Polycom SIP 3.1 manual DTMF Tone Generation, DTMF Event RTP Payload, Acoustic Echo Cancellation

Configuring Your System

packets (also known as Silence Insertion Descriptor (SID) frames) and also decodes CN packets, efficiently regenerating a facsimile of the background noise at the remote end.

Configuration changes can performed centrally at the boot server:

Central (boot server)

Configuration file: sip.cfg

Enable or disable VAD and set the detection threshold.

•For more information, refer to Voice Activity Detection <vad/> on page A-52.

DTMF Tone Generation

The phone generates dual tone multi-frequency (DTMF) tones in response to user dialing on the dial pad. These tones are transmitted in the real-time transport protocol (RTP) streams of connected calls. The phone can encode the DTMF tones using the active voice codec or using RFC 2833 compatible encoding. The coding format decision is based on the capabilities of the remote end point.

Configuration changes can performed centrally at the boot server:

Central	Configuration file:	Set the DTMF tone levels, autodialing on and off times, and other
(boot server)	sip.cfg	parameters.
		• For more information, refer to Dual Tone Multi-Frequency
		<DTMF/> on page A-28.

DTMF Event RTP Payload

The phone is compatible with RFC 2833 - RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals. RFC 2833 describes a standard RTP-compatible technique for conveying DTMF dialing and other telephony events over an RTP media stream. The phone generates RFC 2833 (DTMF only) events but does not regenerate, nor otherwise use, DTMF events received from the remote end of the call.

Configuration changes can performed centrally at the boot server:

Central	Configuration file:	Enable or disable RFC 2833 support in SDP offers and specify the
(boot server)	sip.cfg	payload value to use in SDP offers.
		• For more information, refer to Dual Tone Multi-Frequency
		<DTMF/> on page A-28.

Acoustic Echo Cancellation

The phone employs advanced acoustic echo cancellation (AEC) for hands-free operation. Both linear and non-linear techniques are employed to aggressively reduce echo yet provide for natural full-duplex communication patterns.

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