7 Transport layer
37.4723GPPRelease 17Signalling transportTSW1 interface
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
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Change history |
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Date |
Meeting |
TDoc |
CR |
Rev |
Cat |
Subject/Comment |
New version |
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2018-05 |
RAN3#100 |
R3-183554 |
BL TS submission for approval. |
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2019-08 |
RAN3#105 |
R3-194678 |
Add the description of procedure for the W1 signalling transport protocol |
0.1.0 |
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2019-10 |
RAN3#105-Bis |
R3-196134 |
Add the description of References, Definitions and abbreviations. |
0.1.0 |
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2019-11 |
RAN3#106-Bis |
R3-197634 |
Change the version number to 0.2.0. |
0.2.0 |
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2019-12 |
RP-86 |
RP-192954 |
TS submitted to TSG RAN plenary for approval |
1.3.0 |
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2019-12 |
RP-86 |
TS approved by TSG RAN plenary |
16.0.0 |
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2020-07 |
RP-88-e |
RP-201236 |
0002 |
– |
F |
SCTP Payload Protocol Identifier for W1AP |
16.1.0 |
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2020-09 |
RP-89-e |
RP-201948 |
0003 |
– |
F |
SCTP port number allocatd by IANA |
16.2.0 |
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2022-03 |
SA#95-e |
Promotion to Release 17 without technical change |
17.0.0 |
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