3 Definitions of terms, symbols and abbreviations

37.4733GPPApplication Protocol (W1AP)Release 17TSW1 interface

3.1 Terms

For the purposes of the present document, the terms 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].

elementary procedure: W1AP consists of Elementary Procedures (EPs). An Elementary Procedure is a unit of interaction between ng-eNB-CU and ng-eNB-DU. These Elementary Procedures are defined separately and are intended to be used to build up complete sequences in a flexible manner. If the independence between some EPs is restricted, it is described under the relevant EP description. Unless otherwise stated by the restrictions, the EPs may be invoked independently of each other as standalone procedures, which can be active in parallel. The usage of several W1AP EPs together is specified in stage 2 specifications (e.g., TS 37.470 [5]).

An EP consists of an initiating message and possibly a response message. Two kinds of EPs are used:

– Class 1: Elementary Procedures with response (success and/or failure).

– Class 2: Elementary Procedures without response.

For Class 1 EPs, the types of responses can be as follows:

Successful:

– A signalling message explicitly indicates that the elementary procedure successfully completed with the receipt of the response.

Unsuccessful:

– A signalling message explicitly indicates that the EP failed.

– On time supervision expiry (i.e., absence of expected response).

Successful and Unsuccessful:

– One signalling message reports both successful and unsuccessful outcome for the different included requests. The response message used is the one defined for successful outcome.

Class 2 EPs are considered always successful.

NGEN-DC operation: Used in the present document when the W1AP is applied for ng-eNB-CU and ng-eNB-DU in NG-RAN.

ng-eNB: As defined in TS 38.300 [6].

ng-eNB-CU: As defined in TS 37.470 [5].

ng-eNB-DU: As defined in TS 37.470 [5].

ng-eNB-CU UE W1AP ID: As defined in TS 38.401 [4].

ng-eNB-DU UE W1AP ID: As defined in TS 38.401 [4].

UE-associated signalling: When W1AP messages associated to one UE uses the UE-associated logical W1-connection for association of the message to the UE in ng-eNB-DU and ng-eNB-CU.

UE-associated logical W1-connection: The UE-associated logical W1-connection uses the identities ng-eNB-CU UE W1AP ID and ng-eNB-DU UE W1AP ID according to the definition in TS 38.401 [4]. For a received UE associated W1AP message the ng-eNB-CU identifies the associated UE based on the ng-eNB-CU UE W1AP ID IE and the ng-eNB-DU identifies the associated UE based on the ng-eNB-DU UE W1AP ID IE. The UE-associated logical W1-connection may exist before the W1 UE context is setup in ng-eNB-DU.

3.2 Symbols

Void.

3.3 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].

5GC 5G Core Network

5QI 5G QoS Identifier

AMF Access and Mobility Management Function

CN Core Network

CG Cell Group

CGI Cell Global Identifier

DL Downlink

EN-DC E-UTRA-NR Dual Connectivity

NE-DC NR-E-UTRA Dual Connectivity

NGEN-DC NG-RAN E-UTRA-NR Dual Connectivity

NSSAI Network Slice Selection Assistance Information

RANAC RAN Area Code

RRC Radio Resource Control

S-NSSAI Single Network Slice Selection Assistance Information

TAC Tracking Area Code

TAI Tracking Area Identity