Kin Wah Kwong

On the feasibility and efficacy of protection routing in IP networks

With network components increasingly reliable, routing is playing an ever greater role in determining network reliability. This has spurred much activity in improving routing stability and reaction to failures and rekindled interest in centralized routing solutions, at least within a single routing domain. Centralizing decisions eliminates uncertainty and many inconsistencies and offers added flexibility in computing routes that meet different criteria. However, it also introduces new challenges, especially in reacting to failures where centralization can increase latency. This paper leverages the flexibility afforded by centralized routing to address these challenges. Specifically, we explore when and how standby backup forwarding options can be activated while waiting for an update from the centralized server after the failure of an individual component (link or node). We provide analytical insight into the feasibility of such backups as a function of network structure and quantify their computational complexity. We also develop an efficient heuristic reconciling protectability and performance, and demonstrate its effectiveness in a broad range of scenarios. The results should facilitate deployments of centralized routing solutions.

Building heterogeneous peer-to-peer networks: protocol and analysis

In this paper, we propose a simple protocol for building heterogeneous unstructured peer-to-peer (P2P) networks. The protocol consists of two parts--the joining process and the rebuilding process. The basic idea for the joining process is to use a random walk to assist new incoming peers in selecting their suitable neighbors in terms of capacity and connectivity to achieve load-balancing. The rebuilding process specifies how the nodes should react when they lose links. In particular, we examine two representative schemes, namely the probabilistic-rebuilding scheme and the adaptive-rebuilding scheme. Furthermore, we provide a detailed analysis to investigate our proposed protocol under any heterogenous P2P environment. We prove that the topology structure of the P2P network depends heavily on the node heterogeneity. The analytical results are validated by the simulations. Our framework provides a guideline to engineer and optimize a P2P network in different respects under a heterogeneous environment. The ultimate goal of this paper is to stimulate further research to explore the fundamental issues in heterogeneous P2P networks.

Always acyclic distributed path computation

Distributed routing algorithms may give rise to transient loops during path recomputation, which can pose significant stability problems in high-speed networks. We present a new algorithm, Distributed Path Computation with Intermediate Variables (DIV), which can be combined with any distributed routing algorithm to guarantee that the directed graph induced by the routing decisions remains acyclic at all times. The key contribution of DIV, besides its ability to operate with any routing algorithm, is an update mechanism using simple message exchanges between neighboring nodes that guarantees loop-freedom at all times. DIV provably outperforms existing loop-prevention algorithms in several key metrics such as frequency of synchronous updates and the ability to maintain paths during transitions. Simulation results quantifying these gains in the context of shortest path routing are presented. In addition, DIVs universal applicability is illustrated by studying its use with a routing that operates according to a nonshortest path objective. Specifically, the routing seeks robustness against failures by maximizing the number of next-hops available at each node for each destination.

On the Feasibility and Efficacy of Protection Routing in IP Networks

With network components increasingly reliable, routing is playing an ever greater role in determining network reliability. This has spurred much activity in improving routing stability and reaction to failures, and rekindled interest in centralized routing solutions, at least within a single routing domain. Centralizing decisions eliminates uncertainty and many inconsistencies, and offers added flexibility in computing routes that meet different criteria. However, it also introduces new challenges; especially in reacting to failures where centralization can increase latency. This paper leverages the flexibility afforded by centralized routing to address these challenges. Specifically, we explore when and how standby backup forwarding options can be activated, while waiting for an update from the centralized server after the failure of an individual component (link or node). We provide analytical insight into the feasibility of such backups as a function of network structure, and quantify their computational complexity. We also develop an efficient heuristic reconciling protectability and performance, and demonstrate its effectiveness in a broad range of scenarios. The results should facilitate deployments of centralized routing solutions.

Improving service differentiation in IP networks through dual topology routing

The convergence on IP of a wide variety of traffic types has strengthened the need for service differentiation. Service differentiation relies on two equally important components: (i) resource allocation, i.e., what resources does a given service class have access to; and (ii) contention resolution, i.e., how is access to shared resources arbitrated between services classes. The latter has been well studied with numerous mechanisms, e.g., scheduling and buffer management, supporting it in modern routers. In contrast, relatively few studies exist on the former, and in particular on the impact of routing that determines the resources a given service class is assigned to. This is the focus of the paper, which seeks to investigate how routing influences a networks ability to efficiently support different service classes. Of particular interest is the extent to which the ability to route service classes separately is beneficial. This question is explored for a base configuration involving two classes with either similar or entirely different service objectives (cost functions). The papers contributions are in demonstrating and quantifying the benefits that the added flexibility of different (dual) routing affords, and in developing an efficient heuristic for computing jointly optimal routing solutions. The former can motivate the deployment of newly standardized multi-topology routing (MTR) functionality. The latter is a key enabler for the effective use of such capability.

