7.2 Iuh

25.4673GPPRelease 17Stage 2TSUTRAN architecture for 3G Home Node B (HNB)

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

Figure 7.2-1 shows the protocol structure for Iuh, following the structure described in TS 25.401 [4].

Figure 7.2-1: I_uh–Interface Protocol Stack.

7.2.1 Iupc-Iuh Interface Control Plane Protocol Stack

Figure 7.2.1-1 shows the control plane protocol stack for connectivity between a HNB and a SAS via the HNB-GW.

Figure 7.2.1-1: Iupc-Iuh Interfaces Protocol Stack for connectivity between a HNB and a SAS via the HNB-GW.

7.2.2 Interworking between the PCAP User Adaptation Layer (PUA) and the Signalling Connection Control Part (SCCP)

7.2.2.1 General

This section describes the usage of PUA and SCCP for connectivity between a HNB and a SAS via HNB-GW.

RNL signalling between a SAS and a HNB-GW utilises services provided by the SCCP (ITU-T Rec. Q.711 [32] / ITU-T Rec. Q.712 [33]/ ITU-T Rec. Q.713 [34]/ ITU-T Rec. Q.714 [35]) as defined for Iupc interface signalling transport between an RNC and a SAS (see 3GPP TS 25.450 [37]), since the HNB-GW is seen as an RNC for connection via Iupc interface to the SAS.

The Interworking functions at the HNB-GW deal with:

– extracting or inserting the PCAP transaction ID information on the Iuh connection or on the Iupc connection of the SAS-HNB signalling connectivity,

– Iupc mapping of PCAP transaction IDs to provide the SAS with a consistent view aligned with the HNB-GW acting as one RNC,

– Iuh mapping of PCAP transaction ID on messages from the SAS to a local PCAP transaction ID for the HNB and mapping of local PCAP transaction ID on messages from the HNB to the corresponding PCAP transaction ID for the SAS.

– Iuh mapping of PCAP transaction ID received from the SAS to direct connectionless messages to the correct HNB.

– for connection oriented signalling, performing appropriate mapping between PUA level and SCCP level using the PUA context id and the SCCP connection information.

– For connectionless signalling, ensuring uniqueness of the PCAP Transaction ID for connectionless PCAP messages mapped to the same SCCP connection.

– respective routing of PCAP messages (see 3GPP TS 25.453[38]) based on available address information.

In general, (i) Iupc connectivity between the HNB-GW and the SAS is established by configuration, while (ii) the Iuh connectivity for support of PCAP between the HNB and the HNB-GW is performed via the HNB registration procedure.

The following subclauses describe the interworking between PUA and SCCP at the HNB-GW.

7.2.2.2 Establishment of signalling connection over Iuh and Iupc connections between HNB and SAS via HNB-GW

Figure 7.2.2.2-1: Establishment of signalling connection over Iupc and Iuh connections between HNB and SAS via HNB-GW – HNB Initiated.

1. If the Source HNB is configured for Iupc-connectivity via the HNB-GW, and wants to send a PCAP message to the SAS for which a signalling connection over the Iuh and Iupc connections has to be established, it issues a PUA:CONNECT message containing the PUA Context Id and the PCAP PDU₁.

2. The HNB-GW identifies the signalling interface to which the PCAP message shall be routed to and maintains a mapping between the PUA-based signalling connection and the SCCP-based signalling connection for the HNB-SAS end-to-end. If the SAS indicator is included in the PUA: Connect message the HNB-GW may use this to route the PCAP message to the selected SAS.

3. The HNB-GW sends PCAP PDU₁ to the SAS and the SAS sends back PCAP PDU₂ (see TS 25.450 [37]).

4. The HNB-GW routes the PCAP PDU₂ towards the Source HNB.

5. The HNB-GW sends a PUA:Direct Transfer message, including PCAP PDU₂ if any, received from the SAS to the source HNB.

7.2.2.3 Establishment of signalling connection over Iuh – Refusal from SAS

Figure 7.2.2.3-1: Establishment of signalling connection over Iuh and Iupc connections between HNB and SAS via HNB-GW – HNB Initiated with refusal from SAS.

3. The HNB-GW sends PCAP PDU₁ to the SAS as received from the HNB via SCCP Connection Request and the SAS refuses the connection request (see TS 25.450 [37]).

4. The HNB-GW maps the SCCP:CREF message into a PUA:DISCONNECT.

5. The HNB-GW sends a PUA:DISCONNECT message to the source HNB, including the optional PCAP PDU₂ if received from the SAS.

7.2.2.4 Transport of PCAP signalling messages via signalling connection established over Iupc and Iuh connections

7.2.2.4.1 HNB initiated

Figure 7.2.2.4.1-1: Transport of PCAP messages via signalling connection over Iuh and Iupc connections – HNB initiated.

If the Source HNB wants to send a PCAP message to the SAS for which a connection oriented data transfer service is already established for a location session, it issues a PUA:DIRECT TRANSFER message towards the HNB-GW which contains the PUA Context Id and the PCAP PDU.

The HNB-GW will forward the PCAP PDU to the SAS within an SCCP message.

7.2.2.4.2 SAS initiated

Figure 7.2.2.4.2-1: Transport of PCAP messages via signalling connection over Iupc and Iuh connections – SAS initiated.

If the SAS wants to send a PCAP message to the Receiving HNB for which a connection oriented data transfer service is already established for a location session, it will send to the HNB-GW the PCAP PDU within an SCCP message.

The HNB-GW will then generate a PUA:DIRECT TRANSFER message and will route the PCAP PDU to the correct HNB.

7.2.2.5 Release of signalling connection over Iupc and Iuh Connections

Figure 7.2.2.5-1: Release of established signalling connection over Iupc and Iuh connections – HNB initiated.

If an HNB wants to release a signalling connection previously established over Iupc and Iuh connections towards a SAS, it sends a PUA:DISCONNECT message, which includes the PUA Context Id and may include a PCAP PDU. The HNB-GW maps the PUA:DISCONNECT message to an SCCP:Release message and triggers the SCCP connection release procedure defined in TS 25.450 [37] for the coresponding SCPP connection.

7.2.2.6 Transport of PCAP signalling messages via the connectionless data transfer service

7.2.2.6.1 HNB initiated

Figure 7.2.2.6.1-1: Connectionless data transfer over Iuh and Iupc connections – HNB initiated.

If the HNB wants to send in a connectionless manner a PCAP PDU to the HNB-GW for the SAS, it issues a PUA:CONNECTIONLESS TRANSFER message containing the PCAP PDU. The HNB-GW then generates and routes the PCAP PDU within a connectionless SCCP message towards the SAS. If the SAS indicator is included in the PUA: Connectionless Transfer message the HNB-GW may use this to route the PCAP message to the selected SAS.

7.2.2.6.2 SAS initiated

Figure 7.2.2.6.2-1: Connectionless data transfer over Iupc and Iuh connections – SAS initiated.

If the SAS sends a PCAP PDU to the HNB-GW for the Receiving HNB, the HNB-GW has to be able to route the message to the correct HNB. The HNB-GW uses the PCAP transaction ID to determine the correct destination HNB. Then the HNB-GW issues a PUA:CONNECTIONLESS TRANSFER message containing the PCAP PDU.