ISO 29281-1:2013

INTERNATIONAL ISO
STANDARD 29281-1
First edition
2013-04-15
Intelligent transport systems —
Communication access for land mobiles
(CALM) — Non-IP networking —
Part 1:
Fast networking & transport layer
protocol (FNTP)
Systèmes intelligents de transport — Accès aux communications des
services mobiles terrestres (CALM) — Réseautique non-IP —
Partie 1: Réseautique rapide et protocole de la couche transport
Reference number
©
ISO 2013
© ISO 2013
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ii © ISO 2013 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Abbreviated terms . 2
5 Architectures . 2
5.1 Modes of operation . 2
5.2 FNTP reference architecture . 3
5.3 Communication principles. 3
5.4 Implementation architectures . 4
6 Protocol elements . 6
6.1 Service access points . 6
6.2 FNTP NPDU . 7
6.3 Protocol management elements .11
7 Protocol procedures .13
7.1 Service access points .13
7.2 Port management .13
7.3 Maintenance of entries in forwarding tables .13
7.4 Initial settings of forwarding tables in ITS-S hosts .14
7.5 Initial settings of forwarding tables in ITS-S routers .15
7.6 Transmitting packets .15
7.7 Receiving packets.18
7.8 Management of forwarding tables .20
7.9 CIP management.21
8 NF-SAP services .22
8.1 Overview .22
8.2 NF-FNTP-PORT .22
8.3 NF-FNTP-COMM .23
9 Conformance .25
10 Test methods .26
Annex A (normative) ASN.1 modules .27
Bibliography .31
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. 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. 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.
The committee responsible for this document is ISO/TC 204, Intelligent transport systems.
This first edition of ISO 29281-1, together with ISO 29281-2, cancels and replaces ISO 29281:2011.
ISO 29281 consists of the following parts, under the general title Intelligent transport systems —
Communication access for land mobiles (CALM) — Non-IP networking:
— Part 1: Fast networking and transport layer protocol (FNTP)
— Part 2: Legacy system support
iv © ISO 2013 – All rights reserved

Introduction
This part of ISO 29281 is part of a series of International Standards for communications access for land
mobiles (CALM). An introduction to the whole set of International Standards is provided in ISO 21217.
This part of ISO 29281 is part 1 of a multipart standard which determines the intelligent transport
systems (ITS) non-IP communications.
An essential protocol for non-IP communications is the “Fast networking & transport layer protocol”
(FNTP). FNTP distinguishes:
— a basic port mapper protocol, primarily used for single-hop communications between ITS stations;
— protocol extensions for
— N-hop groupcast;
— LPP;
— secured communication;
— ITS station-internal forwarding of packets between ITS-S host ITS-SCUs and ITS-S router ITS-SCUs.
FNTP is validated in the CVIS project.
INTERNATIONAL STANDARD ISO 29281-1:2013(E)
Intelligent transport systems — Communication access for
land mobiles (CALM) — Non-IP networking —
Part 1:
Fast networking & transport layer protocol (FNTP)
1 Scope
This part of ISO 29281 specifies a protocol of the ITS-S networking and transport layer in support of
efficient ad hoc single-hop communications with optional N-hop broadcast.
This protocol supports ITS station-internal forwarding of packets, i.e. between ITS-S routers and ITS-S
hosts and vice versa. The protocol is named “Fast Networking & Transport Protocol” (FNTP).
2 Normative references
The following referenced documents are indispensable for the application 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 21217, Intelligent transport systems — Communications access for land mobiles (CALM) — Architecture
ISO 21218, Intelligent transport systems — Communications access for land mobiles (CALM) — Access
technology support
ISO 24102-1, Intelligent transport systems — Communications access for land mobiles (CALM) — ITS station
management — Part 1: Local management
ISO 24102-3, Intelligent transport systems — Communications access for land mobiles (CALM) — ITS station
management — Part 3: Service access points
ISO 24102-4, Intelligent transport systems — Communications access for land mobiles (CALM) — ITS station
management — Part 4: Station-internal management communications
ISO 24102-5, Intelligent transport systems — Communications access for land mobiles (CALM) — ITS station
management — Part 5: Fast service advertisement protocol (FSAP)
ETSI TS 102 985-1, Intelligent Transport Systems (ITS); Communications Access for Land Mobiles (CALM);
Test specifications for non-IP networking (ISO 29281); Part 1: Protocol implementation conformance
“statement (PICS) proforma
ETSI TS 102 985-2, Intelligent Transport Systems (ITS); Communications Access for Land Mobiles (CALM);
Test specifications for non-IP networking (ISO 29281); Part 2: Test suite structure & test purposes (TSS&TP)
ETSI TS 102 985-3, Intelligent Transport Systems (ITS); Communications Access for Land Mobiles (CALM);
Test specifications for non-IP networking (ISO 29281); Part 3: Abstract test suite and partial PIXIT (ATS)
specification
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21217, ISO 24102-3, ISO 24102-4
and the following apply.
