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TECHNICAL SPECIFICATION
Universal Mobile Telecommunications System (UMTS);
LTE;
5G;
NR;
Multi-connectivity;
Overall description;
Stage-2
(3GPP TS 37.340 version 15.5.0 Release 15)
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3GPP TS 37.340 version 15.5.0 Release 15 1 ETSI TS 137 340 V15.5.0 (2019-05)
Reference
RTS/TSGR-0237340vf50
Keywords
5G,LTE,UMTS
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3GPP TS 37.340 version 15.5.0 Release 15 2 ETSI TS 137 340 V15.5.0 (2019-05)
Intellectual Property Rights
Essential patents
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Foreword
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
.
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 37.340 version 15.5.0 Release 15 3 ETSI TS 137 340 V15.5.0 (2019-05)
Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions, symbols and abbreviations . 7
3.1 Definitions . 7
3.2 Abbreviations . 8
4 Multi-Radio Dual Connectivity . 8
4.1 General . 8
4.1.1 Common MR-DC principles . 8
4.1.2 MR-DC with the EPC . 8
4.1.3 MR-DC with the 5GC . 9
4.1.3.1 E-UTRA-NR Dual Connectivity . 9
4.1.3.2 NR-E-UTRA Dual Connectivity . 9
4.1.3.3 NR-NR Dual Connectivity . 9
4.2 Radio Protocol Architecture . 9
4.2.1 Control Plane . 9
4.2.2 User Plane . 10
4.3 Network interfaces . 12
4.3.1 Control Plane . 12
4.3.1.1 Common MR-DC principles . 12
4.3.1.2 MR-DC with EPC . 13
4.3.1.3 MR-DC with 5GC . 13
4.3.2 User Plane . 13
4.3.2.1 Common MR-DC principles . 13
4.3.2.2 MR-DC with EPC . 14
4.3.2.3 MR-DC with 5GC . 14
5 Layer 1 related aspects . 14
6 Layer 2 related aspects . 14
6.1 MAC Sublayer . 14
6.2 RLC Sublayer . 15
6.3 PDCP Sublayer . 15
6.4 SDAP Sublayer . 15
7 RRC related aspects. 15
7.1 System information handling . 15
7.2 Measurements . 15
7.3 UE capability coordination . 16
7.4 Handling of combined MN/SN RRC messages. 17
7.5 SRB3 . 17
7.6 Split SRB . 17
7.7 SCG/MCG failure handling . 18
7.8 UE identities . 18
7.9 Inter-node Resource Coordination . 18
8 Bearer handling aspects . 18
8.1 QoS aspects . 18
8.2 Bearer type selection . 20
8.3 Bearer type change . 20
8.4 User data forwarding . 21
9 Security related aspects . 21
ETSI
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3GPP TS 37.340 version 15.5.0 Release 15 4 ETSI TS 137 340 V15.5.0 (2019-05)
10 Multi-Connectivity operation related aspects . 22
10.1 General . 22
10.2 Secondary Node Addition . 22
10.2.1 EN-DC . 22
10.2.2 MR-DC with 5GC . 23
10.3 Secondary Node Modification (MN/SN initiated) . 25
10.3.1 EN-DC . 25
10.3.2 MR-DC with 5GC . 29
10.4 Secondary Node Release (MN/SN initiated) . 33
10.4.1 EN-DC . 33
10.4.2 MR-DC with 5GC . 35
10.5 Secondary Node Change (MN/SN initiated) . 37
10.5.1 EN-DC . 37
10.5.2 MR-DC with 5GC . 40
10.6 PSCell change . 43
10.7 Inter-Master Node handover with/without Secondary Node change . 43
10.7.1 EN-DC . 43
10.7.2 MR-DC with 5GC . 45
10.8 Master Node to eNB/gNB Change . 47
10.8.1 EN-DC . 47
10.8.2 MR-DC with 5GC . 49
10.9 eNB/gNB to Master Node change . 50
10.9.1 EN-DC . 50
10.9.2 MR-DC with 5GC . 51
10.10 RRC Transfer . 52
10.10.1 EN-DC . 52
10.10.2 MR-DC with 5GC . 53
10.11 Secondary RAT data volume reporting . 55
10.11.1 EN-DC . 55
10.11.2 MR-DC with 5GC . 56
10.12 Activity Notification. 56
10.12.1 EN-DC . 56
10.12.2 MR-DC with 5GC . 57
10.13 Notification Control Indication . 58
10.13.1 EN-DC . 58
10.13.2 MR-DC with 5GC . 59
10.14 PDU Session Split at UPF . 59
10.14.1 PDU Session Split at UPF during PDU session resource setup . 59
10.14.2 PDU Session Split at UPF during PDU session resource modify (5GC initiated) . 60
10.14.3 PDU Session Split at UPF (RAN initiated) . 61
11 Service related aspects. 62
11.1 Roaming and Access Restrictions . 62
12 X2/Xn Interface related aspects . 63
13 Other aspects . 63
13.1 Interference avoidance for in-device coexistence . 63
Annex A (informative): Layer 2 handling for bearer type change . 64
Annex B (informative): Change history . 66
History . 69
ETSI
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3GPP TS 37.340 version 15.5.0 Release 15 5 ETSI TS 137 340 V15.5.0 (2019-05)
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.
