INTRODUCTION

In circuit-switched calls over CDMA, acoustic background noise is encoded in eighth rate packets and transmitted periodically, for example every 20 msec. Although it is necessary for circuit-switched calls to transmit a packet periodically, the same is not true for packet-switched calls. It is possible to achieve capacity savings and extend battery life for VoIP calls by using a discontinuous transmission scheme (DTX).

This specification provides requirements for source controlled variable rate vocoders to implement DTX. It is recognized that there exists a great deal of flexibility in the way DTX can be implemented. The purpose of this specification is not to specify a particular solution, but to provide a set of requirements to ensure interoperability between different implementations.

This specification uses the following verbal forms: "Shall" and "shall not" identify requirements to be followed strictly to conform to the standard and from which no deviation is permitted. "Should" and "should not" indicate that one of several possibilities is recommended as particularly suitable, without mentioning or excluding others; that a certain course of action is preferred but not necessarily required; or that (in the negative form) a certain possibility or course of action is discouraged but not prohibited. "May" and "need not" indicate a course of action permissible within the limits of the standard. "Can" and "cannot" are used for statements of possibility and capability, whether material, physical, or causal.