Comments here are pretty well correct, but the lines blur across the networks as to names, & who exactly does what.
The play-out is generally just a bunch of computer servers that play-out the programs & commercials, & send the data out to the TX sites, these servers are monitored & directed by the MCR at each network.
The MCR operator can also manually direct the transmitter to use the main or the alternate (backup) input feed, & they can manually change from the main to backup transmitter (which generally in metro areas will involve a site change).
Of course all the systems are set up, that incase of failure, everything will instantly automatically change over.
Every piece of transmission equipment has redundancy, & has a backup/alternate path to air.
All Networks do a manual Disaster Recovery test each week, where they change from main to alternate & back, if all goes well, the viewers will never notice the change.
The Nine Play-out & MCR is at Frenchs Forrest in Sydney.
The TEN Play-out & MCR is at Pyrmont in Sydney.
The Seven Play-out & MCR is at Docklands in Melbourne, however Martin Place in Sydney is a pseudo play-out for Seven because so much Live TV comes out of there each day, (I think it’s 10-14 hours per weekday of normal programming is Live out of Martin Place Sydney).
Disaster Recovery for the Seven Network (studios) in case a disaster happens in Sydney (building fire, major tech fault, etc.) is Seven Perth. Unless it’s like an hour before the programs due to go to air, because of the time zone differences, they can fly the talent to Perth & the program can go live as scheduled from the Perth studios for the Eastern States.
I’m not sure where Studio Disaster Recovery is for Nine & Ten?