6.3 Parameters
38.3233GPPNRPacket Data Convergence Protocol (PDCP) specificationRelease 17TS
6.3.1 General
If not otherwise mentioned in the definition of each field then the bits in the parameters shall be interpreted as follows: the left most bit string is the first and most significant and the right most bit is the last and least significant bit.
Unless otherwise mentioned, integers are encoded in standard binary encoding for unsigned integers. In all cases the bits appear ordered from MSB to LSB when read in the PDU.
6.3.2 PDCP SN
Length: 12 or 18 bits as indicated in table 6.3.2-1. The length of the PDCP SN is configured by upper layers (pdcp-SN-SizeUL, pdcp-SN-SizeDL, or sl-PDCP-SN-Size in TS 38.331 [3]).
Table 6.3.2-1: PDCP SN length
|
Length |
Description |
|
12 |
SRBs, UM DRBs, AM DRBs (including sidelink SRBs and sidelink DRBs), UM MRBs and AM MRBs |
|
18 |
UM DRBs, AM DRBs (including sidelink DRBs for unicast), UM MRBs and AM MRBs |
NOTE: For NR sidelink communication for groupcast and broadcast, only 12 bits PDCP SN length is used for the sidelink DRBs.
6.3.3 Data
Length: Variable
This field includes one of the followings:
– Uncompressed PDCP SDU (user plane data, or control plane data);
– Compressed PDCP SDU (user plane data only).
NOTE: All fields other than PDCP PDU header and MAC-I belong to Data field.
6.3.4 MAC-I
Length: 32 bits
This field carries a message authentication code calculated as specified in clause 5.9.
For SRBs for Uu interface, the MAC-I field is always present. If integrity protection is not configured, the MAC-I field is still present but should be padded with padding bits set to 0.
For sidelink SRB1, SRB2 and SRB3, the MAC-I field is present only when the sidelink SRB1, SRB2 and SRB3 are configured with integrity protection.
For DRBs (including sidelink DRBs for unicast), the MAC-I field is present only when the DRB is configured with integrity protection.
6.3.5 COUNT
Length: 32 bits
The COUNT value is composed of a HFN and the PDCP SN. The size of the HFN part in bits is equal to 32 minus the length of the PDCP SN.
Figure 6.3.5-1: Format of COUNT
NOTE: COUNT does not wrap around.
6.3.6 R
Length: 1 bit
Reserved. In this version of the specification reserved bits shall be set to 0. Reserved bits shall be ignored by the receiver.
6.3.7 D/C
Length: 1 bit
This field indicates whether the corresponding PDCP PDU is a PDCP Data PDU or a PDCP Control PDU.
Table 6.3.7-1: D/C field
|
Bit |
Description |
|
0 |
Control PDU |
|
1 |
Data PDU |
6.3.8 PDU type
Length: 3 bits
This field indicates the type of control information included in the corresponding PDCP Control PDU.
Table 6.3.8-1: PDU type
|
Bit |
Description |
|
000 |
PDCP status report |
|
001 |
Interspersed ROHC feedback |
|
010 |
EHC feedback |
|
011 |
UDC feedback |
|
100-111 |
Reserved |
6.3.9 FMC
Length: 32 bits
First Missing COUNT. This field indicates the COUNT value of the first missing PDCP SDU within the reordering window, i.e. RX_DELIV.
6.3.10 Bitmap
Length: Variable. The length of the bitmap field can be 0.
This field indicates which SDUs are missing and which SDUs are correctly received in the receiving PDCP entity. The bit position of Nth bit in the Bitmap is N, i.e., the bit position of the first bit in the Bitmap is 1.
Table 6.3.10-1 Bitmap
|
Bit |
Description |
|
0 |
PDCP SDU with COUNT = (FMC + bit position) modulo 232 is missing. |
|
1 |
PDCP SDU with COUNT = (FMC + bit position) modulo 232 is correctly received. |
6.3.11 Interspersed ROHC feedback
Length: Variable
This field contains one ROHC packet with only feedback, i.e. a ROHC packet that is not associated with a PDCP SDU as defined in clause 5.7.4.
6.3.12 SDU Type
Length: 3 bits
PDCP SDU type, i.e. Layer-3 Protocol Data Unit type as specified in [13] and [18]. PDCP entity may handle the SDU differently per SDU Type, e.g. ROHC is applicable to IP SDU but not Non-IP SDU, Ethernet SDU, Unstructured SDU and ARP SDU.
Table 6.3.12-1: SDU Type
|
Bit |
Description |
|
000 |
IP |
|
001 |
Non-IP |
|
010 |
Ethernet |
|
011 |
Unstructured |
|
100 |
ARP |
|
101-111 |
Reserved |
6.3.13 KNRP-sess ID
Length: 16 bits
KNRP-sess Identity as specified in TS 33.536 [14].
For the SLRB that does not need integrity and ciphering protection, the UE shall set KNRP-sess ID to "0" in the PDCP PDU header.
6.3.14 FE
Length: 1 bit
Indication of whether checksum error is detected or not. Value ‘1’ means checksum error is detected and the UE shall reset the compression buffer.
Table 6.3.14-1: FE field
|
Bit |
Description |
|
0 |
No Error |
|
1 |
Checksum Error Notification |