DCU acts as an internal data hub

DCU is an internal data hub that distributes information among in-vehicle modules.

When the DCU receives data from CCU (which may originate from the cloud) or other internal components, it routes that data to corresponding modules, such as the head-unit, IVI, cluster, or various ECUs.

But this doesn’t mean that DCU only receives data from CCU. The flow is more like:

Server <-> CCU <-> DCU <-> H/U, IVI, ECU, ...

So DCU can request/response data within modules as well.

Depending on the OEM, a DCU may include a small modem or connectivity chipset for specific internal features, but this does not mean the DCU communicates with the external network (CCU is a network gateway).