1. In terms of network purpose, a carrier network provides internet services to citizens for profit; therefore, operators only pay attention to downlink data and valuable area coverage. Public safety, meanwhile, usually requires a full-coverage nationwide network with more uplink data(e.g., video surveillance).
2. In some cases, the carrier network may be shut down for security purpose(e.g., criminals might remotely control a bomb via s public carrier network).
3. In big events, the carrier network can become congested and cannot guarantee quality of Service(QoS).