ETSI TS 129 573 V15.6.0 (2022-10)

5G; 5G System; Public Land Mobile Network (PLMN) Interconnection; Stage 3 (3GPP TS 29.573 version 15.6.0 Release 15)

RTS/TSGC-0429573vf60

General Information

• Status: Not Published
• Technical Committee: 3GPP CT 4 - MAP/CAMEL/GTP/BCH/SS/TrFO/IMS/GUP/WLAN (formely CN4)
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Completion Date: 12-Oct-2022

Standards Content (Sample)

TECHNICAL SPECIFICATION
5G;
5G System;
Public Land Mobile Network (PLMN) Interconnection;
Stage 3
(3GPP TS 29.573 version 15.6.0 Release 15)


3GPP TS 29.573 version 15.6.0 Release 15 1 ETSI TS 129 573 V15.6.0 (2022-10)

Reference
RTS/TSGC-0429573vf60
Keywords
5G
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: [phone]  Fax: [phone]

Siret N° 348 623 562 00017 - APE 7112B
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° w061004871

Important notice
The present document can be downloaded from:
http://www.etsi.org/standards-search
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the prevailing version of an ETSI
deliverable is the one made publicly available in PDF format at www.etsi.org/deliver.
Users of the present document should be aware that the document may be subject to revision or change of status.
Information on the current status of this and other ETSI documents is available at
https://portal.etsi.org/TB/ETSIDeliverableStatus.aspx
If you find errors in the present document, please send your comment to one of the following services:
https://portal.etsi.org/People/CommiteeSupportStaff.aspx
If you find a security vulnerability in the present document, please report it through our
Coordinated Vulnerability Disclosure Program:
https://www.etsi.org/standards/coordinated-vulnerability-disclosure
Notice of disclaimer & limitation of liability
The information provided in the present deliverable is directed solely to professionals who have the appropriate degree of
experience to understand and interpret its content in accordance with generally accepted engineering or
other professional standard and applicable regulations.
No recommendation as to products and services or vendors is made or should be implied.
No representation or warranty is made that this deliverable is technically accurate or sufficient or conforms to any law
rule and/or regulation and further, no representation or warranty is made of merchantability or fitness
and/or governmental
for any particular purpose or against infringement of intellectual property rights.
In no event shall ETSI be held liable for loss of profits or any other incidental or consequential damages.

Any software contained in this deliverable is provided "AS IS" with no warranties, express or implied, including but not
limited to, the warranties of merchantability, fitness for a particular purpose and non-infringement of intellectual property
rights and ETSI shall not be held liable in any event for any damages whatsoever (including, without limitation, damages
for loss of profits, business interruption, loss of information, or any other pecuniary loss) arising out of or related to the use
of or inability to use the software.
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© ETSI 2022.
All rights reserved.
ETSI
3GPP TS 29.573 version 15.6.0 Release 15 2 ETSI TS 129 573 V15.6.0 (2022-10)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The declarations
pertaining to these essential IPRs, if any, are publicly available for ETSI members and non-members, and can be
found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to
ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the
ETSI Web server (https://ipr.etsi.org/).
Pursuant to the ETSI Directives including the ETSI IPR Policy, no investigation regarding the essentiality of IPRs,
including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not
referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become,
essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
DECT™, PLUGTESTS™, UMTS™ and the ETSI logo are trademarks of ETSI registered for the benefit of its

