Ibrahim Hokelek

Genetic algorithms for self-spreading nodes in MANETs

We present a force-based genetic algorithm for self-spreading mobile nodes uniformly over a geographical area. Wireless mobile nodes adjust their speed and direction using a genetic algorithm, where each mobile node exchanges its genetic information of speed and direction encoded in its chromosomes with the neighboring nodes. Simulation experiments show encouraging results for the performance of our force-based genetic algorithm with respect to normalized area coverage..

Bio-inspired topology control for knowledge sharing mobile agents

We present different approaches for knowledge sharing bio-inspired mobile agents to obtain a uniform distribution of the nodes over a geographical terrain. In this application, the knowledge sharing agents in a mobile ad hoc network adjust their speed and directions based on genetic algorithms (GAs). With an analytical model, we show that the best fitness value is obtained when the number of neighbors for a mobile agent is equal to the mean node degree. The genetic information that each mobile agent exchanges with other neighboring agents within its communication range includes the nodes location, speed, and movement direction. We have implemented a simulation software to study the effectiveness of different GA-based algorithms for network performance metrics including node densities, speed, and number of generations that a GA runs. Compared to random-walk and Hill Climbing approaches, all GA-based cases show encouraging results by converging towards a uniform node distribution.

Uniform distribution of mobile agents using genetic algorithms for military applications in MANETs

There has been increased research interest in providing uniform distribution of autonomous mobile nodes controlled by active running software agents over an unknown geographical area in mobile ad-hoc networks (MANETs). This problem becomes more challenging under the harsh and bandwidth limited conditions imposed by military applications. In this framework, the software agent running at the application layer for each autonomous mobile node adjusts its direction and speed by using local information from its neighbors. A genetic algorithm (GA) is used by each node to select the ldquofitterrdquo speed and direction options among exponentially large number of choices converging towards a uniform distribution. For a military application example, consider that in the observed occurrence of a threat situation, if the number of autonomous mobile agents change with time (e.g., losing assets during an operation), the remaining agents should reposition themselves to compensate the lost in coverage and network connectivity. We implemented simulation software to evaluate the effectiveness of GAs within these types of military applications. The results show that GAs can be applied to autonomous mobile nodes and are an effective tool for providing a robust solution for network area coverage under restrained communication conditions.

On stability analysis of virtual backbone in mobile ad hoc networks

Service discovery architectures and cluster-assisted routing protocols in mobile ad-hoc networks (MANETs) heavily use formation and maintenance of a virtual backbone (VB), where the most stable mobile nodes with higher node degree are dynamically selected as the backbone nodes. In this paper we present a novel analytic model for VB stability in MANETs. The model employs the dynamics of node movements, where link creation/failure is modeled via a random walk with probabilistic state-transition matrix. The backbone formation algorithm gives preference to the nodes with the smaller number of link changes and the higher degree. Therefore, the link arrivals and departures determine the probability (and thus the expected time) for a mobile node to leave, join, or remain in the backbone, i.e., the stability of a dynamic structure of VB.

Reliable and dynamic access to services in battlefield ad hoc networks

Survivable access to resources and services in battlefield networks can be provided through name servers (NS) that gather service/resource registrations and resolve the queries from the requesting nodes. Functionally equivalent services can also be pooled so that the queries would be. resolved to multiple entries, accessed as a single logical reliable server pool (RSP). We defined a new RSP architecture called dynamic survivable resource pooling (DSRP) that utilizes a virtual backbone (VB) for ad hoc network as a dynamic structure for hosting NS. A mesh of NS connected by a set of virtual links are used to relay service registrations, requests, and replies. In this paper, we give an overview of the RSP and VB, show how the DSRP is designed based on these two schemes, and outline battlefield applications such as situation awareness, network security, distributed robotics, and QoS in red-black networks.

