Patent ID: 6317595
Filing Date: 2001-11-13
Classification: H04M,H04W

Abstract:
A method of transferring from a first call to a second call within a trunked digital radio communications system that includes a first transmitting user terminal that communicates with a receiving user terminal in the first call over a first working channel via a base station, the method comprising the steps of:transmitting from a second transmitting user terminal to the base station a second call over a second working channel, that identifies the receiving user terminal;transmitting from the base station to the receiving user terminal transfer data in the first call on the first working channel, the transfer data identifying the second call and the second working channel;detecting the transfer data in the first call on the first working channel at the receiving user terminal; andtransferring to the second call on the second working channel at the receiving user terminal based upon the transfer data, wherein the second working channel includes a second working channel downlink that links the base station to the receiving user terminal and wherein a current call is transmitted from the base station to the receiving user terminal on the second working channel downlink; andtransmitting verification data in the current call on the second working channel downlink that identifies the current call within the trunked digital radio communications system, said step of transmitting verification data comprising:transmitting a frame number that identifies a control frame within the second working channel downlink;transmitting a data type that identifies the current call as information data or as voice data;transmitting a color code that identifies the current call within the trunked digital radio communications system; andtransmitting a call type identifier that identifies the current call as an encrypted call or an unencrypted call.