7 Transport layer
37.4823GPPE1 signalling transportRelease 17TS
NOTE: The transport layer structure and mechanism specified in this section are also used between ng-eNB-CU-CP and ng-eNB-CU-UP or between eNB-CP and eNB-UP, unless stated otherwise. With this understanding, in this section each instance of gNB-CU-CP could be treated as eNB-CP or ng-eNB-CU-CP, and each gNB-CU-UP could be treated as eNB-UP or ng-eNB-CU-UP, for eNB or ng-eNB CP/UP separation respectively.
SCTP (IETF RFC 4960 [6]) shall be supported as the transport layer of E1 signalling bearer. The Payload Protocol Identifier assigned by IANA to be used by SCTP for the application layer protocol E1AP is 64 and 67 for DTLS over SCTP (IETF RFC 6083 [11]). The byte order of the ppid shall be big-endian.
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 gNB-CU-CP and gNB-CU-UP shall support a configuration with a single SCTP association per gNB-CU-CP/gNB-CU-UP pair. Configurations with multiple SCTP endpoints per gNB-CU-CP/gNB-CU-UP pair should be supported. When configurations with multiple SCTP associations are supported, the gNB-CU-CP or the gNB-CU-UP may request to dynamically add/remove SCTP associations between the gNB-CU-CP/gNB-CU-UP pair. Within the set of SCTP associations established between one gNB-CU-CP and gNB-CU-UP pair, a single SCTP association shall be employed for E1AP elementary procedures that utilize non-UE-associated signalling with the possibility of fail-over to a new association to enable robustness.
When the configuration with multiple SCTP endpoints per gNB-CU-UP is supported and gNB-CU-UP wants to add additional SCTP endpoints, the gNB-CU-UP Configuration Update procedure shall be the first E1AP procedure triggered on an additional TNLA of an already setup E1 interface instance after the TNL association has become operational, and the gNB-CU-CP shall associate the TNLA to the E1 interface instance using the included gNB-CU-UP ID.
Either the gNB-CU-CP or gNB-CU-UP shall establish the first SCTP association. The additional SCTP associations are established by the gNB-CU-UP. The SCTP Destination Port number value to be used for E1AP is 38462 which is assigned by IANA. When the gNB-CU-CP requests to dynamically add additional SCTP associations between the gNB-CU-CP and gNB-CU-UP pair, the gNB-CU-CP port is selected and signalled by the gNB-CU-CP to the gNB-CU-UP, and it can be port number value 38462 or any dynamic port value as defined by IETF RFC 6335 [12].
Between one gNB-CU-CP and gNB-CU-UP pair:
– A single pair of stream identifiers shall be reserved over an SCTP association for the sole use of E1AP 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 E1AP 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 gNB-CU-CP and the gNB-CU-UP shall use one SCTP association and one SCTP stream, and the SCTP association/stream should not be changed during the communication of the UE-associated signalling until after current SCTP association is failed, or 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 gNB-CU-CP or a gNB-CU-UP, at any time for an already established SCTP association, which shall be handled as defined in IETF RFC 4960 [6] 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.
For MBS-associated signalling, principles specified above for UE-associated signalling shall apply.
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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2022-01 |
R3#114bis-e |
R3-220919 |
Text transferred from TS 38.462 v16.1.0 and references updated to 37.48x series |
0.1.0 |
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2022-01 |
R3#114bis-e |
R3-221120 |
Update the release number and fix typos |
0.2.0 |
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2022-02 |
R3#115-e |
R3-221644 |
Submission to RAN3 #115-e |
0.3.0 |
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2022-02 |
R3#115-e |
R3-222577 |
Change history updated, merge the changes of R3-222519 |
0.3.1 |
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2022-02 |
R3#115-e |
R3-222974 |
RAN3 #115-e post meeting review. |
0.4.0 |
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2022-03 |
RAN#95-e |
RP-220797 |
Version submitted for approval in RAN#95-e |
1.0.0 |
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2022-03 |
RAN#95-e |
RP-220850 |
Agreed Rel-17 CR from other WI is merged. Including REL-17 38.462 changes of R3-222520 of RP-220236 |
1.1.0 |
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2022-03 |
SA#95-e |
Promotion to Release 17 without technical change |
17.0.0 |
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2022-06 |
RAN#96 |
RP-221145 |
0001 |
2 |
D |
Rapporteur clean-ups to 37.482 |
17.1.0 |
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2022-09 |
RAN#97-e |
RP-222188 |
0002 |
– |
F |
Corrections for MBS-associated signalling |
17.2.0 |