ISO 20794-3:2020

Road vehicles — Clock extension peripheral interface (CXPI) — Part 3: Transport and network layer

This document specifies the OSI transport layer and network layer by means of services and protocols. They can be used by different applications. The transport layer: — transforms a message into a single packet; — adds protocol control information for diagnostic and node configuration into each packet; — adds packet identifier for diagnostic and node configuration into each packet; and — performs transport protocol error detection. The transport layer protocol is not used for normal communication except to map the service interface parameters between lower and upper OSI layers. The network layer: — adds a node address for diagnostic and node configuration into each segment; and — observes timing for diagnostic and node configuration of each segment. The network layer is not used for normal communication except to map the service interface parameters between lower and upper OSI layers.

Véhicules routiers — Interface du périphérique d'extension d'horloge (CXPI) — Partie 3: Transport et couche réseau

General Information

• Status: Published
• Publication Date: 04-Feb-2020
• ICS: 43.040.15 - Car informatics. On board computer systems
• Technical Committee: ISO/TC 22/SC 31 - Data communication
• Drafting Committee: ISO/TC 22/SC 31/WG 3 - In-vehicle networks
• Current Stage: 6060 - International Standard published
• Start Date: 05-Feb-2020
• Due Date: 07-Dec-2019
• Completion Date: 05-Feb-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20794-3
First edition
2020-02
Road vehicles — Clock extension
peripheral interface (CXPI) —
Part 3:
Transport and network layer
Véhicules routiers — Interface du périphérique d'extension d'horloge
(CXPI) —
Partie 3: Transport et couche réseau
Reference number
ISO 20794-3:2020(E)
©
ISO 2020

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ISO 20794-3:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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ISO 20794-3:2020(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
4.1 Symbols . 2
4.2 Abbreviated terms . 2
5 Conventions . 3
6 Overview of transport layer and network layer . 3
6.1 Properties . 3
6.2 Packet types . 3
6.3 Error detection and indication . 3
7 Service interface parameters (SIP) . 3
7.1 SIP — General . 3
7.2 SIP — Data type definitions . 4
7.3 SIP — TA, target address . 4
7.4 SIP — SA, source address. 4
7.5 SIP — Ptype, packet type . 4
7.6 SIP — ReqId, request identifier . 4
7.7 SIP — ReqTypeId, request type identifier . 5
7.8 SIP — PDU, protocol data unit . 5
7.9 SIP — Length, length of PDU . 5
7.10 SIP — NMInfo, network management information . . 5
7.11 SIP — SCT, sequence count . 5
7.12 SIP — Result, result . 6
8 Transport layer (TL) . 6
8.1 SI — T_Data.req and T_Data.ind service interface . 6
8.2 SI — T_Data.req and T_Data.ind service interface parameter mapping . 7
8.3 TL — Service interface with T_Ptype parameter mapping . 8
8.3.1 TL — T_Data.req and T_Data.ind with T_Ptype = NormalCom (T_Length = NULL) 8
8.3.2 TL — T_Data.req and T_Data.ind with T_Ptype = NormalCom (T_Length ≥ '0') . 9
8.3.3 TL — T_Data.req and T_Data.ind interface with T_Ptype = DiagNodeCfg .10
8.4 TL — Internal operation .11
8.5 TL — T_PDU .11
8.5.1 TL — T_PDU definition .11
8.5.2 TL — T_PCI definition .11
8.6 TL — Function models .12
8.6.1 TL — Transmission logic .12
8.6.2 TL — Reception logic .13
8.7 TL — Error detection .14
9 Network layer (NL) .14
9.1 SI — N_Data.req and N_Data.ind service interface .14
9.2 SI — N_Data.req and N_Data.ind service interface parameter mapping .15
9.3 NL — Service interface with N_Ptype parameter mapping .16
9.3.1 NL — N_Data.req and N_Data.ind with N_Ptype = NormalCom (N_Length =
NULL) . .16
9.3.2 TL — N_Data.req and N_Data.ind with N_Ptype = NormalCom (N_Length ≥ '0') .17
9.3.3 NL — N_Data.req and N_Data.ind interface with N_Ptype = DiagNodeCfg .18
9.4 NL — Internal operation .19
9.5 NL — N_PDU .19
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9.5.1 NL — N_PDU definition .19
9.5.2 NL — N_NAD definition .19
9.6 NL — Function models.20
9.6.1 NL — Transmission logic .20
9.6.2 NL — Reception logic.20
9.7 NL — Timing definition .21
9.7.1 NL — General .21
9.7.2 NL — Timing constraints .21
9.7.3 NL — Timing parameters .22
9.8 NL — Error detection .22
Bibliography .23
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ISO 20794-3:2020(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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
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).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
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 22, Road vehicles, Subcommittee SC 31,
Data communication.
A list of all parts in the ISO 20794 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 20794-3:2020(E)

