Content for TS 38.323 Word version: 18.0.0

1… 4… 5… 5.4… 5.8… 5.13… 6… 6.2.3… 7… A… B…

5.1 PDCP entity handling 5.1.1 PDCP entity establishment 5.1.2 PDCP entity re-establishment 5.1.3 PDCP entity release 5.1.4 PDCP entity suspend 5.1.5 PDCP entity reconfiguration 5.2 Data transfer 5.2.1 Transmit operation 5.2.2 Receive operation 5.2.2.1 Actions when a PDCP Data PDU is received from lower layers 5.2.2.2 Actions when a t-Reordering expires 5.2.2.3 Actions when the value of t-Reordering is reconfigured 5.2.3 Sidelink transmit operation 5.2.4 Sidelink receive operation 5.3 SDU discard
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5 Procedures p. 15

5.1 PDCP entity handling p. 15

5.1.1 PDCP entity establishment p. 15

When upper layers request a PDCP entity establishment for a radio bearer for Uu or PC5 interface; or for NR sidelink communication for groupcast and broadcast or for sidelink SRB4, when receiving the first PDCP PDU, and there is not yet a corresponding PDCP entity, the UE shall:

establish a PDCP entity for the radio bearer;
set the state variables of the PDCP entity to initial values;
follow the procedures in clause 5.2.

5.1.2 PDCP entity re-establishment p. 15

When upper layers request a PDCP entity re-establishment, the UE shall additionally perform once the procedures described in this clause for Uu or PC5 interface. After performing the procedures in this clause, the UE shall follow the procedures in clause 5.2.

When upper layers request a PDCP entity re-establishment, the transmitting PDCP entity shall:

for UM DRBs and AM DRBs, reset the ROHC protocol for uplink and start with an IR state in U-mode (as defined in RFC 3095 and RFC 4815) if drb-ContinueROHC is not configured in TS 38.331;
for UM DRBs and AM DRBs, reset the EHC protocol for uplink if drb-ContinueEHC-UL is not configured in TS 38.331;
for AM DRBs, reset the UDC compression buffer to all zeros and prefill the dictionary if drb-ContinueUDC is not configured in TS 38.331;
for SRBs and UM DRBs, set TX_NEXT to the initial value;
for SRBs, discard all stored PDCP SDUs and PDCP PDUs;
apply the ciphering algorithm and key provided by upper layers during the PDCP entity re-establishment procedure;
apply the integrity protection algorithm and key provided by upper layers during the PDCP entity re-establishment procedure;
for UM DRBs, for each PDCP SDU already associated with a PDCP SN but for which a corresponding PDU has not previously been submitted to lower layers, and;
for AM DRBs for Uu interface whose PDCP entities were suspended, from the first PDCP SDU for which the successful delivery of the corresponding PDCP Data PDU has not been confirmed by lower layers, for each PDCP SDU already associated with a PDCP SN:
- consider the PDCP SDUs as received from upper layer;
- perform transmission of the PDCP SDUs in ascending order of the COUNT value associated to the PDCP SDU prior to the PDCP re-establishment without restarting the discardTimer or the discardTimerForLowImportance, as specified in clause 5.2.1;
for AM DRBs whose PDCP entities were not suspended, from the first PDCP SDU for which the successful delivery of the corresponding PDCP Data PDU has not been confirmed by lower layers, perform retransmission or transmission of all the PDCP SDUs already associated with PDCP SNs in ascending order of the COUNT values associated to the PDCP SDU prior to the PDCP entity re-establishment as specified below:
- perform header compression of the PDCP SDU using ROHC as specified in the clause 5.7.4 and/or using EHC as specified in the clause 5.12.4;
- If drb-ContinueUDC is configured and if the PDCP SDU has been compressed before:
  - submit the PDCP SDU previously compressed to integrity protection and ciphering function;
- else:
  - perform uplink data compression of the PDCP SDU as specified in clause 5.14.4, and submit the PDCP SDU to integrity protection and ciphering function;
- perform integrity protection and ciphering of the PDCP SDU using the COUNT value associated with this PDCP SDU as specified in the clause 5.9 and 5.8;
- submit the resulting PDCP Data PDU to lower layer, as specified in clause 5.2.1.

