Method for determining a mode of transmission in a frequency band between first and second node devices of a power line communication network, the first node device being located in the network neighbourhood of the second node device and vice versa, the first node device being configured so as to communicate in at least two frequency bands (B1, B2), and the second node device being configured so as to communicate in at least one of said at least two frequency bands, the method being executed by the first node device, the method comprising: - transmitting (S2, S3) a copy of a first message (TM-RQ-B1, TM-RQ-B2) to the second node device in each of said at least two frequency bands, said first message comprising information according to which a channel estimate is requested from the second node device by said first node device, and the method being characterized in that it furthermore comprises: - transmitting, on an extended frequency band, a message (TM-RQ-EB) comprising a reference to said extended frequency band to the second node device, said extended frequency band comprising said at least two frequency bands (B1, B2), and said message comprising information according to which a channel estimate of said extended frequency band is requested from the second node device by said first node device, - receiving (S4, S12) a second message transmitted by the second node device on each frequency band (B1, B2, EB) via which the second node device has received a message comprising information according to which a channel estimate is requested, each second message comprising information representative of a channel estimate for the frequency band (B1, B2, EB) via which said second message is received, - the first node device recording the information, representative of the channel estimate, contained in each received second message, and - determining, based on the recorded information, a transmission mode for transmitting, in one of the frequency bands, a third message to be transmitted subsequently from the first node device to the second node device. - transmitting (S2, S3) a copy of a first message (TM-RQ-B1, TM-RQ-B2) to the second node device in each of said at least two frequency bands, said first message comprising information according to which a channel estimate is requested from the second node device by said first node device, - transmitting, on an extended frequency band, a message (TM-RQ-EB) comprising a reference to said extended frequency band to the second node device, said extended frequency band comprising said at least two frequency bands (B1, B2), and said message comprising information according to which a channel estimate of said extended frequency band is requested from the second node device by said first node device, - receiving (S4, S12) a second message transmitted by the second node device on each frequency band (B1, B2, EB) via which the second node device has received a message comprising information according to which a channel estimate is requested, each second message comprising information representative of a channel estimate for the frequency band (B1, B2, EB) via which said second message is received, - the first node device recording the information, representative of the channel estimate, contained in each received second message, and - determining, based on the recorded information, a transmission mode for transmitting, in one of the frequency bands, a third message to be transmitted subsequently from the first node device to the second node device.