# A Multi-Technology Communication Platform for Urban Mobile Sensing
## 3 Architecture Overview
### DTN Forwarding Strategies  
Developed by the Network Architectures and Protocols (NAP) research group ([[https://www.it.pt/Groups/Index/62](https://www.it.pt/Groups/Index/62)]([https://www.it.pt/Groups/Index/62](https://www.it.pt/Groups/Index/62))), mOVE [37] is a DTN-based architecture supported by the conventional WiFi technology IEEE 802.11a/b/g. Each node receives information from other DTN nodes, stores it (on a persistent storage device), and forwards it according to the neighborhood availability, exploiting a vehicle-to-vehicle (V2V) and a vehicle-to-infrastructure (V2I) multi-hop based communication, leveraging upon the V2X concept. mOVE is implemented in C/C++ programming language and it is designed to be highly modular and extensible. It can be used to develop a large set  
Figure 6: Multi-technology communication overview. of applications which rely on delay tolerant communication using vehicles (or other mobile elements) as carriers of information. The versatility achieved through the proposed architecture grants the possibility to perform a miscellaneous set of tests and evaluations. One of which is the performance evaluation of DTN forwarding schemes. In order to evaluate proposed forwarding strategies, some \"classic\" DTN decision schemes were implemented, more specifically, the _Epidemic_ strategy, which is a flooding-based protocol that aims at the maximization of the delivery ratio and the minimization of the end-to-end delay without considering the limitations of network resources. As a result, several constraints, such as the nodes' buffer size limitation, restricts the practical performance of this protocol. With the aim to increase the delivery ratio while minimizing the network resources consumption, two forwarding/decision strategies were proposed and evaluated over our platform:  
* Contact-Based Controlled Replication with Neighborhood Classification;
* Mobility-Based Controlled Replication with Neighborhood Classification. Due to the characteristics of the proposed platform, such as the high mobility pattern that an opportunistic network presents over a smart city scenario, a high number of contacts between neighbors is expected. Thus, the proposed Contact-based Controlled Replication with Neighborhood Classification strategy estimates a node delivery probability by relating the number of past contacts and the time elapsed since the last encounter with a gateway, instead of using the contact duration and encounter frequency as proposed by the Hybrid of Probability and message Redundancy strategy [30]. On the other hand, different approaches take advantage of the mobility parameters of each neighbor in order to evaluate which one offers a better probability of reaching the destination first, e.g., the GeoSpray [31] and Geo-Routing with Angle-Based Decision [32] strategies. However, unlike these strategies, the proposed Mobility-Based Controlled Replication with Neighborhood Classification estimates a node delivery probability based on the mean velocity and the angle between the forwarder and the receptor node without having the knowledge about the destination location. It is of high importance to understand which neighbors should receive the data packets, i.e., a mobile node should be able to evaluate its vicinity nodes to find the best neighboring node for data forwarding. For this, each node collects personal information and exchanges it with its neighbors through Neighbor Announcement packets. As stated previously, two different vicinity classification approaches were developed, resulting in two forwarding approaches. It follows a brief explanation about each decision strategy, Contacts-Based and Mobility-Based, respectively:  
**Contacts-Based Neighborhood Classification:** This evaluation process classifies a mobile node according to the following information: (1) the number of contacts that occur over a predefined period of time, and (2) the last recorded _timestamp_ in which a node had contacted a gateway station.