pam 4d4D-PAM5 is the method used to transmit data at 1 Gbsec over four wire pairs using five snaling levels. It combines 8B1Q4, Trellis, Viterbi, and 4D coding and decoding, and isAbstract: 4D-PAM-5 trellis coded modulation is experimentally demonstrated and compared with PAM-4 for use in 8λ×50 Gbs metro