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Content for  TS 23.003  Word version:  16.3.0

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28  Numbering, addressing and identification for 5G System (5GS) |R15|

28.1  Introduction

Editor's note: This clause provides general description on numbering, addressing and identification for 5G core network.
This clause describes the format of the parameters, identifiers and information used for the 5G system. For further information on these, see TS 23.501, TS 23.502 and TS 23.503.

28.2  Home Network Domain

The Home Network Domain for 5GC shall be in the format specified in RFC 1035 and RFC 1123 and shall be structured as:
"5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org",
where "<MNC>" and "<MCC>" fields correspond to the MNC and MCC of the operator's PLMN. Both the "<MNC>" and "<MCC>" fields are 3 digits long. If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the NF service endpoint format for inter PLMN routing.
As an example, the Home Network Domain for MCC 345 and MNC 12 is coded as:
  • "5gc.mnc012.mcc345.3gppnetwork.org".
The Home Network Domain for a Stand-alone Non-Public Network (SNPN) shall be in the format specified in RFC 1035 and RFC 1123 and, if not pre-configured in the NF, shall be structured as:
"5gc.nid<NID>.mnc<MNC>.mcc<MCC>.3gppnetwork.org",
where <MNC> and <MCC> shall be encoded as specified above, and the NID shall be encoded as hexadecimal digits as specified in clause 12.7.
As an example, the Home Network Domain for MCC 345, MNC 12 and NID 000007ed9d5 (hexadecimal: assignment mode = 0, PEN = 00007ed9, NID code = d5) is coded as:
  • "5gc.nid000007ed9d5.mnc012.mcc345.3gppnetwork.org".
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28.3  Identifiers for Domain Name System proceduresWord‑p. 108

28.3.1  Introduction

Editor's note: This clause will describe Domain Name System (DNS) related identifiers for 5GS used by the procedures specified in TS 29.303.

28.3.2  Fully Qualified Domain Names (FQDNs)

28.3.2.1  General

Editor's note: This clause provides general information regarding DNS and FQDN.

