Browsing by Author "Nelakuditi, Srihari"

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    Adaptive Proportional Routing: A Localized QoS Routing Approach
    (2002-07-18) Nelakuditi, Srihari; Zhang, Zhi-Li; Tsang, Rose P.; DuHung-Chang, David
    Most of the QoS routing schemes proposed so far require periodic exchange of QoS state information among routers, imposing both communication overhead on the network and processing overhead on core routers. Furthermore, stale QoS state information causes theperformance of these QoS routing schemes to degrade drastically. In order to circumvent these problems, we focus on localized QoS routing schemes where the edge routers make routing decisions using only ``local'' information and thus reducing the overhead at core routers. We first describe virtual capacity based routing (vcr), a theoretical scheme based on the notion of virtual capacity of a route. We then propose proportional sticky routing (psr), an easily realizable approximation of vcr and analyze its performance. We demonstrate through extensive simulations that adaptive proportional routing is indeed a viable alternative to the global QoS routing approach.
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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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    Localized Approach to Providing Quality-of-Service
    (2001-10-30) Nelakuditi, Srihari
    The exponential growth of Internet brings to focus the need to control such large networks. It is desirable to find simple local rules and strategies that can produce coherent and purposeful global behavior. The need for such mechanisms arises in a variety of settings. In quality-of-service based routing, paths for flows are selected basedupon the knowledge of resource availability at network nodes and the QoS requirements of flows. The best-path routing schemes gather global network state information and always select the best path for an incoming flow based on this global view. On the other hand, the proportional routing schemes proportion incoming flows among multiple candidate paths. We show that near-optimal proportions can be obtained using only locally collected information and a few good candidate paths can be selected using infrequently exchanged global information. We demonstrate that proportional routing schemes achieve higher throughput with lower overhead than best-path routing schemes. Video delivery for full quality playback requires a certain amount of network bandwidth and client buffer. But when these resources are limited, a naive video transmission may cause packet drops at the network and frame drops at the client, resulting in wastage of resources. To avoid this, a server may need to preemptively discard frames locally taking advantage of application-specific information. We first formulate the optimal selective frame discard problem and then present several efficient heuristic algorithms. We also develop adaptive selective layer discard algorithms for providing smoother quality playback of a layered video. Distributed dynamic channel assignment algorithms run at each base station in a wireless cellular network attempt to reduce the network-wide call blocking and call dropping probabilities while making assignment decisions based on neighborhood information only. They may also reassign channels being used by calls in progress to make room for another call. We propose two channel selection strategies based on localpacking for compact packing of channels. We also present a reassignment based call admission control scheme that dynamically adjusts the number of guard channels reserved for handoffs based on reassignment frequency in the neighborhood.
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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.