A free, simple, easy-to-implement, standards-based,
feature-rich dialtone for your SIP hardware or softphone...

Engineers Testing or Implementing Plug-N-Dial

Codec Requirements:

All Plug-N-Dial devices and SIP software clients must implement at the very least and offer the following royalty free codecs:

        G711U (PCMU)
        G711A (PCMA) and,
        GSM 06.10 (for low bandwidth applications)

Audio Silence Suppression and Comfort Noise (CN) Generation:

All Plug-N-Dial devices and SIP software clients must implement at the very least and offer the following silence suppression and CN features:

(1) Audio Silence suppression must be an option included for low bandwidth SIP applications.

(2) Audio Comfort Noise (CN) generated must not be sent over the wire. That is, do not transmit CN to the remote participant. It must be simply locally played audible to the user. The reason for this requirement is that not all encoders / decoders understand an RTP payload change(s) in mid session -- this causes a lot of compatibility issues should the CN packets be transmitted in mid session to the remote participant.

The primary objective of Plug-N-Dial standard must be seemless compatibility/interoperability of all SIP user agents.