28.3.2.2  N3IWF FQDN

28.3.2.2.1  General
The N3IWF Fully Qualified Domain Name (N3IWF FQDN) shall be constructed using one of the following formats, as specified in clause 6.3.6 of TS 23.501:
  • Operator Identifier based N3IWF FQDN;
  • Tracking Area Identity based N3IWF FQDN;
  • the N3IWF FQDN configured in the UE by the HPLMN.
The Visited Country FQDN for N3IWF is used by a roaming UE to determine whether the visited country mandates the selection of an N3IWF in this country. The Visited Country FQDN for N3IWF shall be constructed as specified in clause 28.3.2.2.4. The Replacement field used in DNS-based Discovery of regulatory requirements shall be constructed as specified in clause 28.3.2.2.5.
Editor's note: It is FFS whether N3IWF FQDN for emergency service is supported.
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28.3.2.2.2  Operator Identifier based N3IWF FQDN
The N3IWF Fully Qualified Domain Name (N3IWF FQDN) contains an Operator Identifier that shall uniquely identify the PLMN where the N3IWF is located. The N3IWF FQDN is composed of seven labels. The last three labels shall be "pub.3gppnetwork.org". The third and fourth labels together shall uniquely identify the PLMN. The first two labels shall be "n3iwf.5gc". The result of the N3IWF FQDN will be:
"n3iwf.5gc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org"
In the roaming case, the UE can utilise the services of the VPLMN or the HPLMN. In this case, the Operator Identifier based N3IWF FQDN shall be constructed as described above, but using the MNC and MCC of the VPLMN or the HPLMN.
In order to guarantee inter-PLMN DNS translation, the <MNC> and <MCC> coding used in the "n3iwf.5gc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org" format of the Operator Identifier based N3IWF FQDN shall be:
  • <MNC> = 3 digits
  • <MCC> = 3 digits
If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the N3IWF FQDN.
As an example, the Operator Identifier based N3IWF FQDN for MCC 345 and MNC 12 is coded in the DNS as:
  • "n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org".
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28.3.2.2.3  Tracking Area Identity based N3IWF FQDNWord‑p. 109
The Tracking Area Identity based N3IWF FQDN is used to support location based N3IWF selection within a PLMN.
There are two N3IWF FQDNs defined one based on a TAI with a 2 octet TAC and a 5GS one based on a 3 octet TAC.
  1. The Tracking Area Identity based N3IWF FQDN using a 2 octet TAC shall be constructed respectively as:
    "tac-lb<TAC-low-byte>.tac-hb<TAC-high-byte>.tac.n3iwf.5gc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org"
    where
    • the <MNC> and <MCC> shall identify the PLMN where the N3IWF is located and shall be encoded as
      • <MNC> = 3 digits
      • <MCC> = 3 digits
      If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the N3IWF FQDN.
    • the <TAC>, together with the <MCC> and <MNC> shall identify the Tracking Area Identity the UE is located in.
      The TAC is a 16-bit integer. The <TAC-high-byte> is the hexadecimal string of the most significant byte in the TAC and the <TAC-low-byte > is the hexadecimal string of the least significant byte. If there are less than 2 significant digits in <TAC-high-byte> or <TAC-low-byte >, "0" digit(s) shall be inserted at the left side to fill the 2 digit coding;
    As examples,
    • the Tracking Area Identity based N3IWF FQDN for the TAC H'0B21, MCC 345 and MNC 12 is coded in the DNS as:
      "tac-lb21.tac-hb0b.tac.n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org"
  2. The 5GS Tracking Area Identity based N3IWF FQDN using a 3 octet TAC shall be constructed respectively as:
    "tac-lb<TAC-low-byte>.tac-mb<TAC-middle-byte>.tac-hb<TAC-high-byte>.5gstac.n3iwf.5gc.mnc<MNC>.mcc<MCC>.pub.3gppnetwork.org"
    where
    • the <MNC> and <MCC> shall identify the PLMN where the N3IWF is located and shall be encoded as
      • <MNC> = 3 digits
      • <MCC> = 3 digits
      If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the N3IWF FQDN.
    • the <TAC>, together with the <MCC> and <MNC> shall identify the 5GSTracking Area Identity the UE is located in.
      The 5GS TAC is a 24-bit integer. The <TAC-high-byte> is the hexadecimal string of the most significant byte in the TAC and the <TAC-low-byte > is the hexadecimal string of the least significant byte. If there are less than 2 significant digits in <TAC-low-byte>, <TAC-middle-byte> or <TAC-high-byte >, "0" digit(s) shall be inserted at the left side to fill the 2 digit coding;
    As examples,
    • the 5GS Tracking Area Identity based N3IWF FQDN for the 5GS TAC H'0B1A21, MCC 345 and MNC 12 is coded in the DNS as:
      "tac-lb21.tac-mb1a.tac-hb0b.5gstac.n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org"
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28.3.2.2.4  Visited Country FQDN for N3IWFWord‑p. 110
The Visited Country FQDN for N3IWF, used by a roaming UE to determine whether the visited country mandates the selection of an N3IWF in this country, shall be constructed as described below.
The Visited Country FQDN shall contain a MCC that uniquely identifies the country in which the UE is located.
The Visited Country FQDN is composed of seven labels. The last three labels shall be "pub.3gppnetwork.org". The fourth label shall be "visited-country". The third label shall uniquely identify the MCC of the visited country. The first and second labels shall be "n3iwf.5gc". The resulting Visited Country FQDN of N3IWF will be:
  • "n3iwf.5gc.mcc<MCC>.visited-country.pub.3gppnetwork.org"
The <MCC> coding used in this FQDN shall be:
  • <MCC> = 3 digits
As an example, the Visited Country FQDN for MCC 345 is coded in the DNS as:
  • "n3iwf.5gc.mcc345.visited-country.pub.3gppnetwork.org".
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28.3.2.2.5  Replacement field used in DNS-based Discovery of regulatory requirements
If the visited country mandates the selection of an N3IWF in this country, the NAPTR record(s) associated to the Visited Country FQDN shall be provisioned with the replacement field containing the identity of the PLMN(s) in the visited country which may be used for N3IWF selection.
The replacement field shall take the form of an Operator Identifier based N3IWF FQDN as specified in clause 28.3.2.2.2.
For countries with multiple MCC, the NAPTR records returned by the DNS may contain a different MCC than the MCC indicated in the Visited Country FQDN.
As an example, the NAPTR records associated to the Visited Country FQDN for MCC 345, and for MNC 012, 013 and 014, are provisioned in the DNS as:
  • n3iwf.5gc.mcc345.visited-country.pub.3gppnetwork.org
; IN NAPTR order
;              pref.
;                  flag
;                     service
;                        regexp
;                          replacement
  IN NAPTR 100 999 "" ""   n3iwf.5gc.mnc012.mcc345.pub.3gppnetwork.org
  IN NAPTR 100 999 "" ""   n3iwf.5gc.mnc013.mcc345.pub.3gppnetwork.org
  IN NAPTR 100 999 "" ""   n3iwf.5gc.mnc014.mcc345.pub.3gppnetwork.org
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28.3.2.3  PLMN level and Home NF Repository Function (NRF) FQDNWord‑p. 111
28.3.2.3.1  General
When an NF is instantiated, it may register with a PLMN level NF Repository Function (NRF). It may then discover other NF instance(s) in the 5GC by querying the PLMN level NRF. The IP address of the PLMN level NRF can be provisioned into the NF, or the NF can be pre-configured with the FQDN of the PLMN level NRF. If the PLMN level NRF addresses and FDQN are not provisioned into the NF, the NF self-constructs the PLMN level NRF FQDN as per the format specified in clause 28.3.2.3.2.
For NF discovery across PLMNs, the NRF (e.g vNRF) shall self-construct the PLMN level NRF FQDN of the target PLMN (e.g hNRF) as per the format specified in clause 28.3.2.3.2, and the hNRF URI as per the format specified in subclause 28.3.2.3.3, if the NRF has not obtained the NRF FQDN of the target PLMN.
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28.3.2.3.2  Format of NRF FQDN
The NRF FQDN for an NRF in an operator's PLMN shall be constructed by prefixing the Home Network Domain Name (see clause 28.2) of the PLMN in which the NRF is located with the label "nrf." as described below:
  • nrf.5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org
The NRF FQDN for an NRF in an operator's SNPN, if not pre-configured in the NF, shall be constructed by prefixing the Home Network Domain Name (see clause 28.2) of the SNPN in which the NRF is located with the label "nrf." as described below:
  • nrf.5gc.nid<NID>.mnc<MNC>.mcc<MCC>.3gppnetwork.org
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28.3.2.3.3  NRF URI
In absence of any other local configuration available in the vNRF, the API URIs of the hNRF shall be constructed by deriving the API root (see TS 29.501) as follows:
  • the authority part shall be set to the NRF FQDN as specified in clause 28.3.2.3.2
  • the scheme shall be "https"
  • the port shall be the default port for the "https" scheme, i.e. 443.
  • the API prefix optional component shall not be used
EXAMPLE:
For an MCC = 012 and MNC = 345, the API root of the NRF services shall be:
"https://nrf.5gc.mnc345.mcc012.3gppnetwork.org/"
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28.3.2.4  Network Slice Selection Function (NSSF) FQDN

