Christos Politis

Hybrid multilayer mobility management with AAA context transfer capabilities for all-IP networks

This article presents a multilayer mobility management scheme for all-IP networks where local mobility movements (micro-mobility) are handled separately from global movements (macro-mobility). Furthermore, a hybrid scheme is proposed to handle macro-mobility (mobile IP for non-real-time services and SIP for real-time services). The internetworking between micromobility and macro-mobility is implemented at an entity called the enhanced mobility gateway. Both qualitative and quantitative results have demonstrated that the performance of the proposed mobility management is better than existing schemes. Furthermore, a context transfer solution for AAA is proposed to enhance the multilayer mobility management scheme by avoiding the additional delay introduced by AAA security procedures.

Cooperative networks for the future wireless world

Beyond-3G (B3G) systems have been envisaged as an evolution and convergence of mobile/wireless communication systems and IP technologies to offer a multitude of services over a variety of access technologies. To fulfill the vision, it is necessary to understand the requirements with respect to the support of heterogeneity in network accesses, communication services, mobility, user devices, and so on. Besides, it is equally important to promote the necessary research in networking technology by providing a guiding framework of research areas and technical issues with priority. The new architectures and technologies have to address the fundamental assumptions and requirements that govern the design. All these issues are being tackled by the cooperative network group (CoNet) of WWRF; the group is working on a series of white papers outlining B3G visions and roadmap, architectural principles, research challenges, and candidate approaches. This article outlines the CoNet concept, architectural principles, and guidelines for research into cooperative networks assuming that the B3G systems are built over generic IP networking technologies. The article also presents the key research challenges, research framework, and major network components and technologies. The key points are that the system should be layered on demand, encourage reuse if independent modularized functional blocks, support multiple services and service creation, ensure consistent end-to-end connectivity across different access technologies, and cooperate in terms of network control, operations, and maintenance. The architecture includes the endpoints of communications as part of the communications system, and provides a secure and trusted environment in which network functions are performed; the network should self-organize dynamically. Additionally, the article presents the IST WSI architecture proposed to CoNet as reference model along with some approaches to the outlined research challenges. Finally, this study selects three important network components and technologies (i.e., mobility management, multiple access, and moving networks) in order to provide with answers and possible solutions the research challenges presented in earlier sections.

Multilayer mobility management for all-IP networks: pure SIP vs. hybrid SIP/mobile IP

Next generation systems will support mobility based on the continuing advancements in wireless technology. An integrated solution, whereby mobility management is an integral part of the IP layer routing protocol, would be more advantageous for both the operator and the end user. In this paper, we present two mobility management architectures based on SIP and Mobile IP protocols. These configurations mainly allow/provide mobility in two different layers namely the application and network layers and due to that our proposal is so-called multilayered. Such mobility should be present over heterogeneous networks, such as UMTS, WLANs, as well as, fixed networks. The two proposed architectures are evaluated in terms of mobility-related metrics and for two types of traffic, real time and non real time. Finally, we propose the most suitable architecture for mobility management over heterogeneous all-IP infrastructures.

An Adaptive QoS Routing Solution for MANET Based Multimedia Communications in Emergency Cases

The Mobile Ad hoc Networks (MANET) is a wireless network deprived of any fixed central authoritative routing entity. It relies entirely on collaborating nodes forwarding packets from source to destination. This paper describes the design, implementation and performance evaluation of CHAMELEON, an adaptive Quality of Service (QoS) routing solution, with improved delay and jitter performances, enabling multimedia communication for MANETs in extreme emergency situations such as forest fire and terrorist attacks as defined in the PEACE project. CHAMELEON is designed to adapt its routing behaviour according to the size of a MANET. The reactive Ad Hoc on-Demand Distance Vector Routing (AODV) and proactive Optimized Link State Routing (OLSR) protocols are deemed appropriate for CHAMELEON through their performance evaluation in terms of delay and jitter for different MANET sizes in a building fire emergency scenario. CHAMELEON is then implemented in NS-2 and evaluated similarly. The paper concludes with a summary of findings so far and intended future work.

Cognitive vehicular communication for 5G

Device-to-device (D2D) is increasingly becoming a prominent technology within the 5G story, portrayed as a means of offloading traffic from the core network. The ever increasing demand for vehicular traffic consumption is providing the impetus for a new architectural design that can harness the benefits of D2D for vehicular users, taking a step toward offloading vehicular traffic from the core network. We propose the notion of extending D2D for vehicular scenarios with the potential to coordinate vehicular traffic using the LTE band. Furthermore, we then extend this approach by investigating cognitive radio in synergy with a geo-location database, to exploit white spaces as a means of further offloading vehicular users. Our simulation results have shown that our approach can outperform the legacy IEEE 802.11p in terms of delay.

