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Browsing by Author "Lee, Sanghwan"

Now showing 1 - 4 of 4
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    Impact of AS Hierarchy on Multihoming Performance: A Stub Network Perspective
    (2004-02-20) Lee, Sanghwan; Zhang, Zhi-Li; Nelakuditi, Srihari
    Multi-homing, namely, connecting to more than one Internet Service Provider (ISP) for global Internet reachability, is a common practice among many (especially large) customer (or stub) networks. Although the purpose of multi-homing is primarily for enhanced reliability, it has also increasingly been used for load balancing and other performance benefits. This paper is motivated by the following major question: in a multi-homed stub network, is there any significant benefit in carefully selecting one of the several available ISPs to optimise latency (as measured by round trip time, RTT) to various destinations? To answer this question, we carry out a measurement-based study to compare and analyze performance differences in using two different providers in a multi-homed stub network to reach a large number of randomly selected destinations. Our study reveals that there are often performance benefits in selecting the best provider to optimise network latency. Furthermore, for a large fraction of the network prefixes, the RTT differences between the two providers fall into a dominant range. This phenomenon can be attributed to the effect of the AS hierarchy on AS paths: the AS hierarchy often causes the AS paths via the different providers to merge at the core of the Internet, resulting in shared common segments to many network prefixes and ASes. Consequently there is strong correlation among RTTs to many destination networks. Our findings provide some useful insights as to how to perform intelligent provider selection using BGP in a multi-homed stub network.
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    Leopard: A Location-Aware Peer-To-Peer System With No Hot Spot
    (2004-07-27) Yu, Yinzhe; Lee, Sanghwan; Zhang, Zhi-Li
    We propose an alternative approach for building structured peer-to-peer systems. The major design objectives are i) to explicitly incorporate locality information into the system to minimize routing stretch in object look-up service, and ii) to inherently better cope with the ``flash crowd'' problem. Unlike the standard DHT-based approach, where both objects and nodes are assigned a randomly hashed id in the same id space, we separate the object id space from the node space. More specifically, each object is assigned an id in an object id space, whereas each node is assigned a coordinate in a coordinate system (referred to as the node geo space) reflects the ``geographical proximity'' of nodes. The object id space and the node geo space are ``weaved'' together via a novel hashing technique called {em geographically-scoped hashing}. Using this approach, we develop a structured P2P look-up system called Leopard. Through analysis and simulations, we demonstrate that i) in Leopard object look-up latency is proportional to the distance between a requesting node and the target object; ii) in case multiple copies of an object exist, Leopard always locates a near-by copy; and iii) Leopard can effectively handle ``flash crowd'' traffic with near optimal load balancing.
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    On Dimensionality of Coordinate-Based Network Distance Mapping
    (2005-05-25) Lee, Sanghwan; Zhang, Zhi-Li; Sahu, Sambit; Saha, Debanjan
    In this paper, we investigate the veracity of a basic premise, “that network distance is Euclidean”, assumed in a class of recently proposed techniques that embed Internet hosts in a Euclidean space for the purpose of estimating the delay or “distance” between them. Using the classical scaling method on a number of network distance measurement datasets, we observe “non-Euclidean-ness” in the network distance. We find that this “non-Euclideanness” is caused by the clustering effect of Internet hosts. We also observe that the distance between the nodes in the same cluster is significantly more non-Euclidean than the distance between nodes in different clusters. Our correlation dimension based analysis of intrinsic dimensionality of the datasets reveals that the network distances seem to have a fractional dimension between 2 and 3. We observe that further increasing the dimensionality does not improve the accuracy of the embedding in Euclidean space. Motivated by these results, we propose a new hybrid model for embedding the network nodes using only a 2-dimensional Euclidean coordinate system and small adjustment terms. We show that the accuracy of the proposed embedding technique is as good as, if not better than, that of a 7-dimensional Euclidean embedding.
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    Proactive vs Reactive Approaches to Failure Resilient Routing
    (2003-08-06) Lee, Sanghwan; Yu, Yinzhe; Nelakuditi, Srihari; Zhang, Zhi-Li; Chuah, Chen-nee
    Dealing with network failures effectively is a major operational challenge for Internet Service Providers. Commonly deployed link state routing protocols such as OSPF react to link failures through global (i.e., network wide) link state advertisements and routing table recomputations, causing significant forwarding discontinuity after a failure. The drawback with these protocols is that they need to trade off routing stability and forwarding continuity. To improve failure resiliency without jeopardizing routing stability, we propose a proactive local rerouting based approach called failure insensitive routing. The proposed approach prepares for failures using interface-specific forwarding, and upon a failure, suppresses the link state advertisement and instead triggers local rerouting using a backwarding table. In this paper, we formally analyze routing stability and network availability under both proactive and reactive approaches, and show that FIR provides better stability and availability than OSPF.