ETSI
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3GPP TS 37.340 version 15.5.0 Release 15 6 ETSI TS 137 340 V15.5.0 (2019-05)
1 Scope
The present document provides an overview of the multi-connectivity operation using E-UTRA and NR radio access
technologies. Details of the network and radio interface protocols are specified in companion specifications of the 36
and 38 series.
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 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2".
[3] 3GPP TS 38.300: "NR; NR and NG-RAN Overall description; Stage 2".
[4] 3GPP TS 38.331: "NR; Radio Resource Control (RRC) protocol specification".
[5] 3GPP TS 38.423: "NG-RAN; Xn application protocol (XnAP)".
[6] 3GPP TS 38.425: "NG-RAN; NR user plane protocol".
[7] 3GPP TS 38.401: "NG-RAN; Architecture description".
[8] 3GPP TS 38.133: "NG-RAN; Requirements for support of radio resource management".
[9] 3GPP TS 36.423: "Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2
Application Protocol (X2AP)".
[10] 3GPP TS 36.331: "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource
Control (RRC); Protocol specification".
[11] 3GPP TS 23.501: "System Architecture for the 5G System; Stage 2".
[12] 3GPP TS 38.101-1: "User Equipment (UE) radio transmission and reception; Part 1: Range 1
Standalone".
[13] 3GPP TS 38.101-2: "User Equipment (UE) radio transmission and reception; Part 2: Range 2
Standalone".
[14] 3GPP TS 38.101-3: "User Equipment (UE) radio transmission and reception; Part 3: Range 1 and
Range 2 Interworking operation with other radios".
ETSI
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3GPP TS 37.340 version 15.5.0 Release 15 7 ETSI TS 137 340 V15.5.0 (2019-05)
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in 3GPP 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 3GPP
TR 21.905 [1] and 3GPP TS 36.300 [2].
En-gNB: node providing NR user plane and control plane protocol terminations towards the UE, and acting as
Secondary Node in EN-DC.
Master Cell Group: in MR-DC, a group of serving cells associated with the Master Node, comprising of the SpCell
(Pcell) and optionally one or more Scells.
Master node: in MR-DC, the radio access node that provides the control plane connection to the core network. It may
be a Master eNB (in EN-DC), a Master ng-eNB (in NGEN-DC) or a Master gNB (in NR-DC and NE-DC).
MCG bearer: in MR-DC, a radio bearer with an RLC bearer (or two RLC bearers, in case of CA packet duplication)
only in the MCG.
MN terminated bearer: in MR-DC, a radio bearer for which PDCP is located in the MN.
MCG SRB: in MR-DC, a direct SRB between the MN and the UE.
Multi-Radio Dual Connectivity: Dual Connectivity between E-UTRA and NR nodes, or between two NR nodes.
Ng-eNB: as defined in TS 38.300 [3].
PCell: SpCell of a master cell group.
PSCell: SpCell of a secondary cell group.
RLC bearer: RLC and MAC logical channel configuration of a radio bearer in one cell group.
Secondary Cell Group: in MR-DC, a group of serving cells associated with the Secondary Node, comprising of the
SpCell (PSCell) and optionally one or more Scells.
