This section describes the GTP-based S2a/S2b interface implementation on the P-GW and SAEGW.
GTP-based S2b Interface Support on the Standalone P-GW and SAEGW
GTP-based S2b interface support is a license-controlled feature. Contact your Cisco account or support representative for licensing information.
The S2b interface reference point connects the standalone P-GW with the ePDG and the P-GW of the SAEGW with the ePDG. Communication runs between the non-trusted non-3GPP ePDG (Evolved Packet Data Gateway) and the P-GW uses PMIPv6 (Proxy Mobile IP version 6) for providing access to the EPC. GTPv2-C is the signaling protocol used on the S2b. The S2b interface is based on 3GPP TS 29.274.
The S2b interface uses the PMIPv6 protocol to establish WLAN UE sessions with the P-GW. It also supports the transport of P-CSCF attributes and DNS attributes in PBU (Proxy-MIP Binding Update) and PBA (Proxy-MIP Binding Acknowledgment) messages as part of the P-CSCF discovery performed by the WLAN UEs. When the P-CSCF Address information is missing, P-CSCF Discovery is initiated upon an S4-SGSN-to-LTE (and vice versa) handoff. If the P-CSCF Address information is already available, there is no need to explicitly trigger another P-CSCF Discovery upon S4-SGSN to LTE (and vice versa) handoff.
Example: The UE tries to simultaneously connect to different APNs through different access networks only if the home network supports such simultaneous connectivity. The UE determines that the network supports such simultaneous connectivity over multiple accesses if the UE is provisioned with or has received per-APN inter-system routing policies. So the UE can have independent PDN connections via multiple access types.
The access types supported are 4G and WiFi.
The S2b interface implementation on the P-GW and SAEGW supports the following functionality:
- UE connecting to PDN via WiFi access
- UE multiple PDN connections
- Initial Attach
- LTE to WiFi Handoff
- WiFi to LTE Handoff
GTP-based S2a Interface Support on the Standalone P-GW and SAEGW
GTP-Based S2a Interface Support is a licensed-controlled feature. Contact your Cisco account or support representative for detailed licensing information.
Prior to StarOS release 20.0, GTP-based S2a interface support was available on the P-GW. With StarOS release 20.0, GTP-based S2a interface support is also supported on the SAEGW. Operators deploying StarOS release 20.0 on the SAEGW are now able to integrate Trusted WiFi network functionality using this feature.
The S2a interface connects the standalone P-GW and P-GW of the SAEGW with the HSGW of the eHRPD. Specifically, the S2a interface supports the bearer interface by providing signaling and mobility support between a trusted non-3GPP access point (HSGW) and the standalone P-GW or P-GW of the SAEGW. It is based on Proxy Mobile IP but also supports Client Mobile IPv4 FA mode which allows connectivity to trusted non-3GPP IP access points that do not support PMIP.
When the WLAN is considered as trusted by the operator, the Trusted WLAN Access Network (TWAN) is interfaced with the EPC as a trusted non-3GPP access via the S2a interface to the P-GW. Support has been extended for WiFi-to-LTE handovers using Make and Break for the SAEGW service. Multi-PDN handovers are also supported as part of this feature.
Supported functionality includes:
Supported protocols include:
Transport Layer: UDP, TCP
Tunneling: GRE IPv6
Network Layer: IPv4, IPv6
Data Link Layer: ARP
Physical Layer: Ethernet
Relationships to Other Features
This section describes how the GTP-based S2b and S2a interface support feature is related to other features.
- A P-GW service must be configured and operational before GTP-based s2b interface support can be configured on the standalone P-GW and SAEGW.
- GTP-based S2b interface support must also be configured and operational on the ePDG to support this feature.
A P-GW service must be configured and operational before GTP-based S2a interface support can be configured on the standalone P-GW and SAEGW.