4 General
24.2443GPPRelease 17Stage 3TSWireless LAN control plane protocol for trusted WLAN access to EPC
4.1 Overview
WLCP is used between user equipment (UE) and trusted wLAN access gateway (TWAG) for multi-connection mode as specified in 3GPP TS 23.402 [2].
The WLCP comprises procedures for:
– establishment of PDN connections including initial request and handover from a 3GPP access;
– requesting the release of a PDN connection by the UE or notifying the UE of the release of a PDN connection;
– transport of parameters related to PDN connections, such as APN, PDN type, PCO, handover indication, user-plane MAC address of the TWAG etc.;
– IP address allocation; and
– WLCP bearer management including WLCP bearer setup, modification and release when multiple bearer PDN connectivity is used.
Generally, WLCP procedures described in the clause 5 can be performed only after the UE has successfully completed the following steps:
– Authentication and negotiation of the multi-connection mode for the trusted WLAN access as specified in 3GPP TS 24.302 [3]; and
– Establishment of a DTLS connection with the TWAG, according to subclause 4.2.4.
4.2 Protocol stack
4.2.1 General
The protocol stack of WLCP is shown in figure 4.2.1.
Figure 4.2.1: Protocol stack of WLCP
4.2.2 UDP port numbers for WLCP
4.2.2.1 General
The WLCP messages are transported over UDP layer as specified in IETF RFC 768 [8]. The security is provided by the DTLS layer.
The WLCP UDP Port number is 36411.
4.2.2.2 UE procedure
The UE shall use the WLCP UDP port number as the source UDP port and the destination UDP port of WLCP messages.
4.2.2.3 TWAG procedure
The TWAG shall use the WLCP UDP port number as the source UDP port and the destination UDP port of WLCP messages.
4.2.3 IP addresses of WLCP message
4.2.3.1 General
The WLCP/DTLS/UDP packet shall be carried via IPv6 with link local addressing scope or IPv4 as specified in 3GPP TS 23.402 [2].
4.2.3.2 UE procedure
The UE receives one or two TWAG control-plane addresses during the EAP authentication and authorization procedure as specified in 3GPP TS 24.302 [3] subclause 6.4.2.6.3.
NOTE: If two TWAG control-plane addresses are received, one includes an IPv4 address and the other includes an IPv6 link-local address.
If the UE receives one TWAG control-plane address, the UE shall select the TWAG control-plane address. If the UE receives two TWAG control-plane addresses, the UE shall select one of the TWAG control-plane addresses.
The UE shall use the IP address of the selected TWAG control-plane address as the destination IP address of WLCP messages.
The UE shall apply the following procedures to set the source IP address of the WLCP message:
– if the TWAG IP address for WLCP is an IPv4 address and if the UE supports IPv4, the UE shall obtain an IPv4 address via DHCPv4 to be used as the source IP address for WLCP;
– if the TWAG IP address for WLCP is an IPv6 link-local address and if the UE supports IPv6, the UE shall use the IPv6 link-local address configured on the WLAN interface as the source IP address for WLCP; and
– if the TWAG IP addresses for WLCP are an IPv4 address and an IPv6 link-local address, which IP version the UE selects is implementation dependent.
4.2.3.3 TWAG procedure
When the UE initiates a WLCP procedure:
– the TWAG shall use a TWAG control plane address which was included in TWAG_CP_ADDRESS item provided to the UE during EAP-AKA’ authentication as described in 3GPP TS 24.302 [3], as the source IP address for WLCP. If two TWAG control plane addresses were included in TWAG_CP_ADDRESS item provided to the UE during EAP-AKA’ authentication as described in 3GPP TS 24.302 [3], the TWAG shall use the TWAG control plane address of the same IP version as the IP version received from the UE in the WLCP message; and
– the TWAG shall use the source IP address received from the UE in the WLCP message as the destination IP address for further WLCP message to the UE.
When the TWAG initiates a WLCP procedure:
– the TWAG shall use a TWAG control plane address which was included in TWAG_CP_ADDRESS item provided to the UE during EAP-AKA’ authentication as described in 3GPP TS 24.302 [3], as the source IP address for WLCP. If two TWAG control plane addresses were included in TWAG_CP_ADDRESS item provided to the UE during EAP-AKA’ authentication as described in 3GPP TS 24.302 [3], the TWAG shall use the TWAG control plane address of the same IP version as the IP version received from the UE in the WLCP message; and
– the TWAG shall use the source IP address received from the UE in the earlier WLCP message as the destination IP address for further WLCP message to the UE.
