ISO 17515-2:2020

INTERNATIONAL ISO
STANDARD 17515-2
First edition
2020-08
Intelligent transport systems —
Evolved universal terrestrial radio
access network (E-UTRAN) —
Part 2:
Device to device communications
(D2D)
Systèmes intelligents de transport — Réseau d'accès à la radio
terrestre universelle évoluée (E-UTRAN) —
Partie 2: Communications directe entre appareils (D2D)
Reference number
ISO 17515-2:2020(E)
©
ISO 2020

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ISO 17515-2:2020(E)

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ISO 17515-2:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Usage of LTE in ITS . 3
5.1 LTE features used in ITS . 3
5.2 Device-to-device communications (D2D) . 3
5.3 D2D communication basics . 5
5.3.1 General. 5
5.3.2 User plane . 5
5.3.3 Control plane . 6
5.4 Service authorization . 6
5.5 SideLink communication related identities . 7
6 General requirements . 7
7 ITS station . 8
7.1 ITS station and communication architecture . 8
7.2 Service access points . 9
7.2.1 General. 9
7.2.2 Communications service access points .10
7.2.3 Management service access points .10
7.2.4 Security service access points .10
8 Communication interface (CI) protocol stack .10
8.1 Physical layer .10
8.2 Data link layer .10
8.2.1 Basic behaviour .10
8.2.2 Data link layer communication addresses .10
8.2.3 Identification of higher layer protocols.10
8.3 Communication adaptation sub-layer .11
9 Communication interface (CI) management .11
9.1 Basic management .11
9.2 Management adaptation entity (MAE) .11
9.2.1 LTE-D2D parameters and I-Parameters .11
9.2.2 LTE-D2D management commands and MI-SAP commands and requests .11
10 Procedures .12
10.1 Communication interface (CI) procedures .12
10.1.1 Transmit procedure .12
10.1.2 Receive procedure .12
10.2 Management procedures .12
10.2.1 Cross-CI prioritization .12
10.2.2 Operational mode .12
10.2.3 LTE-D2D MAC address mapping .12
10.2.4 CI connection procedure .14
10.2.5 CI state management .14
11 Conformance .14
12 Test methods .14
Annex A (normative) Communication interface (CI) parameters .15
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ISO 17515-2:2020(E)

Annex B (normative) MI-COMMANDs .18
Annex C (normative) MI-REQUESTs .19
Annex D (normative) ASN.1 definitions .20
Annex E (informative) CI state transitions .23
Bibliography .25
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ISO 17515-2:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 204, Intelligent transport systems.
A list of all parts in the ISO 17515 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 17515-2:2020(E)

Introduction
Localized communications are an essential component of hybrid communications in Intelligent
Transport Systems (ITS). Various access technologies are suited for localized communications. An
increasing interest from ITS stakeholders in "Cooperative ITS" and "Urban ITS" is focussed on the access
technology known as LTE, which refers to a packet switched cellular network technology specified by
3GPP. In addition to the "traditional" features of cellular networks, LTE also supports device-to-device
communications (LTE-D2D) which can be efficiently used for ITS.
This document provides complements to LTE-D2D specifications from 3GPP needed to operate it as
an ITS access technology in an ITS station unit as specified in ISO 21217. An implementation of this
document is referred to as an ITS-LTE-D2D communication interface (CI).
ITS-LTE-D2D CIs are capable of:
— operating with the support of an LTE base station, and
— operating without the support of an LTE base station, e.g. outside an LTE coverage area,
as specified by 3GPP.
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INTERNATIONAL STANDARD ISO 17515-2:2020(E)
Intelligent transport systems — Evolved universal
terrestrial radio access network (E-UTRAN) —
Part 2:
Device to device communications (D2D)
1 Scope
This document provides specification on the ITS-Station (ITS-S) access layer for a communication
interface (CI) named "ITS-LTE-D2D".
This specification is appropriate in the context of LTE-D2D communications that are being used for
the dissemination of ITS information from an ITS-SU to other ITS-SUs, where these ITS-SUs can be
either vehicle ITS-SUs, roadside ITS-SUs, or personal ITS-SUs, as specified in ISO 21217. It provides a
combination of options from relevant ETSI/3GPP releases and ITS-station management standards in
ISO 24102 to enable and achieve this objective.
ITS-LTE-D2D CIs are based on the evolved-universal terrestrial radio access network (E-UTRAN)
device-to-device (LTE-D2D) technology standardized at 3GPP Release 13.
This document enables the use of the LTE-D2D technology as an ITS access technology in an ITS station
by reference to respective specifications from 3GPP, and by specifying details of the Communication
Adaptation Layer (CAL) and the Management Adaptation Entity (MAE) of CIs specified in ISO 21218.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 8825-2, Information technology — ASN.1 encoding rules: Specification of Packed Encoding Rules
(PER) — Part 2
ISO 21218, Intelligent transport systems — Hybrid communications — Access technology support
ISO 24102-3, Intelligent transport systems — ITS station management — Part 3: Service access points
3GPP TS 23.303, 3rd Generation Partnership Project; Technical Specification Group Services and System
Aspects; Proximity-based services (ProSe); Stage 2 (Release 13)
3GPP TS 24.334 V15.1.0, 3rd Generation Partnership Project; Technical Specification Group Services
and System Aspects; Proximity-services (ProSe) User Equipment (UE) to ProSe function protocol aspects
(Release 13)
3GPP TS 36.300, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network;
Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access
Network (E-UTRAN); Overall description; Stage 2 (Release 13)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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ISO 17515-2:2020(E)

ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
SideLink
UE to UE interface for direct communication between two or more nearby UEs
Note 1 to entry: The Sidelink corresponds to the PC5 (3.2) interface as defined in 3GPP TS 23.303.
[SOURCE: 3GPP TS 36.300]
3.2
PC5
reference point between ProSe-enabled UEs used for control and user plane for ProSe Direct Discovery
and ProSe Direct Communication
Note 1 to entry: The lower protocol layers of the PC5 reference point can be based on E-UTRA SideLink (3.1)
capabilities.
[SOURCE: 3GPP TS 36.300]
4 Symbols and abbreviated terms
CAL communication adaptation sub-layer
CI communication interface
D2D device-to-device
eNB evolved node B
E-UTRA evolved universal terrestrial radio access
E-UTRAN evolved universal terrestrial radio access network
HSS home subscriber subsystem
ITS intelligent transport systems
ITS-SU ITS station unit
LCID logical channel identifier
MAE management adaptation entity
PPPP ProSe per packet priority
ProSe Proximity based service
RNTI radio network temporary identifier
SL SideLink
SL-RNTI SideLink RNTI
SL-SCH SideLink shared channel
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ISO 17515-2:2020(E)

UE user equipment (mobile LTE device)
UM unacknowledged mode
VCI virtual CI
5 Usage of LTE in ITS
5.1 LTE features used in ITS
The LTE network is a packet-switched cellular network specified by 3GPP. It provides features that may
be used in ITS station units (ITS-SUs), namely device-to-device communications (D2D) as described in 5.2.
5.2 Device-to-device communications (D2D)
D2D communications in LTE (LTE-D2D) are possible via LTE interface, i.e. the LTE PC5 (UE-UE)
communications interface.
The initial primary purpose of LTE-D2D communications identified so far by 3GPP provides proximity
services by using direct communications between UEs, see 3GPP TS 36.300, for example. LTE-D2D
communications can be used for the dissemination of ITS information from an ITS-SU to other ITS-SUs:
see 3GPP TR 23 303, for example, where these ITS-SUs can be either vehicle ITS-SUs, roadside ITS-SUs,
or personal ITS-SUs as specified in ISO 21217.
PC5 is an interface between UE to UE used for direct communications in an LTE-D2D network. In PC5
communications, information dissemination goes directly from a UE to other UEs.
PC5 communications are also referred to as SideLink communications. Two operational modes of
SideLink communications exist:
— operator managed;
1) with dynamic scheduling of resources;
2) without dynamic scheduling of resources;
— non-operator managed.
Table 1 shows the operational modes of E-UTRAN D2D.
Table 1 — Operational modes of E-UTRAN D2D
Served by E-UTRAN Not served by E-UTRAN Out-of-coverage
Scheduled mode eNB indicates the physical radio resource N/A
to be used on a UE-specific basis
(Mode 1)
Autonomous mode A UE on its own selects radio resource A UE on its own selects radio resource
from resource pools allocated on a non-UE from resource pools allocated on a non-UE
(Mode 2)
specific basis specific basis
eNB indicates the physical resource pool eNB indicates the physical resource pool
configuration (via SIB or RRC signalling) configuration (via SIB or RRC signalling)
In the operator-managed mode, the UE may either use communication resources scheduled by the
LTE network or select resources autonomously among resources which are pre-configured by the LTE
network; these resources are reserved for data communications of the LTE-D2D CI.
In accordance with ETSI/3GPP, the non-operator managed mode, the UE may on its own select resources
among pre-configured resources which are stored in UEs.
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In D2D communications, there exist 4 types of scenarios.
a) Scenario A (see Figure 1) can be used for non-operator managed D2D communication where UEs
are located out of LTE network coverage.
Figure 1 — D2D scenario A
b) Scenario B (see Figure 2) can be used for non-operator managed D2D communication where one
of UE is located out of LTE network coverage. Also, it can be used for ProSe UE-to-Network Relay
communication which supports LTE network connectivity to UEs located out of LTE network
coverage.
Figure 2 — D2D scenario B
c) Scenario C (see Figure 3) is for operator managed D2D communication in one LTE base station.
Figure 3 — D2D scenario C
d) Scenario D (see Figure 4) is for operator managed D2D communication in different LTE base
stations.
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Figure 4 — D2D scenario D (3GPP 36.843)
