The OPTI-6100 OC-3 LR Tributary Module (O3TMLR) provides an OC-3 tributary interface to the OPTI-6100 chassis. The mid-speed (MS) module retimes and maps up to three STS-1s or one STS-3c from the OC-3 interface to the high-speed (HS) OMM modules.  Plugging two TRAM Modules into an appropriate slot pair allows redundant equipment protection.