4.2.4 DTLS usage
The UE and the TWAG shall use DTLS according to 3GPP TS 33.402 [9].
4.3 WLCP layer states when single point-to-point connectivity is used
4.3.1 General
In this subclause the possible states of WLCP state machine in the UE and in the TWAG are described when single point-to-point PDN connectivity is used. Each PDN connection to EPC is associated with an individual state machine, and single point-to-point connectivity between the UE and the TWAG is used to transport traffic for all S2a bearer(s) of the PDN connection (see 3GPP TS 23.402 [2]).
4.3.2 WLCP layer states in the UE
4.3.2.1 PDN CONNECTIVITY NOT ESTABLISHED
No PDN connectivity to EPC exists over TWAN (see figure 4.3.2.2.1).
4.3.2.2 PDN CONNECTIVITY ESTABLISHED
The PDN connectivity to EPC is established in the UE (see figure 4.3.2.2.1).
Figure 4.3.2.2.1: The WLCP state machine in the UE (overview)
4.3.2.3 PROCEDURE TRANSACTION INACTIVE
No procedure transaction exists (see figure 4.3.2.4.1).
4.3.2.4 PROCEDURE TRANSACTION PENDING
The UE has initiated a procedure transaction towards the TWAG (see figure 4.3.2.4.1).
Figure 4.3.2.4.1: The procedure transaction states in the UE (overview)
4.3.3 WLCP layer states in the TWAG
4.3.3.1 PDN CONNECTIVITY NOT ESTABLISHED
No PDN connectivity to EPC exists for the UE (see figure 4.3.3.4.1).
4.3.3.2 PDN CONNECTIVITY PENDING
The TWAG has sent PDN connectivity accept towards the UE (see figure 4.3.3.4.1).
4.3.3.3 PDN CONNECTIVITY ESTABLISHED
The PDN connectivity is established in the TWAG (see figure 4.3.3.4.1).
4.3.3.4 PDN DISCONNECT PENDING
The TWAG has initiated a PDN disconnect towards the UE (see figure 4.3.3.4.1).
Figure 4.3.3.4.1: The WLCP states for PDN connectivity handling in the TWAG (overview)
4.3.3.5 PROCEDURE TRANSACTION INACTIVE
No procedure transaction exists.
4.3.3.6 PROCEDURE TRANSACTION PENDING
The TWAG has initiated a procedure transaction towards the UE (see figure 4.3.3.6.1).
Figure 4.3.3.6.1: The procedure transaction states in the TWAG (overview)
4.3A WLCP layer states when multiple bearer PDN connectivity is used
4.3A.1 General
In this subclause the possible states for WLCP bearer in the UE and in the TWAG are described when multiple bearer PDN connectivity is used. Each WLCP bearer context is associated with an individual state machine. This state machine shall be used when both the UE and the TWAG supports the establishment of multiple WLCP bearers per PDN connection where a separate WLCP bearer is established for the default S2a bearer, and for each dedicated S2a bearer established on the S2a interface (see 3GPP TS 23.402 [2]).
4.3A.2 PDN connectivity and default WLCP bearer contextstates in the UE
4.3A.2.1 PDN CONNECTIVITY NOT ESTABLISHED
No PDN connectivity to EPC exists over TWAN (see figure 4.3A.2.2.1).
4.3A.2.1A WLCP BEARER CONTEXT INACTIVE
No default WLCP bearer context exists for the UE (see figure 4.3A.2.2.1A).
4.3A.2.2 PDN CONNECTIVITY ESTABLISHED
The PDN connectivity to EPC is established in the UE (see figure 4.3A.2.2.1).
4.3A.2.2A WLCP BEARER CONTEXT ACTIVE
The default WLCP bearer context exists for the UE (see figure 4.3A.2.2.1A).
Figure 4.3A.2.2.1: PDN connectivity states in the UE (overview)
Figure 4.3A.2.2.1A: Default WLCP bearer context states in the UE (overview)
4.3A.2.3 PROCEDURE TRANSACTION INACTIVE
No procedure transaction exists (see figure 4.3A.2.4.1).
