HybCAST: Rich Content Dissemination in Hybrid Cellular and 802.11 Ad Hoc Networks

We design, implement, and evaluate a middleware system, HybCAST, that leverages a hybrid cellular and ad hoc network to disseminate rich contents from a source to all mobile devices in a predetermined region. HybCAST targets information dissemination over a range of scenarios (e.g., military operations, crisis alerting, and popular sporting events) in which high reliability and low latency are critical and existing fixed infrastructures such as wired networks, 802.11 access points are heavily loaded or partially destroyed. HybCAST implements a suite of protocols that: (i) structures the hybrid network into a hierarchy of two-level ad hoc clusters for better scalability, (ii) employ both data push and pull mechanisms for high reliability and low latency dissemination of rich content, and (iii) implement a near-optimal gateway selection algorithm to minimize the transmission redundancy. To demonstrate its practicality and efficiency, we have implemented and deployed the HybCAST middleware on several Android smart phones and an in-network Linux machine that acts as a dissemination server. The system is evaluated via real experiments using a UMTS network and extensive packet-level simulations. Our experimental results from a live network show that HybCAST achieves 100% reliability with shorter latencies and lower overall energy consumption. Simulation results confirm that HybCAST outperforms other state-of-the-art systems in the literature. For example, HybCAST exhibits a 5 times reduction in the dissemination latencies as compared to other hybrid dissemination protocols, while its energy consumption is a third of a cellular-only dissemination system. Furthermore, the simulation results demonstrate that HybCAST scales well and maintains good performance under varying numbers of mobile devices, diverse content sizes, and device mobility.