3.1
ITS-S port
source and/or destination “endpoint” for communications identified by an integer number
4 Abbreviated terms
FNTP Fast networking & transport protocol
ITS-SP ITS-S port
5 Architectures
5.1 Modes of operation
5.1.1 General context and purpose of FNTP
The “fast networking & transport layer protocol” (FNTP) specified in this part of ISO 29281 is designed
as a protocol of the ITS-S networking and transport layer of the ITS station (ITS-S) architecture which
recognizes the concepts of the bounded, secured and managed ITS-S; and supports the concept of ITS
station communication units (ITS-SCU) to implement roles of an ITS-S in physical units specified (see
ISO 21217, ISO 24102-1, ISO 24102-3 and ISO 24102-4).
FNTP is primarily designed to enable single-hop communication between peer ITS stations with
minimum protocol overhead, and supports optional features.
NOTE ISO 15628 legacy systems support specified in [2] makes use of FNTP.
FNTP supports any kind of ad hoc access technology, e.g. CALM M5, CALM IR. FNTP may be used to
connect source and destination “endpoints” identified by “ITS-S port” (ITS-SP) numbers in peer ITS
stations, where peer ITS stations are uniquely identified by a Link-ID (usually MAC address contained
in it) of the access layer specified in ISO 21218. Consequently, FNTP is a port mapper protocol, usually
located in the transport layer of the OSI model.
5.1.2 Basic mode of operation
The basic mode of operation is the simplest option of FNTP, which is just providing single-hop
communications between instances of ITS stations without applying any of the options of FNTP.
5.1.3 Extended mode of operation
The extended mode of operation supports options of the FNTP, e.g.:
— ITS station-internal forwarding;
— secure communications;
— N-hop broadcast;
— LPP support;
— CIP management.
2 © ISO 2013 – All rights reserved

ITS station-internal forwarding is a special option referred to as “station-internal forwarding mode
of operation”.
Other options may be added in a future revision of this part of ISO 29281.
5.2 FNTP reference architecture
Figure 1 illustrates the location of FNTP in the ITS station (ITS-S) specified in ISO 21217, and the
communication relations with other protocol entities.
API
Communications
ITS Management Entity
ITS-S Facilities Layer
NF-SAP
CI Selection
ITS-S Networking & Transport Layer
Manager
Port management
FNTP
IN-SAP
CI Manager
ITS-S Access Layer
ISO 21216 ISO 21215 ISO 21214 LAN CI
Other CIs
supporting supporting supporting ITS station-
MAC MAC MAC internal
groupcast groupcast groupcast network
frames frames frames access
Figure 1 — FNTP reference architecture
The “Port management” is specified as part of FNTP, but may also be used for other ITS-S networking
and transport layer protocols.
The “CI Selection Manager” is specified in ISO 24102-1. The “CI Manager” is specified in ISO 24102-1
and ISO 21218. These two managers are supporting FNTP, but FNTP does not necessarily depend on
these managers.
5.3 Communication principles
5.3.1 Transmission
Transmission requests may be presented by the ITS-S facilities layer via the NF-SAP. Sources and
destinations of messages in the ITS-S facilities layer are identified by ITS-SP numbers.
MF-SAP
MI-SAP MN-SAP
SI-SAP SN-SAP SF-SAP
ITS-S Security Entity
Valid transmission requests to a groupcast MAC address are given by a “well-known” destination port
address in combination with an existing groupcast VCI. The value of the source port address is irrelevant
with respect of validity of a transmission request in case no reply is expected. Replies to groupcast
messages are expected, e.g. in case of the service advertisement message specified in ISO 24102-5.
