16.1.4A Control Plane

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

16.1.4A.1 Negotiation of connection mode

The negotiation of the connection mode (Single-Connection mode, Multi-Connection mode or Transparent Single-Connection mode) takes place during the EAP-AKA’ access authentication.

– The network indicates the supported connection modes (Transparent Single-Connection mode, Single-Connection mode, Multi-Connection mode or any combination of them).

– The UE then requests either Single-Connection mode or Multi-Connection mode. If none of these modes is supported by both UE and network, Transparent Single-Connection mode is used if supported by the network. In case the UE requests Single-Connection mode, it includes also a request for either EPC-routed traffic or NSWO. In case the UE requests Single-Connection mode and EPC-routed traffic, the UE may further indicate e.g. handover, APN and PDN type.

– If both the UE and the network support Multi-Connection mode, the UE requests multi connection mode.

– The network provides an appropriate result code to the UE, depending on if the request is granted or rejected.

A Multi-Connection mode capable UE may or may not be able to operate in single connection mode.

When a Multi-Connection mode capable UE connects to a network that is only capable of single connection mode, the UE operates in single connection mode, if the UE supports single connection mode.

The EAP-AKA’ enhancements needed are described on clause 16.1.4A.2

16.1.4A.2 EAP-AKA’ extensions

EAP-AKA ‘ authentication signaling RFC 5448 [72] is extended in order to negotiate the connection mode: Single-Connection mode, Multi-Connection mode or Transparent Single-Connection mode, and to carry additional information needed for single connection mode.

NOTE 1: The selection by the UE and the use of Transparent Single-Connection mode (pre-Rel-12) do not require the support of any following EAP-AKA’ extension.

EAP-AKA’ authentication signaling is extended in order to exchange the following parameters:

1) In the UE to network direction:

– The requested connection mode (Single-Connection mode or Multiple-Connection mode);

– If the UE requests an emergency attach, an indication that the UE requests an emergency attach;

– In case Single-Connection mode is requested;

– The requested connectivity (NSWO or PDN connection), and

– In case the requested connectivity is a PDN connection: the PDN type (IPv4, IPv6, or IPv4v6), an optional hand-over indicator, optionally the requested APN (mandatory if the handover indication is provided), optionally a Protocol Configuration Options (PCO)

2) In the network to UE direction:

– The supported network connection modes (Transparent Single-Connection mode and/or Single Connection mode and/or Multi Connection mode);

– An indication on whether the network supports emergency services;

The supported TWAG WLCP IP version(s) if Multi-connection mode is supported;

– In case Single-Connection mode is requested:

– Whether the requested connectivity (NSWO or a PDN connection) has been granted;

– For PDN connection: the Selected APN, the selected PDN type (IPv4, IPv6, or IPv4v6), and optionally Protocol Configuration Options (PCO), Session Management back-off timer.

– In case Multi-Connection mode was requested:

– Whether NSWO is allowed or not.

– The TWAG IP address(es) of the control plane to be used for WLCP.

NOTE 2: For Multi-Connection mode, WLCP is always used for PDN connection establishment once the UE has been successfully authenticated.

16.1.4A.3 PDN connection management Control plane

16.1.4A.3.1 WLAN Control Protocol (WLCP)

WLCP is a control protocol between UE and TWAG. It applies to the support of Multi-Connection mode and enables management of PDN connectivity over a Trusted WLAN Access Network.

WLCP provides session management functionality required for:

– Establishment of PDN connections;

– Establishment of multiple bearers per PDN connection;

– Handover (from a 3GPP access) of PDN connections;

– Request the release of a PDN connection by the UE or notify the UE of the release of a PDN connection;

– IP address assignment (i.e. delivery of the IPv4 address through WLCP);

NOTE: Both IPv4 address assignment and IPv6 address assignment (SLAAC) can be supported in conjunction with WLCP.

The following PDN parameters are used:

– APN, PDN/PDP type, UE IP address/prefix, Protocol Configuration Options (PCO), Request type (initial request, handover) and optionally a Session Management back-off timer;

– The TWAG MAC address associated to the PDN connection or to the bearer.

– For emergency services, an indication that the UE has requested a PDN connection for emergency services.

The following WLCP bearer parameters are used:

– Traffic Filter Templates (TFTs) and Bearer QoS information;

WLCP signalling is protected using DTLS as described in TS 33.402 [45].

WLCP signalling is transported over DTLS, UDP and IP between the UE and the TWAG. The UE and the TWAG shall use a specific UDP port dedicated to WLCP when transporting the WLCP signalling. The WLCP/UDP traffic shall be carried with one of the following options:

– via IPv6 with link local addressing scope;

– via IPv4.

The UE uses the IPv6 link local address configured on the WLAN interface or the IPv4 address assigned via DHCPv4 by the network as the source IP address for WLCP. If NSWO is not authorized, then the UE is not expected to send traffic other than WLCP protocol traffic from this source IP address. The UE receives an indication from the AAA via EAP whether the TWAG supports IPv4 or IPv6, or both for WLCP. If the network indicates that it only supports one IP version for WLCP and the UE does not support this IP version for WLCP, then the UE may operate in Single Connection mode (if the UE and network support Single Connection mode), or Transparent Single Connection mode may be used if supported by the network.

The UE receives a TWAG IPv6 address with link local scope or a TWAG IPv4 address, or both as part of the EAP authentication, as descried in clause 16.2.1, to be used for WLCP signalling.

The selection of IPv4 and IPv6 is UE implementation dependant if both versions are supported by the UE and the TWAG for WLCP.

NOTE 1: WLCP protocol is a specific 3GPP protocol for which the details are defined in TS 24.244 [76].

NOTE 2: Aspects, such as segmentation, retransmission, are specified in stage 3 specifications.