Calls can be circuit switched data calls or analog modem calls.
Because the Cisco Signaling Controller SC2200 does not directly control the bearer channels on an access server, the access server must perform the loopbacks and tone generation or tone detection required for continuity testing. Continuity testing is required for North American SS7 compliance. Used to test individual DS0 channels before establishing a call. Restrictions ITU-based networks use only the loopback method for continuity testing. However, ANSI networks may use the tone generation, tone detection, or loopback methods.