Valid transmission requests to a unicast MAC address are given by any valid destination port address in
combination with an existing unicast VCI. The value of the source port address is irrelevant with respect
of validity of a transmission request in case no reply is expected.
Transmission requests are presented by the FNTP to the ITS-S access layer using services of the IN-SAP.
NOTE In a CALM compliant ITS station, assignment of VCIs to ITS-S applications is done automatically by the
CI selection management specified in ISO 24102-1.
5.3.2 Reception
Reception notifications may be presented by the ITS-S access layer to the FNTP using services of the IN-
SAP. Sources and destinations of messages are identified by ITS-SP numbers contained in the FNTP NPDU.
Valid notified packets addressed to an ITS-SP are given by a known destination port address. Which CI
was used for reception of the packet, and which is the source port address of the packet, are not relevant
for the validity of the packet, but are relevant for a potential reply.
Notifications of received packets are presented by the FNTP to the ITS-S facilities layer using services
of the NF-SAP.
5.3.3 FNTP ITS-SPs
Allocation and deletion of dynamic and static well-known “ITS-S port” (ITS-SP) numbers is specified in 8.2.
NOTE Static well-known ITS-SP numbers are assigned to ITS applications by a registration authority, see [4].
5.4 Implementation architectures
FNTP may support the implementation architectures introduced in ISO 21217 and illustrated in
Figures 2, 3 and 4 with the peer ITS stations A and B, indicating FNTP in the ITS-S networking and
transport layer.
Combined ITS-S router / host Combined ITS-S router / host
A B
Applications Applications
Facilities layer Facilities layer
Networking & transport Networking & transport
layer (FNTP) layer (FNTP)
Access layer (CIs) Access layer (CIs)
Communication link between ITS-Ss
Figure 2 — Implementation architecture I
In case the FNTP is implemented in an ITS-SCU which does not have both roles of ITS-S host and ITS-S
router, the ITS station-internal network shall be supported. This situation is illustrated in Figures 3 and 4.
4 © ISO 2013 – All rights reserved
Management
Security
Management
Security
ITS-S host A
Applications
ITS-S router A
Facilities layer
Networking & transport Networking & transport
layer (FNTP) layer (FNTP)
Access layer (LAN CI) LAN CI Other CIs
ITS station-internal network A
ITS-S host B
Applications
ITS-S router B
Facilities layer
Networking & transport Networking & transport
layer (FNTP) layer (FNTP)
Access layer (LAN CI) LAN CI Other CIs
ITS station-internal network B
Figure 3 — Implementation architecture II
Management Management
Security Security
Management Management
Security Security
Communiaction link between
ITS-Ss
ITS-S host A
Applications
ITS-S router A
Facilities layer
Networking & transport Networking & transport
layer (FNTP) layer (FNTP)
Access layer (LAN CI) LAN CI Other CIs
ITS station-internal network A
Combined ITS-S router / host B
Applications
Facilities layer
Networking & transport
layer (FNTP)
Access layer
(CIs)
Figure 4 — Implementation architecture III
6 Protocol elements
6.1 Service access points
6.1.1 IN-SAP
The FNTP shall support IN-SAP functionality as specified in ISO 21218.
The FNTP is identified in the IN-SAP with the appropriate SAP address “fast communication without
IPv6 addresses” as specified in ISO 21218. Only the even value of the two possible address values shall
be applied for FNTP, as FNTP does not distinguish commands and responses.
NOTE An EtherType value for the FNTP [3] might be allocated to be used in MAC frames. However, this is
outside the scope of this part of ISO 29281.
6.1.2 NF-SAP
The FNTP shall support NF-SAP functionality with details specified in this part of ISO 29281.
6.1.3 MN-SAP
The FNTP shall support MN-SAP functionality identified in this part of ISO 29281 and specified in ISO 24102-3.
6 © ISO 2013 – All rights reserved
Management
Management
Security
Management
Security
Communication link between
ITS-Ss
Security
6.1.4 SN-SAP
The FNTP may support functionality of the SN-SAP specified in ISO 24102-3 in order to enable secure
communications.