Members. 3GPP™ and LTE™ are trademarks of ETSI registered for the benefit of its Members and of the 3GPP
Organizational Partners. oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and of the ®
oneM2M Partners. GSM and the GSM logo are trademarks registered and owned by the GSM Association.
Legal Notice
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. These shall be
interpreted as being references to the corresponding ETSI deliverables.
The cross reference between 3GPP and ETSI identities can be found under http://webapp.etsi.org/key/queryform.asp.
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
3GPP TS 29.573 version 15.6.0 Release 15 3 ETSI TS 129 573 V15.6.0 (2022-10)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 6
1 Scope . 8
2 References . 8
3 Definitions and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 9
4 General Description . 9
4.1 Introduction . 9
4.2 N32 Interface . 9
4.2.1 General . 9
4.2.2 N32-c Interface . 10
4.2.3 N32-f Interface . 10
4.3 Protocol Stack . 11
4.3.1 General . 11
4.3.2 HTTP/2 Protocol . 11
4.3.2.1 General . 11
4.3.2.2 HTTP standard headers . 11
4.3.2.3 HTTP custom headers . 12
4.3.2.4 HTTP/2 connection management . 12
4.3.3 Transport Protocol . 12
4.3.4 Serialization Protocol . 12
5 N32 Procedures . 13
5.1 Introduction . 13
5.2 N32 Handshake Procedures (N32-c) . 13
5.2.1 General . 13
5.2.2 Security Capability Negotiation Procedure . 13
5.2.3 Parameter Exchange Procedure . 14
5.2.3.1 General . 14
5.2.3.2 Parameter Exchange Procedure for Cipher Suite Negotiation . 14
5.2.3.3 Parameter Exchange Procedure for Protection Policy Exchange . 15
5.2.4 N32-f Context Termination Procedure . 17
5.2.5 N32-f Error Reporting Procedure . 17
5.3 JOSE Protected Message Forwarding Procedure on N32 (N32-f) . 18
5.3.1 Introduction. 18
5.3.2 Use of Application Layer Security. 18
5.3.2.1 General . 18
5.3.2.2 Protection Policy Lookup . 19
5.3.2.3 Message Reformatting . 19
5.3.2.4 Message Forwarding to Peer SEPP . 21
5.3.3 Message Forwarding to Peer SEPP when TLS is used . 22
6 API Definitions . 22
6.1 N32 Handshake API . 22
6.1.1 API URI . 22
6.1.2 Usage of HTTP . 22
6.1.2.1 General . 22
6.1.2.2 HTTP standard headers . 22
6.1.2.2.1 General . 22
6.1.2.2.2 Content type . 22
6.1.2.3 HTTP custom headers . 23
ETSI
3GPP TS 29.573 version 15.6.0 Release 15 4 ETSI TS 129 573 V15.6.0 (2022-10)
6.1.2.3.1 General . 23
6.1.3 Resources . 23
6.1.3.1 Overview . 23
6.1.4 Custom Operations without Associated Resources . 23
6.1.4.1 Overview . 23
6.1.4.2 Operation: Security Capability Negotiation . 23
6.1.4.2.1 Description . 23
6.1.4.2.2 Operation Definition . 23
6.1.4.3 Operation: Parameter Exchange . 24
6.1.4.3.1 Description . 24
6.1.4.3.2 Operation Definition . 24
6.1.4.4 Operation: N32-f Context Terminate . 25
6.1.4.4.1 Description . 25
6.1.4.4.2 Operation Definition . 25
6.1.4.5 Operation: N32-f Error Reporting . 25
6.1.4.5.1 Description . 25
6.1.4.5.2 Operation Definition . 25
6.1.5 Data Model . 26
6.1.5.1 General . 26
6.1.5.2 Structured data types . 27
6.1.5.2.1 Introduction . 27
6.1.5.2.2 Type: SecNegotiateReqData . 27
6.1.5.2.3 Type: SecNegotiateRspData . 27