When upper layers request a PDCP entity re-establishment, the receiving PDCP entity shall:

process the PDCP Data PDUs that are received from lower layers due to the re-establishment of the lower layers, as specified in the clause 5.2.2.1;
for SRBs, discard all stored PDCP SDUs and PDCP PDUs;
for SRBs, UM DRBs and UM MRBs, if t-Reordering is running:
- stop and reset t-Reordering;
- for UM DRBs and UM MRBs, deliver all stored PDCP SDUs to the upper layers in ascending order of associated COUNT values after performing header decompression;
for AM DRBs and AM MRBs for Uu interface, perform header decompression using ROHC for all stored PDCP SDUs if drb-ContinueROHC is not configured in TS 38.331;
for AM DRBs for PC5 interface, perform header decompression using ROHC for all stored PDCP IP SDUs;
for AM DRBs and AM MRBs for Uu interface, perform header decompression using EHC for all stored PDCP SDUs if drb-ContinueEHC-DL is not configured in TS 38.331;
for UM DRBs, AM DRBs, UM MRBs and AM MRBs, reset the ROHC protocol for downlink and start with NC state in U-mode (as defined in RFC 3095 and RFC 4815) if drb-ContinueROHC is not configured in TS 38.331;
for UM DRBs, AM DRBs, UM MRBs and AM MRBs, reset the EHC protocol for downlink if drb-ContinueEHC-DL is not configured in TS 38.331;
for SRBs and UM DRBs, set RX_NEXT and RX_DELIV to the initial value;
for UM MRBs and AM MRBs, set RX_NEXT and RX_DELIV to the initial value if initialRX-DELIV is configured in TS 38.331;
apply the ciphering algorithm and key provided by upper layers during the PDCP entity re-establishment procedure;
apply the integrity protection algorithm and key provided by upper layers during the PDCP entity re-establishment procedure.

5.1.3 PDCP entity release p. 17

When upper layers request a PDCP entity release for a radio bearer for Uu or PC5 interface, the UE shall:

discard all stored PDCP SDUs and PDCP PDUs in the transmitting PDCP entity;
for UM DRBs, AM DRBs, UM MRBs and AM MRBs, deliver the PDCP SDUs stored in the receiving PDCP entity to upper layers in ascending order of associated COUNT values after performing header decompression, if not decompressed before;
release the PDCP entity for the radio bearer.

5.1.4 PDCP entity suspend p. 17

When upper layers request a PDCP entity suspend, the transmitting PDCP entity shall:

set TX_NEXT to the initial value;
discard all stored PDCP PDUs;

When upper layers request a PDCP entity suspend, the receiving PDCP entity shall:

if t-Reordering is running:
- stop and reset t-Reordering;
- deliver all stored PDCP SDUs to the upper layers in ascending order of associated COUNT values after performing header decompression;
set RX_NEXT and RX_DELIV to the initial value, except for MRB.

5.1.5 PDCP entity reconfiguration |R16| p. 18

When upper layers reconfigure the PDCP entity to configure DAPS, the UE shall:

establish a ciphering function for the radio bearer and apply the ciphering algorithm and key provided by upper layers for the ciphering function;
establish an integrity protection function for the radio bearer and apply the integrity protection algorithm and key provided by upper layers for the integrity protection function;
establish a header compression protocol for the radio bearer and apply the header compression configuration provided by upper layers for the header compression protocol.

When upper layers reconfigure the PDCP entity to release DAPS, the UE shall:

release the ciphering function associated to the released RLC entity for the radio bearer;
release the integrity protection function associated to the released RLC entity for the radio bearer;
release the header compression protocol associated to the released RLC entity for the radio bearer.

5.2 Data transfer p. 18

5.2.1 Transmit operation p. 18

At reception of a PDCP SDU from upper layers, the transmitting PDCP entity shall:

if discardTimerForLowImportance is configured and PSI based SDU discard is activated, and the PDCP SDU belongs to a low importance PDU Set:
- start the discardTimerForLowImportance associated with this PDCP SDU;
else:
- start the discardTimer associated with this PDCP SDU (if configured).

For a PDCP SDU received from upper layers, the transmitting PDCP entity shall:

associate the COUNT value corresponding to TX_NEXT to this PDCP SDU;

NOTE 1:
Associating more than half of the PDCP SN space of contiguous PDCP SDUs with PDCP SNs, when e.g., the PDCP SDUs are discarded or transmitted without acknowledgement, may cause HFN desynchronization problem. How to prevent HFN desynchronization problem is left up to UE implementation.
perform header compression of the PDCP SDU using ROHC as specified in the clause 5.7.4 and/or using EHC as specified in the clause 5.12.4;
perform uplink data compression of the PDCP SDU as specified in clause 5.14.4;
perform integrity protection, and ciphering using the TX_NEXT as specified in the clause 5.9 and 5.8, respectively;
set the PDCP SN of the PDCP Data PDU to TX_NEXT modulo 2^{[pdcp-SN-SizeUL]};
increment TX_NEXT by one;
submit the resulting PDCP Data PDU to lower layer as specified below.

