The buffer manager provides the first line of defense against abusive flows that transmit excessive number of packets. The pipelined-sections buffer management scheme described in our earlier work [S.Y. Cheung et al., April 2001] can discriminate between compliant and abusive flows. It can also provide a lossless guarantee to compliant leaky bucket rate constrained flows using very low buffer reservations. In this paper, we present an improved version of the pipelined sections buffer management method that has O(1) run time complexity and can also provide a fairness and delay guarantee to leaky bucket compliant flows

Existing packet schedulers that provide fair sharing of an output link can be divided into two classes: sorted priority and frame-based. Sorted priority methods provide excellent approximation for weighted fair queueing (WFQ) while frame-based methods are more computationally efficient. We present a new packet scheduling algorithm called bin sort fair queueing (BSFQ) that combines the strengths of both type of schedulers. As a result, BSFQ is highly scalable and can provide very good approximation for WFQ. We prove that BSFQ can provide end-to-end delay and fairness guarantees to conformant flows. BSFQ also has a built-in buffer management function that can protect packets of conformant flows from nonconformant traffic. The performance of BSFQ and its ability to detect nonconformant flows are studied using simulations and compared to those of the deficit round robin method.

The techniques used to provide quality of service in packet switched networks are buffer management and packet scheduling. The first line of defense against abusive flows that transmit excessive number of packets is the buffer manager. When the number of packets of a flow exceeds a threshold, new arrivals from that flow will be rejected. This threshold must be set to a level that is sufficiently high to provide specific guarantees to the flow and it must also be minimal so that the buffer manager will detect abusive behavior at the earliest possible moment. A buffer management technique that provides the same guarantees using a lower threshold will be more discriminating because it recognizes flow violations earlier. We present the new pipelined sections buffer management technique that is highly scalable and can provide rate guarantees to leaky bucket constrained flows using very low buffer reservations.

CCF (Collaborative Computing Frameworks) is a suite of software systems, communications protocols, and tools that enable collaborative, computer-based cooperative work. CCF constructs a virtual work environment on multiple computer systems connected over the Internet, to form a Collaboratory. In this setting, participants interact with each other, simultaneously access and operate computer applications, refer to global data repositories or archives, collectively create and manipulate documents or other artifacts, perform computational transformations, and conduct a number of other activities via telepresence. Research issues addressed in this project include problem solving environments and methodologies for laboratory and instrument-based scientific disciplines, and computer science issues in heterogeneous distributed systems. New approaches are being investigated and developed for fast multiway communication, robust geographically distributed data management methodologies, high-performance computational transforms inlined within collaboration sessions, and related auxiliary issues such as active documents, security, archival storage, and experiment management and control. In this paper, we discuss the design philosophy and systems rationale behind CCF, describe the major subsystems of the collaborative computing environment, and discuss the salient features of the system.

The Collaborative Computing Transport Layer (CCTL) is a communication substrate consisting of a suite of multiparty protocols, providing varying service qualities among process groups. CCTL explicitly supports distributed collaborative and multimedia applications. CCTL is based on a two-level group hierarchy. Logical interconnections among entities, called channels, define an efficient and light-weight group mechanism. Channels support a variety of service qualities such as reliability and message ordering. Related channels can also be combined to form sessions, heavy-weight groups which provide a default atomic multicast service. CCTL supports membership protocols tailored to the quality of service offered by a channel, including a relaxed form of virtual synchrony. In this paper, we present three membership protocols and compare and relate our implementations to alternatives. Our two-level architecture allows simple and efficient implementation of the membership protocols.

In a fair multicast video distribution scheme each receiver should receive a video stream with a quality that is commensurate with its capabilities or the capabilities of the path leading to it, regardless of other receivers or network paths. This fairness problem results from the fact that multicast communication trades economy of bandwidth with granularity of control. Distributing video using individual feedback-controlled point-to-point streams results in high bandwidth utilization but the granularity of control is high as communication parameters can be negotiated individually with each receiver. In contrast, using a single multicast stream has good bandwidth economy, but very low granularity of control. In this paper we propose, implement and experiment with a system that spans the spectrum represented by the two extremes above. In the scheme, called destination set grouping (DSG), a source maintains a small number of video streams, carrying the same video but each targeted at receivers with different capabilities. Each stream is feedback-controlled within prescribed limits by its group of receivers. Receivers may move among streams as their capabilities or the capabilities of the network paths leading to them change. The scheme is shown to improve fairness significantly at a small bandwidth cost.

In conventional multicast communication, the source carries a single conversation with all destination nodes. If a node on the path to any destination becomes congested the throughput to all destinations is reduced, thus treating same destination nodes unfairly. We consider a window-controlled multipoint connection and study the use of destination set grouping, where the destination set can be split into disjoint subgroups with the source carrying independent conversations with each subgroup. We present a dynamic grouping protocol which can adjust the grouping and the window sizes per group in response to changing network conditions. The performance of the protocol is studied using simulation and compared with single-group multicasting.

