9.1 Architecture and Reference Points

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

9.1.1 Architecture for Optimized Handovers between E-UTRAN Access and cdma2000 HRPD Access

Figure 9.1.1-1: Architecture for optimised handovers between E-UTRAN access and cdma2000 HRPD access (non-roaming case)

Figure 9.1.1-2: Architecture for optimised handovers between E-UTRAN access and cdma2000 HRPD access (roaming case; Home routed)

NOTE 1: Optimized handover supported by this architecture is intended for the scenario where the operator owns both the E-UTRAN access and the HRPD access, or where there is a suitable inter-operator agreement in place.

NOTE 2: Gxc is used only in the case of PMIP variant of S5 or S8.

NOTE 3: For further specification of the functions and interfaces of the HRPD Serving GW (HS‑GW) refer to 3GPP2 X.S0057 [51]. The HRPD in this specification refers to the evolved HRPD as defined in 3GPP2 X.S0057 [51].

Depicted in Figure 9.1.1-1 is an access specific architecture providing support for optimised E‑UTRAN-HRPD handovers. in the non-roaming case. Depicted in figure 9.1.1-2 is an access specific architecture providing support for optimised E‑UTRAN-HRPD handovers in the roaming case with Home routed traffic.

9.1.2 Reference Points

9.1.2.1 Reference Point List

S101: It enables interactions between EPS and HRPD access to allow for pre-registration and handover signalling with the target system.

S103: This User Plane interface is used to forward DL data to minimize packet losses in mobility from E-UTRAN to HRPD.

9.1.2.2 Requirements for the S101 Reference Point

The S101 interface supports procedures for Pre-Registration, Session Maintenance and Active handovers between E-UTRAN and HRPD networks. This is based on tunnelling over S101 signalling of one technology while the UE is in the other technology. The HRPD air interface messages tunnelled over S101 in E‑UTRAN to HRPD mobility are defined in 3GPP2 C.S0087‑0 [49].

The S101 reference point shall support the following requirements:

– HRPD and E-UTRAN/EPS messages shall be transported as opaque containers without modifications by the MME or HRPD AN.

– Messages may carry separate information IEs to indicate status, message types (e.g. handover command) forwarding addresses etc. as required by signalling procedures.

– Provide identifiers (i.e. S101 Session ID) to distinguish messages belonging to different UEs in order to allow responses originating from the target system to an UE to be appropriately forwarded to the UE by the source system.

– Reliable transport for S101 messages should be provided at the application layer and will not require transport layer reliability mechanism.

9.1.2.3 S101 Protocol Stack

The figure below shows the protocol stack for the S101 interface.

Legend:

– S101 Application Protocol (S101-AP): It is the Application Layer Protocol between the MME and HRPD AN

– User Datagram Protocol (UDP): This protocol transfers messages. UDP is defined in RFC 768 [71].

– S101 Application Protocol (S101-AP) provides application layer reliability for its messages, if required.

Figure 9.1.2.3-1: Protocol Stack for the S101 Reference Point

9.1.2.4 S101 Session Identifier

All S101 messages contain a S101 Session ID which serves to identify the UE context at the MME and the HRPD AN. The S101 Session ID uniquely and globally identifies the UE.

9.1.2.5 Requirements for the S103 Reference Point

The S103 interface between the Serving GW and HS‑GW supports the forwarding of DL data during mobility from E-UTRAN to HRPD. Signalling procedures on the S101 interface are used to set up tunnels on the S103 interface.

The S103 reference point shall support the following requirements:

– The S103 interface shall support the ability to tunnel traffic on a per-UE, per-PDN basis

– The S103 interface shall support Generic Routing Encapsulation (GRE) RFC 2784 [23] including the Key Field extension RFC 2890 [24]. The Key field value of each GRE packet header uniquely identifies the PDN connectivity that the GRE packet payload is associated with.

9.1.2.6 S103 Protocol Stack

The figure below shows the protocol stack for the S103 interface.

Figure 9.1.2.6-1: Protocol Stack for the S103 Reference Point

Legend:

– On the S103 interface, the tunnelling layer implements GRE encapsulation with the Key Field extension RFC 2784 [23], RFC 2890 [24].