Content for TS 38.351 Word version: 18.2.0
6 Protocol data units, formats, and parameters
6.1 Protocol data units
6.1.1 Data PDU
6.2 Formats
6.2.1 General
6.2.2 Data PDU
6.3 Parameters
6.3.1 General
6.3.2 UE ID
6.3.3 BEARER ID
6.3.4 Data
6.3.5 R
6.3.6 D/C
$ Change history
6 Protocol data units, formats, and parameters p. 19
6.1 Protocol data units p. 19
6.1.1 Data PDU p. 19
The SRAP Data PDU is used to convey the following with or without the PDU header:
- Upper layer data.
6.2 Formats p. 19
6.2.1 General p. 19
An SRAP Data PDU is a bit string that is byte aligned (i.e. multiple of 8 bits) in length. The formats of SRAP Data PDUs are described in clause 6.2.2 and their parameters are described in clause 6.3.
6.2.2 Data PDU p. 19
Figure 6.2.2-1 shows the format of the U2N SRAP Data PDU with SRAP header being configured. This SRAP Data PDU format is applicable to U2N SRAP SDU except those for SRB0 delivered over PC5 interface.
Figure 6.2.2-2 shows the format of the U2N SRAP Data PDU consisting only of a data field without any SRAP header. This SRAP Data PDU format is applicable to U2N SRAP SDU for SRB0 delivered over PC5 interface.
Figure 6.2.2-3 shows the format of the U2U SRAP Data PDU. This SRAP Data PDU format is applicable to U2U SRAP SDU delivered over PC5 interface.
6.3 Parameters p. 20
6.3.1 General p. 20
If not otherwise mentioned in the definition of each field the bits in the parameters shall be interpreted as follows: the left most bit 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 UE ID p. 20
Length:
8 bits.
In U2N Relay case, this field carries local identity of U2N Remote UE. In U2U Relay case, there are two UE ID fields: the first one carrying the local identity of SRC U2U Remote UE, the second one carrying the local identity of DST U2U Remote UE.
6.3.3 BEARER ID p. 20
Length:
5 bits.
In U2N Relay case, this field carries information to identify Uu radio bearer for U2N Remote UE. For SRBs, the value is set to SRB Identity (which is configured by RRC parameter srb-Identity). For DRBs, the value is set to DRB Identity (which is configured by RRC parameter drb-Identity) minus 1.
In U2U Relay case, this field carries information to identify end-to-end PC5 radio bearer for U2U Remote UE. For SL-SRBs, the value is set to 0/1/2/3 for SL-SRB 0/1/2/3 respectively. For SL-DRBs, the value is set to the 5 LSBs of slrb-PC5-ConfigIndex used in end-to-end SL DRB configuration procedure as specified in TS 38.331.
6.3.4 Data p. 20
Length:
Variable
This field carries the SRAP SDU (i.e. PDCP PDU or RRC PDU).
6.3.5 R p. 20
Length:
1 bit
Reserved. In this release, reserved bits shall be set to 0. Reserved bits shall be ignored by the receiver.
6.3.6 D/C p. 21
Length:
1 bit
This field indicates whether the corresponding SRAP PDU is an SRAP Data PDU or an SRAP Control PDU (not used in this release).
| Bit | Description |
|---|---|
| 0 | SRAP Data PDU |
| 1 | SRAP Control PDU (not used in this release) |
$ Change history p. 22
