ETSI TS 138 340 V17.0.0 (2022-05)

5G; NR; Backhaul Adaptation Protocol (BAP) specification (3GPP TS 38.340 version 17.0.0 Release 17)

RTS/TSGR-0238340vh00

General Information

• Status: Not Published
• Technical Committee: 3GPP RAN 2 - Radio layer 2 specification and Radio layer 3 RR specification
• Current Stage: 12 - Completion
• Completion Date: 09-May-2022

Standards Content (Sample)

ETSI TS 138 340 V17.0.0 (2022-05)






TECHNICAL SPECIFICATION
5G;
NR; Backhaul Adaptation Protocol (BAP) specification
(3GPP TS 38.340 version 17.0.0 Release 17)

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3GPP TS 38.340 version 17.0.0 Release 17 1 ETSI TS 138 340 V17.0.0 (2022-05)

Reference
RTS/TSGR-0238340vh00
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ETSI

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3GPP TS 38.340 version 17.0.0 Release 17 2 ETSI TS 138 340 V17.0.0 (2022-05)
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Legal Notice
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Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI

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3GPP TS 38.340 version 17.0.0 Release 17 3 ETSI TS 138 340 V17.0.0 (2022-05)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 7
2 References . 7
3 Definitions of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Abbreviations . 8
4 General . 8
4.1 Introduction . 8
4.2 Architecture . 8
4.2.1 BAP structure. 8
4.2.2 BAP entities . 8
4.3 Services . 9
4.3.1 Services provided to upper layers . 9
4.3.2 Services expected from lower layers . 9
4.4 Functions . 10
4.5 Configurations . 10
5 Procedures . 11
5.1 BAP entity handling . 11
5.1.1 BAP entity establishment . 11
5.1.2 BAP entity release . 11
5.2 Data transfer . 11
5.2.1 Transmitting operation . 11
5.2.1.1 General . 11
5.2.1.2 BAP routing ID selection . 12
5.2.1.2.1 BAP routing ID selection at IAB-node . 12
5.2.1.2.2 BAP routing ID selection at IAB-donor-DU . 12
5.2.1.3 Routing . 13
5.2.1.4 Mapping to BH RLC Channel . 14
5.2.1.4.1 Mapping to BH RLC Channel for BAP Data Packets from collocated BAP entity at IAB-
node . 14
5.2.1.4.2 Mapping to BH RLC Channel for BAP SDUs from upper layers at IAB-node . 15
5.2.1.4.3 Mapping to BH RLC Channel at IAB-donor-DU . 16
5.2.2 Receiving operation . 17
5.3 Flow control . 17
5.3.1 Flow control feedback . 17
5.3.1.1 Transmitting operation . 17
5.3.1.2 Receiving operation . 18
5.3.2 Flow control polling. 18
5.4 BH RLF related indications . 18
5.4.1 Transmitting operation . 18
5.4.2 Receiving operation . 19
5.5 Handling of unknown, unforeseen, and erroneous protocol data . 19
6 Protocol data units, formats, and parameters . 19
6.1 Protocol data units . 19
6.1.1 Data PDU . 19
6.1.2 Control PDU . 19
6.2 Formats . 20
6.2.1 General . 20
6.2.2 Data PDU . 20
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3GPP TS 38.340 version 17.0.0 Release 17 4 ETSI TS 138 340 V17.0.0 (2022-05)
6.2.3 Control PDU . 20
6.2.3.1 Control PDU for flow control feedback . 20
6.2.3.2 Control PDU for flow control polling . 22
6.2.3.3 Control PDU for BH RLF indication . 22
6.2.3.4 Control PDU for BH RLF detection indicatio n . 22
6.2.3.5 Control PDU for BH RLF recovery indication . 22
6.3 Parameters . 22
6.3.1 General . 22
6.3.2 DESTINATION . 22
6.3.3 PATH . 23
6.3.4 Data . 23
6.3.5 R . 23
6.3.6 D/C. 23
6.3.7 PDU type . 23
6.3.8 BH RLC channel ID . 23
6.3.9 BAP Routing ID . 24
6.3.10 Available Buffer Size. 24
Annex A (informative): Change history . 25
History . 26