6.1.5.2.4 Type: SecParamExchReqData . 28
6.1.5.2.5 Type: SecParamExchRspData . 28
6.1.5.2.6 Type: ProtectionPolicy . 29
6.1.5.2.7 Type: ApiIeMapping . 29
6.1.5.2.8 Type: IeInfo . 30
6.1.5.2.9 Type: ApiSignature . 31
6.1.5.2.10 Type: N32fContextInfo . 31
6.1.5.2.11 Type: N32fErrorInfo . 31
6.1.5.2.12 Type: FailedModificationInfo . 31
6.1.5.2.13 Type: N32fErrorDetail . 32
6.1.5.2.14 Type: CallbackName . 32
6.1.5.3 Simple data types and enumerations . 32
6.1.5.3.1 Introduction . 32
6.1.5.3.2 Simple data types . 32
6.1.5.3.3 Enumeration: SecurityCapability. 32
6.1.5.3.4 Enumeration: HttpMethod . 33
6.1.5.3.5 Enumeration: IeType . 33
6.1.5.3.6 Enumeration: IeLocation . 33
6.1.5.3.7 Enumeration: N32fErrorType . 33
6.1.5.3.8 Enumeration: FailureReason . 34
6.1.5.4 Binary data . 34
6.1.6 Error Handling . 34
6.1.6.1 General . 34
6.1.6.2 Protocol Errors . 34
6.1.6.3 Application Errors . 34
6.2 JOSE Protected Message Forwarding API on N32 . 34
6.2.1 API URI . 34
6.2.2 Usage of HTTP . 34
6.2.2.1 General . 34
6.2.2.2 HTTP standard headers . 35
6.2.2.2.1 General . 35
6.2.2.2.2 Content type . 35
6.2.2.3 HTTP custom headers . 35
6.2.2.3.1 General . 35
6.2.3 Resources . 35
6.2.3.1 Overview . 35
6.2.4 Custom Operations without Associated Resources . 35
6.2.4.1 Overview . 35
6.2.4.2 Operation: JOSE Protected Forwarding . 35
ETSI
3GPP TS 29.573 version 15.6.0 Release 15 5 ETSI TS 129 573 V15.6.0 (2022-10)
6.2.4.2.1 Description . 35
6.2.4.2.2 Operation Definition . 36
6.2.5 Data Model . 36
6.2.5.1 General . 36
6.2.5.2 Structured data types . 37
6.2.5.2.1 Introduction . 37
6.2.5.2.2 Type: N32fReformattedReqMsg . 37
6.2.5.2.3 Type: N32fReformattedRspMsg . 38
6.2.5.2.4 Type: DataToIntegrityProtectAndCipherBlock . 38
6.2.5.2.5 Type: DataToIntegrityProtectBlock . 39
6.2.5.2.6 Type: RequestLine . 39
6.2.5.2.7 Type: HttpHeader . 40
6.2.5.2.8 Type: HttpPayload . 41
6.2.5.2.9 Type: MetaData . 44
6.2.5.2.10 Type: Modifications . 44
6.2.5.2.11 Type: FlatJweJson . 45
6.2.5.2.12 Type: FlatJwsJson . 46
6.2.5.2.13 Type: IndexToEncryptedValue . 46
6.2.5.2.14 Type: EncodedHttpHeaderValue . 46
6.2.5.3 Simple data types and enumerations . 46
6.2.5.3.1 Introduction . 46
6.2.5.3.2 Simple data types . 46
6.2.5.3.3 Void . 47
6.2.5.3.4 Void . 47
6.2.6 Error Handling . 47
6.2.6.1 General . 47
6.2.6.2 Protocol Errors . 47
6.2.6.3 Application Errors . 47
Annex A (normative): OpenAPI Specification . 48
A.1 General . 48
A.2 N32 Handshake API . 48
A.3 JOSE Protected Message Forwarding API on N32-f . 53
Annex B (informative): Examples of N32-f Encoding . 57
B.1 General . 57
B.2 Input Message Containing No Binary Part . 57
B.3 Input Message Containing Multipart Binary Part . 58
Annex C (informative): End to end call flows when SEPP is on path . 59
C.1 General . 59
C.2 TLS security between SEPPs . 60
C.2.1 When http URI scheme is used . 60
C.2.2 When https URI scheme is used . 62
C.3 Application Layer Security between SEPPs. 65
C.3.1 When http URI scheme is used . 65
C.3.2 When https URI scheme is used . 67
Annex D (informative): Withdrawn API versions . 72
D.1 General . 72
D.2 N32 Handshake API . 72
Annex E (informative): Change history . 73
History . 73