Secondary node: in MR-DC, the radio access node, with no control plane connection to the core network, providing
additional resources to the UE. It may be an en-gNB (in EN-DC), a Secondary ng-eNB (in NE-DC) or a Secondary
gNB (in NR-DC and NGEN-DC).
SCG bearer: in MR-DC, a radio bearer with an RLC bearer (or two RLC bearers, in case of CA packet duplication)
only in the SCG.
SN terminated bearer: in MR-DC, a radio bearer for which PDCP is located in the SN.
SpCell: primary cell of a master or secondary cell group.
SRB3: in EN-DC, NGEN-DC and NR-DC, a direct SRB between the SN and the UE.
Split bearer: in MR-DC, a radio bearer with RLC bearers both in MCG and SCG.
Split PDU Session (or PDU Session split): a PDU Session whose QoS Flows are served by more than one SDAP
entities in the NG-RAN.
Split SRB: in MR-DC, a SRB between the MN and the UE with RLC bearers both in MCG and SCG.
User plane resource configuration: in MR-DC with 5GC, encompasses radio network resources and radio access
resources related to either one or more PDU sessions, one or more QoS flows, one or more DRBs, or any combination
thereof.
ETSI
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3GPP TS 37.340 version 15.5.0 Release 15 8 ETSI TS 137 340 V15.5.0 (2019-05)
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in 3GPP 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
3GPP TR 21.905 [1] and 3GPP TS 36.300 [2].
DC Intra-E-UTRA Dual Connectivity
EN-DC E-UTRA-NR Dual Connectivity
MCG Master Cell Group
MN Master Node
MR-DC Multi-Radio Dual Connectivity
NE-DC NR-E-UTRA Dual Connectivity
NGEN-DC NG-RAN E-UTRA-NR Dual Connectivity
NR-DC NR-NR Dual Connectivity
SCG Secondary Cell Group
SN Secondary Node
4 Multi-Radio Dual Connectivity
4.1 General
4.1.1 Common MR-DC principles
Multi-Radio Dual Connectivity (MR-DC) is a generalization of the Intra-E-UTRA Dual Connectivity (DC) described in
36.300 [2], where a multiple Rx/Tx UE may be configured to utilise resources provided by two different nodes
connected via non-ideal backhaul, one providing NR access and the other one providing either E-UTRA or NR access.
One node acts as the MN and the other as the SN. The MN and SN are connected via a network interface and at least
the MN is connected to the core network.
NOTE 1: MR-DC is designed based on the assumption of non-ideal backhaul between the different nodes but can
also be used in case of ideal backhaul.
NOTE 2: All MR-DC normative text and procedures in this version of the specification show the aggregated node
case. The details about non-aggregated node for MR-DC operation are described in TS38.401[7].
4.1.2 MR-DC with the EPC
E-UTRAN supports MR-DC via E-UTRA-NR Dual Connectivity (EN-DC), in which a UE is connected to one eNB
that acts as a MN and one en-gNB that acts as a SN. The eNB is connected to the EPC via the S1 interface and to the
en-gNB via the X2 interface. The en-gNB might also be connected to the EPC via the S1-U interface and other en-gNBs
via the X2-U interface.
The EN-DC architecture is illustrated in Figure 4.1.2-1 below.
ETSI
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3GPP TS 37.340 version 15.5.0 Release 15 9 ETSI TS 137 340 V15.5.0 (2019-05)
M ME/S-GW M ME/S-GW
EPC
S
1 U
- -
U 1
S
S
1
1
S
X2-U E-UTRAN
en-gNB
en-gNB
X2
eNB eNB
Figure 4.1.2-1: EN-DC Overall Architecture
4.1.3 MR-DC with the 5GC
4.1.3.1 E-UTRA-NR Dual Connectivity
NG-RAN supports NG-RAN E-UTRA-NR Dual Connectivity (NGEN-DC), in which a UE is connected to one ng-eNB
that acts as a MN and one gNB that acts as a SN. The ng-eNB is connected to the 5GC and the gNB is connected to the
ng-eNB via the Xn interface.
4.1.3.2 NR-E-UTRA Dual Connectivity
NG-RAN supports NR-E-UTRA Dual Connectivity (NE-DC),
...