Browsing by Author "Nadeem, Tamer"
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Item ATP: Autonomous Transport Protocol(2003-09-25) Elsayed, Tamer; Hussein, Mohamed; Youssef, Moustafa; Nadeem, Tamer; Youssef, Adel; Iftode, LiviuIn this report we present the design of the Autonomous Transport Protocol (ATP). The basic service provided by ATP is a reliable transport connection between two endpoints (identified by content identifiers) independent of their physical location. Autonomy allows dynamic endpoints relocation on different end hosts without disrupting the transport connection between them. ATP depends on the existence of an underlying Instance-Based Network (IBN) to achieve its goals. An IBN provides the flexibility of having different instances of the same content. It is up to the user of the IBN network to define the relation between these instances. An IBN allows its user to to map a content to a particular node. Application endpoints can send messages to other content-identified endpoints. Routing in the IBN is instance-based; the IBN can route a message to a specific content instance or to the nearest instance, if no exact match is found for the destination content instance. Moreover, the IBN replicates the stored contents in order to provide fault tolerance and IBN nodes along the query path can cache a content to provide fast answers to future queries. The ATP layer in the intermediate nodes between the source and destination endpoints can actively participate in the connection, for example, to buffer data for the destination endpoints during periods of unavailability. Data is transferred by a combination of active and passive operations, where the ATP layer of a node can decide whether to actively push the data to the destination or to passively wait for the destination endpoint to pull the data. The decision to whether to use the active or passive modes can be taken by a local policy on the node running the ATP protocol. (UMIACS-TR-2003-52)Item Efficient Cross Layer Designs for IEEE 802.11 Wireless Networks(2006-04-24) Nadeem, Tamer; Agrawala, Ashok; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Various properties of wireless networks, such as mobility, frequent disconnections and varying channel conditions, have made it a challenging task to design networking protocols for wireless communications. In this dissertation, we address several problems related to both the routing layer and medium access control (MAC) layer in wireless networks aiming to enhance the network performance. First, we study the effect of the channel noise on the network performance. We present mechanisms to compute energy-efficient paths in noisy environments for ad hoc networks by exploiting the IEEE 802.11 fragmentation mechanism. These mechanisms enhance the network performance up to orders of magnitude in terms of energy and throughput. We also enhance the IEEE 802.11 infrastructure networks with a capability to differentiate between different types of unsuccessful transmissions to enhance the network performance. Second, we study the effects of the physical layer capture phenomena on network performance. We modify the IEEE 802.11 protocol in a way to increase the concurrent transmissions by exploiting the capture phenomena. We analytically study the potential performance enhancement of our mechanism over the original IEEE 802.11. The analysis shows that up to 35% of the IEEE 802.11 blocking decisions are unnecessary. The results are verified by simulation in which we show that our enhanced mechanism can achieve up to 22% more throughput. Finally, we exploit the spatial reuse of the directional antenna in the IEEE 802.11 standards by developing two novel opportunistic enhancement mechanisms. The first mechanism augments the IEEE 802.11 protocol with additional information that gives a node the flexibility to transmit data while other transmissions are in its vicinity. The second mechanism changes the access routines of the IEEE 802.11 data queue. We show analytically how the IEEE 802.11 protocol using directional antenna is conservative in terms of assessing channel availability, with as much as 60% of unnecessary blocking assessments and up to 90% when we alter the accessing mechanism of the data queue. By simulation, we show an improvement in network throughput of 40% in the case of applying the first mechanism, and up to 60% in the case of applying the second mechanism.Item Efficient Time-Based Topology-Dependent Scheduling for Radio Packet Networks(2002-08-01) Nadeem, Tamer; Agrawala, AshokIn Radio Packet Network (RPN), unconstrained transmission may lead to collision of two or more packets. Time Division Multiple Access (TDMA) protocol is a common used protocol to schedule collision-free transmission for such networks. TDMA transmission allows a number of users to access a single radio channel without interference by allocating unique time slots to each user. In TDMA network, time is divided into frames and a frame consists of time slots. For networks where each node is a neighbor for all the other nodes, each node should assign a different time slot in TDMA frame to transmit in it to have collision-free transmission. Typically, those time slots are ended by \emph{guard times} for propagation delays. Those guard times are fixed for all time slots regardless the actual needed propagation delays. In this paper, we propose a topology-dependent algorithm that automatically schedules collision-free channel access and specify the time instant when a node is to send a packet. We use variable guard times, instead of the fixed ones, calculated using the actual needed propagation delays between sources and destinations. We show that with such scheduling algorithm, a 90% saving in the original guard times could be achieved that increases the network utilization by about 10%. Also UMIACS-TR-2002-57Item Rover Technology: Enabling Scalable Location-Aware Computing(2002-01-31) Banerjee, Suman; Agarwal, Sulabh; Kamel, Kevin; Kochut, Andrzej; Kommareddy, Christopher; Nadeem, Tamer; Thakkar, Pankaj; Trinh, Bao; Youssef, Adel; Youssef, Moustafa; Larsen, Ron; Shankar, A. Udaya; Agrawala, AshokLocation-aware computing involves the automatic tailoring of information and services based on the current location of the user. We have designed and implemented Rover, a system that enables location-based services, as well as the traditional time-aware, user-aware and device-aware services. To achieve system scalability to very large client sets, Rover servers are implemented in an "action-based" concurrent software architecture that enables fine-grained application-specific scheduling of tasks. We have demonstrated feasability through implementations for both outdoor and indoor environments on multiple platforms. (Also UMIACS-TR 2001-89)Item Survey on Wireless and Mobile ATM Networks(2002-04-04) Nadeem, Tamer; Miller, RaymondThe phenomenal growth in cellular telephony over the past several years has demonstrated the value people place on mobile voice communications. The goal of next generation wireless systems is to enable mobile users to access, manipulate and distribute multimedia content anywhere anytime. New mobile and wireless services will include Internet access to interactive multimedia, video conferencing and imaging as well as traditional services such as voice, email and web access. As the demand for mobile multimedia services grows, wireless extensions to existing broadband and Internet technologies will be required to support the seamless deliver of voice, video and data to mobile terminals with high quality. In this context, the advent of Wireless Asynchronous Transfer Mode (WATM) technology is intended to provide a direct extension of the core ATM network and services. A survey on wirless and mobile ATM networks is conducted in this paper.Item TrafficView: Towards a Scalable Traffic Monitoring System(2003-11-25) Nadeem, Tamer; Dashtinezhad, Sasan; Liao, Chunyuan; Iftode, LiviuVehicles are part of people's life in modern society, into which more and more high-tech devices are integrated, and a common platform for inter-vehicle communication is necessary to realize an intelligent transportation system supporting safe driving, dynamic route scheduling, emergency message dissemination, and traffic condition monitoring. TrafficView, which is a part of the e-Road project, defines a framework to disseminate and gather information about the vehicles on the road. Using such a system will provide a vehicle driver with road traffic information, which helps driving in situations as foggy weather, or finding an optimal route in a trip several miles long. This paper describes the basic design of TrafficView and different algorithms used in the system. (UMIACS-TR-2003-98)