ETSI
3GPP TS 29.573 version 15.6.0 Release 15 6 ETSI TS 129 573 V15.6.0 (2022-10)
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, modal verbs have the following meanings:
shall indicates a mandatory requirement to do something
shall not indicates an interdiction (prohibition) to do something
The constructions "shall" and "shall not" are confined to the context of normative provisions, and do not appear in
Technical Reports.
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
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
The constructions "can" and "cannot" are not 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
ETSI
3GPP TS 29.573 version 15.6.0 Release 15 7 ETSI TS 129 573 V15.6.0 (2022-10)
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
The constructions "is" and "is not" do not indicate requirements.

ETSI
3GPP TS 29.573 version 15.6.0 Release 15 8 ETSI TS 129 573 V15.6.0 (2022-10)
1 Scope
The present document specifies the stage 3 protocol and data model for the PLMN interconnection Interface. It provides
stage 3 protocol definitions and message flows, and specifies the APIs for the procedures on the PLMN interconnection
interface (i.e N32).
The 5G System stage 2 architecture and procedures are specified in 3GPP TS 23.501 [2] and 3GPP TS 23.502 [3].
The Technical Realization of the Service Based Architecture and the Principles and Guidelines for Services Definition
are specified in 3GPP TS 29.500 [4] and 3GPP TS 29.501 [5].
The stage 2 level N32 procedures are specified in 3GPP TS 33.501 [6].
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 23.501: "System Architecture for the 5G System; Stage 2".
[3] 3GPP TS 23.502: "Procedures for the 5G System; Stage 2".
[4] 3GPP TS 29.500: "5G System; Technical Realization of Service Based Architecture; Stage 3".
[5] 3GPP TS 29.501: "5G System; Principles and Guidelines for Services Definition; Stage 3".
[6] 3GPP TS 33.501: "Security architecture and procedures for 5G system".
[7] IETF RFC 7540: "Hypertext Transfer Protocol Version 2 (HTTP/2)".
[8] IETF RFC 8259: "The JavaScript Object Notation (JSON) Data Interchange Format".
[9] IETF RFC 7231: "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content".
[10] IETF RFC 7230: "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing".
[11] IETF RFC 793: "Transmission Control Protocol".
[12] 3GPP TS 29.571: "5G System; Common Data Types for Service Based Interfaces Stage 3".
[13] IETF RFC 7518: "JSON Web Algorithms (JWA)".
[14] IETF RFC 7516: "JSON Web Encryption (JWE)".
[15] IETF RFC 4648: "The Base16, Base32, and Base64 Data Encodings".
[16] IETF RFC 7515: "JSON Web Signature (JWS)".
[17] IETF RFC 6901: "JavaScript Object Notation (JSON) Pointer".
[18] 3GPP TS 29.510: "Network Function Repository Services; Stage 3".
[19] 3GPP TS 23.003: "Numbering, addressing and identification".
ETSI
3GPP TS 29.573 version 15.6.0 Release 15 9 ETSI TS 129 573 V15.6.0 (2022-10)
[20] 3GPP TR 21.900: "Technical Specification Group working methods".
3 Definitions 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].
c-SEPP: The SEPP that is present on the NF service consumer side is called the c-SEPP.
p-SEPP: The SEPP that is present on the NF service producer side is called the p-SEPP.
NOTE: For the purpose of N32-c procedures, the two interacting SEPPs are called "initiating" SEPP and
"responding" SEPP. The c-SEPP and p-SEPP terminology is not used in this specification though it is
used in 3GPP TS 33.501 [6].
c-IPX: The IPX on the NF service consumer side.
p-IPX: The IPX of the NF service producer side.
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].
IPX IP Exchange Service
JOSE Javascript Object Signing and Encryption
JWE JSON Web Encryption
JWS JSON Web Signature
PRINS PRotocol for N32 INterconnect Security
SEPP Security and Edge Protection Proxy
TLS Transport Layer Security
4 General Description
4.1 Introduction
This clause provides a general description of the interconnect interfaces used between the PLMNs for transporting the
service based interface message exchanges.
4.2 N32 Interface
4.2.1 General
The N32 interface is used between the SEPPs of a VPLMN and a HPLMN in roaming scenarios. The SEPP that is on
the NF service consumer side is called the c-SEPP and the SEPP that is on the NF service producer is called the p-
SEPP. The N32 interface can be logically considered as 2 separate interfaces as given below.
- N32-c, a control plane interface between the SEPPs for performing initial handshake and negotiating the
parameters to be applied for the actual N32 message forwarding.
- N32-f, a forwarding interface between the SEPPs which is used for forwarding the communication between the
NF service consumer and the NF service producer after applying application level security protection.
ETSI
3GPP TS 29.573 version 15.6.0 Release 15 10 ETSI TS 129 573 V15.6.0 (2022-10)
4.2.2 N32-c Interface
The following figure shows the scope of the N32-c interface.

