What is CBRS?
Citizens Broadband Radio Service
In 2015, the FCC (Federal Communications Commission) adopted rules for shared commercial use of the 3550-3700 MHz band (3.5 GHz band). The Commission established the CBRS (Citizens Broadband Radio Service) and created a three-tiered access and authorization framework to accommodate shared federal and non-federal use of the band. Rules governing the Citizens Broadband Radio Service are found in Part 96 of the Commission’s rules.
The Wireless Innovation Forum and OnGo Alliance are some of the best places to learn more.

TEIR 1: Incumbent users (I), mostly made up of Navy Ships and Radar stations along the US coastline. They get full protected access.
TEIR 2: Priority licensees (PAL), these are gained by FCC auction. They get protected access from Gaa license carriers of Tier 3 users.
TEIR 3: Generally authorized (Gaa), which is lightly licensed. Open for public or private use. Full unprotected* spectrum access.
*Unprotected means that if the network is congested
Tier 1 and 2 transaction have priority.
This has nothing to due with network security.