28.3.2.4.1  General
For roaming service, the vNSSF may invoke the Nnssf_NSSelection_Get service operation from the hNSSF. For routing of the HTTP/2 messages across the PLMN, the vNSSF self-constructs the FQDN of the hNSSF as per the format specified in clause 28.3.2.4.2 and the URI of the hNSSF as per the format specified in clause 28.3.2.4.3. The Home Network is identified by the PLMN ID of the SUPI provided to the vNSSF by the NF Service Consumer (e.g. the AMF).
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28.3.2.4.2  Format of NSSF FQDN
The NSSF FQDN for an NSSF in an operator's PLMN shall be constructed by prefixing its Home Network Domain Name (see clause 28.2) with the label "nssf." as described below:
  • nssf.5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org
The NSSF FQDN for an NSSF in an operator's SNPN, if not pre-configured in the NF, shall be constructed by prefixing the Home Network Domain Name (see clause 28.2) of the SNPN in which the NSSF is located with the label "nssf." as described below:
  • nssf.5gc.nid<NID>.mnc<MNC>.mcc<MCC>.3gppnetwork.org
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28.3.2.4.3  NSSF URIWord‑p. 112
In absence of any other local configuration available in the vNSSF, the API URIs of the hNSSF shall be constructed by deriving the API root (see TS 29.501) as follows:
  • the authority part shall be set to the NSSF FQDN as specified in clause 28.3.2.4.2
  • the scheme shall be "https"
  • the port shall be the default port for the "https" scheme, i.e. 443.
  • the API prefix optional component shall not be used
EXAMPLE:
For an MCC = 012 and MNC = 345, the API root of the NSSF services shall be:
"https://nssf.5gc.mnc345.mcc012.3gppnetwork.org/"
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28.3.2.5  AMF Name

