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Handle F1 Reset at DU, and ensure state re-init on F1Setup

Xin Zhe Khooi requested to merge impl_f1reset_and_fix_f1setup into develop

This MR implements the following:

  1. F1Reset handling at the DU -- DU_handle_RESET, and DU_send_RESET_ACKNOWLEDGE.
    • This includes one patch to the RACH handling ( 721c1605) when the UE states are absent after RESET to prevent the DU from crashing
  2. Ensure the UE-related states are always cleared on every F1SetupRequest (especially when DU re-establishes its SCTP connection with the CU).
    • Quoted from TS38.473 8.2.3.2, "This procedure erases any existing application level configuration data in the two nodes and replaces it by the one received. This procedure also re-initialises the F1AP UE-related contexts (if any) and erases all related signalling connections in the two nodes like a Reset procedure would do."
    • Impact: Now, restarting the CU midway will not result in a crash.

Both (1) and (2) use similar logic in re-init/initializing the UE-related states in the DU, i.e., clear MAC/RLC, F1, and GTP.

HOWEVER, I am not 100% sure whether my interpretation of the standards is correct for the above, i.e., Reset and F1Setup.

So, feedback and discussions are welcome.

Thanks!

Note:

  • F1Reset handling at the DU is currently limited to the entire "f1-Interface", i.e., all states are cleared.
  • F1Reset handling is not implemented at the CU; neither CU/DU currently sends out the F1Reset.
  • F1Reset handling at the DU is tested using a transparent SCTP proxy in F1-C.
Edited by Xin Zhe Khooi

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