems for asynchronous transfer mode networks using variable virtual paths

Abstract: A system comprises a first asynchronous transfer mode switch, a second asynchronous transfer mode switch, and a system control module. The first asynchronous transfer mode switch and the second asynchronous transfer mode switch are interconnected with one another via a physical interface. The first asynchronous transfer mode switch is in communication with the with the second asynchronous transfer mode switch via a virtual connection on the physical interface. The virtual connection has a corresponding bandwidth. The system control module is in communication with the first asynchronous transfer mode switch. The system control module is in communication with the second asynchronous transfer mode switch via the first asynchronous transfer mode switch and the physical interface. The system control module dynamically controls the corresponding bandwidth of the virtual connection over time. The system control module is centralized for the first asynchronous transfer mode switch and the second asynchronous transfer mode switch. The physical interface has a corresponding utilization level and further wherein the system control module periodicallly and continuouly checks the utilization level to determine what the corresponding bandwidth should be. A process comprises creating at least one virtual path extending from a first location to a second location through at least one asynchronous transfer mode switch for a customer in response to a customer request, selectively destroying at least one selected virtual channel of the at least one virtual channel of the virtual path as needed, checking each selected virtual channel of the at least one virtual channel that is created with the connection admission control module of each asynchronous transfer mode switch that the virtual path extend through to determine whether the selected virtual channel will fit in the virtual path, and checking the customer contract and the time of day to determine necessary adjustments.

Multimedia mail, conference recording and documents in video conferencing

Abstract: A multimedia collaboration system that integrates separate real-time and asynchronous networks--the former for real-time audio and video, and the latter for control signals and textual, graphical and other data--in a manner that is interoperable across different computer and network operating system platforms and which closely approximates the experience of face-to-face collaboration, while liberating the participants from the limitations of time and distance. These capabilities are achieved by exploiting a variety of hardware, software and networking technologies in a manner that preserves the quality and integrity of audio/video/data and other multimedia information, even after wide area transmission, and at a significantly reduced networking cost as compared to what would be required by presently known approaches. The system architecture is readily scalable to the largest enterprise network environments. It accommodates differing levels of collaborative capabilities available to individual users and permits high-quality audio and video capabilities to be readily superimposed onto existing personal computers and workstations and their interconnecting LANs and WANs. In a particular preferred embodiment, a plurality of geographically dispersed multimedia LANs are interconnected by a WAN. The demands made on the WAN are significantly reduced by employing multi-hopping techniques, including dynamically avoiding the unnecessary decompression of data at intermediate hops, and exploiting video mosaicing, cut-and-paste and audio mixing technologies so that significantly fewer wide area transmission paths are required while maintaining the high quality of the transmitted audio/video.

System and method for asynchronous store and forward data replication

Abstract: A system and method for asynchronous store and forward data replication is presented. The system and method utilizes one-way, unacknowledged communication messages between systems in a computer network to transfer locally modified data to other systems having a copy of the data. The asynchronous store and forward data replication system and method utilizes existing computer networks and/or network control software as a transport agent to deliver the communication messages. Utilization of one-way, unacknowledged communication messages allows data replication across foreign networks such as the Internet or other wide area networks.

Synchronization in video conferencing

Abstract: A multimedia collaboration system that integrates separate real-time and asynchronous networks--the former for real-time audio and video, and the latter for control signals and textual, graphical and other data--in a manner that is interoperable across different computer and network operating system platforms and which closely approximates the experience of face-to-face collaboration, while liberating the participants from the limitations of time and distance. These capabilities are achieved by exploiting a variety of hardware, software and networking technologies in a manner that preserves the quality and integrity of audio/video/data and other multimedia information, even after wide area transmission, and at a significantly reduced networking cost as compared to what would be required by presently known approaches. The system architecture is readily scalable to the largest enterprise network environments. It accommodates differing levels of collaborative capabilities available to individual users and permits high-quality audio and video capabilities to be readily superimposed onto existing personal computers and workstations and their interconnecting LANs and WANs. In a particular preferred embodiment, a plurality of geographically dispersed multimedia LANs are interconnected by a WAN. The demands made on the WAN are significantly reduced by employing multi-hopping techniques, including dynamically avoiding the unnecessary decompression of data at intermediate hops, and exploiting video mosaicing, cut-and-paste and audio mixing technologies so that significantly fewer wide area transmission paths are required while maintaining the high quality of the transmitted audio/video.

Asynchronous transfer of video

Abstract: Video transfers across IP and ATM networks have received much research attention during the last ten years. Various video services are expected in the future, enabled by the rapid development in video coding and broadband network technology. This article gives an introduction to the issues involved in asynchronous video transfers. Brief overviews of video coding, rate control, and multiplexing, as well as delay, error, and loss control are also given.

