Person:

Ammar, Mostafa H.

Permanent Link

https://hdl.handle.net/1853/71056

Associated Organization(s)

Organizational Unit

School of Computer Science

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Publication Search Results

Now showing 1 - 10 of 25

Message Ferries as Generalized Dominating Sets in Intermittently Connected Mobile Networks

(Georgia Institute of Technology, 2009) Ammar, Mostafa H. ; Polat, Bahadir K. ; Sachdeva, Pushkar ; Zegura, Ellen W.

Message ferrying is a technique for routing data in wireless and mobile networks in which one or more mobile nodes are tasked with storing and carrying data between sources and destinations. To achieve connectivity between all nodes, message ferries may need to relay data to each other. While useful as a routing technique for wireless mobile networks in general, message ferrying is particularly useful in intermittently connected networks where traditional MANET routing protocols are not usable. A wireless and mobile network is said to possess intrinsic message ferrying capability if a subset of the nodes can act as message ferries by virtue of their own mobility pattern, without introducing additional nodes or modifying existing node mobility. Our goal in this work is to provide a formalism by which one can characterize intrinsic message ferrying capability. We first observe that the use of message ferries is the mobile generalization of the well-known use of connected dominating set-based routing in wireless networks. We next consider the problem of identifying the set of nodes in a mobile network which can act as message ferries by virtue of their mobility pattern. To this end, we define the concept of a connected message ferry dominating set (CMFDS) in a manner that achieves data delivery within certain performance bounds. We then develop algorithms that can be used to find such a set within a mobile, wireless network. The general CMFDS algorithm is built around a core algorithm that determines whether a single node in the network can act as a ferry. We provide some illustrative examples to show the application of our algorithm to several mobility patterns.
Multicasting in Delay Tolerant Networks: Semantic Models and Routing Algorithms

(Georgia Institute of Technology, 2006) Zhao, Wenrui ; Ammar, Mostafa H. ; Zegura, Ellen W.

Delay tolerant networks (DTNs) are a class of emerging networks that experience frequent and long-duration partitions. These networks have a variety of applications in situations such as crisis environments and deep-space communication. In this paper, we study the problem of multicasting in DTNs. Multicast supports the distribution of data to a group of users, a service needed for many potential DTN applications. While multicasting in the Internet and mobile ad hoc networks has been studied extensively, due to the unique characteristic of frequent partitioning in DTNs, multicasting in DTNs is a considerably different and challenging problem. It not only requires new definitions of multicast semantics but also brings new issues to the design of routing algorithms. In this paper, we propose new semantic models for DTN multicast and develop several multicast routing algorithms with different routing strategies. We present a framework to evaluate these algorithms in DTNs. To the best of our knowledge, this is the first study of multicasting in DTNs. Our objectives are to understand how routing performance is affected by the availability of knowledge about network topology and group membership and to guide the design of DTN routing protocols. Using ns simulations, we find that efficient multicast routing for DTNs can be constructed using only partial knowledge. In addition, accurate topology information is generally more important in routing than up-to-date membership information. We also find that routing algorithms that forward data along multiple paths achieve better delivery ratios, especially when available knowledge is limited.
Hierarchical Power Management in Disruption Tolerant Networks with Traffic-Aware Optimization

(Georgia Institute of Technology, 2006) Jun, Hyewon ; Ammar, Mostafa H. ; Corner, Mark D. ; Zegura, Ellen W.

Disruption tolerant networks (DTNs) are wireless mobile networks that are characterized by frequent partitions and long delays. Such networks can be used in highly-challenged environment in which energy resources are limited. Efficient power management, therefore, is essential for their success. In this paper, we present a hierarchical power management in DTNs where nodes are equipped with two complementary radios: a long-range, high power radio and a short range, low-power radio. In this architecture, energy can be conserved by using the low-power radio to discover communication opportunities with other nodes and then wake up the high-power radio to undertake the data transmission. We develop a generalized power management framework and its variations around this idea and evaluate their relative performance. In addition, for the case in which traffic load can be predicted, we devise approximation algorithms to control the sleep/wake-up cycling to provide maximum energy conservation while discovering enough communication opportunities to handle a given traffic load. We evaluate our schemes and our choice of parameters through ns-2 simulations. Our simulation results show that the generalized power management mechanism could augment the usefulness of the low power radio and achieve better energy efficiency than mechanisms relying on one radio for discovery. In addition, our approximation algorithms reduce energy consumption from 73% to 93% compared with the case without power management. We also observe that while an additional low power radio does reduce the energy consumption needed for discovery, the improvement could be negligible in mobile DTNs due to the low density of nodes.
Overlay Network Assignment in PlanetLab With NetFinder

