Methods and systems for negotiating the capability of a data signal detector include a sender gateway sending a first signaling containing data signal detector support capability message during voice band data transmission (301); a receiver gateway determining, according to the received first signaling, whether the sender gateway sends the data in a manner of containing a data signal detector, and determining whether to enable a non-voice decoder to decode mute packets (302). The sender gateway sends data in a manner of not containing a data signal detector according to the received second signaling (304). Embodiments of the present invention are applicable to a fax service in a packet-based network. Data signal detector capability negotiation may be implemented during voice band transmission. Embodiments of the present invention further disclose a sender gateway and a receiver gateway with ability for negotiating the capability of a data signal detector.