Securing AODV against wormhole attacks in emergency MANET multimedia communications

The nature of Mobile Ad hoc NETworks (MANETs) makes them suitable to be utilized in the context of an extreme emergency for all rescue teams. We use the term emergency MANETs (eMANETs) in order to describe Next Generation Networks (NGNs) which are deployed in emergency cases such as forest fires and terrorist attacks. Secure routing in MANETs is critical. Due to the absence of a central authority, intermediate nodes act as routers forwarding packets across a multihop path. A well known attack against the conventional operation of routing protocols such as the Ad hoc On-demand Distance Vector (AODV) routing protocol, is the wormhole attack. Secure routing in eMANETs is critical due to the fact that secure multimedia communications should be established among the devices of the recovery workers. In this paper we propose a novel routing mechanism called AODV-Wormhole Attack Detection Reaction AODV-WADR to defend eMANETs against wormhole attacks. Our simulations are carried out using the network simulator ns-2 and they show that AODV-WADR does not introduce high overhead, reducing significantly the amount of packet loss caused by malicious wormhole nodes. These are critical requirements for eMANETs where lightweight security mechanisms should be applied and malicious activities should be circumvented.

A game theoretic approach for securing AODV in emergency Mobile Ad Hoc Networks

In many extreme emergency cases such as forest fires or tube terrorist attacks, the rescuers have difficulty using traditional legacy networks due to destruction or collapse of the infrastructure in such events. We use the term emergency Mobile Ad hoc NETworks (eMANETs) in order to describe Next Generation Networks (NGNs) which are deployed in emergency cases. The security of these networks is critical. Especially secure routing is important given the fact that potential attackers aim to disrupt the appropriate operation of the routing protocol within an eMANET. In this paper we propose a game theoretic approach called AODV-GT (AODV-Game Theoretic) and we integrate this into the reactive Ad hoc On-demand Distance Vector (AODV) routing protocol to provide defense against blackhole attacks. AODV-GT is based on the concept of non-cooperative game theory. AODV-GT outperforms AODV in terms of malicious dropped packets when blackhole nodes exist within the eMANET. Our simulations were implemented using the network simulator ns-2.

Find the Weakest Link: Statistical Analysis on Wireless Sensor Network Link-Quality Metrics

Routing protocol plays an important role in data communication. A wireless sensor network (WSN) is usually deployed in scenarios where efficient and energy-aware routing protocols are desired. In wireless sensors, the radio-frequency (RF) modules consume most of the energy. Routing metrics are important in determining paths and maintaining the quality of service in routing protocols. The most efficient metrics need to send packets to maintain link-quality measurement using the RF module. In this article, two prominent link-quality metrics-received signal strength indication (RSSI) and link-quality indication (LQI)-are introduced; the symmetry of RSSI and LQI in two directions has been studied, and relations between the expected transmission count (ETX), RSSI, and LQI as link-quality metrics have been analyzed. The evaluation in this article is based on a series of WSN test beds in real scenarios. The collected data from the test beds show symmetry in the RSSI in both directions as well as a significant correlation between the RSSI and distance, making RSSI a suitable link-quality metric for use in routing protocols for devices that work in limited-resources scenarios.

Managing the radio spectrum

In this article, we focus on the vision of spectrally aware CR that comprises handsets automatically making use of under-utilized spectrum by sequentially hopping into spectrum gaps across a broad frequency range. The topics discussed in this article are based on a project funded by Ofcom (the U.K. Communications Regulator) to investigate the issues surrounding the introduction of CR technology.

An enhanced routing metric for ad hoc networks based on real time testbed

The deployment of wireless ad-hoc networks compared to traditional infrastructure based networks offers several advantages such as fully distributed mobile operation, easy discovery of joining wireless devices and quick cheap network setup. The design of an effective routing protocol is one of the main challenges in the ad-hoc networking paradigm and the utilisation of an adequate link cost metric is essential. In this paper, the validity of ETX (Expected Transmission Count) as a link cost metric is investigated by studying its behaviour in real-time testbeds. In our performance evaluation, the ETX performance was studied in different distance scenarios. Subsequently, the main observation was that ETX values was not steady over time and usually fluctuated for a fixed scenario. Fluctuation in the ETX values affects a routing protocol in wrongly identifying the best path based on current ETX link cost and therefore new methods for ETX calculation are proposed in this paper. These different methods for ETX link cost calculation are compared with each other and the best link cost formula has been proposed as a new method for ETX calculation towards the end of the paper. The new ETX calculation is called AETX that could be used as a link cost in routing protocols that reflects the balance required between the consistency of a link metric value over time for fixed scenarios and the flexibility required to detect actual changes in link metric values. We finally provide conclusions about our research and some avenues for future work.