The Tmedia TMG3200 and TMG7800, as well as the Tdev TMP6400, can accommodate an interface for up to two SONET or SDH lines: one for operating as the active link with the other link operating in standby mode for emergency switchover.
In the case of a SONET interface, an OC3 line interface is configured to serve a selection of line services. In the case of an SDH interface, an STM-1 Optical line interface with related line services are configured. A conceptual image is shown below:
Note: Combination of E1s and T1s within a DS3 is not supported.