Introduction
ISO 20794 (all parts) specifies the application (partly), application layer, transport layer, network
layer, data link layer, and physical layer requirements of an in-vehicle network called "clock extension
peripheral interface (CXPI)".
CXPI is an automotive low-speed single-wire network. It is an enabler for reducing vehicle weight and
fuel consumption by reducing wire counts to simple devices like switches and sensors.
CXPI serves as and is designed for automotive control applications, for example door control group,
light switch, and HVAC (Heating Ventilation and Air Conditioning) systems.
The CXPI services, protocols, and their key characteristics are specified in different parts according to
the OSI layers.
— Application and application layer
— application measurement and control data communication to exchange information between
applications in different nodes based on message communication;
— wake-up and sleep functionality;
— two kinds of communication methods can be selected at system design by each node:
i) the event-triggered method, which supports application measurement- and control-based
(event-driven) slave node communication, and
ii) the polling method, which supports slave node communication based on a periodic master
schedule;
— performs error detection and reports the result to the application;
— application error management.
— Transport layer and network layer
— transforms a message into a single packet;
— adds protocol control information for diagnostic and node configuration into each packet;
— adds packet identifier for diagnostic and node configuration into each packet;
— performs error detection and reports the result to higher OSI layers.
— Data link layer and physical layer
— provides long and short data frames;
— adds a frame identifier into the frame;
— adds frame information into the frame;
— adds a cyclic redundancy check into the frame;
— performs byte-wise arbitration and reports the arbitration result to higher OSI layers;
— performs frame type detection in reception function;
— performs error detection and reports the result to higher OSI layers.
— performs Carrier Sense Multiple Access (CSMA);
— performs Collision Resolution (CR);
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— generates a clock, which is transmitted with each bit to synchronise the connected nodes on the
CXPI network;
— supports bit rates up to 20 kbit/s.
To achieve this, it is based on the Open Systems Interconnection (OSI) Basic Reference Model specified
[1]
in ISO/IEC 7498-1 and ISO/IEC 10731 , which structures communication systems into seven layers.
Figure 1 illustrates an overview of communication frameworks beyond the scope of this document
including related standards:
— vehicle normal communication framework, which is composed of ISO 20794-2, and ISO 20794-5;
[3]
— vehicle diagnostic communication framework, which is composed of ISO 14229-1, ISO 14229-2 ,
[4]
and ISO 14229-8 ;
[7]
— presentation layer standards, e.g. vehicle manufacturer specific or ISO 22901-1 ODX ;
— lower OSI layers framework, which is composed of ISO 20794-3, ISO 20794-4, ISO 20794-6, and
ISO 20794-7 conformance testing.
[4]
ISO 20794 (all parts) and ISO 14229-8 are based on the conventions specified in the OSI Service
[1]
Conventions (ISO/IEC 10731) as they apply for all layers and the diagnostic services.
Figure 1 — ISO 20794 documents reference according to OSI model
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INTERNATIONAL STANDARD ISO 20794-3:2020(E)
Road vehicles — Clock extension peripheral interface
(CXPI) —
Part 3:
Transport and network layer
1 Scope
This document specifies the OSI transport layer and network layer by means of services and protocols.
They can be used by different applications.
The transport layer:
— transforms a message into a single packet;
— adds protocol control information for diagnostic and node configuration into each packet;
— adds packet identifier for diagnostic and node configuration into each packet; and
— performs transport protocol error detection.
The transport layer protocol is not used for normal communication except to map the service interface
parameters between lower and upper OSI layers.
The network layer:
— adds a node address for diagnostic and node configuration into each segment; and
— observes timing for diagnostic and node configuration of each segment.
The network layer is not used for normal communication except to map the service interface parameters
between lower and upper OSI layers.
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 7498-1, Information technology — Open Systems Interconnection — Basic Reference Model: The
Basic Model
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 7498-1 and the
following apply.
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/
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3.1
normal communication
NormalCom
measurement and control data
3.2
higher OSI layers
application, presentation, session, transport, and network layers according to ISO/IEC 7498-1:1994
3.3
lower OSI layers
data link and physical layers according to ISO/IEC 7498-1:1994
4 Symbols and abbreviated terms
4.1 Symbols
ms millisecond
| vertical bar indicates choice; either the left-hand side or the right-hand side of the vertical
bar appears
4.2 Abbreviated terms
A_ prefix for application layer
AL application layer
DiagNodeCfg diagnostic and node configuration
Mtype message type
N_ prefix for network layer
NAD node address
NormalCom normal communication
NL network layer
OSI open systems interconnection
PDU protocol data unit
Ptype packet type
ReqId request identifier
SA source address
SAP service access point
SF single frame
SIP service interface parameter
T_ prefix for transport layer
T_Data transport data service primitive
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ISO 20794-3:2020(E)

