Epidemic Dissemination of Presence Information in Mobile Instant Messaging Systems

This paper presents an approach for exchanging presence information between users of an instant messaging system in a mobile ad hoc network. As major feature, presence information is transferred when mobile users get in direct contact, similar to the spread of an infections disease. By exploiting node mobility, presence information is epidemically distributed throughout the network, effectively overcoming network partitions. We show how to apply the Passive Distributed Indexing Protocol, which implements a general-purpose lookup service for mobile applications building upon epidemic data dissemination, for implementing the exchange of presence information. The effectiveness of the approach is illustrated in a simulation study using the network simulator ns-2. Building upon the results, we present the architecture of a mobile instant messaging system that supports the widely adopted Extensible Messaging and Presence Protocol (XMPP), an IETF standardized protocol for instant messaging

Web Search From a Bus

Opportunistic connections to the Internet from open wireless access points is now commonly possible in municipal areas. Vehicular networks can opportunistically connect to the internet for several seconds via open access points. In this paper, we adapt the interactive process of web search and retrieval to vehicular networks with intermittent Internet access. Our system, called Thedu has mobile nodes use an Internet proxy to collect search engine results and prefetch result pages. The mobiles nodes download the pre-fetched web pages from the proxy. Our contribution is a novel set of techniques to make aggressive but selective prefetching practical, resulting in a significantly greater number of relevant web results returned to mobile users. To evaluate our scheme, we deployed Thedu on DieselNet, our vehicular testbed of buses operating in a micro-urban area around Amherst, MA. Using a simulated workload, we find that users can expect four times as many useful responses to web search queries compared to not using Thedu. Moreover, the mean latency in receiving the first relevant response for a query is 2.7 minutes when deployed in a semi-urban region with a sparser distribution of APs compared to big cities

Consistency mechanisms for a distributed lookup service supporting mobile applications

This paper presents a general-purpose distributed lookup service, denoted Passive Distributed Indexing (PDI). PDI stores entries in form of (key, value) pairs in index caches located in each mobile device. Index caches are filled by epidemic dissemination of popular index entries. By exploiting node mobility, PDI can resolve most queries locally without sending messages outside the radio coverage of the inquiring node. Thus, PDI reduces network traffic for the resolution of keys to values. For keeping index caches coherent, configurable value timeouts implementing implicit invalidation and lazy invalidation caches implementing explicit invalidation are introduced. Inconsistency in index caches due to weak connectivity or node failure is handled by value timeouts. Lazy invalidation caches reduce the fraction of stale index entries due to modified data at the origin node. Similar to index caches, invalidation caches are filled by epidemic distributions of invalidation messages. Simulation results show that with the suitable integration of both invalidation mechanisms, more than 95% of results delivered by PDI index caches are up-to-date for the considered scenario

Exploiting epidemic data dissemination for consistent lookup operations in mobile applications

This paper presents a general-purpose distributed lookup service, denoted Passive Distributed Indexing (PDI). PDI stores entries in form of (key, value) pairs in index caches located at mobile devices. Index caches are filled by epidemic dissemination of popular index entries. By exploiting node mobility, PDI can resolve most queries locally without sending messages outside the radio coverage of the inquiring node. For keeping index caches coherent, configurable value timeouts implementing implicit invalidation and lazy invalidation caches implementing explicit invalidation are introduced. Inconsistency in index caches due to weak connectivity or node failure is handled by value timeouts. Lazy invalidation caches reduce the fraction of stale index entries due to modified data at the origin node. Similar to index caches, invalidation caches are filled by epidemic distributions of invalidation messages. We evaluate the performance of PDI for a mobile P2P file sharing a mobile instant messaging application. Simulation results show that with the suitable integration of both invalidation mechanisms, up to 80% of the lookup operations return correct results and more than 90% of results delivered by PDI index caches are up-to-date

Some requirements for autonomic routing in self-organizing networks

International audienceThis paper addresses some requirements of self-organizing networks as well as interoperability problems due to merges and splits phenomena. In a mobile environment, merges and splits characterize the spatial overlap between two self-organized networks. While merge refers to the time when two disjoint networks meet and overlap, split refers to the time of partition. In a dynamic environment, AutoComm (AC) principles bring a new support for interoperability since current protocol heterogeneity is observed at all stack layers from the radio interface to applications. In this paper, we reconsider the formalization of a community and its requirements. We then characterize the split and merge phenomena and their implications. We give some requirements that must fulfill solutions to merging (high context-awareness) in order for AC groups to self-scale. Finally, we propose a merging solution for overlapping wireless self-organized networks using heterogeneous routing protocols

Mobile Distributed Information Retrieval For Highly-Partitioned Networks

We propose and evaluate a mobile, peer-to-peer Information Retrieval system. Such a system can, for example, support medical care in a disaster by allowing access to a large collections of medical literature. In our system, documents in a collection are replicated in an overlapping manner at mobile peers. This provides resilience in the face of node failures, malicious attacks, and network partitions. We show that our design manages the randomness of node mobility. Although nodes contact only direct neighbors (who change frequently) and do not use any ad hoc routing, the system maintains good IR performance. This makes our design applicable to mobility situations where routing partitions are common. Our evaluation shows that our scheme provides significant savings in network costs, and increased access to information over ad-hoc routing-based approaches; nodes in our system require only a modest amount of additional storage on average

Mobile Distributed Information Retrieval For Highly-Partitioned Networks

We propose and evaluate a mobile, peer-to-peer Information Retrieval system. Such a system can, for example, support medical care in a disaster by allowing access to a large collections of medical literature. In our system, documents in a collection are replicated in an overlapping manner at mobile peers. This provides resilience in the face of node failures, malicious attacks, and network partitions. We show that our design manages the randomness of node mobility. Although nodes contact only direct neighbors (who change frequently) and do not use any ad hoc routing, the system maintains good IR performance. This makes our design applicable to mobility situations where routing partitions are common. Our evaluation shows that our scheme provides significant savings in network costs, and increased access to information over ad-hoc routing-based approaches; nodes in our system require only a modest amount of additional storage on average