6.2 FNTP NPDU
6.2.1 Structure
An FNTP NPDU shall consist of two fields as illustrated in Figure 5, i.e. the FNTP header and the FNTP body.
FNTP NPDU
FNTP header FNTP body
Figure 5 — Structure of an FNTP NPDU
ASN.1 details of the FNTP NPDU shall be as specified in Annex A.
6.2.2 FNTP header
6.2.2.1 Structure
The FNTP header illustrated in Figure 6 shall consists of two address fields for sourcePort and
destinationPort, an FNTP control field, and Options fields as required by the value contained in the
FNTP control field.
FNTP header
sourcePort destinationPort
FNTP Control Options
PortNumber PortNumber
Figure 6 — Structure of an FNTP NPDU header
6.2.2.2 sourcePort and destinationPort
The FNTP header shall contain the numbers of source port and destination port of the given hop,
respectively, as illustrated in Figure 6, i.e. indicating “end-points” as specified in Table 1.
Table 1 — ITS port numbers
Port Acronym Description Field
number size
0 PORT_SAM Groupcast manager, i.e. the sourcePort and destinationPort of “Service 1 octet
Advertisement Messages” (SAM) and “Service Context Messages” (CTX)
specified in ISO 24102-5(FSAP).
1 - 127 PORT_DYN Sub-division into a number range for static ports (PORT_REG) and for
PORT_REG dynamic ports (PORT_DYN) preferably is done by a port number registra-
tion authority, or by future revisions of this document.
Dynamic numbers are for general usage excluding “Legacy CI Port Man-
ager” and “15628 Kernel Emulator” specified in [2].
128 - PORT_DYN Sub-division into a number range for static ports (PORT_REG) and for 2 octets
32716 PORT_REG dynamic ports (PORT_DYN) preferably is done by a port number registra-
tion authority, or by future revisions of this document.
Dynamic numbers are for general usage including “Legacy CI Port Man-
ager” and “15628 Kernel Emulator” specified in [2].
32717 - PORT_RES Reserved for special purposes.
32764 PORT_IIC Port number for ITS station-internal management communications speci-
fied in ISO 24102-4.
32765 PORT_RTR FNTP management port in an ITS-S router, used in ITS station-internal
forwarding mode of operation.
32766 PORT_HST FNTP management port in an ITS-S host, used in ITS station-internal for-
warding mode of operation.
32767 PORT_UNK Unknown / don’t care.
NOTE Values of port numbers as shown above are examples. Assignment of numbers is expected to be done
by a port number registration authority, see [4].
6.2.2.3 Selection of options
6.2.2.3.1 FNTP control field
Details of the “FNTP Control” and “Options” fields depends on the mode of operation:
— basic mode of operation;
— extended mode of operation.
The “FNTP Control” field value allows distinguishing details of these two modes of operation as specified
in Table 2. The FNTP control field is a one octet bit-field as specified in Table 2.
The basic mode of operation is indicated by the value zero in the “FNTP Control” field. In this case, the
FNTP NPDU is referred to as “FNTP basic NPDU” in this part of ISO 29281.
In the extended mode of operation, at least one “Option” field is present. Bit B7 indicates presence or
absence of the first optional element following the FNTP control field; Bit B6 indicates presence or
absence of the second optional element following the FNTP control field; and so on; Bit B0 indicates
presence or absence of the last optional element following the FNTP control field. Presence of an optional
element shall be indicated by a value ‘1’b in the respective bit field.
Reserved bits shall be set to the value ‘0’.
8 © ISO 2013 – All rights reserved

Table 2 — “FNTP Control” field (implemented as OPTION selector in ASN.1)
B7 B6 B5 B4 B3 B2 B1 B0 Description
‘0’ ‘0’ ‘0’ ‘0’ ‘0’ ‘0’ ‘0’ ‘0’ Used in the NF-FNTP-COMM service to indicate,
that no extension is to be applied.
