The value of the parameter six. This parameter provides the start-stop DTE with the ability to decide whether or not and in what format PAD service signals are transmitted. The value 0 means no service signals are transmitted to the start-stop DTE. Value 1 indicates service signals other than the prompt PAD service signal are transmitted in the standard format. The value 4 indicates prompt PAD service signal is transmitted in the standard format. The value 5 is a combination of value 1 and value 4, i.e. all service signals including prompt are transmitted in standard format. The transmission of service signals is controlled by values 0, 1, 4, 5.