Legacy Clients Research Articles

Collusion-Resistant Jamming for Securing Legacy Clients in Wireless Networks

Existing physical layer security schemes are inapplicable to legacy devices operating on long coherence-time channels, since they demand changes in the physical layer. To this end, a new physical-layer security scheme is developed to secure legacy clients. In this scheme, secret keys are generated by a client and transmitted to the access point (AP). To protect these keys, a separated device called secrecy protector (SP) transmits jamming signals to prevent eavesdroppers from overhearing the keys. The SP is equipped with multiple antennas, each of which transmits an independent jamming stream with a pseudo-preamble. Since the SP can share jamming signals with the AP secretly, the AP can use a certain analog network coding scheme to remove jamming signals and decode the keys. In contrast, eavesdroppers have no knowledge of jamming signals to decode the keys. However, the long coherence-time channels are vulnerable to eavesdroppers, as they can guess the channel coefficients in a brute force way and then remove the jamming signals. Thus, frequency diversity is exploited to enhance the security of the system. Moreover, the design of jamming mechanisms resists collusion among eavesdroppers. Therefore, secret keys can be secretly shared between the AP and a client. The developed scheme is implemented on a software-defined radio platform. Performance results demonstrate that it can effectively deliver secure communications without any changes to the physical layer of legacy clients.

POEM: Minimizing Energy Consumption for WiFi Tethering Service

Despite the rapidly increasing number of public WiFi hotspots, their coverage is still limited to indoor and office/business environments. WiFi tethering is thus a useful and economic means of providing on-the-go mobile users’ Internet connection. One of the main problems of WiFi tethering is the excessive power consumption of mobile access points (APs), or tethered smartphones. Since the power-saving mechanism, defined and deployed in the IEEE 802.11 standard, is intended for clients only, the WiFi interface of a mobile AP never enters the sleep mode. In this paper, we propose a simple but effective system, called power-efficient mobile (POEM), which reduces energy consumption of a mobile AP by allowing its WiFi interface to sleep even during data transfer. The POEM exploits the inherent bandwidth asymmetry between the WiFi and the WWAN interfaces of a mobile AP by buffering the data packets received via the WWAN interface at the mobile AP, thereby allowing the WiFi interface to enter the sleep mode. Compared with the other power-saving solutions for WiFi tethering, the POEM is able to handle various types of applications, such as video steaming and file download, designed to support legacy clients (i.e., clients without POEM), and is also efficient in reducing the clients’ energy consumption. We have implemented and conducted an extensive evaluation of the POEM’s effectiveness in an android/linux-based test bed. Our experimental results show that the POEM can allow the WiFi interface of a mobile AP to sleep for up to 90% of the total transfer time without significantly affecting system throughput or end-to-end delay.

Distributed channel assignment algorithms for 802.11n WLANs with heterogeneous clients

As the latest IEEE 802.11 standard, 802.11n applies several new technologies, such as multiple input multiple output (MIMO), channel bonding, and frame aggregation to greatly improve the rate, range and reliability of wireless local area networks (WLANs). In 802.11n WLANs, access points (APs) are often densely deployed to provide satisfactory coverage. Thus nearby APs should operate at non-overlapping channels to avoid mutual interference. It is challenging to assign channels in legacy 802.11a/b/g WLANs due to the limited number of channels. Channel assignment becomes more complex in 802.11n WLANs, as the channel bonding in 802.11n allows WLAN stations (APs and clients) to combine two adjacent, non-overlapping 20MHz channels together for transmission. On the other hand, IEEE 802.11n is backward compatible, such that 802.11n clients will coexist with legacy clients in 802.11n WLANs. Legacy clients may affect the performance of nearby 802.11n clients, and reduce the effectiveness of channel bonding. Based on these observations, in this paper, we study channel assignment in 802.11n WLANs with heterogeneous clients. We first present the network model, interference model, and throughput estimation model to estimate the throughput of each client. We then formulate the channel assignment problem into an optimization problem, with the objective of maximizing overall network throughput. Since the problem is NP-hard, we give a distributed channel assignment algorithm based on the throughput estimation model. We then present another channel assignment algorithm with lower complexity, and aim at minimizing interference experienced by high-rate, 802.11n clients. We have carried out extensive simulations to evaluate the proposed algorithms. Simulation results show that our algorithms can significantly improve the network throughput of 802.11n WLANs, compared with other channel assignment algorithms.

Efficient and Secure Web Services by using Multi Agents

Mobile agents are an excellent technology for implementing Web services. Within a set of federated Web services, mobile agents can reduce bandwidth requirements and mitigate the effects of high-latency network connections. This paper presents a model for implementing Web services with mobile agents where agents are free to move between cooperating Web servers to implement the service functionality. Also for increasing security of web services, we illustrate a novel distributed protocol for multi agent environments. In this approach, the encrypted private key and the message are broken into different parts carrying by different agents, which make it difficult for malicious entities to mine the private key for message encryption, while the private key for the encrypted key is allocated on the predetermined destination nodes. On the other hand, all of the previously proposed encryption algorithms can be applied in the proposed approach that deteriorates the key discovery process. To improve the overall security, the paper makes use of Advanced Encryption Standard (AES) as the encryption base for message encryption. Our mobile agent Web services present typical WSDL interfaces, so mobile agent functionality can be consumed from legacy clients, and federated services can be gradually migrated to a mobile agent implementation. General Terms Multi agent, Cryptographic Protocol, Mobile Agents, Security, and Web services et. al.

CopperCore service integration

In an e-learning environment there is a need to integrate various e-learning services like assessment services, collaboration services, learning design services and communication services. In this article we present the design and implementation of a generic integrative service framework, called CopperCore Service Integration (CCSI). We will concentrate on the integration of two services: CopperCore, an IMS Learning Design service and an IMS Question and Test Interoperability service called Assessment Provision through Interoperable Segments (APIS). One of the design goals of the architecture was to minimize the intrusion for both the services as well as any legacy client that already uses these services. The result of this work is that the flow of learning activities can be made dependent on test results.