SATNAC 2007 Conference Papers


Title:                   A Joint IEEE802.21 and Cross Layer Model

Authors:              Mohamed Abdelatif (University of Cape Town),
Anthony Chan (University of Cape Town), George Kalebaila (University of Cape Town)

Abstract:             In the near future devices will be required to roam across heterogeneous networks with seamless ease. These devices have to contend with problems of heterogeneity inherent in the different link access technologies. Mobility management protocols that are traditionally not equipped to handoff between dissimilar networks will have to take decisions necessary for service continuity. Recent efforts by the IEEE802.21 group have culminated in a draft standard introducing Media Independent Handover Services. The standard provides a framework that abstracts link-specific characteristics from higher layered mobility protocols. This will enable various mobility protocols to handoff uniformly and seamlessly across heterogeneous networks. A Media Independent Handover Function (MIHF) is designed to translate different network interface messages to generic events that can accessed by the higher-layered mobility protocols. However the message load on the MIHF can reduce the response time of event notification and command delivery to and from the mobility protocols. A more time-sensitive solution is presented by introducing a Cross Layer Manager (XLM) into the protocol stack. The results show that better performance is achieved to reduce the number of unserviced events and commands. This shows a critical improvement that would make the XLM model feasible for Next-Generation mobility management.


Title:                   A Silent SMS Denial of Service (DoS) Attack

Authors:              Neil Croft (University of Pretoria),
Martin Olivier (University of Pretoria) 

Abstract:             Global System for Mobile communications (GSM) is a popular mobile communications network. Short Message Service (SMS) is an easily adopted person-to-person communications technology for mobile devices. The GSM architecture allows for the insertion of mass application-generated SMS messages directly into the network infrastructure. This is achieved througha SMS Mobile Switching Centre (SMSC) using a variety of request-response protocols, for example Short Message Peer-To-Peer Protocol (SMPP). Through protocol manipulation, an application may generate an SMS which neither displays on the mobile handset nor provides an acoustic signal. Known as a “Silent” SMS, this occurs where the mobile handset must acknowledge receipt of the short message but may discard its contents. A “Silent” SMS may help police services detect the existence of a mobile handset without the intended party knowing about the request. In contrast, a mass continuous send of “Silent” SMS messages will constitute an invisible Denial of Service (DoS) attack on a mobile handset. Such a mobile handset DoS attack may be conducted for economic advantage to elude another party from communicating. This paper describes, from a technical perspective, how a silent application-generated denial of service (DoS) SMS attack is conducted. We then investigate possible ways of thwarting such an attack at a GSM network level. Furthermore we explore related SMS attacks on the GSM network.


Title:                   Optimization of Hybrid Token-CDMA MAC System Using Cross-Layer Information

Authors:              I-Sheng Liu (University of KwaZulu-Natal),
Fambirai Takawira (University of KwaZulu-Natal), Hong Jun Xu (University of KwaZulu-Natal)

Abstract:             This paper presents a joint medium access control and physical (MAC-PHY) layers solution for optimizing the system performance in the hybrid Token-CDMA MAC system. The proposed scheme is designed in order to provide continuous monitoring of the performance achieved by the users and adjusting transmission parameters using different spreading factors. Various performance metrics are used to demonstrate effectiveness of the cross-layer interaction for the hybrid Token-CDMA MAC protocol.


Title:                   QoS Provisioning Using Cross-Layer Design

Authors:              Tahmid Quazi (University of Kwa-Zulu Natal),
Hongjun Xu (University of Kwa-Zulu Natal), Fambirai Takawira (University of Kwa-Zulu Natal)

Abstract:             Guaranteeing QoS is critical to the functioning of multimedia applications over mobile wireless networks. However, currently the challenge of QoS provisioning is being faced using the legacy layered protocol architecture where each layer provides a separate, independent solution, with its own optimized adaptation and protection mechanisms. Cross-layer design has been proposed as a methodology to extend that paradigm in wireless links where there is interdependence between the layers and hence opportunity for information sharing. Recently Crosslayer adaptation mechanisms have been proposed that attempt to solve the QoS provisioning problem. However, most of these mechanisms only use the lower (physical and data link) layers and the possibility of using higher protocol layers remain unexplored. As a result restrictions are placed on the system which introduces functional and efficiency limitations. In this paper we highlight one such limitation, namely the inability to insert more than one class of traffic in a physical layer frame. We then propose a physical and application layer Cross-layer adaptation mechanism that overcomes this. The performance results of the scheme shows that the Cross-layer mechanism can be efficiently applied for the purpose of QoS provisioning in wireless links.


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