The AMF Name FQDN shall uniquely identify an AMF.
The AMF Name FQDN for an AMF within an operator's PLMN shall be constructed as follows:
  • "<AMF-id>.amf.5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org"
where
  • the <MNC> and <MCC> shall identify the PLMN where the AMF is located and shall be encoded as
    • <MNC> = 3 digits
    • <MCC> = 3 digits
    If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the AMF Name FQDN.
  • the <AMF-id> shall contain at least one label.
As example,
  • If <AMF-id> is amf1.cluster1.net2, the AMF Name FQDN for MCC 345 and MNC 12 is:
    "amf1.cluster1.net2.amf.5gc.mnc012.mcc345.3gppnetwork.org"
The AMF Name FQDN for an AMF within an operator's SNPN, if not pre-configured in the NF, shall be constructed as follows:
  • "<AMF-id>.amf.5gc.nid<NID>.mnc<MNC>.mcc<MCC>.3gppnetwork.org"
where
  • <MNC> and <MCC> shall be encoded as specified above;
  • NID shall be encoded as hexadecimal digits as specified in clause 12.7.
As example,
  • If <AMF-id> is amf1.cluster1.net2, the AMF Name FQDN for MCC 345, MNC 12 and NID 000007ed9d5 (hexadecimal) is:
    "amf1.cluster1.net2.amf.5gc.nid000007ed9d5.mnc012.mcc345.3gppnetwork.org"
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28.3.2.6  5GS Tracking Area Identity (TAI) FQDNWord‑p. 113
The 5GS Tracking Area Identity (TAI) FQDN shall be constructed as follows:
  • "tac-lb<TAC-low-byte>.tac-mb<TAC-middle-byte>.tac-hb<TAC-high-byte>.5gstac. 5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org"
where the <TAC>, together with the <MCC> and <MNC> shall identify the 5GS Tracking Area Identity, and shall be encoded as follows:
  • <MNC> = 3 digits
  • <MCC> = 3 digits
    If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the 5GS TAI FQDN.
  • The 5GS TAC is a 24-bit integer. The <TAC-high-byte> is the hexadecimal string of the most significant byte in the TAC and the <TAC-low-byte > is the hexadecimal string of the least significant byte. If there are less than 2 significant digits in <TAC-low-byte>, <TAC-middle-byte> or <TAC-high-byte >, "0" digit(s) shall be inserted at the left side to fill the 2 digits coding;
As an example, the 5GS Tracking Area Identity for the 5GS TAC H'0B1A21, MCC 345 and MNC 12 is coded in the DNS as:
  • "tac-lb21.tac-mb1a.tac-hb0b.5gstac.5gc.mnc012.mcc345.3gppnetwork.org"
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28.3.2.7  AMF Set FQDN

