Explanation:
In a dial-in mode, the destination initiates a session to the router and subscribes to data to be streamed.
Dialin mode is supported over gRPC in only 64-bit platforms In a dial-out mode, the router initiates a session to the destinations based on the subscription.
All 64-bit IOS XR platforms (except for NCS 6000 series routers) support gRPC and TCP protocols. All 32-bit IOS XR platforms support only TCP.
Reference:
https://www.cisco.com/c/en/us/td/docs/iosxr/asr9000/telemetry/b-telemetry-cg-asr9000-61x/b- telemetry-cgasr9000-61x_chapter_010.html#id_36445