Crossing networks are derivative by design: they import the reference price from lit-market quotes and simply pair off buyers and sellers. Some run continuously, others at scheduled call times through the day.
They suit natural two-sided institutional flow and large size, because a cross avoids both the bid-ask-spread and the signalling of working an order in the open book.
Example: a scheduled cross at 11:00 collects 400,000 shares of buy interest and 250,000 of sell. It matches 250,000 at the prevailing midpoint of 33.05, pro-rating participation, and the unmatched 150,000 goes back to its owners to be worked elsewhere.
Related: alternative-trading-system, dark-pool, midpoint-peg, block-order