Four video assistant referees will be present at every game at the World Cup in Russia with replays to be shown on giant screens inside the stadiums, FIFA said.
"Everything will be centralised in a single location in Moscow and all referees will be based in Moscow," explained FIFA's referees' chief Pierluigi Collina during a training seminar organised at Coverciano, near Florence.
Over the next two weeks two groups of 36 referees and 63 assistants will be trained for the World Cup in Coverciano, with workshops organised on the VAR system which will be used at the tournament for the first time.
Another former Italian referee Roberto Rosetti explained how VAR would work during the tournament.
"There will be four VAR officials. The VAR principal will communicate with the main referee and can suggest that he comes to verify images on the sidelines," explained Rosetti.
"The VAR assistant number one will be in charge of following the match live while the review is taking place. VAR assistant number two will be specially in charge of off-side."