SEPP in SEPP in
N32-c
PLMN A PLMN B
Figure 4.2.2-1: N32-c Interface
The N32-c interface provides the following functionalities:
- Initial handshake procedure between the SEPP in PLMN A (called the initiating SEPP) and the SEPP in PLMN
B (called the responding SEPP), that involves capability negotiation and parameter exchange as specified in
3GPP TS 33.501 [6].
4.2.3 N32-f Interface
The following figure shows the scope of the N32-f interface.

SEPP in SEPP in
PLMN A PLMN B
IPX IPX
(PLMN A (PLMN B
N32-f N32-f N32-f
Side) Side)
Figure 4.2.3-1: N32-f Interface
The N32-f interface shall be used to forward the HTTP/2 messages of the NF service producers and the NF service
consumers in different PLMN, through the SEPPs of the respective PLMN. The application layer security protection
functionality of the N32-f is used only if the PRotocol for N32 INterconnect Security (PRINS) is negotiated between
the SEPPs using N32-c.
The N32-f interface provides the following application layer security protection functionalities:
- Message protection of the information exchanged between the NF service consumer and the NF service producer
across PLMNs by applying application layer security mechanisms as specified in 3GPP TS 33.501 [6].
- Forwarding of the application layer protected message from a SEPP in one PLMN to a SEPP in another PLMN.
Such forwarding may involve IPX providers on path.
- If IPX providers are on the path from SEPP in PLMN A to SEPP in PLMN B, the forwarding on the N32-f
interface may involve the insertion of content modification instructions which the receiving SEPP applies after
verifying the integrity of such modification instructions.
If TLS is the negotiated security policy between the SEPP, then the N32-f shall involve only the forwarding of the
HTTP/2 messages of the NF service producers and the NF service consumers without any reformatting at the SEPPs
and/or the IPXs.
ETSI
3GPP TS 29.573 version 15.6.0 Release 15 11 ETSI TS 129 573 V15.6.0 (2022-10)
4.3 Protocol Stack
4.3.1 General
The protocol stack for the N32 interface is shown below in Figure 4.2.1-1
Application
HTTP/2
TLS
TCP
IP
L2
Figure 4.3.1-1: N32 Protocol Stack
The N32 interfaces (N32-c and N32-f) use HTTP/2 protocol (see clause 4.2.2) with JSON (see clause 4.2.4) as the
application layer serialization protocol. For the security protection at the transport layer, the SEPPs shall support TLS as
specified in 3GPP TS 33.501 [6].
For the N32-f interface, the application layer (i.e the JSON payload) encapsulates the complete HTTP/2 message
between the NF service consumer and the NF service producer, by transforming the HTTP/2 headers and the body into
specific JSON attributes as specified in clause 6.2.
4.3.2 HTTP/2 Protocol
4.3.2.1 General
HTTP/2 as described in IETF RFC 7540 [7] shall be used for N32 interface.
4.3.2.2 HTTP standard headers
The HTTP request standard headers and the HTTP response standard headers that shall be supported on the N32
interface are defined in Table 4.2.2.2-1 and in Table 4.2.2.2-2 respectively.
Table 4.3.2.2-1: Mandatory to support HTTP request standard headers
Name Reference Description
Accept IETF RFC 7231 [9] This header is used to specify response media types that are
acceptable.
Accept-Encoding IETF RFC 7231 [9] This header may be used to indicate what response content-
encodings (e.g gzip) are acceptable in the response.
Content-Length IETF RFC 7230 [10] This header is used to provide the anticipated size, as a decimal
number of octets, for a potential payload body.
Content-Type IETF RFC 7231 [9] This header is used to indicate the media type of the associated
representation.
ETSI
...