Figure 6-1: Elements of the Public Switched Telephone Network(PSTN) 净 4. Signaling System Transport is the actual transmission of voice Signaling is the control of calling (setup, teardown, billing, etc. SS7 in the United States C7 in Europe 6-96-9 Figure 6-1: Elements of the Public Switched Telephone Network (PSTN) 4. Signaling System Transport is the actual transmission of voice. Signaling is the control of calling (setup, teardown, billing, etc.). SS7 in the United States C7 in Europe