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TS 36.462
E-UTRAN and WLAN – Xw Interface –
Signalling Transport

V18.0.0 (PDF)  2024/03  10 p.
V17.0.0  2022/03  10 p.
V16.0.0  2020/06  10 p.
V15.0.0  2018/06  10 p.
V14.0.0  2017/03  10 p.
V13.0.0  2016/03  10 p.
Dr. Kimba dit Adamou, Boubacar
China Mobile Com. Corporation

Content for  TS 36.462  Word version:  16.0.0

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1  ScopeWord‑p. 5

The present document specifies the standards for Signalling Transport to be used across the Xw interface. The Xw interface is a logical interface between the eNB and the WT. The present document describes how the Xw-AP signalling messages are transported over Xw.

2  ReferencesWord‑p. 5

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.
TR 21.905: "Vocabulary for 3GPP Specifications".
RFC 2460  (1998-12): "Internet Protocol, Version 6 (Ipv6) Specification".
RFC 791(1981-09):  "Internet Protocol".
RFC 2474  (1998-12): "Definition of the Differentiated Services Field (DS Field) in the Ipv4 and Ipv6 Headers".
RFC 4960  (2007-09): "Stream Control Transmission Protocol".

3  Definitions, symbols and abbreviationsWord‑p. 5

3.1  DefinitionsWord‑p. 5

For the purposes of the present document, the terms and definitions given in TR 21.905 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.
logical interface between eNB and WT.

3.2  AbbreviationsWord‑p. 5

For the purposes of the present document, the abbreviations given in TR 21.905 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.
Internet Assigned Numbers Authority
Internet Engineering Task Force
Point-to-Point Protocol
Request for Comments
Stream Control Transmission Protocol
WLAN Termination

4  Xw signalling bearerWord‑p. 6

4.1  Function and protocol stackWord‑p. 6

Xw signalling bearer provides the following functions:
  • Provision of reliable transfer of Xw-AP message over Xw interface.
  • Provision of networking and routeing function;
  • Provision of redundancy in the signalling network;
  • Support for flow control and congestion control.
The protocol stack for Xw Signalling Bearer is shown in Figure 4.1-1 and details on each protocol are described in the following sections.
Copy of original 3GPP image for 3GPP TS 36.462, Fig. 4.1-1: Xw signalling bearer protocol stack
Figure 4.1-1: Xw signalling bearer protocol stack
(⇒ copy of original 3GPP image)
The Transport Network Layer is based on IP transport, comprising SCTP on top of IP.

5  Data link layerWord‑p. 6

The support of any suitable Data Link Layer protocol, e.g. PPP, Ethernet, etc., shall not be prevented.

6  IP layerWord‑p. 6

The eNB shall support Ipv6 (RFC 2460) and/or Ipv4 (RFC 791).
The IP layer of Xw only supports point-to-point transmission for delivering Xw-AP message.
The eNB shall support the Diffserv Code Point marking as described in RFC 2474.

7  Transport layerWord‑p. 6

SCTP (RFC 4960) shall be supported as the transport layer of Xw signalling bearer. The Payload Protocol Identifier assigned by IANA to be used by SCTP for the application layer protocol XwAP is 59.
SCTP refers to the Stream Control Transmission Protocol developed by the Sigtran working group of the IETF for the purpose of transporting various signalling protocols over IP network.
There shall be only one SCTP association established between one eNB and WT pair.
The eNB shall establish the SCTP association. The SCTP Destination Port Number value assigned by IANA to be used for XwAP is 36462.
Within the SCTP association established between an eNB and WT pair;
  • A single pair of stream identifiers shall be reserved for the sole use of XwAP elementary procedures that utilize non UE-associated signalling.
  • At least one pair of stream identifiers shall be reserved for the sole use of XwAP elementary procedures that utilize UE-associated signalling. However a few pairs (i.e. more than one) should be reserved.
  • A single UE-associated signalling shall use one SCTP stream and the stream should not be changed during the communication of the UE-associated signalling.
Transport network redundancy may be achieved by SCTP multi-homing between two endpoints, of which one or both is assigned with multiple IP addresses. SCTP endpoints shall support a multi-homed remote SCTP endpoint. For SCTP endpoint redundancy an INIT may be sent from WT or eNB, at any time for an already established SCTP association, which shall be handled as defined in Section 5.2 of RFC 4960.
The SCTP congestion control may, using an implementation specific mechanism, initiate higher layer protocols to reduce the signalling traffic at the source and prioritise certain messages.

$  Change HistoryWord‑p. 7

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