ZyXEL Elite 2864 User Guide - Page 179

In ZyXEL voice mode, three states exist that roughly correspond to the flow direction of the digitized voice data; the Voice Command State (no data transfer other than event reports), the Voice Transmission State (digitized voice data transfer from the DTE to the DCE), and the Voice Receival State (digitized voice data transfer from the DCE to the DTE). Note that the voice data DTE/DCE transfer is half-duplex. The DCE may issue event detection reports at any time, regardless of the DCE state. These reports may be tone or cadence events in nature (such as calling tone detection), or they may be a result of external switching functions of Telco line activities (Ring), or they may be a combination (Caller ID). ZyXEL provides the Service Level C Event Detection Capabilities of IS-101 as follows : Event Description RING Ringback Fax or Data Answer (e.g., 2100Hz) BUSY DIALTONE DTMF Received Fax Calling Tone Presumed Hang-up (SILENCE) Time-out Presumed End of Message (QUIET) Time-out Mandatory Receive Buffer Overrun Mandatory Transmission Buffer Underrun DCE Voice State Command Command Command Receive, and Command Receive, and Command Receive, Transmit, and Command Receive, Transmit, and Command Receive Receive Receive Transmit Voice Command State The DCE is in the Voice Command State and ready to accept commands when the DCE is operating in voice mode and is not communicating with a remote station, nor with any local devices which are capable of translating analog signals to voice (e.g., speaker) or translating voice to analog signals (e.g., microphone). The DCE considers data transfers from the DTE to be commands, and returns responses back to the DTE after completing the processing of the commands. While accepting or processing commands, the DCE also monitors the line which connects the DCE to the remote station or to the local device to detect events, which the DCE later reports to the DTE pertaining to signals carried over the line, such as tones, and pertaining to PSTN generated control and notification signals, such as ringing. The Voice Command State provides several DTE options. The modem may wait for an unspecified time after playing a welcome message, or switch to other modes as part of a DTE call discrimination algorithm. 16-3