12875295
A comparison of multicast feedback control mechanisms
In reliable multicast applications, packet loss needs to be reported by having group members send feedback messages. This results in the well-known feedback implosion problem. The available feedback control mechanisms can be classified as timer-based, hierarchy-based and router-assisted, among which the timer-based approach is more preferable due to its simplicity and flexibility. This paper compares the performance of a set of multicast protocols that use either the traditional timer-based feedback control or a combination of the traditional timers and some representatives in the feedback control. We investigate how the use of representatives and deterministic timers improves feedback control performance.
17891154
A Credit-Based Active Queue Management (AQM) Mechanism to Achieve Fairness in the Internet
Router-based algorithms to address the TCP-friendliness problem have focused on providing fairness to TCP connections by penalizing UDP unresponsive flows. As a result, current schemes have overlooked their effect on streaming applications. In addition, current schemes have not been widely implemented in practice because of their high complexity and their inability to provide fairness when multiple unresponsive flows, packets of different sizes, and bursty traffic are present. All these aspects and scenarios, commonly found in practice, are rarely addressed in the literature. In this paper, we present Achieving Fairness using a Credit-based mechanism or AFC, a simple Fair Active Queue Management (FAQM) mechanism that aims to solve the unfairness problems generated under these realistic conditions. Simulation results show that AFC provides smoother transfer rates for unresponsive flows transmitting real-time traffic, handles multiple heavy unresponsive flows better, improves the fairness among TCP connections with different round-trip delays, and achieves good fairness even under bursty traffic and packets of different sizes.
16981937
Network traffic characterization of distributed database applications
The authors' efforts in characterizing the traffic of distributed database systems are described. This is an important class of applications considering that database or transaction processing systems form the core of several key commercial applications. Specific traffic source models for this application class have not been developed which is imperative for their successful deployment in emerging networks. The main contribution of the paper is to present the relationship between a distributed database application scenario and the corresponding network traffic characteristics, thus providing guidelines to these applications to compute their traffic descriptors accurately.
8291592
Performance analysis of the send-on-demand: A distributed database concurrency control protocol for high-speed networks
In this paper, we consider an application of high-speed wide area networks, viz. that of distributed database systems (DDBS). In a high-speed environment, although the transmission delay decreases, the propagation delay (communication latency) now becomes the throughput thwarting factor. Existing Concurrency Control (CC) protocols do not address the communication latency problem. This paper is a continuation of our research work in this area. First, we very briefly summarize our previously reported research results, viz. the issues that are important for DDBS in high-speed wide area networks, and the description of a new CC protocol called 'send-on-demand'. A detailed comparison of this protocol with that of locking is provided, using analytical and simulation techniques. The datacycle scheme performs very well in a read-oriented environment, and the rest of the paper deals with developing and comparing hybrid CC schemes using datacycling for queries. Altogether, the performance of four concurrency control schemes is compared.
3132692
Distributed Database Systems in High-Speed Wide-Area Networks
The issues involved in developing a distributed database system (DDBS) in a high-speed environment are discussed. The inadequacy of existing database protocols in utilizing the gigabit network is described. A concurrency control protocol that performs better than traditional DDBSs in high-speed networks is developed. Both analytical and simulation results are presented. The focus is on the concurrency control aspect of DDBS since this protocol is at the heart of the overall functioning of the distributed system. >
30095382
Performance Analysis of Generalized Selective Packet Discarding Schemes
Selective packet discarding schemes have been mostly developed and analyzed in the context of ATM networks. However, similar schemes could be applied to non-ATM or more general networks. The analysis of selective packet discarding schemes in a general packet switching environment has been limited to the basic dropping schemes, i.e., Partial Packet Discard (PPD) and Early Packet Discard (EPD), and for only the single traffic source case. In this paper, we extend the mathematical analysis of PPD and EPD for multiple sources and include simulation results to verify the analytical results. Finally, to place the performance of the generalized EPD and PPD in the context of other packet dropping schemes, we also provide simulation results of the Drop from Front (DfF), and preemptive Partial Packet Discard (pPPD) schemes.