4.3A.2.4 PROCEDURE TRANSACTION PENDING
The UE has initiated a procedure transaction towards the TWAG (see figure 4.3A.2.4.1).
Figure 4.3A.2.4.1: The procedure transaction states in the UE (overview)
4.3A.2A Dedicated WLCP bearer context states in the UE
4.3A.2A.1 Substate WLCP BEARER CONTEXT INACTIVE
No dedicated WLCP bearer context exists (see figure 4.3A.2.2.1).
4.3A.2A.2 Substate WLCP BEARER CONTEXT ACTIVE
The dedicated WLCP bearer context is active in the UE (see figure 4.3A.2.2.1).
Figure 4.3A.2A.2.1: Dedicated WLCP bearer context states in the UE (overview)
4.3A.3 WLCP layer PDN connectivity and default WLCP bearer context states in the TWAG
4.3A.3.1 PDN CONNECTIVITY NOT ESTABLISHED
No PDN connectivity to EPC exists for the UE (see figure 4.3A.3.5.1).
4.3A.3.1A WLCP BEARER CONTEXT INACTIVE
No WLCP bearer context exists for the UE (see figure 4.3A.3.5.1A).
4.3A.3.2 PDN CONNECTIVITY PENDING
The TWAG has sent PDN connectivity accept towards the UE (see figure 4.3A.3.5.1).
4.3A.3.2A WLCP BEARER CONTEXT ACTIVE PENDING
The TWAG has sent PDN connectivity accept towards the UE (see figure 4.3A.3.5.1).
4.3A.3.3 PDN CONNECTIVITY ESTABLISHED
The PDN connectivity is established in the TWAG (see figure 4.3A.3.5.1).
4.3A.3.3A WLCP BEARER CONTEXT ACTIVE
The WLCP bearer context is active in the TWAG (see figure 4.3A.3.5.1A).
4.3A.3.4 PDN DISCONNECT PENDING
The TWAG has initiated a PDN disconnect towards the UE (see figure 4.3A.3.5.1).
4.3A.3.4A WLCP BEARER CONTEXT INACTIVE PENDING
The TWAG has initiated a PDN disconnect request or WLCP bearer context release for the default WLCP bearer towards the UE (see figure 4.3A.3.5.1A).
4.3A.3.5 WLCP BEARER MODIFY PENDING
The TWAG has initiated a WLCP bearer context modification towards the UE (see figure 4.3A.3.5.1A).
Figure 4.3A.3.5.1: PDN connectivity states in the TWAG (overview)
Figure 4.3A.3.5.1A: Default WLCP bearer context states in the TWAG (overview)
4.3A.3A WLCP layer dedicated bearer context states in the TWAG
4.3A.3A.1 WLCP BEARER CONTEXT INACTIVE
No WLCP bearer context exists for the UE (see figure 4.3A.3A.5.1).
4.3A.3A.2 WLCP BEARER CONTEXT ACTIVE PENDING
The TWAG has initiated a WLCP bearer context setup towards the UE (see figure 4.3A.3A.5.1).
4.3A.3A.3 WLCP BEARER CONTEXT ACTIVE
The WLCP bearer context is active in the TWAG (see figure 4.3A.3A.5.1).
4.3A.3A.4 WLCP BEARER CONTEXT INACTIVE PENDING
The TWAG has initiated a WLCP bearer context release towards the UE (see figure 4.3A.3A.5.1).
4.3A.3A.5 WLCP BEARER CONTEXT MODIFY PENDING
The TWAG has initiated a WLCP bearer context modification towards the UE (see figure 4.3A.3A.5.1).
Figure 4.3A.3A.5.1: Dedicated WLCP bearer context states in the TWAG (overview)
4.4 IP address allocation
WLCP provides the following functionalities related to IP address allocation for multi-connection mode:
– requesting PDN type by the UE;
– allocating IPv4 address to the UE; and
– allocating IPv6 interface identifier to the UE.
IPv6 network prefix is assigned via stateless address autoconfiguration method as specified in 3GPP TS 23.402 [2].
Deferred IPv4 address allocation is not supported in the current release of this specification.