6 Protocol data units, formats, and parameters
38.3403GPPBackhaul Adaptation Protocol (BAP) specificationNRRelease 17TS
6.1 Protocol data units
6.1.1 Data PDU
The BAP Data PDU is used to convey one of the following in addition to the PDU header:
– upper layer data.
6.1.2 Control PDU
The BAP Control PDU is used to convey one of the following in addition to the PDU header:
– flow control feedback per BH RLC channel;
– flow control feedback per BAP routing ID;
– flow control polling;
– BH RLF related indication;
6.2 Formats
6.2.1 General
A BAP PDU is a bit string that is byte aligned (i.e. multiple of 8 bits) in length. The formats of BAP PDUs are described in clause 6.2.2, 6.2.3 and their parameters are described in clause 6.3.
6.2.2 Data PDU
Figure 6.2.2-1 shows the format of the BAP Data PDU.
Figure 6.2.2-1: BAP Data PDU format
6.2.3 Control PDU
6.2.3.1 Control PDU for flow control feedback
Figure 6.2.3.1-1 and 6.2.3.1-2 show the formats of the BAP Control PDU for flow control feedback.
Figure 6.2.3.1-1: BAP Control PDU format for flow control feedback per BH RLC channel
Figure 6.2.3.1-2: BAP Control PDU format for flow control feedback per BAP routing ID
6.2.3.2 Control PDU for flow control polling
Figure 6.2.3.2-1 shows the formats of the BAP Control PDU for flow control polling.
Figure 6.2.3.2-1: BAP Control PDU format for flow control feedback polling
6.2.3.3 Control PDU for BH RLF indication
Figure 6.2.3.3-1 shows the format of the BAP Control PDU for BH RLF indication.
Figure 6.2.3.3-1: BAP Control PDU format for BH RLF indication
6.2.3.4 Control PDU for BH RLF detection indication
Figure 6.2.3.4-1 shows the format of the BAP Control PDU for BH RLF detection indication.
Figure 6.2.3.4-1: BAP Control PDU format for BH RLF detection indication
6.2.3.5 Control PDU for BH RLF recovery indication
Figure 6.2.3.5-1 shows the format of the BAP Control PDU for BH RLF recovery indication.
Figure 6.2.3.5-1: BAP Control PDU format for BH RLF recovery indication
6.3 Parameters
6.3.1 General
If not otherwise mentioned in the definition of each field, 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 DESTINATION
Length: 10 bits.
This field carries the BAP address of the destination IAB-node or IAB-donor-DU.
6.3.3 PATH
Length: 10 bits.
This field carries the BAP path identity.
6.3.4 Data
Length: Variable
This field carries the BAP SDU (i.e. IP packet).
6.3.5 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.
6.3.6 D/C
Length: 1 bit
This field indicates whether the corresponding BAP PDU is a BAP Data PDU or a BAP Control PDU.
Table 6.3.6-1: D/C field
|
Bit |
Description |
|
0 |
BAP Control PDU |
|
1 |
BAP Data PDU |
6.3.7 PDU type
Length: 4 bits
This field indicates the type of control information included in the corresponding BAP Control PDU.
Table 6.3.7-1: PDU type
|
Bit |
Description |
|
0000 |
Flow control feedback per BH RLC channel |
|
0001 |
Flow control feedback per BAP routing ID |
|
0010 |
Flow control feedback polling |
|
0011 |
BH RLF indication |
|
0100 |
BH RLF detection indication |
|
0101 |
BH RLF recovery indication |
|
0110-1111 |
Reserved |
6.3.8 BH RLC channel ID
Length: 16 bits.
This field indicates the identity of the BH RLC channel whose flow control information is provided in the flow control feedback.
6.3.9 BAP Routing ID
Length: 20 bits.
This field indicates BAP routing identity, for which the flow control information is provided in the flow control feedback. It contains the BAP address in the leftmost 10 bits and the BAP path identity in the rightmost 10 bits.
6.3.10 Available Buffer Size
Length: 24 bits.
This field indicates the maximum traffic volume the transmitter should send. The unit is kilobyte.
Annex A (informative):
Change history
|
Change history |
|||||||
|
Date |
Meeting |
TDoc |
CR |
Rev |
Cat |
Subject/Comment |
New version |
|
10/2019 |
RAN2#107bis |
R2-1914006 |
skeleton |
0.0.0 |
|||
|
10/2019 |
RAN2#107bis |
R2-1914008 |
Captured agreements made before RAN2#107bis |
0.1.0 |
|||
|
02/2020 |
RAN2#109e |
R2-2002113 |
Captured agreements made in RAN2#108 |
0.3.0 |
|||
|
03/2020 |
RAN2#109e |
R2-2002345 |
Captured agreements made in RAN2#109e |
0.4.0 |
|||
|
03/2020 |
RP-87 |
RP-200113 |
Version submitted for approval in RAN#87-e |
1.0.0 |
|||
|
03/2020 |
RP-87 |
Updated to Rel-16 |
16.0.0 |
||||
|
07/2020 |
RP-88 |
RP-201179 |
0001 |
4 |
F |
Miscellaneous corrections to 38.340 for IAB |
16.1.0 |
|
09/2020 |
RP-89 |
RP-201923 |
0006 |
1 |
F |
Miscellaneous corrections to 38.340 for IAB |
16.2.0 |
|
RP-89 |
RP-201923 |
0007 |
– |
F |
Corrections on flow control BAP control PDU |
16.2.0 |
|
|
12/2020 |
RP-90 |
RP-202772 |
0009 |
1 |
F |
Miscellaneous corrections to 38.340 for IAB |
16.3.0 |
|
03/2021 |
RP-91 |
RP-210691 |
0012 |
1 |
F |
Correction on the illustration of BAP entity |
16.4.0 |
|
RP-91 |
RP-210691 |
0014 |
1 |
F |
Miscellaneous corrections to 38.340 for IAB |
16.4.0 |
|
|
06/2021 |
RP-92 |
RP-211472 |
0015 |
2 |
F |
Miscellaneous corrections on BAP transmitting operation and default routing |
16.5.0 |
|
RP-92 |
RP-211472 |
0018 |
1 |
F |
Corrections to the handling of unknown, unforeseen, and erroneous protocol data |
16.5.0 |
|
|
03/2022 |
RP-95 |
RP-220486 |
0020 |
2 |
B |
Introduction of eIAB to TS 38.340 |
17.0.0 |
|
06/2022 |
RP-96 |
RP-221718 |
0024 |
1 |
F |
Miscellaneous CR for TS 38.340 |
17.1.0 |
|
09/2022 |
RP-97 |
RP-222523 |
0029 |
1 |
F |
Miscellaneous corrections in TS 38.340 for eIAB |
17.2.0 |