System and method for obtaining a message type identifier through an in-band modem

摘要

A system and method is provided for obtaining a message type identifier embedded in a vocoder packet via a speech codec (in-band) such as found in a wireless communication network. The vocoder packet is received and decoded. The decoded vocoder packet is filtered until a synchronization signal is detected, with the filtering comprising correlating the decoded vocoder packet with a predetermined sequence to generate the synchronization signal. The polarity of the synchronization signal is determined, and the message type identifier is derived based on the polarity of the detected synchronization signal. A first polarity identifies a first message type, and a second polarity identifies a second message type.