Users of the Transport Layer specify QoS or ToS parameters as part of a request for a communications channel. QoS parameters define different levels of service based on the requirements of an application. For example, an interactive application that needs good response time would specify high QoS values for connection establishment delay, throughput, transit delay, and connection priority. However, a file transfer application needs reliable, error-free data transfer more than it needs a prompt connection, thus it would request high QoS parameters for residual error rate/probability.