In this document, D2D scenarios A, B, and C are considered and specifications for use in the C-ITS
context are provided.
5.3 D2D communication basics
5.3.1 General
In D2D communications, in accordance with 3GPP 36.300, the UE supporting SideLink communication
can operate in two modes for resource allocation:
— Scheduled resource allocation is characterized by:
— UE requests resources for SideLink communication to the eNB. The eNB schedules resources for
transmission of SideLink control information and data;
— UE receives the scheduled resource for SideLink communication and transmits Sidelink control
information and data via the resource.
— UE autonomous resource selection is characterized by:
— A UE on its own selecting resources among pre-configured resources. Sidelink communication
is performed by managing Sidelink control information and data.
5.3.2 User plane
Figure 5 shows the protocol stack for the user plane, where PDCP, RLC, MAC, and PHY sublayers
(terminated at the UE) perform the functions for the user plane.
Figure 5 — User-Plane protocol stack for SideLink communication
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5.3.3 Control plane
A UE does not establish and maintain a logical connection between UEs for SideLink communication
except for one-to-one SideLink communication including ProSe UE-to-Network Relay operation. The
control plane for one-to-one SideLink communication is shown in Figure 6.
Figure 6 — Control-Plane protocol stack for one-to-one SideLink communication
5.4 Service authorization
Service authorization and revocation for LTE-D2D communication is performed for allowing UE’s D2D
communication as specified in 3GPP TS23.303.
In accordance with 3GPP, the LTE network pre-configures the UE with the authorization information for
a list of networks where the UE is authorized to perform direct communication. If there is no associated
UE context, the ProSe Function gets the subscription information for ProSe direct communication from
HSS in Figure 7.
Figure 7 — Pre-configuration for ProSe direct communication
The UE gets the service authorization for ProSe direct communication with a given validity time, from
the ProSe Function of the HPLMN (see Figure 8).
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Figure 8 — Service authorization for ProSe direct communication
5.5 SideLink communication related identities
The following identities are used for SideLink communication:
— SL-RNTI (SideLink Radio Network Temporary Identifier): Unique identification used for SideLink
communication scheduling;
— Source Layer-2 ID: Identifies the sender of the data in SideLink communication. The Source Layer-2
ID is 24 bits long and is used together with Destination Layer-2 ID and LCID for identification of the
RLC UM entity and PDCP entity in the receiver;
— Destination Layer-2 ID: Identifies the target of the data in SideLink communication. The Destination
Layer-2 ID is 24 bits long and is split in the MAC layer into two bit strings:
1) One bit string is the LSB part (8 bits) of Destination Layer-2 ID and is forwarded to the physical
layer as Group Destination ID. This identifies the target of the intended data in SideLink control
information and is used for filtering of packets at the physical layer.
2) The second bit string is the MSB part (16 bits) of the Destination Layer-2 ID and is carried
within the MAC header. This is used for filtering of packets at the MAC layer.
No Access Stratum signalling is required for group formation and to configure Source Layer-2 ID,
Destination Layer-2 ID and Group Destination ID in the UE. These identities are either provided by a
higher layer or derived from identities provided by a higher layer. In case of groupcast and broadcast,
[11]
the ProSe UE ID provided by the higher layer is used directly as the Source Layer-2 ID and the ProSe
[11]
Layer-2 Group ID provided by the higher layer is used directly as the Destination Layer-2 ID in the
MAC layer. In case of one-to-one communications, the higher layer provides Source Layer-2 ID and
Destination Layer-2 ID.
6 General requirements
An implementation of an ITS-LTE-D2D CI is based on relevant specifications from 3GPP:
— 3GPP TS 23.303,
— 3GPP TS 24.334 V15.1.0, and
— 3GPP TS 36.300.
NOTE Further 3GPP specifications related to LTE-D2D and referenced in the basic specifications are e.g.
[11] - [20].
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ISO 17515-2:2020(E)