ETSI

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3GPP TS 38.340 version 17.0.0 Release 17 5 ETSI TS 138 340 V17.0.0 (2022-05)
Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
In the present document, certain modal verbs have the following meanings:
shall indicates a mandatory requirement to do something
shall not indicates an interdiction (prohibition) to do something
NOTE 1: The constructions "shall" and "shall not" are confined to the context of normative provisions, and do not
appear in Technical Reports.
NOTE 2: The constructions "must" and "must not" are not used as substitutes for "shall" and "shall not". Their use
is avoided insofar as possible, and they are not used in a normative context except in a direct citation from
an external, referenced, non-3GPP document, or so as to maintain continuity of style when extending or
modifying the provisions of such a referenced document.
should indicates a recommendation to do something
should not indicates a recommendation not to do something
may indicates permission to do something
need not indicates permission not to do something
NOTE 3: The construction "may not" is ambiguous and is not used in normative elements. The unambiguous
constructions "might not" or "shall not" are used instead, depending upon the meaning intended.
can indicates that something is possible
cannot indicates that something is impossible
NOTE 4: The constructions "can" and "cannot" shall not to be used as substitutes for "may" and "need not".
will indicates that something is certain or expected to happen as a result of action taken by an agency
the behaviour of which is outside the scope of the present document
will not indicates that something is certain or expected not to happen as a result of action taken by an
agency the behaviour of which is outside the scope of the present document
might indicates a likelihood that something will happen as a result of action taken by some agency the
behaviour of which is outside the scope of the present document
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3GPP TS 38.340 version 17.0.0 Release 17 6 ETSI TS 138 340 V17.0.0 (2022-05)
might not indicates a likelihood that something will not happen as a result of action taken by some agency
the behaviour of which is outside the scope of the present document
In addition:
is (or any other verb in the indicative mood) indicates a statement of fact
is not (or any other negative verb in the indicative mood) indicates a statement of fact
NOTE 5: The constructions "is" and "is not" do not indicate requirements.
ETSI

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3GPP TS 38.340 version 17.0.0 Release 17 7 ETSI TS 138 340 V17.0.0 (2022-05)
1 Scope
The present document provides description of the Backhaul Adaptation Protocol (BAP).
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 38.300: "NG Radio Access Network; Overall description".
[3] 3GPP TS 38.331: "NR Radio Resource Control (RRC); Protocol Specification".
[4] 3GPP TS 38.322: "NR Radio Link Control (RLC) protocol specification".
[5] 3GPP TS 38.473: "NG-RAN F1 application protocol (F1AP) protocol specification".
[6] 3GPP TS 38.401: "NG-RAN; Architecture description".
3 Definitions of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the terms given in TR 21.905 [1] and the following apply. A term defined in
the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
BH RLC channel: an RLC channel between two nodes, which is used to transport backhaul packets, as defined in TS
38.300 [2].
Boundary IAB-node: an IAB-node with one RRC interface terminating at a different IAB-donor than the F1 interface,
as defined in TS 38.401 [6].
Egress BH RLC channel: a BH RLC channel on which a packet is transmitted by a node.
Egress link: a radio link on which a packet is transmitted by a node.
F1-terminating donor: The IAB-donor of an IAB-node, which manages the F1 interface with this IAB-node.
IAB-donor: as defined in TS 38.300 [2].
IAB-donor-DU: as defined in TS 38.401 [6].
IAB-node: as defined in TS 38.300 [2].
Ingress BH RLC channel: a BH RLC channel on which a packet is received by a node.
Ingress link: a radio link on which a packet is received by a node.
Non-F1-terminating donor: The IAB-donor for an IAB-node, which does not have F1 interface with this IAB-node.
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3GPP TS 38.340 version 17.0.0 Release 17 8 ETSI TS 138 340 V17.0.0 (2022-05)
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
TR 21.905 [1].
BH Backhaul
DSCP Differentiated Services Code Point
IAB Integrated Access and Backhaul
MT Mobile Termination
TEID Tunnel Endpoint Identifier
4 General
4.1 Introduction
The present document describes the functionalities of BAP.
4.2 Architecture
4.2.1 BAP structure
Figure 4.2.1-1 represents one possible structure for the BAP sublayer; it should not restrict implementation. The figure
is based on the radio interface protocol architecture defined in TS 38.300 [2].


