NB-SSH: NB-IoT-Based Remote SSH Access to UAVs Under Symmetric NAT

When NB-IoT is used to monitor UAVs, developers need to access a UAV via SSH (Secure Shell). However, NB-IoT services are sometimes behind symmetric NAT, and NB-IoT modules can only be controlled by specific AT commands, rendering existing NAT traversal software not applicable. This letter proposes NB-SSH, which provides remote SSH service to UAVs that are behind symmetric NAT. NB-SSH has two variants, in one of which the client side does not need to install any software, and in the other the UAV appears to the client as a neighbor. We implement both variants and evaluate them in a real-world environment.