16477654
Efficient peer location on the Internet
We consider the problem of locating nearby application peers over the Internet. We define a new peer-location scheme (called Tiers), that scales to large application peer groups. Tiers creates a hierarchy of peers, and provides an efficient and scalable solution to the peer-location problem. Tiers can be implemented entirely in the application-layer and does not require the deployment of either any additional measurement services, or well-known reference points in the network.We have evaluated the performance of Tiers through detailed experiments. Our results show that Tiers is able to locate the nearest peers quickly (≪ 1 s) and accurately on wide-area Internet-like topologies. We have also compared the performance of Tiers with two other schemes, Beaconing and Distributed Binning, both of which are known to have good performance. Both these techniques are reference-points based schemes and are efficient for overlays with a small number of peers (e.g. ≤32). Our results show that Tiers significantly outperforms both these schemes. Tiers is particularly efficient for large overlay networks, has an order of magnitude lower control overhead for overlays with 512 peers and still achieves greater accuracy in locating the nearest peers.
8561751
Partially overlapped channels not considered harmful
Many wireless channels in different technologies are known to have partial overlap. However, due to the interference effects among such partially overlapped channels, their simultaneous use has typically been avoided. In this paper, we present a first attempt to model partial overlap between channels in a systematic manner. Through the model, we illustrate that the use of partially overlapped channels is not always harmful. In fact, a careful use of some partially overlapped channels can often lead to significant improvements in spectrum utilization and application performance. We demonstrate this through analysis as well as through detailed application-level and MAC-level measurements. Additionally, we illustrate the benefits of our developed model by using it to directly enhance the performance of two previously proposed channel assignment algorithms --- one in the context of wireless LANs and the other in the context of multi-hop wireless mesh networks. Through detailed simulations, we show that use of partially overlapped channels in both these cases can improve end-to-end application throughput by factors between 1.6 and 2.7 in different scenarios, depending on wireless node density. We conclude by observing that the notion of partial overlap can be the right model of flexibility to design efficient channel access mechanisms in the emerging software radio platforms.
14357613
Construction of an efficient overlay multicast infrastructure for real-time applications
This paper presents an overlay architecture where service providers deploy a set of service nodes (called MSNs) in the network to efficiently implement media-streaming applications. These MSNs are organized into an overlay and act as application-layer multicast forwarding entities for a set of clients. We present a decentralized scheme that organizes the MSNs into an appropriate overlay structure that is particularly beneficial for real-time applications. We formulate our optimization criterion as a "degree-constrained minimum average-latency problem" which is known to be NP-hard. A key feature of this formulation is that it gives a dynamic priority to different MSNs based on the size of its service set. Our proposed approach iteratively modifies the overlay tree using localized transformations to adapt with changing distribution of MSNs, clients, as well as network conditions. We show that a centralized greedy approach to this problem does not perform quite as well, while our distributed iterative scheme efficiently converges to near-optimal solutions.
3090624
Eliminating handoff latencies in 802.11 WLANs using multiple radios: applications, experience, and evaluation
Deployment of Voice-over IP (VoIP) and other real-time streaming applications has been somewhat limited in wireless LANs today, partially because of the high handoff latencies experienced by mobile users. Our goal in this work is to eliminate handoff latency by exploiting the potential of multiple radios in WLAN devices. Our proposed approach, called MultiScan, is implemented entirely on the client-side, and, unlike prior work, MultiScan requires neither changing the Access Points (APs), nor having knowledge of wireless network topology. MultiScan nodes rely on using their (potentially idle) second wireless interface to opportunistically scan and pre-associate with alternate APs and eventually seamlessly handoff ongoing connections. In this paper we describe our implementation of MultiScan, present detailed evaluations of its effect on handoff latency and evaluate performance gains for MultiScan-enhanced wireless clients running Skype, a popular commercial VoIP application.
7316736
Efficient probabilistic packet marking
Probabilistic packet marking is a general technique which routers can use to reveal internal network information to end-hosts. Such information is probabilistically set by the routers in headers of regular IP packets on their way to destinations. A number of potential applications have been identified, such as IP traceback, congestion control, robust routing algorithms, dynamic network reconfiguration, and locating Internet bottlenecks, etc. In this paper, we define EPPM, an efficient general probabilistic packet marking scheme with a wide range of potential applications, of which locating Internet bottlenecks and IP traceback are investigated as two representative examples to demonstrate its effectiveness. Our proposed scheme imposes only a single-bit overhead in the IP packet headers. More importantly, it significantly reduces the number of IP packets required to convey the relevant information when compared to the prior best known scheme (almost by two orders of magnitude)