When is the winter transfer period?

That is, in the middle of the season, the time is 65438+1 October1to 30. You can buy players while playing, but if a player has registered for the Champions League in his old club, he can't play in a new club. In fact, the summer transfer is also done while playing. Take the Premier League as an example, it usually starts in mid-August, but the transfer period will not end until September 1.