‘1’ no no no no no no no Option 0: ITS station-internal forwarding. The
value value value value value value value related Options field is present.
no ‘1’ no no no no no no Option 1: Support of secure communications. The
value value value value value value value related Options field is present.
no no ‘1’ no no no no no Option 2: N-hop broadcast. The related Options
value value value value value value value field is present.
no no no ‘1’ no no no no Option 3: So far undefined feature. The related
value value value value value value value Options field is of ASN.1 NULL type. Reserved for
future.
no no no no ‘1’ no no no Option 4: So far undefined feature. The related
value value value value value value value Options field is of ASN.1 NULL type. Reserved for
future.
no no no no no ‘1’ no no Option 5: So far undefined feature. The related
value value value value value value value Options field is of ASN.1 NULL type. Reserved for
future.
no no no no no no ‘1’ no Option 6: LPP support. The related Options field is
value value value value value value value present.
no no no no no no no ‘1’ Option 7: CIP support. The related Options field is
value value value value value value value present.
An FNTP NPDU with “FNTP Control” field containing a value different to ‘00000000’b is referred to as
“FNTP extended NPDU” in this International Standard.
6.2.2.3.2 ITS station-internal forwarding
In order to forward an FNTP NPDU station-internally between an ITS-S host and an ITS-S router or vice
versa, the FNTP header shall contain values as specified in Table 3.
Table 3 — FNTP header values for station-internal forwarding
Forwarding direction sourcePort field destinationPort field
From FNTP management in ITS-S router to FNTP PORT_RTR PORT_HST
management in ITS-S host
From FNTP management in ITS-S host to FNTP PORT_HST PORT_RTR
management in ITS-S router
The FNTP Options field for station-internal forwarding shall be as illustrated in Figure 7.
"Options" for station-internal forwarding
ITS-SCU-ID Link-ID VCI in sourcePort destinationPort
Counter
ITS-S host ITS-S router PortNumber PortNumber
Figure 7 — FNTP header Options field for station-internal forwarding
ASN.1 details of the FNTP header Options field for station-internal forwarding illustrated in Figure 7
shall be as specified in Annex A.
The format of ITS-SCU-ID shall be as specified in ISO 24102-1. The format of Link-ID shall be as specified
in ISO 21218.
The field “Counter” shall contain a cyclic packet counter being unique in the source ITS-SCU. The size of
this field shall be one octet as specified in Annex A.
The fields sourcePort and destinationPort contain the port numbers used in the link between the peer
ITS stations.
An FNTP NPDU for ITS station-internal forwarding is referred to as “FNTP forwarding NPDU” in this
part of ISO 29281.
6.2.2.3.3 Secure communications
The FNTP Options field in support of secure communications shall be as illustrated in Figure 8.
"Options" in support of secure communications
Length Security elements
Figure 8 — FNTP header Options field in support of secure communications
Details of secure communications are not specified in this version of this part of ISO 29281.
ASN.1 details of the FNTP header Options field in support of secure communications illustrated in
Figure 8 shall be as specified in Annex A.
6.2.2.3.4 N-hop broadcast
The FNTP Options field for N-hop broadcast shall be as illustrated in Figure 9.
"Options" for N-hop broadcast
FNTP hop count
Figure 9 — FNTP header Options field for N-hop broadcast
ASN.1 details of the FNTP header Options field for N-hop broadcast illustrated in Figure 9 shall be as
specified in Annex A.
The FNTP hop count indicates to the receiving ITS station the number of allowed subsequent hops.
6.2.2.3.5 LPP support
The related Options field shall contain the LPP header as specified in [1].
6.2.2.3.6 CIP management
The FNTP Options field for CIP management shall be as illustrated in Figure 10.
"Options" for CIP management
RX Length RX CIPs TX Length TX CIPs
Figure 10 — FNTP header Options field for CIP management
The RX Length field indicates the length in octets of the RX CIPs field. The TX Length field indicates the
length in octets of the TX CIPs field. At least either RX CIPs or TX CIPS shall be present. Details of CIPs
10 © ISO 2013 – All rights reserved

depend on the ITS-S access technology selected for communications and are outside the scope of this
part of ISO 29281.
ASN.1 details of the FNTP header Options field for CIP management illustrated in Figure 10 shall be as
specified in Annex A.
6.2.3 FNTP body
The FNTP body field shall contain an ITS-FPDU specified in ISO 21217 as illustrated in Figure 11.
FNTP body
ITS-FPDU
Figure 11 — FNTP body for basic mode of operation
6.3 Protocol management elements
6.3.1 Service look-up table
The FNTP shall maintain look-up information as illustrated in Figure 12.
