Order entry gateways are the market participant client applications that communicate with the exchange matching engine over the order entry protocols. These have to deal with order flow in a reliable manner, sending orders to the exchange, modifying and canceling those orders, and getting notifications when these orders are accepted, canceled, executed, and so on. Oftentimes, market participants run a second variant of order entry gateways that simply receive order-executed notifications to check consistency against the primary order entry gateway order flow. These are called drop-copy gateways.