TELEPHONE INTERFACE MODULE (TIM)

14.1.8 TRANSMIT AUDIO

The transmit audio from the PCM channel stream is processed to analog and sent to the telephone line (see Figure 14-14). The functional paths of the transmit audio are:

1.Voice Path

The transmit voice is processed from the PCM channel stream by the same CODEC and time slot determination circuitry as in the receive audio voice path section above. The digitized voice is converted to analog and filtered by the CODEC to a high pass filter to eliminate low frequency audio. The audio is level adjusted by an amplifier buffer and gated into a summing amplifier buffer. The audio gating provides on/off control of the voice audio to the telephone line. The summing buffer has a level adjustment to set the outgoing line level and drives the unbalanced side of the telephone line hybrid.

2.Mobile Speech Detection

The audio for mobile speech detection comes from the CODEC amplifier buffer. The bandpass filter is centered at the audio frequency recognized for voice peaks. The filtered audio is rectified and detected for the presence of voice. The output of the detector is an input to the logic unit.

3.DTMF Generation

The DTMF signaling is generated on the TIM and transmitted toward the telephone line. The logic unit provides the inputs to the DTMF generation circuit. The generator outputs the desired tones and is adjusted to the proper level with respect to the voice path by an amplifier. The tones pass through a logic unit controlled audio transmission gate, summing amplifier buffer, to the telephone line.

14.2 4-WIRE E&M INTERFACE DESCRIPTION

The 4-Wire E&M Interface Card connects the Switch with a 4-Wire audio circuit that supports Ear and Mouth (E&M) signaling.

14.2.1 AUDIO

The audio circuit consists of a transmit (Tx) pair and a receive (Rx) pair. The Tx pair transmits audio and DTMF digits. The Rx pair receives audio and DTMF digits. Dial Tone detection is also supported by the Rx pair.

14.2.2 E&M LEADS

The E&M leads can be configured for Type I, II, III, IV and V signaling by changing S201 on the personality card (see Figure 14-21).

The E-Lead is a single input that monitors for - 48V, or ground. This lead is used to detect inbound ringing (detected as battery reversals), receive pulse dialed digits (detected as battery reversals), wink start pulse (detected as a single battery reversal), and an answer or hang-up by the connected circuit (detected as a lead reversal). This lead can be set up for -48V or ground idle states by changing S201, section 7 and 8.

The M-Lead is a single output that signals to the connected circuit with -48V, or ground. This lead is used to request service (battery reversal), send a wink start pulse (battery reversal), signal a hang-up or answer to the circuit (battery reversal), transmit pulse dial digits (sent as battery reversals). The state of this lead is configured by S201, section 1 through 6.

NOTE: If this card is connected to a 2-Wire circuit, a Termset is required. This card supports pulse dialing for both inbound and outbound. Pulse dialing is described as full battery reversal, not click detection from the Central Office (CO). If click detection is required, an external device is needed to support this feature.

The E&M Interface Card installation instructions are not for a specific installation because of the many unique configurations. The field engineer customizes or alters the installation for the appropriate interface requirements.

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