# A Survey of LoRaWAN for IoT: From Technology to Application
## 8 Extensions
### Multi-Modal Networks  
Performance of heterogeneous IoT applications can be improved by usage of multi-technology networks. Different technologies have their pros and cons in terms of offered throughput, power consumption, covered distances, traffic latencies, etc. Different heterogeneous application can benefit by on-the-fly smart selection of communication technology based on their requirements. To this end, LoRaWAN is seen as one of the possible technology, that, in addition to other technologies such as Wi-Fi, NB-IoT, SigFox or other LPWANs, can improve flexibility and reliability of the communication [127; 128; 111; 129; 130; 131].  
In [127], a dual-technology (LoRaWAN and NB-IoT) node was prototyped and its communication feasibility over both networks was demonstrated. The NB-IoT network can be used for emergency traffic or to close the loop for auction downlink traffic in different use-cases. In [128], feasibility of using LoRaWAN and NB-IoT for demand-side management of energy system was demonstrated together with a possible network architecture.  
In [111; 112], a network architecture based on multi-modal nodes has been presented for collecting environment sensor data. For short range communication, IEEE 802.11n is used, while LoRa is used for long distance communication. In [129], a Smart City test-bed has been deployed by using multi-modal gateways that include a number of technologies: IEEE 802.1 ac, DASH7, Bluetooth (Low Energy), IEEE 802.15.4, IEEE 802.15.4g and LoRa.  
In [130], author presented a framework for LoRa and IEEE 802.11 ah inter-working with focus on resource management, network selection and support for mobile nodes, while, in [131], a multi-modal network architecture was presented. In [131], network architecture is composed of a number of multi-modal IoT device (LoRa, SigFox, NB-IoT, and DASH7), several independently operated wireless access networks and the virtual network operator. Virtual network operator offers a unified managing interface for multi-modal network devices and makes possible the device handover from one network to another. Multi-modal end nodes implement the network convergence layer on top of different MAC and PHY layers offering an abstraction toward node's application. In [58], a demo implementation of such an approach is presented, where a CoAP-UDP-IPV6 stack in combination with a custom SCHC adaptation layer on top of LoRaWAN and Dash7 MAC layer. Although the logic layer for switching the technology is missing, the architecture is promising.  
As it is stated in [131] there are several challenges for multi-modal network implementation. Protocol stack design and management is one of the challenges. First steps in SCHC specifications are currently being done; however, techniques for how rules and static context are installed are still missing. In addition, another concern is application security over different technologies. Finally, different technology detection mechanisms should be implemented for different used technologies that makes the solution hard and not scalable. Moreover, different detections mechanisms might have different performance in terms of detection latency. This will make the switching from one to another technology slower compared to the reverse direction.