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TECHNICAL SPECIFICATION
Universal Mobile Telecommunications System (UMTS);
LTE;
Nq and Nq' Application Protocol (Nq-AP);
Stage 3
(3GPP TS 29.405 version 16.0.0 Release 16)
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3GPP TS 29.405 version 16.0.0 Release 16 1 ETSI TS 129 405 V16.0.0 (2020-07)
Reference
RTS/TSGC-0429405vg00
Keywords
LTE,UMTS
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3GPP TS 29.405 version 16.0.0 Release 16 2 ETSI TS 129 405 V16.0.0 (2020-07)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is 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
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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 .
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
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Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions, symbols and abbreviations . 6
3.1 Definitions . 6
3.2 Abbreviations . 7
4 General Description . 7
5 Procedures for Nq-AP . 7
5.1 Introduction . 7
5.2 IMSI and APN Information Retrieval Procedure . 7
5.2.1 General . 7
5.2.2 IMSI and APN Information Retrieval Procedure Initiation . 7
5.2.2.1 Procedures in the RCAF . 7
5.2.2.2 Procedures in the MME . 8
5.3 APN Information Retrieval Procedure . 8
5.3.1 General . 8
5.3.2 APN Information Retrieval Procedure Initiation . 8
5.3.2.1 Procedures in the RCAF . 8
5.3.2.2 Procedures in the SGSN . 9
6 Transport . 9
6.1 General . 9
6.2 IP layer . 9
6.3 Transport layer . 9
7 Error Handling . 10
7.1 General . 10
7.2 Message too short . 10
7.3 Unknown or unforeseen message type . 10
7.4 Missing mandatory information element . 10
7.5 Information elements unknown or unforeseen in the message . 10
7.6 Out of sequence information elements . 10
7.7 Repeated information elements . 10
7.8 Syntactically incorrect mandatory information element. . 11
7.9 Syntactically incorrect optional information elements . 11
7.10 Conditional information element errors . 11
7.11 Information elements with semantically incorrect contents . 11
7.12 NqAP Message of Invalid Length . 11
8 Messages Description . 12
8.1 NqAP-IMSI-APN-INFORMATION-REQUEST Message . 12
8.1.1 Message definition . 12
8.2 NqAP-IMSI-APN-INFORMATION-RESPONSE Message . 12
8.2.1 Message definition . 12
8.3 NqAP-APN-INFORMATION-REQUEST Message . 12
8.3.1 Message definition . 12
8.4 NqAP-APN-INFORMATION-RESPONSE Message . 13
8.4.1 Message definition . 13
9 Information Elements . 13
9.1 Overview . 13
9.1.1 Presence requirements for Information Elements . 13
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9.1.2 Grouped Information Elements . 14
9.2 Message Type . 14
9.3 Information Element Coding . 15
9.3.1 Information Element Types . 15
9.3.2 Information Element Format. 15
9.4 Information elements . 15
9.4.1 International Mobile Subscriber Identity (IMSI) . 15
9.4.2 Access Point Name (APN) . 16
9.4.3 RAN Entity Identifier . 16
9.4.4 Subscriber-Information . 17
9.4.5 RAN Associated Information . 18
9.4.6 Cause . 18
9.4.7 Fully Qualified Domain Name (FQDN) . 19
Annex A (informative): Change history . 20
History . 21
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Foreword
rd
This Technical Specification has been produced by the 3 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.
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1 Scope
The present document specifies the procedures and the Nq and Nq' Application Protocol (Nq-AP) messages used on the
Nq/Nq' interfaces between the RAN Congestion Awareness Function (RCAF) and the Mobility Management Entity
(MME) or the Serving GPRS Support Node (SGSN). The related stage 2 requirements are specified in 3GPP
TS 23.401 [2] and 3GPP TS 23.060 [3].
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 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) access".
[3] 3GPP TS 23.060: "General Packet Radio Service (GPRS); Service description; Stage 2".
[4] 3GPP TS 29.303: "Domain Name System Procedures; Stage 3"
[5] 3GPP TS 23.003: "Numbering, addressing and identification".
[6] IETF RFC 791 (September 1981): "Internet Protocol".
[7] IETF RFC 2460 (December 1998): "Internet Protocol, Version 6 (IPv6) Specification".
[8] IETF RFC 4960 (September 2007): "Stream Control Transmission Protocol".
[9] ITU-T Recommendation E.212: "The international identification plan for mobile terminals and
mobile users".
[10] 3GPP TS 36.413: "Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1
Application Protocol (S1AP)".
[11] IETF RFC 1035: "Domain Names - Implementation and Specification".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in 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 TR 21.905 [1].
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3.2 Abbreviations
For the purposes of the present document, the abbreviations given in 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
TR 21.905 [1].
RCAF RAN Congestion Awareness Function
4 General Description
This document describes the procedures, messages and information elements over the Nq and Nq' interfaces between
the MME/SGSN and the RCAF to transfer the IMSI/APN information associated to the eNodeB or E-UTRAN cells or
UTRAN Service Area experiencing user plane congestion.