Trade-off analysis of Multi Topology Routing based IP fast reroute mechanisms

To seamlessly support real-time services such as voice and video over next generation IP networks, routers must continue their forwarding tasks in case of link/node failures by limiting the service disruption time to sub-100 ms. IETF Routing Area Working Group (RTGWG) has been working on standardizing IP Fast Reroute (IPFRR) methods with a complete alternate path coverage. In this paper, a trade-off analysis of Multi Topology Routing (MTR) based IPFRR technologies targeting full coverage, namely Multiple Routing Configurations (MRC) and Maximally Redundant Trees (MRT), are presented. We implemented a comprehensive analysis tool to evaluate the performance of MRC and MRT mechanisms on various synthetic network topologies. The performance results show that MRTs alternative path lengths are not scalable with respect to the network size and density while the alternative path lengths of MRC only slightly change as the network size and density vary. We believe that this is an important scalability result providing a guidance in the selection of MTR-based IPFRR mechanism for improving the availability in ISP networks.

An integrated soft handoff approach to IP fast reroute in wireless mobile networks

This paper presents an integrated approach to IP fast reroute (IPFRR) of both unicast and multicast paths in wireless mobile networks. A distinct feature of the proposed approach is that, instead of modifying existing routing protocols, it employs a soft handoff technique, i.e., temporarily installs pre-computed Loop Free Alternative Paths (LFAPs) until the co-existing routing protocol converges to new routes. The proposed approach builds on our previously proposed IPFRR technology and uses the concept of pre-computed LFAPs not only for local but also for remote link failures within a certain neighborhood to achieve full alternative path coverage for a single link failure. This papers contributions include: i) bandwidth efficient fast failure detection by integrating two novel mechanisms, namely probing and link quality prediction, ii) a novel method for calculating LFAPs, iii) a framework for switching seamlessly between LFAPs and OSPF paths, iv) a multicast fast reroute mechanism, and v) implementation in eXtensible Open Router Platform (XORP). We also present a generic framework for handling multiple simultaneous failures in the integrated IPFRR. The performance evaluation has been performed in both indoor and outdoor environments with real 802.11 radio links. The results confirm that our IPFRR technology consistently provides significant convergence time improvement during a single link failure event.

Realistic wireless emulation for performance evaluation of tactical MANET protocols

Traditional approaches for testing MANET protocols and applications prior to field experimentation often involve simulation tools or small-sized physical testbeds. However, simulation tools typically do not run in real-time and rely on simplified models rather than a real system, while physical testbeds are prohibitively expensive to build and operate. A more practical method is to use emulation tools as they provide high-fidelity network modeling in a cost-effective manner without sacrificing realism. In this paper, we present the use of Wireless IP Scalable EmulatoR (WISER) and its capabilities for testing and evaluating two network routing agents, namely Congestion Control Agent (CCA) and Soft Handoff Agent (SHA), developed for tactical MANETs under the CERDEC PILSNER program. These two agents are integrated within the WISER framework, providing them a scalable and realistic wireless MANET testbed which otherwise was not readily available. Experiments demonstrating interoperability of these technologies are included.

WISER: realistic and scalable wireless mobile IP network emulator

WISER is a scalable network emulation tool for networks with several hundred heterogeneous wireless nodes. It provides high-fidelity network modeling, exchanges packets in real-time, and faithfully captures the complex interactions among network entities. WISER runs on inexpensive COTS platforms and represents multiple full network stacks, one for each individual virtual node. It supports a flexible open source router platform (XORP) to implement routing protocol stacks. WISER offers wireless MAC emulation capabilities for different types of links, waveforms, radio devices, etc. We present experiments to demonstrate WISERs capabilities enabling a new paradigm for performance evaluation of mobile sensor and ad-hoc networks.

Controlling SIP server overload with priority based request scheduling

In this paper, we introduce a priority based SIP server scheduling mechanism in which the original incoming SIP requests have strict priority over the retransmitted requests. The proposed mechanism provides the network administrator with the ability to configure the buffer size of a SIP server to a moderately high value without causing the server crash due to retransmissions. A new field on the SIP request line is introduced to identify an incoming SIP request is a new arrival or retransmission without parsing its content completely. Numerical experiments using our analysis tool show that the proposed scheduling mechanism provides significantly and consistently better scalability at high buffer sizes compared to the conventional first-in-first-out scheduling. The proof of concept implementation in the JAIN-SIP stack demonstrates the superiority of the proposed solution using the realistic scenarios.