ITS-S router ITS-S host
Service
Link Port
PortNumber
Service Port
ITS-SCU-ID Service Priority
PortNumber
Figure 12 — Service look-up table
“Link Port” shall contain the port number used in the FNTP header in the link to a peer station or in the ITS
station-internal network link, pointing indirectly to the ITS-SP of the service in the ITS-S host. “Service
Port” shall contain the port number which points directly to the ITS-SP of the service in the ITS-S host.
NOTE 1 The value in “Service Port” thus is not necessarily disclosed to the peer entity. In case ITS-S host and
ITS-S router functionality is implemented in the same ITS-SCU, “Link Port” and “Service Port” may have the same
value, and the look-up information becomes obsolete.
“ITS-SCU-ID” shall identify the ITS-SCU of the ITS-S host where the service resides. “Service Priority”
shall contain the maximum allowed user priority of the service.
NOTE 2 The term “service” used in this context means protocol functionality in the ITS-S facilities layer
addressable by an ITS-SP number, which is using the communication service offered by an ITS-S networking and
transport layer protocol, i.e. the FNTP.
This look-up information is part of the information contained in forwarding tables specified in 6.3.2.
6.3.2 Forwarding table
The FNTP shall maintain information as illustrated in Figure 13 needed to perform the protocol
procedures specified in this part of ISO 29281.
REMOTE LOCAL
Information how to reach a remote port
ITS-S router ITS-S host Timeout
(either in peer ITS-S or peer ITS-SCU)
Link Port Link Port
Link-ID CI Status Service User Priority
PortNumber PortNumber
Service Port
ITS-SCU-ID Service Priority
PortNumber
Figure 13 — Forwarding table
The elements below “REMOTE” allow accessing an ITS-SP in a peer ITS station or in a peer ITS-SCU of
the same ITS-S.
— The elements in column “Link Port” shall carry the port numbers as used in the communication link.
A “Link Port” is unique only in combination with the corresponding “Link-ID”.
— The element “Link-ID” specified in ISO 21218 shall carry the Link-ID of the VCI which connects to the
peer entity via the communication link.
— The element “CI Status” shall contain the CI status specified in ISO 21218.
NOTE 1 In case of ITS-S internal forwarding of FNTP NPDUs, Link Port is either PORT_HST or PORT_RTR, and
Link-ID points to a BC-VCI which connects to the ITS station-internal network.
The elements below “LOCAL” allow accessing an ITS-SP in the local entity.
— The elements in column “Link Port” shall carry the port number as used in the link identifying the
local ITS-SP to be used for a potential reply by the peer station. A “Link Port” is unique only at the
local ITS-SCU containing the ITS-S router functionality.
NOTE 2 The two elements “Link Port” thus are the sourcePort and destinationPort port numbers used in the
link between peer entities (ITS-Ss or ITS-SCUs), i.e. in the header shown in Figure 6.
— The element “Service” shall be as specified in 6.3.
— The element “Priority” shall contain the user priority as specified in ISO 21218 to be used for
communications. The value of “Priority” for an unknown priority shall be zero. The maximum value
of “Priority” shall be as given in “Service Priority” of the service look-up table.
NOTE 3 In case of ITS-S internal forwarding of FNTP NPDUs, Link Port is either PORT_HST or PORT_RTR, and
Link-ID identifies the access technology which connects to the ITS station-internal network.
The elements in column “Timeout” contain time information on the validity of this entry. The value of
“Timeout” is given by implementation.
12 © ISO 2013 – All rights reserved

7 Protocol procedures
7.1 Service access points
7.1.1 General
As SAPs per definition describe a functional behaviour only, SAPs may be implemented in different ways.
Requirements set up in this part of ISO 29281 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, allowing
for proprietary solutions.
7.1.2 IN-SAP
The FNTP shall interact with the ITS-S access layer specified in ISO 21217 using services of the IN-SAP
specified in ISO 21218.
The FNTP shall support the IN-UNITDATA service of the IN-SAP specified in ISO 21218.
The FNTP may use the IN-UNITDATA-STATUS service of the IN-SAP. The IN-UNITDATA-STATUS service
is specified in ISO 21218.
NOTE Usage of the information given by the IN-UNITDATA-STATUS service is not specified in this part of
ISO 29281.
