OpenSky, created By HARRIS is a 2 slot IPInternet protocol TDMATime Division Multiple Access Trunk System. Operations available on 700, 800 and 900MHz. "Currently (May 2018), there are no scanners or software that are capable of monitoring OpenSky transmissions." (information From www.RadioReference.com)
OpenSky is encrypted and was also used as the Pennsylvania Statewide Radio Network from 2003-2022. as of 2017 the Pennsylvania Statewide Radio Network is working on migrating to APCO 25 Phase 2 (P25 Phase 2,) with most to all the law enforcement agencies having full encryption enabled.
As of 2022, there are still towers actively transmitting.