Digital trunking system and telephone system communication method, exchanger and system

The invention discloses a digital trunking system and telephone system communication method which is aimed to improve the communication convenience and experience between a telephone terminal and a trunking terminal. The digital trunking system and telephone system communication method includes: an exchanger receives a first service request sent from the telephone terminal connected with the exchanger, wherein the first service request includes a trunking calling header field which is used for indicating a trunking function; if the object of the first service request comprises the trunking terminal, the exchanger sends the first service request to the trunking system so as to enable the trunking system to send the first service request to the trunking terminal connected with the trunking system to connect the telephone terminal with the trunking terminal for communication, the exchanger has been connected with the trunking system through an SIP extension protocol, and the trunking calling header field is defined in the SIP extension protocol. The digital trunking system and telephone system communication method is capable of improving the communication convenience and experience between the telephone terminal and the trunking terminal.