The Nq interface is located between the RCAF and the MME. The Nq' interface is located between the RCAF and the
SGSN.
Both the Nq and the Nq' interfaces use the Nq-AP protocol. The Nq-AP protocol described in this document uses a
Type, Length and Value (TLV) encoding of messages over an SCTP transport. The SCTP transport is described in
clause 6. The Nq-AP messages and the Information Elements are described in clause 8 and 9 respectively.
5 Procedures for Nq-AP
5.1 Introduction
The Nq interface is used between the RCAF and MME for the IMSI and APN information retrieval procedures as
specified in sub-clause 5.9.3 of 3GPP TS 23.401 [2].
The Nq' interface is used between the RCAF and SGSN for the APN information retrieval procedure as specified in
sub-clause 6.17 of 3GPP TS 23.060 [3].
5.2 IMSI and APN Information Retrieval Procedure
5.2.1 General
The IMSI and APN information retrieval procedure is used between the RCAF and the MME over the Nq interface. The
RCAF uses this procedure to retrieve from the MME:
- the IMSIs that are currently in ECM-CONNECTED state and having active E-RABs under a given eNodeB or
E-UTRAN cell;
- for each IMSI the list of APNs currently having active PDN connections.
The RCAF selects the MME(s) serving a user plane congested eNodeB or an E-UTRAN cell through the DNS
procedure as specified in sub-clause 5.4 of 3GPP TS 29.303 [4].
5.2.2 IMSI and APN Information Retrieval Procedure Initiation
5.2.2.1 Procedures in the RCAF
When the RCAF needs to retrieve the IMSI(s) / APN(s) information for a given user plane congested area, the RCAF
shall send the NqAP-IMSI-APN-INFORMATION-REQUEST message towards the MME(s).
The RCAF shall include in the NqAP-IMSI-APN-INFORMATION-REQUEST message:
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- the Global eNodeB ID IE(s) if it requests the IMSI(s) and APN(s) for a given user plane congested area at an
eNodeB level;
- the ECGI IE(s) if it requests the IMSI(s) and APN(s) for a given user plane congested area at an E-UTRAN cell
level.
NOTE: For a given user plane congested area, the RCAF retrieves the IMSI and APN information from the MME
at a eNodeB level or E-UTRAN cell level based on local policy at the RCAF.
5.2.2.2 Procedures in the MME
When the MME receives the NqAP-IMSI-APN-INFORMATION-REQUEST message from the RCAF, the MME shall
report in the NqAP-IMSI-APN-INFORMATION-RESPONSE message, for each eNodeB or E-UTRAN cell requested
by the RCAF, that has at least one subscriber:
- the Macro eNodeB ID or Home eNodeB ID or the E-UTRAN cell ID in the RAN Entity value field of the RAN
Entity Identifier IE for which the MME(s) report the IMSI and the APN information.
- all the subscribers that are currently in ECM-CONNECTED state and having active E-RABs, except the
subscribers involved in an Emergency call, under the given eNodeB or E-UTRAN cell in the Subscriber-
Information IE. Multiple instances of the Subscriber-Information IE shall be included if there are multiple
subscribers under the given eNodeB or E-UTRAN cell.
- for each subscriber, the IMSI in the IMSI IE and APNs currently having active PDN connections in the
APN IE. Multiple instances of the APN IE shall be included under a Subscriber-Information IE if the
subscriber has active PDN connections towards multiple APNs.
The information reported by the MME for each eNodeB or E-UTRAN cell shall be encoded as an instance of the RAN
Associated Information IE.
For a single NqAP-IMSI-APN-INFORMATION-REQUEST message from the RCAF, the MME may send multiple
NqAP-IMSI-APN-INFORMATION-RESPONSE messages.
There shall be no NqAP-IMSI-APN-INFORMATION-RESPONSE sent, if the MME does not find any subscriber
under any of the requested eNodeB or E-UTRAN cell.
5.3 APN Information Retrieval Procedure
5.3.1 General
The APN information retrieval procedure is used between the RCAF and the SGSN over the Nq' interface. The RCAF
uses this procedure to retrieve from the SGSN:
- the APNs that are currently having PDP contexts activated for each IMSI provided by the RCAF.
The RCAF selects the SGSN(s) serving a user plane congested SAI through the DNS procedure as specified in sub-
clause 5.5 of 3GPP TS 29.303 [4].
5.3.2 APN Information Retrieval Procedure Initiation
5.3.2.1 Procedures in the RCAF
When the RCAF needs to retrieve the APN(s) for the list of IMSI(s) experiencing RAN user plane congestion, the
RCAF shall send the NqAP-APN-INFORMATION-REQUEST message towards the SGSN(s).
