Overlay network monitoring enables distributed Internet applications to detect and recover from path outages and periods of degraded performance within seconds. For an overlay network with n end hosts, existing systems either require O(n²) measurements, and thus lack scalability, or can only estimate the latency but not congestion or failures. Our earlier extended abstract [1] briefly proposes an algebraic approach that selectively monitors k linearly independent paths that can fully describe all the O(n²) paths. The loss rates and latency of these k paths can be used to estimate the loss rates and latency of all other paths. Our scheme only assumes knowledge of the underlying IP topology, with links dynamically varying between lossy and normal. In this

Abstract — Continuous monitoring and diagnosis of network performance are of crucial importance for the Internet access service and virtual private network (VPN) service providers. Various operational constraints, which are crucial to the practice, are largely ignored in previous monitoring system designs, or are simply replaced with load balancing problems which do not work for real heterogeneous networks. Given these real-world challenges, in this paper, we design a V Scope monitoring system with the following contributions. First, we design a greedy-assisted linear programming algorithm to select as few monitors as possible that can monitor the whole network under the operational constraints. Secondly, VScope takes a multi-round measurement approach to further reduce monitors deployment/management cost, by scheduling the path measurements in different rounds under the operational constraints. Evaluations based on several real VPN topologies from a tier-1 ISP as well as some other synthetic topologies demonstrate that VScope is promising to solve the aforementioned challenges. 1.

Abstract — This paper describes Service Clouds, a distributed infrastructure designed to facilitate rapid prototyping and deployment of services that enhance communication performance, robustness, and security. The infrastructure combines adaptive middleware functionality with an overlay network substrate in order to support dynamic instantiation and reconfiguration of services. The Service Clouds architecture includes a collection of lowlevel facilities that can be either invoked directly by applications or used to compose more complex services. After describing the Service Clouds architecture, we present results of two experimental case studies conducted on the PlanetLab Internet testbed, the first to improve throughput of bulk data transfer, and the second to enhance the robustness of multimedia streaming. I.

In unstructured peer-to-peer (P2P) systems, there exists a serious topology mismatch problem between physical and logical network. We first analyze the relationship between the property of the overlay and the corresponding message duplications incurred by queries in a given overlay, and prove that computing an optimal overlay with global knowledge is an NP-hard problem. Motivated by the analysis results, we design a distributed overlay optimization algorithm, THANCS, to attack topology mismatch. We demonstrate its performance by comprehensive simulations in dynamic environments. The proposed THANCS has three major strengths. First, it does not need any global knowledge. Second, its optimization convergent speed is fast. Third, it is orthogonal with other types of advanced search approaches. 1.

Overlay network monitoring enables distributed Internet applications to detect and recover from path outages and periods of degraded performance within seconds. For an overlay network with n end hosts, existing systems either require O(n 2) measurements, and thus lack scalability, or can only estimate the latency but not congestion or failures. Our earlier extended abstract [1] briefly proposes an algebraic approach that selectively monitors k linearly independent paths that can fully describe all the O(n 2) paths. The loss rates and latency of these k paths can be used to estimate the loss rates and latency of all other paths. Our scheme only assumes knowledge of the underlying IP topology, with links dynamically varying between lossy and normal. In this paper, we improve, implement and extensively evaluate such a monitoring system. We further make the following contributions: i) scalability analysis indicating that for reasonably large n (e.g., 100), the growth of k is bounded as O(n log n), ii) efficient adaptation algorithms for topology changes, such as the addition or removal of end hosts and routing changes, iii) measurement load balancing schemes, iv) topology measurement error handling, and v) design and implementation of an adaptive streaming media system as a representative application. Both simulation and Internet experiments demonstrate we obtain highly accurate path loss rate estimation while adapting to topology changes within seconds and handling topology errors.

Abstract. Network monitoring is essential to the correct and efficient operation of overlay networks, and active measurement is a key design problem in network monitoring. Unfortunately, almost all active probing algorithms ignore the measurement conflict problem: Active measurements conflict with each other- due to the nature of these measurements, the associated overhead, and the network topology- which results in reporting incorrect results. In this paper, we consider the problem of scheduling periodic QoS measurement tasks in overlay networks. We first show that this problem is NP-complete, and then propose a conflict-aware scheduling algorithm whose goal is to maximize the number of measurement tasks that can run concurrently, based on a well known approximation algorithm. Simulation results show that our algorithm achieves 25 % better schedulability over the existing algorithm. Finally, we discuss various practical considerations, and identify several interesting research problems in this context. 1

In unstructured peer-to-peer (P2P) systems, there exists a serious topology mismatch problem between physical and logical network. We first analyze the relationship between the property of the overlay and the corresponding message duplications incurred by queries in a given overlay, and prove that computing an optimal overlay with global knowledge is an NP-hard problem. Motivated by the analysis results, we design a distributed overlay optimization algorithm, THANCS, to attack topology mismatch. We demonstrate its performance by comprehensive simulations in dynamic environments. The proposed THANCS has three major strengths. First, it does not need any global knowledge. Second, its optimization convergent speed is fast. Third, it is orthogonal with other types of advanced search approaches. 1.

The Internet has successfully provided a set of protocols for global deployment and re-liable transportation services. With the tremendous growth of the Internet, emerging applications have been continuously demanding the Internet infrastructure to provide new value-added services. In this dissertation, we first focus on the issue of proving the most commonly used value-added Internet service, namely, multicasting. The second part of this dissertation focuses on overlay networks, which is a feasible and flexible approach to quickly deploy value-added services on top of the existing Internet infrastructure. Most multicast applications are inherently QoS (quality of service) sensitive and desire QoS support from the underlying network. Our focus is to design and develop efficient protocols to support QoS-aware and failure-resilient multicasting services in various environments: (1) Integrated services (IntServ) environment: we propose an IP-based QoS-aware multicasting protocol called QMIS based on per-flow reservation. On top of a novel bounded flooding technique, QMIS can increase the

Abstract—Accurate fault detection and localization is essential to the efficient and economical operation of ISP networks. In addition, it affects the performance of Internet applications such as VoIP, and online gaming. Fault detection algorithms typically depend on spatial correlation to produce a set of fault hypotheses, the size of which increases by the existence of lost and spurious symptoms, and the overlap among network paths. The network administrator is left with the task of accurately locating and verifying these fault scenarios, which is a tedious and time-consuming task. In this paper, we formulate the problem of finding a set of overlay paths that can debug the set of suspected faulty IP links. These overlay paths are chosen from the set of existing measurement paths, which will make overlay measurements meaningful and useful for fault debugging. We study the overlap among overlay paths using various real-life Internet topologies of the two major service carriers in the U.S. We found that with a reasonable number of concurrent failures, it is possible to identify the location of the IP links faults with 60 % to 95 % success rate. Finally, we identify some interesting research problems in this area. I.

this paper, we improve, implement and extensively evaluate such a monitoring system. We further make the following contributions: i) scalability analysis indicating that for reasonably large n (e.g., 100), the growth of k is bounded as O(n log n), ii) e#cient adaptation algorithms for topology changes, such as the addition or removal of end hosts and routing changes, iii) measurement load balancing schemes, and iv) topology measurement error handling. Both simulation and Internet experiments demonstrate we obtain highly accurate path loss rate estimation while adapting to topology changes within seconds and handling topology errors