timing transparent transcoding (TTT)

Timing Transparent Transcoding (TTT) is used to adapt a Gigabit Ethernet signal to the data rate of the ODU-0 Optical Data Unit.

This data rate adaptation is necessary because the payload data rate of ODU-0 with 1.244 Gbit/s is not sufficient for the transmission of Gigabit Ethernet with 1 Gbit/s. The actual data rate of Gigabit Ethernet is lower than that of ODU-0 due to the 8.244 Gbit/s of ODU-0. The actual data rate of Gigabit Ethernet is 1.25 Gbit/s due to the 8B/10B coding used by the Physical Coding Sublayer( PCS) of Gigabit Ethernet, which is higher than the supported data rate of the payload signal.

The TTT signal is at the input of the optical transport network and reduces the transmitted bit rate with a transparent mapping mechanism, however, the information for restoring the PCS signal is retained at the output of the optical transport network.