There's more information on the network elements of the system on the federal FirstNet web site.
The law that established FirstNet specified that the network shall be based on the minimum technical requirements on the commercial standards for Long Term Evolution (LTE) service. LTE is the evolution of a proven technology, which is now in its fourth generation. With each generation comes improvement in speed and functionality. Standards work to enhance and evolve 4G LTE is continuing on a global basis. FirstNet is involved in the standards process and working closely with public safety organizations to support the development of standards and functionality that meet the needs of the public safety users that FirstNet will serve. Much of the current focus is on an international set of standards that will allow FirstNet to offer mission-critical voice (MCV) when these capabilities become available. The same MCV technologies will then work across all standards-based equipment and networks worldwide.
FirstNet broadly defines its LTE network in distinct layers: Core Network, Transport Backhaul, Radio Access Network (RAN) and Public Safety Device:
FirstNet is responsible for building the enhanced packet core network, a key component for ensuring that users have a single interoperable platform nationwide. The core network has six primary functions: it switches data, processes and reformats information, stores and maintains data and keeps it secure. Applications and services and operational and business support systems also reside in the core network. The core will interface with other state, local and federal networks, including 911 and the Internet. Essentially, the core serves as a giant umbrella covering all of the United States including the territories and the District of Columbia. The core is connected to radio access networks in each state via the backhaul layer of the network. FirstNet launched the core in spring of 2018. With the launch of the Evolved Packet Core (EPC), public safety traffic can be separated from commercial traffic. The EPC enables subscribers to take advantage of end-to-end encryption, around the clock security monitoring of the network, and creation of local control functions that allow incident commanders and eligible FirstNet subscribers to unlock different levels of network priority in an emergency.
Radio Access Network
The RAN portion of the network consists of the radio base station infrastructure that connects to user devices. RAN includes cell towers, as well as mobile hotspots embedded in vehicles that backhaul to the core network over satellite or other types of wireless infrastructure. Comprehensive RAN planning is required to optimize coverage, capacity and performance for a nationwide network. Initial modeling has shown that tens of thousands of radio base stations are needed to cover at least 99 percent of the population and the national highway system. Population coverage alone won’t suffice for public safety. State by state, FirstNet needs to understand public safety coverage needs. During consultation, FirstNet worked with the states to determine the coverage expectations and priorities that must be included in the RAN deployment plan to enable public safety to meet its mission, no matter where it takes them.
Public Safety Devices
Devices are all the user access points that will send and receive information over the network. Everything from smartphones to laptops, tablets, dongles and a wide variety of specialty devices will be developed for FirstNet users. The goal is to create devices that are rugged enough to withstand the many public safety environmental issues, but still be easy to use and convenient to carry. Devices will also have to be easy to administer and secure. With the potential for millions of users, FirstNet will have the scale and leverage to drive development and procurement of devices at the best possible prices. Scale can also spur interest from a number of new vendors, which can enhance vendor/design diversity, increase competition and help lower prices for public safety devices. In the future, FirstNet will work with industry to develop device types and applications to meet public safety use cases identified by public safety users. FirstNet devices and applications will undergo a variety of testing and certification in areas including interference, operation, environmental factors and security.