(Georgia Institute of Technology, 2006) Zhu, Yong ; Ammar, Mostafa H.

PlanetLab has been widely used in the networking community to test and deploy user-defined overlays. Serving as a meta testbed to support multiple overlay networks, PlanetLab has significantly lowered the barriers to build new overlays. However, PlanetLab users always face the problem of selecting a set of nodes and interconnecting them to form the desired overlay network. Unfortunately, such a task is usually carried out manually by individual users and sometimes in an ad-hoc manner. In this paper, we develop NetFinder, an automatic overlay network configuration tool to efficiently allocate PlanetLab resources to individual overlays. NetFinder continuously monitors the resource utilization of PlanetLab and accepts a user-defined overlay topology as input and selects the set of PlanetLab nodes and their interconnection for the user overlay. Experimental results indicate that overlay networks constructed by NetFinder have more stable and significantly higher bandwidth than alternative schemes and near optimal available CPU.
Capacity Enhancement Using Throw-Boxes in Mobile Delay Tolerant Networks

(Georgia Institute of Technology, 2006) Zhao, Wenrui ; Chen, Yang ; Ammar, Mostafa H. ; Corner, Mark D. ; Levine, Brian ; Zegura, Ellen W.

Delay tolerant networks (DTNs) are a class of emerging networks that are subject to frequent and long-duration partitions. Due to intermittent connectivity, DTNs might be significantly limited in supporting application needs, for example, leading to low throughput or high delay. To address this problem, we propose the use of throw-boxes to improve data delivery performance. Throw-boxes are small, inexpensive devices equipped with wireless interfaces and deployed to relay data between mobile nodes. Being small and inexpensive, throwboxes represent a flexible and cost-effective approach to enhance network capacity. In this paper, we systematically study two inter-related issues, namely deployment and routing, in using throw-boxes for throughput enhancement. Specifically, we develop algorithms for throw-box deployment and data forwarding under various routing strategies, including single path, multi-path and epidemic routing. Using extensive ns simulations, we evaluate the utility of throw-boxes and the impact of various routing and deployment strategies on network performance. Our objective is to guide the design and operations of throw-box-enhanced DTNs. We find that throw-boxes are very effective in improving both data delivery ratio and delay, especially for multi-path routing and environments with regular node movement.
On the Predictability of Large Transfer TcP Throughput

(Georgia Institute of Technology, 2005) Dovrolis, Constantine ; Ammar, Mostafa H. ; He, Qi

With the advent of overlay and peer-to-peer networks, Grid computing, and CDNs, network performance prediction becomes an essential task. Predicting the throughput of large TCP transfers, in particular, has attracted much attention. In this work, we focus on the design, empirical evaluation, and analysis of TCP throughput predictors for a broad class of applications. We first classify TCP throughput prediction techniques into two categories: Formula-Based (FB) and History-Based (HB). Within each class, we develop representative prediction algorithms, which we then evaluate empirically over the RON testbed. FB prediction relies on mathematical models that express the TCP throughput as a function of the characteristics of the network path (e.g., RTT, loss rate, available bandwidth). FB prediction does not rely on previous TCP transfers in the given path, and it can be performed with non-intrusive network measurements. We show, however, that the FB method is accurate only if the TCP transfer is window-limited to the point that it does not saturate the underlying path, and explain the main causes of the prediction errors. HB techniques predict the throughput of TCP flows from a time series of previous TCP throughput measurements on the same path, when such a history is available. We show that even simple HB predictors, such as Moving Average and Holt-Winters, using a history of limited and sporadic samples, can be quite accurate. On the negative side, HB predictors are highly pathdependent. Using simple queueing models, we explain the cause of such path dependencies based on two key factors: the load on the path, and the degree of statistical multiplexing.
On the Predictability of Large Transfer TCP Throughput

(Georgia Institute of Technology, 2005) He, Qi ; Dovrolis, Constantine ; Ammar, Mostafa H.