7 ITS station
7.1 ITS station and communication architecture
The ITS station architecture specified in ISO 21217 is presented in Figure 9. The ITS-LTE-D2D CI is
allocated in the ITS-S access layer of the ITS station architecture.
Figure 9 — ITS station architecture
Figure 10 shows the architecture diagram of an ITS-LTE-D2D CI communications interface (CI)
embedded in the general ITS station architecture.
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ISO 17515-2:2020(E)

Figure 10 — LTE-D2D CI architecture
The communication protocol layers of the ITS-LTE-D2D CI specified by 3GPP are:
a) Physical layer (PHY);
b) Data link layer (DLL).
An ITS-LTE-D2D CI as specified in this document is an ITS wireless CI:
— of MedType c-ITSatt-iso17515 as specified in ISO 17419;
— of CI class CIC-l6 as specified in ISO 21218 for one-to-many communications either with support of
a base station of a cellular network or without support of the base station;
— of CI access class CIAC-4, or CIAC-3, or CIAC-2 as specified in ISO 21218, dependent on the commercial
agreements with an operator of the cellular network.
An ITS-LTE-D2D CI provides the functionality of the IN-SAP specified in ISO 21218, and uses the
functionality of a MI-SAP, and a SI-SAP specified in ISO 24102-3.
7.2 Service access points
7.2.1 General
Requirements set up in this document to support SAPs and the related service primitives thus mean
to support the functionality. This support may be implemented either in a strict meaning, i.e. using the
ASN.1 definitions of the service primitives as "PDU" definitions, or in an abstract meaning, i.e. allowing
for proprietary solutions.
NOTE As Service Access Points (SAPs) per definition describe functional behaviour only, SAPs can be
implemented in different ways.
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7.2.2 Communications service access points
An ITS-LTE-D2D CI shall support the IN-SAP functionality as specified in ISO 21218.
7.2.3 Management service access points
An ITS-LTE-D2D CI shall support the MI-SAP functionality of ISO 24102-3 with details as specified in
ISO 21218.
7.2.4 Security service access points
An ITS-LTE-D2D CI shall support the SI-SAP functionality of ISO 24102-3 with details as specified in
ISO 21218.
8 Communication interface (CI) protocol stack
8.1 Physical layer
The basic behaviour of the LTE-D2D CI physical layer shall be as specified in the respective LTE
standards from 3GPP, see Clause 6.
8.2 Data link layer
8.2.1 Basic behaviour
The basic behaviour of the LTE-D2D CI data link layer shall be as specified in the respective LTE
standards from 3GPP, see Clause 6.
8.2.2 Data link layer communication addresses
LTE-D2D SideLink commu
...