5 Procedures

38.3513GPPNRRelease 17Sidelink Relay Adaptation Protocol (SRAP) SpecificationTS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.1 SRAP entity handling

5.1.1 SRAP entity establishment

When upper layers request establishment of an SRAP entity, UE shall:

– establish an SRAP entity;

– follow the procedures in clause 5.

5.1.2 SRAP entity release

When upper layers request release of an SRAP entity, UE shall:

– release the SRAP entity and the related SRAP configurations.

5.2 DL Data transfer

5.2.1 Receiving operation of U2N Relay UE

Upon receiving an SRAP Data PDU from lower layer, the receiving part of the SRAP entity on the Uu interface of U2N Relay UE shall:

– deliver the SRAP data packet to the transmitting part of the collocated SRAP entity on the PC5 interface.

5.2.2 Transmitting operation of U2N Relay UE

The transmitting part of the SRAP entity on the PC5 interface of U2N Relay UE receives SRAP data packets from the receiving part of the SRAP entity on the Uu interface of the same U2N Relay UE.

When the transmitting part of the SRAP entity on the PC5 interface has an SRAP Data PDU to transmit, the transmitting part of the SRAP entity on the PC5 interface shall:

– Determine the egress link in accordance with clause 5.2.2.1;

– Determine the egress RLC channel in accordance with clause 5.2.2.2;

– if the SRAP Data PDU is for SRB0 (the BEARER ID field is 0, and the bearer is identified as SRB based on sl-RemoteUE-RB-Identity associated with the entry containing the sl-EgressRLC-ChannelUu which matches the Uu Relay RLC Channel of the LCID from which the SRAP Data PDU is received):

– Removes the SRAP header from the SRAP Data PDU;

– Submit this SRAP Data PDU to the determined egress RLC channel of the determined egress link.

5.2.2.1 Egress link determination

For a SRAP Data PDU to be transmitted, SRAP entity shall:

– if there is an entry in sl-SRAP-Config-Relay, whose sl-LocalIdentity matches the UE ID field in SRAP Data PDU:

– Determine the egress link on PC5 interface corresponding to sl-L2Identity-Remote configured for the concerned sl-LocalIdentity as specified in TS 38.331 [3].

5.2.2.2 Egress RLC channel determination

For a SRAP Data PDU to be transmitted, the SRAP entity shall:

– if the SRAP Data PDU is for SRB0 (the BEARER ID field is 0 and the bearer is identified as SRB based on sl-RemoteUE-RB-Identity associated with the entry containing the sl-EgressRLC-ChannelUu which matches the Uu Relay RLC Channel of the LCID from which the SRAP Data PDU is received):

– Determine the egress PC5 Relay RLC channel in the determined egress link corresponding to logicalChannelIdentity for SL-RLC0 as specified in TS 38.331 [3];

– else if there is an entry in sl-SRAP-Config-Relay, whose sl-LocalIdentity matches the UE ID field in SRAP Data PDU, which includes an sl-RemoteUE-RB-Identity that matches the SRB identity or DRB identity of the SRAP Data PDU determined by the BEARER ID field (For the BEARER ID shared by both SRB and DRB, SRB and DRB are differentiated based on sl-RemoteUE-RB-Identity associated with the entry containing the sl-EgressRLC-ChannelUu which matches the Uu Relay RLC Channel of the LCID from which the SRAP Data PDU is received):

– Determine the egress PC5 Relay RLC channel in the determined egress link corresponding to sl-EgressRLC-ChannelPC5 configured for the concerned sl-LocalIdentity and concerned sl-RemoteUE-RB-Identity as specified in TS 38.331 [3].

5.2.3 Receiving operation of U2N Remote UE

Upon receiving an SRAP Data PDU from lower layer, the receiving part of the SRAP entity shall:

– if the SRAP Data PDU is not for SRB0 (not received from SL-RLC0 as specified in TS 38.331 [3]):

– if sl-RemoteUE-RB-Identity is configured:

– remove the SRAP header of this SRAP Data PDU and deliver the SRAP SDU to upper layer corresponding to the BEARER ID field of this SRAP Data PDU (For the BEARER ID shared by both SRB and DRB, SRB and DRB are differentiated based on sl-RemoteUE-RB-Identity associated with the entry containing the sl-EgressRLC-ChannelPC5 which matches the PC5 Relay RLC Channel of the LCID from which the SRAP Data PDU is received, and for DRB, the upper layer entity for BEARER ID plus 1);

– else

– remove the SRAP header of this SRAP Data PDU and deliver the SRAP SDU to PDCP entity of SRB1 by ignoring the UE ID field and BEARER ID field of this SRAP Data PDU;

– else:

– deliver the SRAP SDU (i.e., same as SRAP PDU for SRB0) to upper layer, i.e., RRC layer entity (TS 38.331 [3]).

5.3 UL Data transfer

5.3.1 Transmitting operation of U2N Remote UE

The transmitting part of the SRAP entity on the PC5 interface of U2N Remote UE can receive SRAP SDU from upper layer, and constructs SRAP Data PDU as needed (see clause 4.2.2).