Adaptive topology formation for peer-to-peer video streaming

In this paper we propose an adaptive P2P video streaming framework to address the challenges due to bandwidth heterogeneity and peer churn on the Internet. This adaptive streaming framework consists of two major components, source rate adaptation and adaptive overlay topology formation, to maximize the video quality and fully utilize the overall peer upload capacity. In the source rate adaptation, the video server adapts the video source rate automatically based on the local measurement of peers’ download rates, so that the P2P network is not overloaded beyond its bandwidth capacity and peers are able to achieve smooth video playback. To combat bandwidth heterogeneity, we propose to construct a desirable link-level homogeneous overlay topology using a Markov chain Monte Carlo method, so that peers achieve an equal per-connection upload/download bandwidth. In this link-level homogeneous network, video flows do not encounter any bottlenecks along the delivery paths, and peers achieve high download rates to ensure smooth video playback. We also design a fully distributed algorithm to implement the dual mechanisms of the adaptive topology formation and the source rate maximization. To evaluate the performance of our streaming framework, we conduct both mathematical analysis and extensive simulations. The simulation results confirm our analysis and show that the proposed distributed algorithm is able to maximize the video playback quality with fast convergence.

Media overlay construction via a Markov chain Monte Carlo method

In this paper, we consider the fairness issue of BT and tackle the problem with a general framework using proactive topology adaptations. The topology formed possesses a special link-level homogeneity property with each peer having the same capacity per out-degree value. Such property guarantees that each directional link has the same uploading bandwidth. Together with the Tit-for-Tat policy, peers upload and download at the same rate over each connection and therefore achieve fairness.

A congestion-aware search protocol for heterogeneous peer-to-peer networks

Peer-to-Peer (P2P) file sharing is the hottest, fastest growing application on the Internet. When designing Gnutella-like applications, the most important consideration is the scalability problem, because P2P systems typically support millions of users online concurrently. Gnutella suffers from poor scaling due to its flooding-based search, resulting in excessive amounts of repeated query messages. Therefore, a good search protocol plays an important role in a system’s scalability. However, congestion, due to large query loads from users, definitely impacts on the performance of search protocols, and this consideration has received little attention from the research community. In this paper, we propose a congestion-aware search protocol for unstructured P2P networks. Our protocol consists of three parts—Congestion-Aware Forwarding, Random Early Stop and Emergency Signaling. The aim of our protocol is to integrate congestion control and object discovery functionality so that the search protocol can achieve good performance under congested networks and flash crowds. We perform extensive simulations to study our proposed protocol. The results show that our protocol can significantly reduce the hit delay while maintaining the high hit rate and also the congestion problems such as query loss and the peer overloading problem can be effectively alleviated.

Balancing performance, robustness and flexibility in routing systems

Modern networks face the challenging task of handling increasingly diverse traffic that is displaying a growing intolerance to disruptions. This has given rise to many initiatives, and in this paper we focus on multiple topology routing as the primary vehicle for meeting those demands. Specifically, we seek routing solutions capable of not just accommodating different performance goals, but also preserving them in the presence of disruptions. The main challenge is computational, i.e., to identify among the enormous number of possible routing solutions the one that yields the best compromise between performance and robustness. This is where our principal contribution lies, as we expand the definition of critical links - a key concept in improving the efficiency of routing computation - and develop a precise methodology to efficiently converge on those solutions. Using this new methodology, we demonstrate that one can compute routing solutions that are both flexible in accommodating different performance requirements and robust in maintaining them in the presence of failures and traffic fluctuations.

A congestion-aware search protocol for unstructured peer-to-peer networks

Peer-to-Peer (P2P) file sharing is the hottest, fastest growing application on the Internet. When designing Gnutella-like applications, the most important consideration is the scalability problem. Recently, different search protocols have been proposed to remedy the problems in Gnutellas flooding. However, congestion due to large query loads from users and peer heterogeneity definitely impact on the performance of search protocols, and this consideration has received little attention from the research community. In this paper, we propose a congestion-aware search protocol for unstructured P2P networks. The aim of our protocol is to integrate congestion control and object discovery functionality so that it can achieve good performance under congested networks and flash crowds. The simulation results show that our protocol can largely reduce a hit delay while maintaining a high hit rate, and the congestion problems such as query loss and system overloading can be effectively alleviated.