TA target address
TL transport layer
w/ with
w/o without
5 Conventions
This document is based on the conventions discussed in the OSI Service Conventions as specified in
ISO/IEC 10731.
6 Overview of transport layer and network layer
6.1 Properties
The transport layer and network layer have the following properties:
— addition (transmission) and elimination (reception) of transport- and network-specific header
information to A_PDU;
— creation of T_PDU and N_PDU;
— mapping of service interface parameters between application and transport layer;
— mapping of service interface parameters between transport and network layer;
— determination of packet types to identify normal communication measurement and/or control data,
diagnostic and node configuration data; and
— target address type and address handling of packet transmission and reception.
6.2 Packet types
The transport layer only supports single packets (no segmentation of application layer messages).
6.3 Error detection and indication
For detecting errors, the following measures are specified:
— transport layer packet type error;
— transport protocol control information single frame data length error;
— transport protocol control information single frame data length extension error; and
— node related error detection and error signalling.
To confirm an error occurrence during data transmission and reception, higher OSI layers are notified
by an error indication.
7 Service interface parameters (SIP)
7.1 SIP — General
The following subclauses specify the service interface parameters and data types, which are used by
the transport and network layer services.
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7.2 SIP — Data type definitions
This requirement specifies the data type definitions of the CXPI service interface parameters.
REQ 0.1 SIP — Data type definitions
The data types shall be in accordance to:
— Enum = 8-bit enumeration
— Unsigned Byte = 8-bit unsigned numeric value
— Unsigned Word = 16-bit unsigned numeric value
— Byte Array = sequence of 8-bit aligned data
— 2-bit Bit String = 2-bit binary coded
— 8-bit Bit String = 8-bit binary coded
— 16-bit Bit String = 16-bit binary coded
7.3 SIP — TA, target address
This requirement specifies the target address parameter values of the CXPI service interface.
REQ 0.2 SIP — TA, target address
The TA parameter shall be of data type Unsigned Byte and shall be used to identify the target address of the
information to be transmitted.
Range: [01 to FF ]
16 16
7.4 SIP — SA, source address
This requirement specifies the source address parameter values of the CXPI service interface.
REQ 0.3 SIP — SA, source address
The SA parameter shall be of data type Unsigned Byte and shall be used to identify the source address of the
received information.
Range: [01 to FF ]
16 16
7.5 SIP — Ptype, packet type
This requirement specifies the packet type parameter values of the CXPI service interface.
REQ 0.4 SIP — Ptype, packet type
The Ptype parameter shall be of data type Enum and shall be used to identify the packet type and range of ad-
dress information included in a service call.
Range: [NormalCom, DiagNodeCfg]
7.6 SIP — ReqId, request identifier
This requirement specifies the request identifier parameter values of the CXPI service interface.
REQ 0.5 SIP — ReqId, request identifier
The ReqId parameter shall be of data type Unsigned Byte and shall contain the request identifier.
Range: [01 to 7F ]
16 16
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7.7 SIP — ReqTypeId, request type identifier
This requirement specifies the request type identifier parameter value of the CXPI service interface.
REQ 0.6 SIP — ReqTypeId, request type identifier
The ReqTypeId parameter shall be of data type Unsigned Byte and shall contain the request type identifier.
Range: [00 ]
16
NOTE  ReqTypeId is used by the application to enable the polling method. It has a fixed value.
7.8 SIP — PDU, protocol data unit
This requirement specifies the protocol data unit parameter values of the CXPI service interface.
REQ 0.7 SIP — PDU, protocol data unit
