arXiv subjects

Ahmed Helmy

Publications and source records attributed to Ahmed Helmy.

43 records · Page 3Linked to original sources

arXiv2002

Small Large-Scale Wireless Networks: Mobility-Assisted Resource Discovery

In this study, the concept of small worlds is investigated in the context of large-scale wireless ad hoc and sensor networks. Wireless networks are spatial graphs that are usually much more clustered than random networks and have much higher path length characteristics. We observe that by adding only few random links, path length of wireless networks can be reduced drastically without affecting clustering. What is even more interesting is that such links need not be formed randomly but may be confined to a limited number of hops between the connected nodes. This has an important practical implication, as now we can introduce a distributed algorithm in large-scale wireless networks, based on what we call contacts, to improve the performance of resource discovery in such networks, without resorting to global flooding. We propose new contact-based protocols for adding logical short cuts in wireless networks efficiently. The new protocols take advantage of mobility in order to increase reachability of the search. We study the performance of our proposed contact-based architecture, and clarify the context in which large-scale wireless networks can be turned into small world networks.

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arXiv2002

Fair Stateless Aggregate Traffic Marking using Active Queue Management Techniques

In heterogeneous networks such as today's Internet, the differentiated services architecture promises to provide QoS guarantees through scalable service differentiation. Traffic marking is an important component of this framework. In this paper, we propose two new aggregate markers that are stateless, scalable and fair. We leverage stateless Active Queue Management (AQM) algorithms to enable fair and efficient token distribution among individual flows of an aggregate. The first marker, Probabilistic Aggregate Marker (PAM), uses the Token Bucket burst size to probabilistically mark incoming packets to ensure TCP-friendly and proportionally fair marking. The second marker, Stateless Aggregate Fair Marker (F-SAM) approximates fair queueing techniques to isolate flows while marking packets of the aggregate. It distributes tokens evenly among the flows without maintaining per-flow state. Our simulation results show that our marking strategies show upto 30% improvement over other commonly used markers while marking flow aggregates. These improvements are in terms of better average throughput and fairness indices, in scenarios containing heterogeneous traffic consisting of TCP (both long lived elephants and short lived mice) and misbehaving UDP flows. As a bonus, F-SAM helps the mice to win the war against elephants.

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arXiv2001

Architectural Framework for Large-Scale Multicast in Mobile Ad Hoc Networks

Emerging ad hoc networks are infrastructure-less networks consisting of wireless devices with various power constraints, capabilities and mobility characteristics. An essential capability in future ad hoc networks is the ability to provide scalable multicast services. This paper presents a novel adaptive architecture to support multicast services in large-scale wide-area ad hoc networks. Existing works on multicast in ad hoc networks address only small size networks. Our main design goals are scalability, robustness and efficiency. We propose a self-configuring hierarchy extending zone-based routing with the notion of contacts based on the small world graphs phenomenon and new metrics of stability and mobility. We introduce a new geographic-based multicast address allocation scheme coupled with adaptive anycast based on group popularity. Our scheme is the first of its kind and promises efficient and robust operation in the common case. Also, based on the new concept of rendezvous regions, we provide a bootstrap mechanism for the multicast service; a challenge generally ignored in previous work.

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arXiv2001

State Analysis and Aggregation Study for Multicast-based Micro Mobility

IP mobility addresses the problem of changing the network point-of-attachment transparently during movement. Mobile IP is the proposed standard by IETF. Several studies, however, have shown that Mobile IP has several drawbacks, such as triangle routing and poor handoff performance. Multicast-based mobility has been proposed as a promising solution to the above problems, incurring less end-to-end delays and fast smooth handoff. Nonetheless, such architecture suffers from multicast state scalability problems with the growth in number of mobile nodes. This architecture also requires ubiquitous multicast deployment and more complex security measures. To alleviate these problems, we propose an intra-domain multicast-based mobility solution. A mobility proxy allocates a multicast address for each mobile that moves to its domain. The mobile uses this multicast address within a domain for micro mobility. Also, aggregation is considered to reduce the multicast state. We conduct multicast state analysis to study the efficiency of several aggregation techniques. We use extensive simulation to evaluate our protocol's performance over a variety of real and generated topologies. We take aggregation gain as metric for our evaluation. Our simulation results show that in general leaky aggregation obtains better gains than perfect aggregation. Also, we notice that aggregation gain increases with the increase in number of visiting mobile nodes and with the decrease in number of mobility proxies within a domain.

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arXiv2000

Systematic Testing of Multicast Routing Protocols: Analysis of Forward and Backward Search Techniques

In this paper, we present a new methodology for developing systematic and automatic test generation algorithms for multipoint protocols. These algorithms attempt to synthesize network topologies and sequences of events that stress the protocol's correctness or performance. This problem can be viewed as a domain-specific search problem that suffers from the state space explosion problem. One goal of this work is to circumvent the state space explosion problem utilizing knowledge of network and fault modeling, and multipoint protocols. The two approaches investigated in this study are based on forward and backward search techniques. We use an extended finite state machine (FSM) model of the protocol. The first algorithm uses forward search to perform reduced reachability analysis. Using domain-specific information for multicast routing over LANs, the algorithm complexity is reduced from exponential to polynomial in the number of routers. This approach, however, does not fully automate topology synthesis. The second algorithm, the fault-oriented test generation, uses backward search for topology synthesis and uses backtracking to generate event sequences instead of searching forward from initial states. Using these algorithms, we have conducted studies for correctness of the multicast routing protocol PIM. We propose to extend these algorithms to study end-to-end multipoint protocols using a virtual LAN that represents delays of the underlying multicast distribution tree.

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arXiv2000

Systematic Performance Evaluation of Multipoint Protocols

The advent of multipoint (multicast-based) applications and the growth and complexity of the Internet has complicated network protocol design and evaluation. In this paper, we present a method for automatic synthesis of worst and best case scenarios for multipoint protocol performance evaluation. Our method uses a fault-oriented test generation (FOTG) algorithm for searching the protocol and system state space to synthesize these scenarios. The algorithm is based on a global finite state machine (FSM) model. We extend the algorithm with timing semantics to handle end-to-end delays and address performance criteria. We introduce the notion of a virtual LAN to represent delays of the underlying multicast distribution tree. As a case study, we use our method to evaluate variants of the timer suppression mechanism, used in various multipoint protocols, with respect to two performance criteria: overhead of response messages and response time. Simulation results for reliable multicast protocols show that our method provides a scalable way for synthesizing worst-case scenarios automatically. We expect our method to serve as a model for applying systematic scenario generation to other multipoint protocols.

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arXiv2000

Multicast-based Architecture for IP Mobility: Simulation Analysis and Comparison with Basic Mobile IP

With the introduction of a newer generation of wireless devices and technologies, the need for an efficient architecture for IP mobility is becoming more apparent. Several architectures have been proposed to support IP mobility. Most studies, however, show that current architectures, in general, fall short from satisfying the performance requirements for wireless applications, mainly audio. Other studies have shown performance improvement by using multicast to reduce latency and packet loss during handoff. In this study, we propose a multicast-based architecture to support IP mobility. We evaluate our approach through simulation, and we compare it to mainstream approaches for IP mobility, mainly, the Mobile IP protocol. Comparison is performed according to the required performance criteria, such as smooth handoff and efficient routing. Our simulation results show significant improvement for the proposed architecture. On average, basic Mobile IP consumes almost twice as much network bandwidth, and experiences more than twice as much end-to-end and handoff delays, as does our proposed architecture. Furthermore, we propose an extension to Mobile IP to support our architecture with minimal modification.

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