Browsing by Author "Youssef, Moustafa"
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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 Characterizing the IEEE 802.11 Traffic: The Wireless Side(2004-04-19) Yeo, Jihwang; Youssef, Moustafa; Agrawala, AshokMany studies on measurement and characterization of wireless LANs have been performed recently. Most of these measurements have been conducted from the wired portion of the network based on wired monitoring or SNMP statistics. In this paper we argue that traffic measurements from a wireless vantage point in the network are more appropriate than wired measurements or SNMP statistics, to expose the wireless medium characteristics and their impact on the traffic patterns. While it is easier to make consistent measurements in the wired part of a network, such measurements can not observe the significant vagaries present in the wireless medium itself. As a consequence constructing an accurate measurement system from a wireless vantage point is important but usually quite difficult due to the noisy wireless channel. In our work we have explored the various issues in implementing such a system to monitor traffic in an IEEE 802.11 based wireless network. We show the effectiveness of the wireless monitoring by quantitatively comparing it with SNMP and measurements at wired vantage points. We also show the analysis of a typical computer science department network traffic using the wireless monitoring technique. Our analysis reveals rich information about the PHY/MAC layers of the IEEE 802.11 protocol such as the typical traffic mix of different frame types, their temporal characteristics, correlation with the user activities and the error characteristics of the wireless medium. Moreover, we identify anomalies in the operation of the IEEE 802.11 MAC protocol. Our results show excessive retransmissions of some management frame types reducing the useful throughput of the wireless network. We also find that some features of the protocol, which were designed to reduce the retransmission errors, are not used. In addition, most of the clients fail to adapt the data rate according to the signal condition between them and the access point, which further reduce the useful throughput. (UMIACS-TR-2004-15)Item Handling Samples Correlation in the Horus System(2003-08-01) Youssef, Moustafa; Agrawala, AshokWe present an autoregressive model for modeling samples autocorrelation from the same access point in WLAN location determination systems. Our work is in the context of the Horus system, which is a probabilistic WLAN location determination system. We show that the autocorrelation between consecutive samples from the same access point can be as high as 0.9. Using our model, we describe a technique to use multiple signal strength samples from each access point, taking the high autocorrelation into account, to achieve better accuracy. Implementation of the technique in the Horus system shows that the average system accuracy is increased by more than 50%. Our results show that assuming independence of samples from the same access point can lead to degraded performance as the number of samples used in the estimation algorithm is increased, due to the wrong independence assumption. We also discuss how to incorporate the new technique with other algorithms for enhancing the performance of WLAN location determination systems. (UMIACS-TR-2003-75)Item The Overlapped K-hop (OK) Clustering Algorithm(2006-02-09T17:16:41Z) Youssef, Adel; Youssef, Moustafa; Younis, Mohamed; Agrawala, A.Clustering is a standard approach for achieving efficient and scalable performance in wireless sensor networks. Clustering algorithms are mostly heuristic in nature and aim at generating the minimum number of disjoint clusters. In this report, we formulate the overlapping multi-hop clustering problem as an extension to the k-dominating set problem. Then we propose a fast, randomized, distributed multi-hop clustering algorithm (OK) for organizing the sensors in a wireless sensor network into overlapping clusters with the goal of minimizing the overall communication overhead, and processing complexity. OK assumes a quasi-stationary network where nodes are location-unaware and have equal significance. No synchronization is needed between nodes. OK is scalable; the clustering formation terminates in a constant time regardless of the network topology or size. The protocol incurs low overhead in terms of processing cycles and messages exchanged. We analyze the effect of different parameters (e.g. node density, network connectivity) on the performance of the clustering algorithm in terms of communication overhead, node coverage, and average cluster size. The results show that although we have overlapped clusters, the OK clustering algorithm still produces approximately equal-sized clusters.Item 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)