The customer is prohibited from stepping inside the bid/ask spread and thereby reducing its execution fees. Contrary to the CLOB model, customers can only trade with dealers. They can not trade with other customers, and importantly, they can not make markets themselves.
Customers are restricted from crossing into the bid/ask spread, which helps in lowering their trading expenses. In contrast to the CLOB model, they can only engage in trades with dealers. Customers are prohibited from dealing directly with each other or creating market orders.