When submitting a PDCP PDU to lower layer, the transmitting PDCP entity shall:

if the transmitting PDCP entity is associated with one SRAP entity:
- submit the PDCP PDU to the associated SRAP entity;
else, if the transmitting PDCP entity is associated with one RLC entity:
- submit the PDCP PDU to the associated RLC entity;
else, if the transmitting PDCP entity is associated with one or more RLC entities and, either one SRAP entity or the N3C:
- if PDCP duplication is activated for the RB:
  - if the PDCP PDU is a PDCP Data PDU:
    - duplicate the PDCP Data PDU and submit the PDCP Data PDU to both the primary path and secondary path, including any associated Uu RLC entities activated for PDCP duplication;
  - else:
    - submit the PDCP Control PDU to the primary path;
- else (i.e., PDCP duplication is deactivated for the RB):
  - if the total amount of PDCP data volume, RLC data volume pending for initial transmission (as specified in TS 38.322) in the RLC entity, and data volume pending for either transmission in the N3C (if available) or mapped SL RLC entity associated with the SRAP entity, is equal to or larger than ul-DataSplitThreshold:
    - submit the PDCP PDU to either the primary path or secondary path;
  - else:
    - submit the PDCP PDU to the primary path;
else, if the transmitting PDCP entity is associated with at least two RLC entities:
- if the PDCP duplication is activated for the RB:
  - if the PDCP PDU is a PDCP Data PDU:
    - duplicate the PDCP Data PDU and submit the PDCP Data PDU to the associated RLC entities activated for PDCP duplication;
  - else:
    - submit the PDCP Control PDU to the primary RLC entity;
- else (i.e. the PDCP duplication is deactivated for the RB or the RB is a DAPS bearer):
  - if the split secondary RLC entity is configured; and
  - if the total amount of PDCP data volume and RLC data volume pending for initial transmission (as specified in TS 38.322) in the primary RLC entity and the split secondary RLC entity is equal to or larger than ul-DataSplitThreshold:
    - submit the PDCP PDU to either the primary RLC entity or the split secondary RLC entity;
  - else, if the transmitting PDCP entity is associated with the DAPS bearer:
    - if the uplink data switching has not been requested:
      - submit the PDCP PDU to the RLC entity associated with the source cell;
    - else:
      - if the PDCP PDU is a PDCP Data PDU:
        
        submit the PDCP Data PDU to the RLC entity associated with the target cell;
      - else:
        
        if the PDCP Control PDU is associated with source cell:
        
        submit the PDCP Control PDU to the RLC entity associated with the source cell;
        
        else:
        
        submit the PDCP Control PDU to the RLC entity associated with the target cell;
  - else:
    - submit the PDCP PDU to the primary RLC entity.

5.2.2 Receive operation p. 20

5.2.2.1 Actions when a PDCP Data PDU is received from lower layers p. 20

In this clause, following definitions are used:

HFN(State Variable): the HFN part (i.e. the number of most significant bits equal to HFN length) of the State Variable;
SN(State Variable): the SN part (i.e. the number of least significant bits equal to PDCP SN length) of the State Variable;
RCVD_SN: the PDCP SN of the received PDCP Data PDU, included in the PDU header;
RCVD_HFN: the HFN of the received PDCP Data PDU, calculated by the receiving PDCP entity;
RCVD_COUNT: the COUNT of the received PDCP Data PDU = [RCVD_HFN, RCVD_SN].

At reception of a PDCP Data PDU from lower layers, the receiving PDCP entity shall determine the COUNT value of the received PDCP Data PDU, i.e. RCVD_COUNT, as follows:

if RCVD_SN < SN(RX_DELIV) - Window_Size:
- RCVD_HFN = HFN(RX_DELIV) + 1.
else if RCVD_SN ≥ SN(RX_DELIV) + Window_Size:
- RCVD_HFN = HFN(RX_DELIV) - 1.
else:
- RCVD_HFN = HFN(RX_DELIV);
RCVD_COUNT = [RCVD_HFN, RCVD_SN].