Barrier synchronization is a commonly used primitive in parallel processing. In this paper, we present different algorithms for barrier synchronization on the widely prevalent multiaccess bus network, and derive analytical performance metrics for each of the proposed schemes, which are then compared against simulation results.>

The authors study the quorumcasting problem which is a generalization of multicasting. While multicasting consists of sending a message to a select group of m nodes in a system of n nodes, quorumcasting sends a message to any q out of these m nodes. The need to communicate with an arbitrary q-subset of a predefined set arises in many distributed applications, such as distributed synchronization and updating a replicated resource. Two straightforward solutions are to send the message to individual members one at a time until q members have responded and to use multicasting to deliver the message to all members. The former solution will have excessive delay and the latter can cause congestion in nodes and/or in the network. The solutions proposed here use a minimum cost tree spanning a q-subset. By choosing an appropriate set of q nodes, the communications cost can be minimized. They present several heuristics to find low cost solutions for the quorumcast routing problem and evaluate the heuristics by comparing their solutions with exact solutions obtained from enumerating the solution space. The heuristic solutions are also compared with "random" solutions, where the q quorum sites are selected at random, and then the problem is treated like a multicast. The results of their tests show that the heuristics compare favorably with the optimal solutions, and that the random solutions perform rather poorly in comparison with the heuristics.>

The point-to-multipoint routing problem is studied for an asynchronous transfer mode (ATM) network that uses virtual paths (VPs). ATM networks with asymmetric and symmetric VPs are considered, and the performance factors studied are bandwidth and establishment and switching costs. A VP with intermediate exit, where a node that performs VP switching can copy the switched packets for the local destination, is proposed and studied. Mathematical formulations of multicast routing problems are presented, and heuristics for finding a low cost multicast routing tree, based on the transshipment simplex algorithm, are developed.>

The author presents a new technique, called controlled request, to combat the unfairness problem in the distributed queue dual bus (DQDB) protocol that achieves 100% throughput. Transmission of requests in the controlled request DQDB method is controlled by a mechanism that is similar to the one used in DQDB to transmit segments. Fairness is achieved by using the bandwidth balancing technique to prevent an overloaded node form continuously transmitting requests. Simulation studies showed that the controlled request DQDB scheme achieves better performance than the DQDB protocol with bandwidth balancing.>

A new protocol for maintaining replicated data that can provide both high data availability and low response time is presented. In the protocol, the nodes are organized in a logical grid. Existing protocols are designed primarily to achieve high availability by updating a large fraction of the copies, which provides some (although not significant) load sharing. In the new protocol, transaction processing is shared effectively among nodes storing copies of the data, and both the response time experienced by transactions and the system throughput are improved significantly. The authors analyze the availability of the new protocol and use simulation to study the effect of load sharing on the response time of transactions. They also compare the new protocol with a voting-based scheme.>

article Free Access Share on Multidimensional voting Authors: Mustaque Ahamad Georgia Institute of Technology, Atlanta Georgia Institute of Technology, AtlantaView Profile , Mostafa H. Ammar Georgia Institute of Technology, Atlanta Georgia Institute of Technology, AtlantaView Profile , Shun Yan Cheung Emory Univ., Atlanta, GA Emory Univ., Atlanta, GAView Profile Authors Info & Claims ACM Transactions on Computer SystemsVolume 9Issue 4Nov. 1991 pp 399–431https://doi.org/10.1145/118544.118552Online:01 November 1991Publication History 37citation564DownloadsMetricsTotal Citations37Total Downloads564Last 12 Months17Last 6 weeks3 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my Alerts New Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

A concept called multidimensional voting, in which the vote and quorum assignments are k-dimensional vectors of nonnegative integers and each dimension is independent of the others, is introduced. Multidimensional voting is more powerful than traditional weighted voting because it is equivalent to the general method for achieving synchronization in distributed systems which is based on coteries (sets of groups of nodes), but its implementation is easier than that of coteries. An efficient algorithm for finding a multidimensional vote assignment for any given coterie is described and examples of its use are shown. It is shown how multidimensional voting can be used to easily implement novel algorithms for synchronizing access to replicated data or to ensure mutual exclusion. These algorithms cannot be implemented by traditional weighted voting.>

A protocol for maintaining replicated data that can provide both high data availability and low response time is presented. Existing protocols are designed primarily to achieve high availability by updating a large fraction of the copies, which provides some (although not significant) load sharing. In the new protocol, transaction processing is shared effectively among nodes storing copies of the data, and both the response time experienced by transactions and the system throughput are improved significantly. Also presented is an analysis of the availability of the new protocol and simulation is used to study the effect of load sharing on the response time of transactions. The new protocol is also compared with a voting-based scheme.>

The problem is discussed of determining the vote assignment and quorum that yields the highest availability in a system where node availabilities can be different and the mix of the read and write operations is arbitrary. For this purpose, an enumeration algorithm is presented that can be used to find the vote and quorum assignments that need to be considered for achieving optimal availability. An analytical method is derived to evaluate the availability of a given system for any vote and quorum assignment. This method and the enumeration algorithm are used to find the optimal vote and quorum assignment for several systems. The algorithm can also be used to obtain the optimal performance when other measures are considered.>

In the weighted voting protocol which is used to maintain the consistency of replicated data, the availability of the data to ready and write operations not only depends on the availability of the nodes storing the data but also on the vote and quorum assignments used. The authors consider the problem of determining the vote and quorum assignments that yield the best performance in a distributed system where node availabilities can be different and the mix of the read and write operations is arbitrary. The optimal vote and quorum assignments depend not only on the system parameters, such as node availability and operation mix, but also on the performance measure. The authors present an enumeration algorithm that can be used to find the vote and quorum assignments that need to be considered for achieving optimal performance. When the performance measure is data availability, an analytical method is derived to evaluate it for any vote and quorum assignment. This method and the enumeration algorithm are used to find the optimal vote and quorum assignment for several systems. The enumeration algorithm can also be used to obtain the optimal performance when other measures are considered.>