QoS is provided by ATM switch on cell level, but in order to provide QoS to applications, ATM layer protocol, AAL protocols and other high layer protocols should be implemented in the teminal.

• ATM交换机在信元级进行QoS处理，为了使应用程序得到QoS，必须在终端上处理ATM层协议、AAL层协议以及高层协议。