The RCAF shall include the following information in the NqAP-APN-INFORMATION-REQUEST message
- the list of IMSI(s) in the IMSI IE. Multiple instances of the IMSI IE shall be included if there are multiple
subscribers for which APN information needs to be queried from the SGSN.
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5.3.2.2 Procedures in the SGSN
When the SGSN receives the NqAP-APN-INFORMATION-REQUEST message from the RCAF, the SGSN shall
report in the NqAP-APN-INFORMATION-RESPONSE message, if there is at least one subscriber's information to
report:
- list of subscribers for which the APN information is provided by the SGSN, in the Subscriber-Information IE.
Multiple instances of the Subscriber-Information IE shall be included if there are multiple subscribers for which
the SGSN is reporting the APN information. Each instance of the Subscriber-Information IE contains:
- the IMSI of the subscriber encoded in the IMSI IE;
- the APNs currently having active PDP contexts with active RABs, encoded in the APN IE. Multiple
instances of the APN IE shall be included under a Subscriber-Information IE if the subscriber has active PDP
contexts towards multiple APNs. Emergency call APNs shall be excluded.
- If the subscriber does not have any PDP context with active RABs, then the SGSN shall not include that
subscriber's information in the NqAP-APN-INFORMATION-RESPONSE.
In a pooled SGSN scenario each SGSN may have only a subset of IMSIs registered. An SGSN shall report the APN
information only for the IMSIs it knows.
For a single NqAP-APN-INFORMATION-REQUEST message from the RCAF, the SGSN may send multiple NqAP-
APN-INFORMATION-RESPONSE messages.
There shall be no NqAP-APN-INFORMATION-RESPONSE sent, if the SGSN does not find any requested subscriber
attached.
6 Transport
6.1 General
This subclause specifies the standards for signalling transport to be used across Nq/Nq' interface. Nq/Nq' interface is a
logical interface between the RCAF and the MME/SGSN. All the Nq-AP messages described in the present document
require an SCTP association between the RCAF and the MME/SGSN.
6.2 IP layer
The RCAF shall support IPv6 (see IETF RFC 2460 [7]) and IPv4 (see IETF RFC 791 [6]).
6.3 Transport layer
SCTP (see IETF RFC 4960 [8]) shall be supported as the transport layer of Nq-AP messages.
Semi-permanent SCTP associations shall be established between the RCAF and MME/SGSN, i.e. the SCTP
associations shall remain up under normal circumstances when the RCAF needs to use the Nq-AP procedures towards
the MME/SGSN.
The RCAF shall initiate establishment of the SCTP association.
Transport network redundancy can be achieved by SCTP multi-homing between two end-points, of which one or both is
assigned with multiple IP addresses. SCTP end-points shall support a multi-homed remote SCTP end-point. For SCTP
endpoint redundancy, an SCTP endpoint (in the RCAF or MME/SGSN) may send an INIT, at any time for an already
established SCTP association, which the other SCTP endpoint shall handle as defined in IETF RFC 4960 [8].
RCAF and MME/SGSN shall support a configuration with a single SCTP association per RCAF/MME (or
RCAF/SGSN) pair. Configurations with multiple SCTP endpoints per RCAF/MME (or RCAF/SGSN) pair may be
supported.
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Within the SCTP association established between one RCAF and one MME/SGSN, both RCAF and MME/SGSN shall
reserve several stream identifiers, based on the INIT message exchange for the sole use of Nq-AP procedures.
The registered port number for Nq-AP is 36424.
The payload protocol identifier to be used for Nq-AP is 0.
7 Error Handling
7.1 General
This subclause specifies procedures for the handling of unknown, unforeseen, and erroneous protocol data by the
receiving entity (i.e. the MME or the RCAF). These procedures are called "error handling procedures". If a protocol
error is detected by the receiving NqAP entity, it should log the event including the erroneous message and may include
the error in a statistical counter.
7.2 Message too short
When the receiving entity receives a message that is too short to contain a complete message type information element,
the receiving entity shall ignore that message.
7.3 Unknown or unforeseen message type
The entity receiving a message with a message type that is not defined or is not implemented, it shall ignore the
message.
The entity receiving a message that is not defined to be received by that entity (e.g. the message is sent in the wrong
direction) shall treat the message as unknown message and shall ignore the message.
7.4 Missing mandatory information element
When the entity receiving a request message diagnoses a "missing mandatory information element" error, the receiving
entity shall ignore the message and shall return a corresponding response message with the cause IE set to "Mandatory
IE missing", together with the type of the missing mandatory IE.
When the entity receiving a response message diagnoses a "missing mandatory information element" error, it shall
ignore the message.
7.5 Information elements unknown or unforeseen in the
message
The receiving entity shall ignore all information elements unknown or unforeseen in a message.
7.6 Out of sequence information elements
The receiving entity shall ignore all information elements that are out of sequence.
7.7 Repeated information elements
If an information element is repeated in a message in which repetition of the information element is not specified, the
receiving entity shall only handle the contents of the information element appearing first
...