This refers to analogue sites, which support voice, fax and data transmission via landlines by adhering to specific protocols established by the ITU-T. Any incoming call is not identifiable with respect to these properties in advance of going "off hook" by the terminal equipment. So after going off hook the calls must be switched to appropriate devices and only the voice-type is immediately accessible to a human, but perhaps, nevertheless should be routed to a TAD (e.g. after the caller has identified itself, or has been identified by a recognized caller ID).