Quick connect parameter exchange

(57) the start-up process, the re-training process, the re-negotiation process, the quick connection process, or other processes of handshaking between summary communications systems, Communication of specific abnormal-conditions information, the Constellation information, pre encoder information, pre filter information, and the information relevant to other communications is included. The above-mentioned communications system communicates one long information sequence including all required communication information. As a result, the above-mentioned communications system begins to transmit the short sequence containing an acknowledgment information part. When one of the above-mentioned communications systems does not receive acknowledgment within the time specified in advance or an event, the communications system concerned can transmit another long information sequence. After such retransmission of message, the communications system which performed the above-mentioned retransmission of message can continue transmission of a long information sequence, or can start transmission of a short sequence again.