Person:

Zegura, Ellen W.

Permanent Link

https://hdl.handle.net/1853/71879

Associated Organization(s)

Organizational Unit

School of Computer Science

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Publication Search Results

Now showing 1 - 8 of 8

Trading Latency for Energy in Wireless Ad Hoc Networks using Message Ferrying

(Georgia Institute of Technology, 2004) Zhao, Wenrui ; Ammar, Mostafa H. ; Zegura, Ellen W. ; Lee, Chungki ; Jun, Hyewon

Power management is a critical issue in wireless ad hoc networks where the energy supply is limited. In this paper, we investigate a routing paradigm, Message Ferrying (MF), to save energy while trading off data delivery delay. In MF, special nodes called ferries move around the deployment area to deliver messages for nodes. The reliance on the movement of ferries to deliver data increases the delivery delay. However, nodes can save energy by disabling their radios when ferries are far away. To exploit this feature, we present a power management framework, in which nodes switch their power management modes based on the knowledge of ferry location. We evaluate the performance of our scheme using ns-2 simulations and compare it with Dynamic Source Routing (DSR). Our simulation results show that MF achieves energy savings as high as 95% compared to DSR without power management and still delivers more than 98% of data. In contrast, a power-managed DSR delivers much less data than MF to achieve similar energy savings. In the scenario of heavy traffic load, the power-managed DSR delivers less than 20% of data. MF also shows robust performance for highly mobile nodes, while the performance of DSR suffers significantly. Thus, delay tolerant applications should use MF rather than a multihop routing protocol to save energy efficiently when both routing approaches are available.
Scheduling Uplink Bandwidth in Application-layer Multicast Trees

(Georgia Institute of Technology, 2004) Srinivasan, Sridhar ; Zegura, Ellen W.

Many applications can benefit from the use of multicast to distribute content efficiently. Due to the limited deployment of network-layer multicast, several application-layer multicast schemes have been proposed. In these schemes, the nodes in the multicast tree are end systems which are typically connected to the network by a single access link. Transmissions to the children of a node in the multicast tree have to share this single uplink, a factor largely ignored by previous work.In this work, we examine the effect of access link scheduling on the latency of content delivery in a multicast tree. Specifically, we examine the general case where multiple packets (comprising a block of data) are sent to each child in turn. We provide an analytical relation to compute the latency at a node in the multicast tree and show the relationship to the packet size and block size used to transfer data.We propose heuristics for tree construction which take link serialization into account. We evaluate this effect using simulations and experiments on the Planet- Lab network and show that using larger block sizes to transfer data can reduce the average finish time of the nodes in the multicast tree at the expense of slightly increased variance.
The Energy-Limited Capacity of Wireless Networks

(Georgia Institute of Technology, 2004) Ammar, Mostafa H. ; Zegura, Ellen W. ; Zhao, Wenrui

The performance of large-scale wireless ad hoc networks is often limited by the broadcasting nature of the wireless medium and the inherent node energy constraints. While the impact of the former on network capacity has been studied extensively in the literature, the impact of energy constraints has not received as much attention. In this paper, we study the capacity limitations resulting from the energy supplies in wireless nodes. We define the energy-limited capacity of a wireless network as the maximum amount of data the network can deliver before the nodes run out of energy. This energy-limited capacity is an important parameter in networks where operating lifetime is critical, such as ad hoc networks deployed in hazardous environments and sensor networks. We study two types of static networks, networks without any infrastructure support and networks where base stations with unlimited energy are deployed to support data forwarding. We consider two kinds of traffic models motivated by ad hoc networks and sensor networks. We derive upper and lower bounds on the energy-limited capacity of these networks. While throughput has been shown to not scale with node density in static networks by previous studies, our results show that, depending on the energy consumption characteristics of wireless communication, the energy-limited capacity can scale well under both traffic models. In addition, we show that the deployment of base stations can improve the energy-limited capacity of the network, especially for networks with sensor traffic.
Routing in Space and Time in Networks with Predictable Mobility

(Georgia Institute of Technology, 2004) Ammar, Mostafa H. ; Zegura, Ellen W. ; Merugu, Shashidhar

We consider the problem of routing in emerging wireless networks where nodes move around explicitly carrying messages to facilitate communication in an otherwise partitioned network. The absence of a path at any instant of time between a source and destination makes the traditional mobile ad hoc routing protocols unsuitable for these networks. However, the explicit node movements create paths over time that include the possibility of a node carrying a message before forwarding to another suitable node. Identifying such paths over space and time is a key challenge in these store, carry and forward networks. In most of these networks, the mobility of nodes is predictable either over a finite time horizon or indefinitely due to periodicity in node motion. We propose a new space-time routing framework for these networks leveraging the predictability in node motion. Specifically, we construct space-time routing tables where the next hop node is selected from the current as well as the future neighbors. Unlike traditional routing tables, our space-time routing tables use both the destination and the arrival time of message to determine the next hop node. We devise an algorithm to compute these space-time routing tables to minimize the end-to-end message delivery delay. Our routing algorithm is based on a space-time graph model derived from the mobility of nodes. We empirically evaluate our approach using simulations and observe improved performance as compared to other approaches based on heuristics.
Bootstrapping in Gnutella: A Preliminary Measurement Study