Upon receiving an SRAP SDU from upper layer, the transmitting part of the SRAP entity on the PC5 interface shall:

– if the SRAP SDU is not for SRB0:

– Determine the UE ID field and BEARER ID field in accordance with clause 5.3.1.1;

– Construct an SRAP Data PDU with SRAP header, where the UE ID field and BEARER ID field are set to the determined values, in accordance with clause 6.2.2;

– else:

– Construct an SRAP Data PDU without SRAP header in accordance with clause 6.2.2.

– Determine the egress RLC channel in accordance with clause 5.3.1.2;

– Submit this SRAP Data PDU to the determined egress RLC channel.

5.3.1.1 UE ID field and BEARER ID field determination

For an SRAP SDU received from upper layer, the SRAP entity shall:

– Determine the UE ID field corresponding to sl-LocalIdentity, configured as specified in TS 38.331 [3];

– Determine the BEARER ID field corresponding to SRB identity for SRB (i.e., set the BEARER ID field to srb-Identity), or corresponding to DRB identity minus 1 for DRB (i.e., set the BEARER ID field to drb-Identity minus 1), from which the SRAP SDU is received, configured as specified in TS 38.331 [3].

5.3.1.2 Egress RLC channel determination

For a SRAP Data PDU to be transmitted, the SRAP entity shall:

– if the SRAP Data PDU is for SRB0:

– Determine the egress PC5 Relay RLC channel in the link with U2N Relay UE corresponding to logicalChannelIdentity for SL-RLC0 as specified in TS 38.331 [3];

– else if there is an entry in sl-SRAP-Config-Remote, whose sl-RemoteUE-RB-Identity matches the SRB identity or DRB identity of the SRAP Data PDU:

– Determine the egress PC5 Relay RLC channel of the link with U2N Relay UE corresponding to sl-EgressRLC-ChannelPC5 configured for the concerned sl-RemoteUE-RB-Identity as specified in TS 38.331 [3].

5.3.2 Receiving operation of U2N Relay UE

Upon receiving an SRAP Data PDU from lower layer, the receiving part of the SRAP entity on the PC5 interface shall:

– deliver the SRAP data packet to the transmitting part of the collocated SRAP entity on the Uu interface.

5.3.3 Transmitting operation of U2N Relay UE

The transmitting part of the SRAP entity on the Uu interface of U2N Relay UE can receive SRAP data packets from the receiving part of the SRAP entity on the PC5 interface of the same U2N Relay UE, and construct SRAP Data PDUs as needed (see clause 4.2.2).

Upon receiving SRAP data packet from the receiving part on the collocated SRAP entity on the PC5 interface, the transmitting part of the SRAP entity on the Uu interface shall:

– if the SRAP Data PDU is received from SL-RLC0 as specified in TS 38.331 [3]:

– Determine the UE ID field and BEARER ID field in accordance with clause 5.3.3.1;

– Construct an SRAP Data PDU with SRAP header, where the UE ID field and BEARER ID field are set to the determined values, in accordance with clause 6.2.2;

– Determine the egress RLC channel in accordance with clause 5.3.3.2;

– Submit this SRAP Data PDU to the determined egress RLC channel.

5.3.3.1 UE ID field and BEARER ID field determination

For an SRAP Data PDU received from SL-RLC0 as specified in TS 38.331 [3], the SRAP entity shall:

– if there is an entry in sl-RemoteUE-ToAddModList, whose sl-L2Identity-Remote matches the Layer-2 ID of the remote UE from which the SRAP Data PDU is received:

– Determine the UE ID field corresponding to sl-LocalIdentity configured for the concerned sl-L2Identity-Remote as specified in TS 38.331 [3];

– Determine the BEARER ID field as 0 (i.e., set BEARER ID field as 0).

5.3.3.2 Egress RLC channel determination

For a SRAP Data PDU to be transmitted, the SRAP entity shall:

– if there is an entry in sl-SRAP-Config-Relay, whose sl-LocalIdentity matches the UE ID field in SRAP Data PDU, and which includes an sl-RemoteUE-RB-Identity matches SRB identity or DRB identity of the SRAP Data PDU determined by the BEARER ID field (For the BEARER ID shared by both SRB and DRB, SRB and DRB are differentiated based on sl-RemoteUE-RB-Identity associated with the entry containing the sl-EgressRLC-ChannelPC5 which matches the PC5 Relay RLC Channel of the LCID from which the SRAP Data PDU is received):

– Determine the egress Uu Relay RLC channel corresponding to sl-EgressRLC-ChannelUu configured for the concerned sl-LocalIdentity and concerned sl-RemoteUE-RB-Identity as specified in TS 38.331 [3].

5.4 Handling of unknown, unforeseen, and erroneous protocol data

For U2N Remote UE, if sl-RemoteUE-RB-Identity is configured, when a SRAP Data PDU with SRAP header that contains a UE ID field or BEARER ID field which is not included in sl-SRAP-Config-Remote is received, the SRAP entity shall:

– discard the received SRAP Data PDU.

For U2N Relay UE, when a SRAP Data PDU with SRAP header that contains a UE ID field or BEARER ID field which is not included in sl-SRAP-Config-Relay is received except that the SRAP Data PDU from SL-RLC1 as specified in TS 38.331 [3] is the first SRAP Data PDU received from a U2N Remote UE, or when a SRAP Data PDU that contains a UE ID which does not match the concerned sl-LocalIdentity corresponding to sl-L2Identity-Remote of the ingress link is received by U2N Relay UE, the SRAP entity shall:

– discard the received SRAP Data PDU.