Aslihan Celik

Distributed energy-efficient hierarchical clustering for wireless sensor networks

Since nodes in a sensor network have limited energy, prolonging the network lifetime and improving scalability become important. In this paper, we propose a distributed weight-based energy-efficient hierarchical clustering protocol (DWEHC). Each node first locates its neighbors (in its enclosure region), then calculates its weight which is based on its residual energy and distance to its neighbors. The largest weight node in a neighborhood may become a clusterhead. Neighboring nodes will then join the clusterhead hierarchy. The clustering process terminates in O(1) iterations, and does not depend on network topology or size. Simulations show that DWEHC clusters have good performance characteristics.

Improving the security of wireless LANs by managing 802.1x disassociation

802.1x is a security protocol based on the frame structure of 802.11. It attempts to provide strong authentication, access control, and WEP (wired equivalent privacy) key management for wireless LANs. Unfortunately, 802.1x misses its goals in access control denial-of-service attacks. Currently, there are no IEEE approved ways to solve this security hole. We propose a central manager, not only to take the responsibility of an authentication server, but also to add functionality to prevent denial of service attacks. We also analyze how the 802.11 MAC layer protocol works with our solution.

DEMAC: an adaptive power control MAC protocol for ad-hoc networks

Transmit power control (TPC) protocols have been proposed to address the limited power supplies in ad hoc networks. However, most of the previous work minimizes the transmit power without considering both the energy wasted in collisions and the energy used to overcome the interference from all the interfering nodes existing in the network. Our previous work shows the optimal transmit power for the maximum throughput and per frame minimum consumed energy exists and occurs when the power level is sufficient to avoid the interference, and causes the least contention between nodes. In this paper, we propose a novel per-frame-based TPC protocol, DEM AC, in ad hoc networks using IEEE 802.11 at low PHY rate. To avoid interference, improve throughput, and save energy, DEMAC adaptively looks for the optimal transmit power based on the network interference and data payload. DEMAC is validated via simulations and is shown to outperform several existing TPC protocols

Data Dissemination to a Large Mobile Network: Simulation of Broadcast Clouds

Research in data broadcasting in a wireless network has addressed the problems of what to broadcast and how to schedule the broadcasts. However, it is still not clear whether a single broadcast for the entire network, or an individual broadcast for each wireless cell is should be prepared. Recently, we proposed the Broadcast Clouds (BC) technique that bunches together wireless cells based on a cost saving principle, and prepares a common broadcast for these. This would presumably reduce the bandwidth cost and increase the service provider’s profit. In this paper, we describe our simulation software, BCSIM, that we use to evaluate the performance of the BC approach, and present the results.

Dynamic scheduling of PCF traffic in an unstable wireless LAN

IEEE 802.11 MAC protocol PCF is intended to facilitate real time traffic, however, the performance of PCF is highly affected by conditions on the WLAN and it has unnecessary overhead. To address these problems, we propose an aging priority scheduling algorithm and a dynamic adaptation algorithm to vary the PCF interval based on the traffic and reduce the overhead. Simulation results show our algorithms are efficient and suitable for PCF traffic.

I-DG: a secure protocol for disseminating data to subscribers via IP multicast

This paper proposes the IP Multicast-enabled Drop Groups (I-DG) protocol as a solution to the problem of efficiently and securely disseminating information to a large number of subscribers in the Internet. The I-DG protocol uses an appropriate IP multicasting protocol as the base and addresses the problems introduced by large scale data dissemination. I-DG provides dynamic subscription to multicast data, efficient secure subscription in IP multicasting, and proposes a solution to content organization in broadcasts.

A scalable approach for broadcasting data in a wireless network

This paper addresses the problem of providing secure access control in broadcast schemes in a wireless network. We consider an environment where clients subscribe to information objects sent via a broadcast onto a wireless network. In this context, a client should only be able to access its objects of interest for its subscription period, and the security system used must not be easily broken. Existing data broadcasting approaches fail to perform well with increased client loads. In this paper, we propose to use the Drop Groups (DG) protocol, that uses a novel grouping criterion. We present the broadcast organization under DG, and demonstrate that our approach is scalable. We use simulation to compare the DG protocol with existing techniques.

Data broadcasting with data item locality and client mobility

Existing broadcasting techniques prepare a data broadcast by appending individual information items together, and send the data broadcast to a common channel from which all the mobile clients download. These techniques, however, fail to elaborate on how to construct the network perimeter within which to send their broadcasts. It is conceivable that these techniques use one of the following approaches: 1. a single broadcast for the entire network is prepared (one-for-all), 2. an individual broadcast for each wireless cell is prepared (one-for-each). In this paper, we explore the performance of both approaches via simulations. Particularly when the data items have locality, i.e., the increased likelihood of being requested at certain geographical areas, we suspect that these approaches have little use. For example, the traffic on a busy intersection might be requested very frequently within 10 miles of that intersection, and is of very little interest to those travelling 100 miles from that area. Hence, with a broadcast protocol that does not consider locality of data items, many clients will receive irrelevant data items.

I-DG and HI-DG: Scalable and Efficient Techniques for Subscription-Based Data Dissemination via IP Multicasting

This paper proposes the IP Multicast-enabled Drop Groups (I-DG) and the Hybrid I-DG (HI-DG) techniques for solving the problem of efficiently and securely disseminating information to a large number of subscribers in the Internet. Possible application areas include stock market information distribution, refreshing the caches of edge servers on the Internet, pay-per-view information delivery. The proposed I-DG technique uses an appropriate IP multicasting protocol as the base and addresses the problems, such as key distribution and subscription, introduced by large scale data dissemination. I-DG provides dynamic and secure subscription to multicast data, and proposes a solution to content organization in broadcasts. The HI-DG technique employs a combination of multicasting and unicasting to reduce the packet load on the network. Simulation shows the efficacy of the two methods. I-DG performs the best when most of the clients subscribe to the same set of items, and HI-DG is best when a subset of data items is more popular.

DG: a scalable approach for broadcasting data securely in wireless networks

This paper addresses the problem of providing secure access control in broadcast schemes in a wireless network. We consider an environment where clients subscribe to information objects sent via a broadcast onto a wireless network. In this context, a client should only be able to access its objects of interest for its subscription period, and the security system used must not be easily broken. Existing data broadcasting approaches fail to perform well with increased client loads. In this paper, we propose to use the Drop Groups (DG) protocol, that uses a novel grouping criterion. We present the broadcast organization under DG, and demonstrate that our approach is scalable. We use simulation to compare the DG protocol with existing techniques.