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Refactor Re-establishment at gNB and remove PDCP Suspend at nrUE

Guido Casati requested to merge nr-pdcp-suspend into develop

This MR implements:

  1. Refactor PDCP re-establishment process for both SRBs and DRBs.

DRBs:

  • Remove direct PDCP reestablishment calls during the generation of RRCReestablishment message generation.
  • Perform PDCP reestablishment after reception or RRCReestablishmentComplete.
  • This adjustment ensures alignment with the subsequent RRCReconfiguration message, which contains RadioBearerConfig with the list of bearers to add/release, followed by PDCP re-establishment at the UE.

SRBs according to 5.3.7.4 of 3GPP TS 38.331:

  • SRB1 shall be re-established at the time of RRCReestablishmentRequest.
  • SRB2 shall be re-established when creating srb-ToAddModList.
  1. Apply default configuration for SRB1 when receiving RRCReestablishmentRequest as defined in 9.2.1 for SRB1, as per 5.3.7.4 of TS 38.331 (RRCReestablishmentRequest):
  • According to 5.3.7.4 of 3GPP TS 38.331, when handling an RRCReestablishmentRequest, the UE should apply the default configuration defined in section 9.2.1 for SRB1.
  1. Remove PDCP Suspend from nrUE:
    • According to clause 5.3.7.2 of 3GPP TS 38.331, PDCP Suspend is not required during RRCReestablishment.
  2. Re-establish RLC for SRB1 only when receiving RRCReestablishmentRequest:
    • As per 5.3.7.4 of TS 38.331:
      • Re-establish RLC for SRB1.
      • For gNB:
        • Re-establish RLC for SRB1 in nr_rlc_update_id.
        • Concurrently re-establish RLC for remaining RBs during RRCReconfiguration.
      • Addressing following issue:
        • RLC TX counters mismatch occurs after re-establishment, leading to control PDUs being discarded until the maximum number of retransmissions is reached, resulting in UL failure.
  3. Introduce Notify Bearer Status change:
    • After receiving RRCReestablishment request, notify Bearer Status change (Suspend) over E1 to CUUP.
    • Also, handle Bearer Status change encoding/decoding. Handling Bearer Context Status Change IE in Bearer Context Modification Request:
    • It involves E1 encoding/decoding and introduces a new enum for E1 Bearer Status Change.
    • Refer to section 9.2.2.4 BEARER CONTEXT MODIFICATION REQUEST of 3GPP TS 38.463 for details.
  4. Fix: check numDlUpParam size when processing DlUpParamList

addressing #739 (closed)

Edited by Guido Casati

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