(Georgia Institute of Technology, 2003) Ammar, Mostafa H. ; Dhamdhere, Amogh Dhananjay ; Raj, Himanshu ; Riley, George F. ; Zegura, Ellen W. ; Karbhari, Pradnya

To join an unstructured peer-to-peer network like Gnutella, peers have to execute a bootstrapping function in which they discover other on-line peers and connect to them. Until this bootstrapping step is complete, a peer cannot participate in file sharing activities. Once bootstrapping is complete, a peer’s experience is strongly influenced by the choice of neighbor peers resulting from the bootstrapping step. Despite its importance, there has been very little attention devoted to understanding the behavior of this bootstrapping function. In this paper, we study the bootstrapping process of a peer in the Gnutella network. This is a preliminary investigation, consisting of 1) an analysis and performance comparison of bootstrapping algorithms of four Gnutella servent implementations, 2) a measurement-based characterization of the global Gnutella Web Caching System (GWebCaches), a primary component of the current bootstrapping functions, and 3) a study of the behavior and experience of a single GWebCache that was setup locally and made part of the global caching infrastructure. Our study highlights the importance of understanding the performance of the bootstrapping function as an integral part of a peer-to-peer system. We find that 1) there is considerable variation among various servent implementations that correlates to their bootstrapping performance, 2) even though the GWebCache system is designed to operate as a truly distributed system in keeping with the peer-to-peer system philosophy, it actually operates more like a centralized infrastructure function, and 3) the GWebCache system is subject to misreporting of peer and cache availability due to stale data and absence of validity checks.
Adding structure to unstructured peer-to-peer networks: the role of overlay topology

(Georgia Institute of Technology, 2003) Merugu, Shashidhar ; Srinivasan, Sridhar ; Zegura, Ellen W.

Our work examines the role of overlay topology on the performance of unstructured peer-to-peer systems. We focus on two metrics of performance: (a) search protocol performance, a local gain perceived directly by a user of the system and (b) utilization of the network, a global property that is of interest to network service providers. We present a class of overlay topologies based on distance between a node and its neighbors. We show, by simulation, that a particular topology instance of this class where every node has many close neighbors and few random neighbors exhibits better properties than other examined instances. In this overlay topology, the chances of locating files are high and the nodes where these files are found are, on average, close to the query source. This improvement in search protocol performance is achieved while decreasing the traffic load on the links in the underlying network. We propose a simple greedy algorithm to construct such topologies where each node operates independently and in a decentralized manner to select its neighbors.
Fast Packet Classification with a Varying Rule Set

(Georgia Institute of Technology, 2001) Merugu, Shashidhar ; Gummalla, Ajay Chandra V. ; Sala, Dolors ; Zegura, Ellen W.

Multi-dimensional packet classification is increasingly important for applications ranging from fire-walls to traffic accounting. Fast link speeds, the desire to classify with fine granularity, and the need for agility in a dynamic environment all pose significant challenges for packet classification. We propose an approach that is capable of handling a changing set of classification rules that span multiple fields. Our approach is based on extracting a relatively small set of bits that uniquely identify the packets satisfying each rule. Changes to the rule set are handled in-line via a fast update mode that adds to the rule table, while a background process performs reoptimization of the full rule table less frequently. The classification process can be efficiently implemented using pipelined hardware and supports high packet arrival rate.
An Evolutionary Framework for AS-Level Internet Topology Modeling

(Georgia Institute of Technology, 2001) Gao, Ruomei ; Zegura, Ellen W.

Models for network topology form a crucial component in the analysis of protocols. This paper systematically investigates a variety of evolutionary models for autonomous-system (AS) level Internet topology. Evolution-based models produce a topology incrementally, attempting to reflect the growth patterns of the actual topology. While evolutionary models are appealing, they have generally agreed less closely with measurements of real data than non-evolutionary models. We attempt to understand what contributes to a "good" evolutionary model. Our systematic study consists of a relatively generic evolutionary model framework, which we populate with different choices for the components. This allows us to compare a variety of instances of models to measurements from real data sets. We study issues such as the initial topology, the type of preferential connectivity used in adding edges, and the role of "growth" edges added between existing nodes. We find that appropriate instantiation of the framework can provide topologies that agree closely with real data. We also use our work to highlight several crucial open problems in topology modeling.