The PDU parameter shall be of data type Byte Array and shall contain the packet data (PDU) content of the
request or response packet to be transmitted/received.
Range: [00 to FF ]
16 16
7.9 SIP — Length, length of PDU
This requirement specifies the length of PDU parameter value of the CXPI service interface.
REQ 0.8 SIP — Length, length of PDU
The Length parameter shall be of data type Unsigned Byte and shall contain the length of the PDU to be
transmitted/received.
Range: [00 to FF ]
16 16
7.10 SIP — NMInfo, network management information
This requirement specifies the network management information parameter values of the CXPI service
interface.
REQ 0.9 SIP — NMInfo, network management information
The NMInfo parameter shall be of data type Enum and shall contain the NM information in the response field.
Type: Enum
Range: 00 = [no request for wakeup_ind, sleep_ind prohibition]
2
        01 = [no request for wakeup_ind, sleep_ind permission]
2
        10 = [request for wakeup_ind, sleep_ind prohibition]
2
        11 = [request for wakeup_ind, sleep_ind permission]
2
7.11 SIP — SCT, sequence count
This requirement specifies the sequence count parameter values of the CXPI service interface.
REQ 0.10 SIP — SCT, sequence count
The SCT parameter shall be of data type Unsigned Byte and shall contain the sequence count information in
the response field to be transmitted/received.
Type: 2-bit Unsigned Byte
Range: [00 to 11 ]
2 2
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7.12 SIP — Result, result
This requirement specifies the result parameter values of the CXPI service interface.
REQ 0.11 SIP — SIP — Result, result
The Result parameter shall be of data type 16-bit Bit String and shall contain the status relating to the
outcome of a service execution. If two or more errors are discovered at the same time, then the transport layer
or network layer entity shall set the appropriate error bit in the Result parameter.
Range: [OK, DLL_Arb_Lost, Err_DLL_Byte, Err_DLL_CRC, Err_DLL_DLC,
        Err_DLL_DLCext_Value, Err_DLL_Parity, Err_DLL_Framing,
        Err_DLL_Value, Err_NL_TIMEOUT_A, Err_TL_Ptype,
        Err_TL_PCI_DL_Value, Err_TL_PCI_DLext_Value]
The result OK shall be issued to the service user when the service execution completed without error.
The result OK shall be issued to a service user on both, the sender and receiver side.
The Err_. shall be issued to the service user when an error is detected.
The Err_. shall be issued to the service user on both, the sender and receiver side.
Length: 16-bit; (1-bit per result)
Range: [0 to 1 ]
2 2
8 Transport layer (TL)
8.1 SI — T_Data.req and T_Data.ind service interface
The service interface defines the service primitives and parameter mapping to the TL.
Figure 2 shows the TL T_Data.req and T_Data.ind service interface.
Key
1 service access point
2 read back from CXPI network provided by lower OSI layer
t time
Figure 2 — TL T_Data.req and T_Data.ind service interface
For normal communication (NormalCom) the sender node transmits, if master node, either a request
protected type identifier field (polling method), or a request protected identifier field (T_Data.req).
All nodes receive the request protected identifier field of type NormalCom (T_Data.ind). The node,
which has corresponding PDU data, transmits the response PDU (T_Data.req) and all nodes receive the
response PDU (T_Data.ind).
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For diagnostic and node configuration (DiagNodeCfg) the sender node transmits a request message
including a protected identifier field and the A_PDU (T_Data.req) onto the CXPI network. All nodes
receive the DiagNodeCfg request message (T_Data.ind). The node(s), which is (are) targeted by the
request message, transmit a DiagNodeCfg response message (T_Data.req) onto the CXPI network.
8.2 SI — T_Data.req and T_Data.ind service interface parameter mapping
This requirement specifies the transport layer service interface parameter mapping to lower OSI layers.
REQ 4.1 SI — T_Data.req and T_Data.ind service interface parameter mapping
The T_Data.req and T_Data.ind service interface parameter mappin
...