Communication system and method using asynchronous and isochronous spectrum for voice and data

Abstract: In a time division, multiple access system, a base station (102) transmits an isochronous beacon (404, 422) at the start of each frame (400), conveying control and timing information. Following the isochronous beacon (404), isochronous time slots (414, 416, 418, 420) are dynamically allocated for communication of isochronous data. After communication of the isochronous data, the remainder of the frame (400) before the next isochronous beacon (422) is used for transmission of packets of asynchronous data. This technique gives priority to the isochronous data, which is real time, while also maximizing the bandwidth allocated for asynchronous data. A single transmitter circuit (124, 158) and receiver circuit (122, 156) at each station are used for communication of both isochronous data and asynchronous data.

Design of a low-latency asynchronous adder using speculative completion

Abstract: A new general method for designing asynchronous datapath components, called speculative completion, is introduced. The method has many of the advantages of a bundled data approach, such as the use of single-rail synchronous datapaths, but it also allows early completion. As a case study, the method is applied to the high-performance parallel BLC adder design of Brent and Kung. Through careful gate-level analysis, performance improvements of up to 30% over a comparable synchronous implementation are expected.

Modeling logical and temporal synchronization in hypermedia systems

Abstract: The paper introduces a unified formal model for the complete and accurate specification of both temporal and logical (i.e., link) synchronization within hypermedia distributed and weakly synchronous systems. This new model extends time Petri nets with hierarchical design capabilities and new firing rules. These new firing rules enlighten the notion of hypermedia synchronization through powerful combinations of temporal and logical synchronization. Moreover, the proposed model offers an easy and concise modeling technique of asynchronous events in hypermedia systems.

Lock-free data structures

Abstract: Data structures which are shared among concurrent processes require some sort of synchronization in order to avoid becoming corrupted by conflicting updates and to ensure that the processes see correct results. This can be accomplished through mutual exclusion; guaranteeing a process exclusive access while performing critical operations on the data structure. While well understood, this approach can have detrimental effects on performance in an asynchronous environment where processes can suffer unpredictable delays. An alternative approach is to avoid the use of mutual exclusion through the use of simple synchronization primitives such as Compare-and-Swap. Such lock-free data structures can be immune from performance degradation due to slow processes. Universal methods for constructing lock-free data structures for any abstract data type are known, but the resulting implementations are much less efficient than using conventional techniques for mutual exclusion such as spin locks. In this thesis, we present lock-free data structures, algorithms, and memory management techniques for several common abstract data types. Our techniques result in implementations that are as efficient, if not more so, than conventional approaches, and thus provide a practical alternative to using spin locks. We demonstrate the efficiency of our techniques experimentally, and we also show how standard axiomatic formal proof methods can be adapted for the verification of our algorithms.

Optimal decorrelating receivers for DS-CDMA systems: a signal processing framework

Abstract: Code division multiple access (CDMA) schemes allow a number of asynchronous users to share a transmission medium with minimum cooperation among them. However, sophisticated signal processing algorithms are needed at the receiver to combat interference from other users and multipath effects. A discrete-time multirate formulation is introduced for asynchronous CDMA systems, which can incorporate multipath effects. This formulation reveals interesting links between CDMA receivers and array processing problems. In this framework, linear receivers are derived that can completely suppress multiuser interference (decorrelating receivers). A criterion is introduced, which guarantees the decorrelating property, while providing optimal solutions in the presence of noise. Parametric FIR designs as well as nonparametric solutions are delineated, and their performance is analyzed. The proposed receivers are resistant to near-far effects and do not require the estimation of the users' and noise powers.

Method and apparatus for asynchronous ppp and synchronous ppp conversion

Abstract: A data communication system referred to as an Asynchronous/Synchronous Converter (110) is provided to facilitate the communications between a data terminal equipment (DTE) (100) device using the asynchronous communication port, and a dial-up router located in a digital network. When running a dial-up TCP/IP program over the asynchronous port, DTEs (100) use a protocol called Asynchronous Point-to-Point Protocol (Asynchronous PPP). On the other hand, dial-up routers usually support Synchronous PPP. The data communication system of the invention connects the DTE (100) to the digital network and ultimately to the dial-up routers and provides two-way conversion between Asynchronous PPP and Synchronous PPP that is transparent to both the DTE (100) and the router. This two-way conversion is enabled in part by the converter intercepting and storing certain link control protocol (LCP) packets and using data in those packets to effect a translation.

