How do ECN brokers differ from STP brokers?

ECN and STP brokers operate using the same model of sending your trade directly to the counterparty and not through a middleman. However, the ECN broker has better order management in that they can merge several small orders together for faster execution, while the STP broker sends every order individually and this can slow down execution time because the order may have to wait slightly longer to get a counterparty. The end result is ECN brokers have faster execution speed than STP brokers.