7 Transport layer

37.4723GPPRelease 16TSW1 signalling transport

SCTP (IETF RFC 4960 [5]) shall be supported as the transport layer of W1-C signalling bearer. The Payload Protocol Identifier assigned by IANA to be used by SCTP for the application layer protocol W1AP is 73.

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.

The ng-eNB-DU and ng-eNB-CU shall support a configuration with a single SCTP association per ng-eNB-DU/ng-eNB-CU pair.

The ng-eNB-DU shall establish the SCTP association. The SCTP Destination Port number value assigned by IANA to be used for W1AP is 37472.

Within the set of SCTP associations established between one ng-eNB-CU and ng-eNB-DU pair, a single SCTP association shall be employed for W1AP elementary procedures that utilize non-UE-associated signalling with the possibility of fail-over to a new association to enable robustness.

Between one ng-eNB-CU and ng-eNB-DU pair:

– A single pair of stream identifiers shall be reserved over an SCTP association for the sole use of W1AP elementary procedures that utilize non UE-associated signalling.

– At least one pair of stream identifiers over one or several SCTP associations shall be reserved for the sole use of W1AP elementary procedures that utilize UE-associated signalling. However, a few pairs (i.e. more than one) should be reserved.

– For a single UE-associated signalling, the ng-eNB-DU shall use one SCTP association and one SCTP stream, and the association/stream should not be changed during the communication of the UE-associated signalling unless TNL binding update is performed.

Transport network redundancy may 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 INIT may be sent from a ng-eNB-CU or ng-eNB-DU, at any time for an already established SCTP association, which shall be handled as defined in IETF RFC 4960[5] in sub clause 5.2.

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.

Annex A (informative):
Change History

Change history

Date

Meeting

TDoc

CR

Rev

Cat

Subject/Comment

New version

2018-05

RAN3#100

R3-183554

BL TS submission for approval.

2019-08

RAN3#105

R3-194678

Add the description of procedure for the W1 signalling transport protocol

0.1.0

2019-10

RAN3#105-Bis

R3-196134

Add the description of References, Definitions and abbreviations.

0.1.0

2019-11

RAN3#106-Bis

R3-197634

Change the version number to 0.2.0.

0.2.0

2019-12

RP-86

RP-192954

TS submitted to TSG RAN plenary for approval

1.3.0

2019-12

RP-86

TS approved by TSG RAN plenary

16.0.0

2020-07

RP-88-e

RP-201236

0002

F

SCTP Payload Protocol Identifier for W1AP

16.1.0

2020-09

RP-89-e

RP-201948

0003

F

SCTP port number allocatd by IANA

16.2.0