Vincent Lenders

Wireless ad hoc podcasting

Podcasting has become popular for dissemination of streaming contents over the Internet. It is based on software clients that query servers for updates of subscribed content feeds. Podcasting may be used for any media content, but it is most commonly associated with audio streams. It provides a simple, no-frills broadcasting system for delay tolerant contents. A main limitation with this system is the inflexible separation of downloading to a docked media player and expending of the data when on the move. We herein present how podcast could be supported by our previously proposed delay-tolerant broadcasting system in order to reduce the expected times between updates and to provide a new ad hoc podcasting mode among mobile nodes. Our system substitutes the client-server paradigm inherent in present podcasting by a peer-to-peer paradigm where mobile nodes provide each other with contents. We present the protocol for this, and an evaluation of solicitation and caching strategies that greatly affect the application-level throughput. Our design is aiming at simplicity in order to enable implementation in mobile phones with media players and other devices that communicate over short ranges by means of Bluetooth or wireless LAN.

Wireless Ad Hoc Podcasting

Podcasting has become popular for dissemination of streaming contents over the Internet. It is based on software clients that query servers for updates of subscribed content feeds. Podcasting may be used for any media content, but it is most commonly associated with audio streams. It provides a simple, no-frills broadcasting system for delay tolerant contents. A main limitation with this system is the inflexible separation of downloading to a docked media player and expending of the data when on the move. We herein present how podcast could be supported by our previously proposed delay-tolerant broadcasting system in order to reduce the expected times between updates and to provide a new ad hoc podcasting mode among mobile nodes. Our system substitutes the client-server paradigm inherent in present podcasting by a peer-to-peer paradigm where mobile nodes provide each other with contents. We present the protocol for this, and an evaluation of solicitation and caching strategies that greatly affect the application-level throughput. Our design is aiming at simplicity in order to enable implementation in mobile phones with media players and other devices that communicate over short ranges by means of Bluetooth or wireless LAN.

Location-based trust for mobile user-generated content: applications, challenges and implementations

The recent explosion in shared media content and sensed data produced by mobile end-users is challenging well-established principles and assumptions in data trust models. A fundamental issue we address in this paper is how to establish some trust level in the authenticity of content created by untrusted mobile users. We advocate a secure localization and certification service that allows content producers to tag their content with with a spatial times-tamp indicating its physical location. At the same time, however, our approach preserves the privacy of producers by not exposing their identity to the potential content consumers. We provide a list of existing and possible applications that would profit from such a secure localization service and sketch possible implementations of the service, highlighting advantages and drawbacks.

HEAT: Scalable Routing in Wireless Mesh Networks Using Temperature Fields

Existing unicast routing protocols are not suited well for wireless mesh networks as in such networks, most traffic flows between a large number of mobile nodes and a few access points with Internet connectivity. In this paper, we propose HEAT, an anycast routing protocol for this type of communication that is designed to scale to the network size and to be robust to node mobility. HEAT relies on a temperature field to route data packets towards the Internet gateways, as follows. Every node is assigned a temperature value, and packets are routed along increasing temperature values until they reach any of the Internet gateways, which are modeled as heat sources. Our major contribution is a distributed protocol to establish such temperature fields. The distinguishing feature of our protocol is that it does not require flooding of control messages. Rather, every node in the network determines its temperature considering only the temperature of its direct neighbors, which renders our protocol particularly scalable to the network size. We analyze our approach and compare its performance with OLSR through simulations with Glomosim. We use realistic mobility patterns extracted from geographical data of large Swiss cities. Our results clearly show the benefit of HEAT versus OLSR in terms of scalability to the number of nodes and robustness to node mobility. The packet delivery ratio with HEAT is more than two times higher than OLSR in large mobile scenarios and we conclude that HEAT is a suitable routing protocol for city-wide wireless mesh networks.

Density-based anycast: a robust routing strategy for wireless ad hoc networks

Existing anycast routing protocols solely route packets to the closest group member. In this paper, we introduce density-based anycast routing, a new anycast routing paradigm particularly suitable for wireless ad hoc networks. Instead of routing packets merely on proximity information to the closest member, density-based anycast routing considers the number of available anycast group members for its routing decision. We present a unified model based on potential fields that allows for instantiation of pure proximity-based, pure density-based, as well as hybrid routing strategies. We implement anycast using this model and simulate the performance of the different approaches for mobile as well as static ad hoc networks with frequent link failures. Our results show that the best performance lies in a tradeoff between proximity and density. In this combined routing strategy, the packet delivery ratio is considerably higher and the path length remains almost as low than with traditional shortest-path anycast routing.

Wireless opportunistic podcasting: implementation and design tradeoffs

Podcasting has become a very popular and successful Internet service in a short time. This success illustrates the interest for participatory broadcasting, but podcasting is alas only available with fixed infrastructure support to retrieve publicized episodes. We aim at changing this limitation and present herein a system architecture based on opportunistic wireless networking that allows us to extend podcasting to ad hoc domains. The design is explained and presented together with a prototype implementation running on hand-held devices. We analyze different design tradeoffs based on measurements from real devices. The prototype is publicly available and its functionality and performance are intended to be demonstrated in the demo session of this workshop.

Link-Diversity Routing: A Robust Routing Paradigm for Mobile Ad Hoc Networks

We present link-diversity routing, a routing paradigm that achieves high path resilience in mobile ad hoc networks. Link-diversity routing chooses each hop of a packets route, so that the choice reflects the amount of outgoing links towards the destination at the intermediate hops. This choice maximizes the opportunities to make progress at every hop in the presence of unpredictable link failures caused by mobility or fading effects. As a result, link diversity routing takes paths which are less prone to fail due to individual link failures than traditional routing. We develop a loop-free and distributed link-diversity routing algorithm. The algorithm is based on an analogy from the heat theory which consists of routing packets along the steepest gradient of a temperature field. We perform simulations of our algorithm with a DSDV-based implementation. Our simulations show that link-diversity routing increases the end-to-end packet delivery ratio to a factor of up to four without any additional protocol overhead compared to the traditional minimum hop- count based DSDV.