7.1.3 NF-SAP
The FNTP shall interact with the ITS-S facilities layer specified in ISO 21217 offering services of the NF-
SAP specified in this part of ISO 29181.
The FNTP shall provide the NF-FNTP-PORT service and the NF-FNTP-COMM service of the NF-SAP
specified in this part of ISO 29281.
7.1.4 MN-SAP
The FNTP shall interact with the ITS-S management entity specified in ISO 21217 using services of the
MN-SAP specified in ISO 24102-3.
7.1.5 SN-SAP
The FNTP may interact with the ITS-S management entity specified in ISO 21217 using services of the
SN-SAP specified in ISO 24102-3.
7.2 Port management
A “Port management” illustrated in Figure 1 is in charge of:
— uniquely assigning dynamic port numbers to local ports;
— mapping local ports to remote ports.
NOTE The port management may serve several ITS networking and transport layer protocols, not just FNTP.
7.3 Maintenance of entries in forwarding tables
The procedures to set, update, or delete an entry in an FNTP forwarding table depends on the
implementation and on the role of the ITS-SCU.
Such maintenance of a forwarding table may be performed partly:
— by the FNTP itself or
— by the ITS station management, either
— locally (same ITS-SCU) or
— locally and remotely (different ITS-SCUs in the same ITS-S).
Remote maintenance of FNTP forwarding tables may be performed with ITS station-internal management
communications specified in ISO 24102-4, if applicable.
Creation of an entry in a forwarding Table shall be notified to the ITS-S management using the service
primitive MN-REQUEST(FWTsetNot(SetNotFNTP)) specified in Annex A and in ISO 24102-3.
Update of an entry in a forwarding Table shall be notified to the ITS-S management using the service
primitive MN-REQUEST(FWTsetNot(UpdateNotFNTP)) specified in Annex A and in ISO 24102-3.
Deletion of an entry in a forwarding Table shall be notified to the ITS-S management using the service primitive
MN-REQUEST(FWTsetNot(DeleteNotFNTP)) of the MN-SAP specified in Annex A and in ISO 24102-3.
7.4 Initial settings of forwarding tables in ITS-S hosts
7.4.1 Allocation and deletion of a port
Upon allocation of a port by means of the NF-FNTP-PORT service, entries in the forwarding tables of the
FNTP as presented in Figure 14 shall be created by the port management.
REMOTE LOCAL
Timeout
ITS-S router ITS-S Host Service
Link Port Link-ID CI Status Priority
Link Port (Port, ITS-SCU-ID, Priority)
PORT_UNK don't know PORT_UNK (of service) of service never (0)
Figure 14 — Forwarding Table host — Allocation of a port number by means of NF-FNTP-PORT
Upon deregistration of the port by means of the NF-FNTP-PORT service, all entries in the forwarding
table related to this service shall be deleted.
7.4.2 Assignment of communication interfaces
In case ITS station internal forwarding is needed, the entry in the forwarding table presented in
Figure 15 is needed. The setting shall be done by the ITS-S management using the service primitive MN-
COMMAND(FWTset(SetFNTP)) specified in Annex A and in ISO 24102-3.
REMOTE LOCAL
Timeout
ITS-S router ITS-S Host Service
Link Port Link-ID CI Status Priority
Link Port (Port, ITS-SCU-ID, Priority)
PORT_RTR BC-VCI active PORT_HST (of service) of service never (0)
Figure 15 — Forwarding table host — Activation of a VCI for ITS station-internal network
14 © ISO 2013 – All rights reserved

In Figure 15, different to the case of communication between ITS stations, for ITS station-internal
forwarding, the entry below:
— “REMOTE” indicates how the ITS-S host ITS-SCU can access an ITS-S router ITS-SCU;
— “ITS-S router Link Port” is used in the ITS station-internal network to identify an ITS-S host ITS-SCU.
The CI selection management may change the assignment of a CI as specified in ISO 24102-1.
Upon deregistration of the port by means of the NF-FNTP-PORT service, all related entries shall be deleted.
7.5 Initial settings of forwarding tables in ITS-S routers
7.5.1 Assignment of communication interfaces
In case ITS station internal forwarding is needed, the entry in the forwarding table presented in
Figure 16 is needed. The setting shall be done by the ITS-S management using the service primitive MN-
COMMAND(FWTset(SetFNTP)) specified in Annex A and in ISO 24102-3.
