Already defined in MTCA.0
IPMB-L: Links the MCMC (MicroTCA carrier management controller) of the MCH with the MMCs (module management controllers) of the AdvancedMC modules in a radial architecture

IPMB-0: Links the MCMC of the MCH with the EMMCs (enhanced module management controllers) of the PMs (power modules) and CU (cooling unit) in a bussed, redundant architecture

New in MTCA.4
I2C-bus: Links the AdvancedMC module with the MicroRTM module. The MicroRTM is treated like a managed FRU (field replaceable unit) of the AdvancedMC module

Not yet defined:
Management of the RTM fans.

MCH = MicroTCA carrier hub