Figure 4.2.1-1: BAP layer, structure view
The BAP sublayer is configured by upper layers TS 38.331 [3] and TS 38.473 [5].
4.2.2 BAP entities
On the IAB-node, the BAP sublayer contains one BAP entity at the MT function and a separate collocated BAP entity
at the DU function. On the IAB-donor-DU, the BAP sublayer contains only one BAP entity. Each BAP entity has a
transmitting part and a receiving part.
NOTE: The modelling of BAP entities does not restrict internal implementation of IAB-nodes, i.e. the exact modelling
of BAP sublayer may vary for different IAB-node implementations.
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3GPP TS 38.340 version 17.0.0 Release 17 9 ETSI TS 138 340 V17.0.0 (2022-05)
The transmitting part of the BAP entity has a corresponding receiving part of a BAP entity at the IAB-node or IAB-
donor-DU across the BH link.
Figure 4.2.2-1 shows one example of the functional view of the BAP sublayer. This functional view should not restrict
implementation. The figure is based on the radio interface protocol architecture defined in TS 38.300 [2].
In the example of Figure 4.2.2-1, the receiving part on the BAP entity delivers BAP PDUs to the transmitting part on
the collocated BAP entity. Alternatively, the receiving part may deliver BAP SDUs to the collocated transmitting part.
When passing BAP SDUs, the receiving part removes the BAP header and the transmitting part adds the BAP header
with the same BAP header content as carried on the BAP PDU header prior to removal. Passing BAP SDUs in this
manner is therefore functionally equivalent to passing BAP PDUs, in implementation. The following specification
therefore refers to the passing of BAP Data Packets.
Besides, BAP entity generates, delivers/receives BAP Control PDU(s) as described in clause 6.1.2. BAP Control PDU
can only be exchanged between peer BAP entities across the BH link.
In addition to functions shown in Figure 4.2.2-1, for a boundary IAB-node, the transmitting part of the BAP entity may
perform BAP header rewriting operation, in accordance with clause 5.2.1.
IAB-DU/IAB-Donor-DU or IAB-MT IAB-MT or IAB-DU/IAB-Donor-DU
Transmitting part of BAP sublayer Receiving part of BAP sublayer
From receiving part of From upper layers To upper layers To transmitting part of
BAP sublayer on same node (IAB-donor-DU and IAB-MT only) (IAB-donor-DU and IAB-MT only) BAP sublayer on same node
BAP BAP
Determine BAP
Control Control
address and Path ID

PDU PDU
Add BAP PDU
Remove BAP PDU

header
header

Routing
Determine if to deliver to upper layers or to the

transmitting part of BAP sublayer
Mapping to BH RLC channel
Egress BH RLC channel Ingress BH RLC channel
Radio Interface (Uu)

Figure 4.2.2-1. Example of functional view of BAP sublayer
4.3 Services
4.3.1 Services provided to upper layers
The following services are provided by the BAP sublayer to upper layers:
- data transfer.
4.3.2 Services expected from lower layers
A BAP sublayer expects the following services from lower layers per RLC entity (for a detailed description see TS
38.322 [4]):
- acknowledged data transfer service;
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3GPP TS 38.340 version 17.0.0 Release 17 10 ETSI TS 138 340 V17.0.0 (2022-05)
- unacknowledged data transfer service.
4.4 Functions
The BAP sublayer supports the following functions:
- Data transfer;
- Determination of BAP destination and path for packets from upper layers;
- Determination of egress BH RLC channels for packets routed to next hop;
- Routing of packets to next hop;
- BAP header rewriting;
- Differentiating traffic to be delivered to upper layers from traffic to be delivered to egress link;
- Flow control feedback and polling signalling;
- Handling of BH RLF related indications;
4.5 Configurations
The configuration of the BAP entity includes:
- The IAB-node's BAP address via RRC.
- The IAB-donor-DU's BAP address via F1AP.
- Mapping from next hop BAP address to downstream egress link via F1AP.
- Mapping from next hop BAP address to upstream egress link via RRC.
- Mapping from upper layer traffic to BAP routing ID in BAP header via F1AP and RRC.
- The BAP routing entries via F1AP.
- Mapping to egress BH RLC channels via F1AP and RRC.
- Flow control feedback type(s) to be provided, if any, via RRC.
BH RLC channels are configured via RRC on the IAB-MT, and via F1AP on the IAB-DU/IAB-donor-DU.
For F1AP configurations, the following mapping, which are derived from the original F1AP signaling, are used in
procedure:
- Uplink Traffic to Routing ID Mapping Configuration.
- Downlink Traffic to Routing ID Mapping Configuration.
- BH Routing Configuration.
- BH RLC Channel Mapping Configuration.
- Uplink Traffic to BH RLC Channel Mapping Configuration.
- Downlink Traffic to BH RLC Channel Mapping Configuration.
- Header Rewriting Configuration.
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3GPP TS 38.340 version 17.0.0 Release 17 11 ETSI TS 138 340 V17.0.0 (2022-05)
5 Procedures
5.1 BAP entity handling
5.1.1 BAP entity establishment
When upper layers request establishment of a BAP
...