An AMF Set within an operator's PLMN is identified by its AMF Set ID, AMF Region ID, MNC and MCC.
A subdomain name shall be derived from the MNC and MCC by adding the label "amfset" to the beginning of the Home Network Realm/Domain (see clause 28.2).
The AMF Set FQDN shall be constructed as follows:
  • set<AMF Set Id>.region<AMF Region Id>.amfset.5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org
where
  • <MNC> = 3 digits
  • <MCC> = 3 digits
    If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the AMF Set FQDN.
  • <AMF Set Id> and <AMF Region Id> are the hexadecimal strings of the AMF Set ID and AMF Region ID. If there are less than 2 significant digits in <AMF Region Id>, "0" digit(s) shall be inserted at the left side to fill the 2 digits coding. If there are less than 3 significant digits in <AMF Set Id>, "0" digit(s) shall be inserted at the left side to fill the 3 digits coding.
As an example, the AMF Set FQDN for the AMF Set 1, AMF Region 48 (hexadecimal), MCC 345 and MNC 12 is coded as:
  • "set001.region48.amfset.5gc.mnc012.mcc345.3gppnetwork.org"
An AMF Set within an operator's Stand-alone Non-Public Network (SNPN) shall be identified by its AMF Set ID, AMF Region ID and by either its Network Identifier (NID), MNC and MCC or an SNPN domain name pre-configured in the NF.
The AMF Set FQDN shall be constructed as follows:
  • set<AMF Set Id>.region<AMF Region Id>.amfset.5gc.nid<NID>.mnc<MNC>.mcc<MCC>.3gppnetwork.org
  • or
  • set<AMF Set Id>.region<AMF Region Id>.amfset.<SNPN domain name>
where
  • <MNC> and <MCC> shall be encoded as specified above;
  • NID shall be encoded as hexadecimal digits as specified in clause 12.7;
  • <SNPN domain name> is a domain name chosen by the SNPN operator.
As an example, the AMF Set FQDN for the AMF Set 1, AMF Region 48 (hexadecimal), NID 000007ed9d5 (hexadecimal), MCC 345 and MNC 12 is coded as:
  • "set001.region48.amfset.5gc.nid000007ed9d5. mnc012.mcc345.3gppnetwork.org"
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28.3.2.8  AMF Instance FQDNWord‑p. 114
The AMF Instance FQDN shall uniquely identify an AMF instance.
The AMF Instance FQDN shall be constructed as:
  • pt<AMF Pointer>.set<AMF Set Id>.region<AMF Region Id>.amfi.5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org
where
  • <MNC> = 3 digits
  • <MCC> = 3 digits
    If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the AMF Instance FQDN.
  • <AMF Pointer>, <AMF Set Id> and <AMF Region Id> are the hexadecimal strings of the AMF Pointer, AMF Set ID and AMF Region ID. If there are less than 2 significant digits in <AMF Pointer> or <AMF Region Id>, "0" digit(s) shall be inserted at the left side to fill the 2 digits coding of the AMF Pointer or AMF Region Id respectively. If there are less than 3 significant digits in <AMF Set Id>, "0" digit(s) shall be inserted at the left side to fill the 3 digits coding.
As an example, the AMF Instance FQDN for the AMF Pointer 12 (hexadecimal), AMF Set 1, AMF Region 48 (hexadecimal), MCC 345 and MNC 12 is coded as:
  • "pt12.set001.region48.amfi.5gc.mnc012.mcc345.3gppnetwork.org"
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28.3.2.9  SMF Set FQDN |R16|

An SMF Set within an operator's network is identified by its NF Set ID as defined in clause 28.12, with NFType set to "smf".
For an SMF Set within an operator's PLMN, a subdomain name shall be derived from the MNC and MCC by adding the label "smfset" to the beginning of the Home Network Realm/Domain (see clause 28.2).
The SMF Set FQDN shall be constructed as follows:
  • set<Set Id>.smfset.5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org
where
  • <MNC> = 3 digits
  • <MCC> = 3 digits
    If there are only 2 significant digits in the MNC, one "0" digit shall be inserted at the left side to fill the 3 digits coding of MNC in the AMF Set FQDN.
  • <Set Id> is the string representing the Set ID part within the NF Set ID defined in clause 28.12.
EXAMPLE:
"set12. smfset.5gc.mnc012.mcc345.3gppnetwork.org" (for the SMF set from MCC 345, MNC 12 and SetID "12")
For an SMF Set within an operator's Stand-alone Non-Public Network (SNPN), the SMF Set FQDN shall be constructed from its Network Identifier (NID), MNC and MCC or an SNPN domain name pre-configured in the NF, as follows:
  • set<Set Id>.smfset.5gc.nid<NID>.mnc<MNC>.mcc<MCC>.3gppnetwork.org
  • or
  • set<Set Id>.smfset.<SNPN domain name>
where
  • <MNC> and <MCC> shall be encoded as specified above;
  • NID shall be encoded as hexadecimal digits as specified in clause 12.7;
  • <SNPN domain name> is a domain name chosen by the SNPN operator.
EXAMPLE:
"set12.smfset.5gc.nid000007ed9d5.mnc012.mcc345.3gppnetwork.org" (for an SMF set from MCC 345, MNC 12, NID 000007ed9d5 (hexadecimal) and SetID "12")
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