REMOTE LOCAL
Timeout
ITS-S router ITS-S Host Service
Link Port Link-ID CI Status Priority
Link Port (Port, ITS-SCU-ID, Priority)
PORT_HST BC-VCI active PORT_RTR (of service) of service never (0)
Figure 16 — Forwarding Table router
In Figure 16, different to the case of communication between ITS stations, for ITS station-internal
forwarding, the entry below:
— “REMOTE” indicates how the ITS-S router ITS-SCU can access an ITS-S host ITS-SCU;
— “ITS-S router Link Port” is used in the ITS station-internal network to identify an ITS-S router ITS-SCU.
The CI selection management may change the assignment of a CI as specified in ISO 24102-1.
Upon deregistration of the port by means of the NF-FNTP-PORT service, all related entries in the
forwarding table shall be deleted.
7.6 Transmitting packets
7.6.1 NF-SAP transmission request
Upon a transmission request received via the NF-SAP by means of the service primitive NF-FNTP-
COMM.request, the FNTP shall first check whether the forwarding table contains an entry in support of
the transmission request.
If no such entry exists, the transmission request shall be discarded and the FNTP shall notify failure of
transmission by means of the service primitive NF-FNTP-COMM.confirm.
A valid entry in a forwarding table in support of a transmission request is given by:
— REMOTE ITS-S entries:
— Valid Link Port, see Table 1,
— CI Status allowing for transmission of a packet specified in ISO 21218, if known.
— LOCAL ITS-S entries:
— Valid Link Port, see Table 1, identifying the local ITS-SP for potential replies by the peer station.
— Valid Service Port, see Table 1, and valid ITS-SCU-ID identifying together uniquely an ITS-SP in
the local ITS station.
NOTE LinkID and CI Status in REMOTE ITS-S may be checked. However, FNTP trusts the decision of the ITS-S
facilities layer on which VCI to be used for transmission.
Without the need to discard the transmission request, the FNTP shall compare the ITS-SCU-ID in
the service look-up table, which is the local ITS-SCU-ID, with the ITS-SCU-ID contained in the Link-ID
presented in the NF-FNTP-COMM.request.
If the two ITS-SCU-IDs are different, ITS station-internal forwarding is needed, and the FNTP shall
perform the “Forwarding host to router procedure”, which is an option of the “Extended procedure”.
Without the need of ITS station-internal forwarding, the FNTP shall check “controlField” specified in
Table 2 given in the service primitive.
— If “controlField” is equal to ‘00000000’b, the “Basic procedure” shall be performed.
— Otherwise, the “Extended procedure” shall be performed.
7.6.2 Basic procedure
The FNTP shall
— create an “FNTP NPDU” illustrated in Figure 5 for basic mode of operation as specified in 5.1.2 with an
— FNTP header illustrated in Figure 6 indicating “destinationPort” equal to “remotePort” and
“sourcePort” equal to “servicePort” as given in the service primitive, “FNTP control field” set
equal to ‘00000000’b,
— FNTP body illustrated in Figure 11 with “ITS-FPDU” equal to “data” given in the service primitive.
— forward the “FNTP NPDU” to the proper VCI by means of the IN-UNITDATA.request service primitive
specified in ISO 21218, if no other service primitive is requested, with “source_address” indicating
the CI to be used for transmission and “destination_address” containing “Link-ID” of VCI to be
used for transmission, “data” equal to the “FNTP NPDU”, “priority” as given by “Priority” in the
forwarding table.
The FNTP may
— notify success of transmission by means of the service primitive NF-FNTP-COMM.confirm.
The FNTP shall
— notify failure of transmission by means of the service primitive NF-FNTP-COMM.confirm.
7.6.3 Extended procedure
The FNTP shall check “controlField” given in the service primitive
— if “controlField” contains a value for an option which is not supported, or an invalid combination
of options, the transmission request shall be discarded, and the FNTP shall notify failure of
transmission by means of the service primitive NF-FNTP-COMM.confirm.
— otherwise the procedure as specified below shall be performed.
16 © ISO 2013 – All rights reserved

The FN
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