After determining the COUNT value of the received PDCP Data PDU = RCVD_COUNT, the receiving PDCP entity shall:

perform deciphering and integrity verification of the PDCP Data PDU using COUNT = RCVD_COUNT;
- if integrity verification fails:
  - indicate the integrity verification failure to upper layer;
  - discard the PDCP Data PDU and consider it as not received;
if RCVD_COUNT < RX_DELIV; or
if the PDCP Data PDU with COUNT = RCVD_COUNT has been received before:
- discard the PDCP Data PDU;

If the received PDCP Data PDU with COUNT value = RCVD_COUNT is not discarded above, the receiving PDCP entity shall:

store the resulting PDCP SDU in the reception buffer;

if RCVD_COUNT ≥ RX_NEXT:

update RX_NEXT to RCVD_COUNT + 1.

if outOfOrderDelivery is configured:

deliver the resulting PDCP SDU to upper layers after performing header decompression using EHC.

if RCVD_COUNT = RX_DELIV:

deliver to upper layers in ascending order of the associated COUNT value after performing header decompression, if not decompressed before;
- all stored PDCP SDU(s) with consecutively associated COUNT value(s) starting from COUNT = RX_DELIV;
update RX_DELIV to the COUNT value of the first PDCP SDU which has not been delivered to upper layers, with COUNT value > RX_DELIV;

if t-Reordering is running, and if RX_DELIV ≥ RX_REORD:

stop and reset t-Reordering.

if t-Reordering is not running (includes the case when t-Reordering is stopped due to actions above), and RX_DELIV < RX_NEXT:

update RX_REORD to RX_NEXT;
start t-Reordering.

5.2.2.2 Actions when a t-Reordering expires p. 21

When t-Reordering expires, the receiving PDCP entity shall:

deliver to upper layers in ascending order of the associated COUNT value after performing header decompression, if not decompressed before:
- all stored PDCP SDU(s) with associated COUNT value(s) < RX_REORD;
- all stored PDCP SDU(s) with consecutively associated COUNT value(s) starting from RX_REORD;
update RX_DELIV to the COUNT value of the first PDCP SDU which has not been delivered to upper layers, with COUNT value ≥ RX_REORD;
if RX_DELIV < RX_NEXT:
- update RX_REORD to RX_NEXT;
- start t-Reordering.

5.2.2.3 Actions when the value of t-Reordering is reconfigured p. 22

When the value of the t-Reordering is reconfigured by upper layers while the t-Reordering is running, the receiving PDCP entity shall:

update RX_REORD to RX_NEXT;
stop and restart t-Reordering.

5.2.3 Sidelink transmit operation |R16| p. 22

For NR sidelink transmission of the SLRB, the UE shall follow the procedures in clause 5.2.1 with following modification:

perform the header compression using ROHC as specified in clause 5.7.4, if SDU Type is IP;
set the PDCP SN of the PDCP Data PDU to TX_NEXT modulo 2[sl-PDCP-SN-Size];
if the transmitting PDCP entity is associated with two RLC entities:
- consider PDCP duplication as activated;
- submit the PDCP control PDU to one of the associated RLC entities.

5.2.4 Sidelink receive operation |R16| p. 22

For sidelink reception of the SLRB, the UE shall follow the procedures in clause 5.2.2 with following modification:

perform the header decompression using ROHC as specified in clause 5.7.5, if SDU Type is IP.

5.3 SDU discard p. 22

When the successful delivery of a PDCP SDU is confirmed by PDCP status report, the transmitting PDCP entity shall discard the PDCP SDU along with the corresponding PDCP Data PDU.

When the discardTimer or discardTimerForLowImportance expires for a PDCP SDU, the transmitting PDCP entity shall:

if pdu-SetDiscard is configured:
- discard all PDCP SDUs belonging to the PDU Set to which the PDCP SDU belongs along with the corresponding PDCP Data PDUs;
NOTE 1:
PDCP SDUs subsequently received from upper layers are also discarded if they belong to the PDU Set.
else:
- discard the PDCP SDU along with the corresponding PDCP Data PDU.

If the corresponding PDCP Data PDU has already been submitted to lower layers, the discard is indicated to lower layers.

For SRBs, when upper layers request a PDCP SDU discard, the PDCP entity shall discard all stored PDCP SDUs and PDCP PDUs.