Distributed approach. As presented in [15] and discussed in previous sections, there exist many discovery mechanisms that are targeted to local network discovery and for discovery in the global network, the Internet. However, it is difficult to find a mechanism that could cover both local and global scopes. This mechanism should merge capabilities from the two different families of discovery mechanisms. In this subsection, we discuss a proposal to integrate a proper mechanism for local discovery scope and a robust and scalable mechanism for global discovery. This way we can extend the discovery operations launched in a local network to other networks, so a client that supports the local mechanism is able to find resources and devices connected to other networks which reside in other locations in a transparent manner, without being specifically prepared for such operation. We propose to integrate mDNS [9], for the local scope, with a DHT mechanism that can provide load balancing, scalability, and robustness when extending the search and discovery operations to the global scope. Also, in the local part of the operations, we can incorporate the optimizations introduced by lmDNS, as previously described in this document, which is specifically designed for IoT workloads. As discussed in previous subsections, DHTs are structures which store key/value mappings across a set of nodes, which in turn relate to the overlay network that hosts the DHT. For our approach, Chord [26] a widely used and well-known overlay network routing algorithm and DHT across the research community will be used. However, the approach discussed here can be adapted with any other overlay network and DHT approach, since they share the same capabilities in terms of key/value storage and retrieval, and therefore offer a similar interface to the client application. To perform the integration, we designed a connector artifact (mDNS / DNS-SD Connector) to be instantiated in the local domain of the elements (resources, devices) that should be published globally. This element uses mDNS/DNS-SD to find the available resources and devices in the local network or location where it is deployed and publishes new entries for each of the DHTs, storing a relation of capability/location (key/value) for each capability offered by the resources. Figure 8: Distributed approach, such as the used for OpenDHT The architecture of the connector, as shown in Figure 9, operates as follows. The devices use mDNS to discover the available ser...