Synchronous and asynchronous

Abstract: bounded responses with a certain probability. This article emphasized similarities between synchronous and asynchronous programming by discussing only strict agreement-the kind of asynchronous agreement closest to synchronous agreement. In reality, the field of asynchronous group communication is vaster-strict agreement being one extreme where all replicas agree, and group agreement the other where replicas managed by members of different parallel groups can disagree. In general, the stronger the agreement achieved by an asyn-chronous protocol, the easier it is to understand and use the protocol. The price is often higher message and time complexity. Conversely, the weaker the agreement provided by an asynchronous protocol, the more difficult it is to understand and use it. Protocols that achieve weak forms of agreement, such as group agreement (also called partitionable operation), may even require human intervention to solve the conflicts created by diverging replicas [22]. Group agreement protocols compensate for such user unfriendliness by providing lower message and time complexity and maximum update availability. The tradeoffs possible between synchronous and asyn-chronous programming, as well as the various possible asynchronous agreement semantics, are not very well understood at present. Work is needed to make these different programming paradigms understandable in a uni-tied framework. This article is intended as a contribution toward this goal. Q

Talking to strangers: an evaluation of the factors affecting electronic collaboration

Abstract: This empirical study examines factors influencing the success of a commercial groupware system in creating group archives and supporting asynchronous communication. The study investigates the use of Lotus Notesm in a workplace setting. We interviewed 21 Notes users and identified three factors that they thought contributed to the successful use of Notes databases for archiving and communication. We then tested the effect of these factors on 15,571 documents in 20 different databases. Contrary to our users’ beliefs, we found the presence of an active database moderator actually inhibited discussions, and reduced browsing. Further paradoxical results were that conversations and the creation of group archives were more successful in databases with large numbers of diverse participants. Conversations and archiving were less successful in smaller, more homogeneous, project teams. Database size was also important: a large database containing huge amounts of information was more likely to be used for further conversations and archiving, than a small one. This result again ran counter to users’ beliefs that small databases are superior. We discuss possible reasons for these findings in terms of critical mass and media competition, and conclude with implications for design.

Synchronous, asynchronous, and causally ordered communication

Abstract: This article studies characteristic properties of synchronous and asynchronous message communications in distributed systems. Based on the causality relation between events in computations with asynchronous communications, we characterize computations which are realizable with synchronous communications, which respect causal order, or where messages between two processes are always received in the order sent. It is shown that the corresponding computation classes form a strict hierarchy. Furthermore, an axiomatic definition of distributed computations with synchronous communications is given, and it is shown that several informal characterizations of such computations are equivalent when they are formalized appropriately. As an application, we use our results to show that the distributed termination detection algorithm by Dijkstra et al. is correct under a weaker synchrony assumption than originally stated.

Asynchronous binding of named objects

Abstract: An object-oriented framework unifies retrieval and browsing of data locally and from remote computer networks The framework includes a class of monikers that operate on behalf of a client program to asynchronously bind or retrieve data referenced by a name without blocking execution of the client This allows the client to provide responsive user interaction including when remotely retrieving data

System and method for voice Playout in an asynchronous packet network

Abstract: A System for Voice Playout in an Unsynchronized Packet Network for use with isochronous and asynchronous data transmission over a communication network having at least one receiving unit and at least one transmitting unit each having independent clocks. A FIFO voice codeword storing device in the receiving unit removes timing jitter from incoming packets--and receives voice packets from a data network. A phase continuous packet clock thereafter removes packets from the FIFO voice codeword storing device which is synchronized to the incoming data rate using the fill status of the FIFO voice codeword storing device as a frequency control signal. A continuous phase resampler removes timing frequency offset without causing packet slips or loss of data. The transmitter inserts the contents of a free running packet counter into each transmitted packet, allowing the receiver to detect lost packets and to properly reproduce silence intervals during Playout. A receive sequence counter increments at the local packet rate to schedule Playouts for multiple voice segments. A clock frequency recovery is utilized where the receiver clock frequency differs from the transmitter clock frequency. When the receive clock is not available, such as voice over packet networks applications, the FIFO voice codeword storing device fill status can control the resampling rate.

Application programming interface for managing and automating data transfer operations between applications over a bus structure

Abstract: An applications programming interface implements and manages isochronous and asynchronous data transfer operations between an application and a bus structure. During an asyncronous transfer the API includes the ability to transfer any amount of data between one or more local data buffers within the application and a range of addresses over the bus structure using one or more asynchronous transactions. An automatic transaction generator may be used to automatically generate the transactions necessary to complete the data transfer. The API also includes the ability to transfer data between the application and another node on the bus structure isochronously over a dedicated channel. During an isochronous data transfer, a buffer management scheme is used to manage a linked list of data buffer descriptors. This linked descriptor list can form a circular list of buffers and include a forward pointer to the next buffer in the list and a backward pointer to the previous buffer in the list for each buffer. The linked descriptor list may also form a linear list to which the application can append additional buffers or remove existing buffers from the list. During isochronous transfers of data, the API provides implementation of a resynchronization event in the stream of data allowing for resynchronization by the application to a specific point within the data. Implementation is also provided for a callback routine for each buffer in the list which calls the application at a predetermined point during the transfer of data.