With the advent of overlay and peer-to-peer networks, Grid computing, and CDNs, network performance prediction becomes an essential task. Predicting the throughput of large TCP transfers, in particular, has attracted much attention. In this work, we focus on the design, empirical evaluation, and analysis of TCP throughput predictors for a broad class of applications. We first classify TCP throughput prediction techniques into two categories: Formula-Based (FB) and History-Based (HB). Within each class, we develop representative prediction algorithms, which we then evaluate empirically over the RON testbed. FB prediction relies on mathematical models that express the TCP throughput as a function of the characteristics of the network path (e.g., RTT, loss rate, available bandwidth). FB prediction does not rely on previous TCP transfers in the given path, and it can be performed with non-intrusive network measurements. We show, however, that the FB method is accurate only if the TCP transfer is window-limited to the point that it does not saturate the underlying path, and explain the main causes of the prediction errors. HB techniques predict the throughput of TCP flows from a time series of previous TCP throughput measurements on the same path, when such a history is available. We show that even simple HB predictors, such as Moving Average and Holt-Winters, using a history of limited and sporadic samples, can be quite accurate. On the negative side, HB predictors are highly path-dependent. Using simple queueing models, we explain the cause of such path dependencies based on two key factors: the load on the path, and the degree of statistical multiplexing.
Reliable End System Multicasting with a Heterogeneous Overlay Network

(Georgia Institute of Technology, 2004-05-03) Zhang, Jianjun ; Liu, Ling ; Pu, Calton ; Ammar, Mostafa H.

This paper presents PeerCast, a reliable and self-configurable peer to peer system for End System Multicast (ESM). Our approach has three unique features compared with existing approaches to application-level multicast systems. First, we propose a capacity-aware overlay construction technique to balance the multicast load among peers with heterogeneous capabilities. Second, we utilize the landmark signature technique to cluster peer nodes of the ESM overlay network, aiming at exploiting the network proximity of end system nodes for efficient multicast group subscription and fast dissemination of information across wide area networks. Third and most importantly, we develop a dynamic passive replication scheme to provide reliable subscription and multicast dissemination of information in an environment of inherently unreliable peers. We also present an analytical model to discuss its fault tolerance properties, and report a set of initial experiments, showing the feasibility and the effectiveness of the proposed approach.
Space–Parallel Network Simulations Using Ghosts

(Georgia Institute of Technology, 2004-05) Riley, George F. ; Jaafar, Talal Mohamed ; Fujimoto, Richard M. ; Ammar, Mostafa H.

We discuss an approach for creating a federated network simulation that eases the burdens on the simulator user that typically arise from more traditional methods for defining space-parallel simulations. Previous approaches have difficulties that arise from the need for global topology knowledge when forwarding simulated packets between the federates. In all but the simplest cases, proper packet forwarding decisions between federates requires routing tables of size O(mn) (m is the number of nodes modeled in a particular simulator instance, and n is the total number of network nodes in the entire topology) in order to determine how packets should be routed between federates. Further, the benefits of the well-known NIx-Vector routing approach cannot be fully achieved without global knowledge of the overall topology. We seek to overcome these difficulties by utilizing a topology partitioning methodology that uses Ghost Nodes. A ghost node is a simulator object in a federate that represents a simulated network node that is spatially assigned to some other federate, and thus that other federate is responsible for maintaining all state associated with the node. However, ghost nodes do retain topology connectivity information with other nodes, allowing all federate in a space-parallel simulation to obtain a global picture of the network topology. We show with experimental results that the memory overhead associated with the ghosts is minimal relative to the overall memory footprint of the simulation.
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.