Mobile ad hoc networks (MANETs) are infrastructureless and distributed communication systems that require sophisticated approaches to routing to cope with node mobility and heterogeneous application requirements. In the past few years, distributed hash table (DHT) has come forth as a useful additional technique to the design and specification of spontaneous and self-organized networks. Researchers have exploited its advantages by implementing it at the network layer and developing scalable routing protocols for MANETs. The implementation of DHT-based routing in a MANET requires different algorithms and specifications compared to routing in the Internet because a MANET has its unique characteristics, such as node mobility, spontaneous networking, decentralized architecture, limited transmission range, dynamic topology, and frequent network partitioning/merging. In this article, we present a comprehensive survey of research related to DHT-based routing that aims at enhancing the scalability of MANETs. We present a vivid taxonomy of DHT-based routing protocols and the guidelines to design such protocols for MANETs. We compare the features, strengths, and weaknesses of existing DHT-based routing protocols and highlight key research challenges that are vital to address. The outcome of the analysis serves as a guide for anyone willing to delve into research on DHT-based routing in MANETs.

In the last few years, distributed hash table (DHT) has come forth as a useful addition to the design and specification of spontaneous, self-organizing networks. Researchers have exploited its advantages by implementing it at the network layer in order to design scalable routing protocols for mobile ad hoc networks. We identify two correlated issues that must be considered when designing DHTbased routing protocol, namely the mismatch problem and resilience of the logical network, which degrades the efficiency of the DHT-based routing protocols. To address these problems, we propose a DHT-based routing protocol that exploits a 3D logical space that takes into account the physical intra-neighbor relationships of a node and exploits a 3D structure to interpret that relationship. In the proposed scheme, each node runs a distributed algorithm to obtain a consecutive logical identifier that reflects its physical proximity in the 3D logical space. Moreover, the protocol utilizes the 3D-structure to maintain multi-paths to a destination node in order to address the scalability problem and gain resilience against a node/link failure. Simulation results show that the proposed approach outperforms the existing DHT-based routing protocol in terms routing overhead, end-to-end delay, path-stretch values and packet-delivery ratio.

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