6.2 Addition of one access to a PDN connection

23.1613GPPNetwork-Based IP Flow Mobility (NBIFOM)Release 17Stage 2TS

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

6.2.1 General

This clause specifies the additional procedures for adding an access to an existing PDN connection over a 3GPP access, a Trusted WLAN access or an Untrusted WLAN when the NBIFOM is supported. In these flows it is assumed that the UE has performed a PDN Connection establishment procedure through one access as specified in clause 6.1. The procedure results in that the UE is simultaneously connected via both accesses and a set of traffic flows can be routed through one access while the remaining traffic flows are routed through the other access.

Each of the accesses has its own default bearer where each bearer has its own Charging Id. The Charging Id for the PDN connection will differ from the Charging Id for the default bearer. The PDN GW shall provide the Charging Id for the PDN connection separately to the SGW/TWAN/ePDG for both the default and any dedicated bearer.

6.2.2 Addition of a 3GPP access

In the case of E-UTRAN, the UE has established a PDN connection over WLAN as described in clause 6.1.2 or 6.1.3 above. Subsequently, the UE requests to establish a PDN connection using the same APN on E-UTRAN, and attempts to use both accesses for the same PDN connection simultaneously. For EUTRAN, the procedure is the same as specified in TS 23.401 [4] clause 5.3.2.1 (Initial attach procedure) and clause 5.10.2 (UE requested PDN Connectivity procedure) with the following additions:

Step 1: The UE indicates handover and includes NBIFOM indication in the PCO in Attach Request (Initial attach) or PDN Connectivity Request (UE requested PDN Connectivity procedure) for the same APN as for the PDN connection established over the Trusted or Untrusted WLAN access previously.

Step 2: Since the handover indication is provided by the UE, the MME selects the same PDN GW that is already assigned for the UE and the PDN connection, and indicates its NBIFOM capability in the Create Session Request to the Serving GW.

Step 3: The Serving GW sends the Create Session Request to the PDN GW, including its NBIFOM capability.

Step 4: When the PDN GW receives handover and NBIFOM indication, the PDN GW does not remove the bearers over the WLAN access for the corresponding PDN connection. The PDN GW initiates an IP-CAN Modification Procedure to notify the PCRF about the additional of 3GPP access together with the RAT type of the access, if dynamic PCC applies. The PCRF may reject the addition of the access if the multi-access IP-CAN session would correspond to an invalid combination of IP-CAN and RAT Types or is not allowed by the subscription.

– The same IP address is allocated for the PDN connection as the one used in WLAN.

– If UE-initiated NBIFOM mode was selected at initial PDN Connection establishment, the UE may include Routing Rules and indicates the default access to the PCRF via PDN GW during this procedure. The PCRF takes a final decision on the default access based on the subscription, and indicate the default access for the PDN Connection to the PDN GW. The default access replied by the network may be different than the default access requested by the UE.

– If network-initiated NBIFOM mode was selected at initial PDN connection establishment, the network does not provide any Routing Rules to the UE during this procedure. The PCRF shall indicate the default access to the PDN GW. The PDN GW indicates the default access to the MME via SGW. The MME indicates the default access to the UE in PDN Connectivity Accept message.

– Appropriate 3GPP bearer setup or modification procedures are executed for the resources associated with the flows that were moved onto the 3GPP access.

Step 5: If the MME, SGW and the PDN GW support NBIFOM and the addition of an access is accepted by the PCRF, the PDN GW generates a Charging Id for the Default Bearer and includes the Charging Ids for the PDN Connection and the Default Bearer in the Create Session Response to the SGW. The PDN GW indicates the support of NBIFOM in the PCO included in Attach Accept / PDN Connectivity Accept to be sent to the UE.

In the case of GERAN/UTRAN, the UE performs the initial PDN connection establishment over GERAN/UTRAN access and addition of a new PDN connection as specified in TS 23.060 [5] clause 9.2.2.1A (PDP context activation using S4) with the following additions:

Step 1: The UE sends Activate PDP context Request, including an NBIFOM indication in the PCO and handover indication.

Step 2: Since the handover indication is provided by the UE, the SGSN selects the same PDN GW that is already assigned for the UE and the PDN connection, and indicates its NBIFOM capability in the Create Session Request to the Serving GW. The SGSN and SGW inform the PDN GW their support of NBIFOM in Create Session Request.

Step 3: The Serving GW sends the Create Session Request to the PDN GW, including its NBIFOM capability.

– The same IP address is allocated for the PDN connection as the one used in WLAN.

– Appropriate 3GPP bearer setup or modification procedures are executed for the resources associated with the flows that were moved onto the 3GPP access.

Step 5: If the SGSN, SGW and the PDN GW support NBIFOM and the addition of an access is accepted by the PCRF, the PDN GW generates a Charging Id for the Default Bearer and includes the Charging Ids for the PDN Connection and the Default Bearer in the Create Session Response to the SGW. The PDN GW indicates the support of NBIFOM in the PCO included in Activate PDP context Accept to be sent to the UE.

6.2.3 Addition of an access using S2a

6.2.3.1 Single-connection mode

This procedure is used to add trusted WLAN access in single-connection mode to an existing PDN Connection. The decision to use the single-connection mode is made during authentication as described in clause 16.2.

Figure 6.2.3.1-1: Addition of trusted WLAN access with SCM and GTP S2a for roaming, LBO and non-roaming scenarios

It is assumed that the UE has established a PDN connection over a 3GPP access and has received from the network an indication that NBIFOM is supported to this PDN connection. In order to use the TWAN access with SCM for the same PDN connection simultaneously, the UE now performs the procedure TS 23.402 [2] clause 16.2 (Initial Attach) with the following additions:

Step 2: During the EAP authentication, the UE negotiates single-connection mode and requests EPC access. The UE indicates handover and the same APN as for the PDN connection established over the 3GPP access. The UE also includes an NBIFOM indication in the PCO that the procedure is for the addition of an access to the PDN connection. The UE cannot include routing rule(s) during the EAP authentication procedure in single-connection mode. If UE-initiated NBIFOM mode was selected at initial PDN Connection establishment, the UE may include an indication for default access for the PDN Connection.

Step 3: Since the handover indication is included, the TWAN selects the same PDN GW as it is already allocated for the PDN connection. The TWAN includes an NBIFOM capability indication in the Create Session Request.

Step 4: Instead of an IP-CAN Session Establishment procedure, the PDN GW performs an IP-CAN Session Modification procedure. The PDN GW indicates to the PCRF the addition of an access for the PDN connection and informs the PCRF about the additional RAT type. The PCRF may reject the addition of the access if the multi-access IP-CAN session would correspond to an invalid combination of IP-CAN and RAT Types or is not allowed by the subscription.

Step 8: If the TWAN and the PDN GW support NBIFOM and the addition of an access is accepted by the PCRF, the PDN GW generates a Charging Id for the Default Bearer and includes the Charging Ids for the PDN Connection and the Default Bearer in the Create Session Response to the TWAN. The PDN GW indicates the support of NBIFOM in the PCO to be sent to the UE.

In network-initiated NBIFOM mode, the network does not provide any routing rules to the UE during this procedure.

NOTE: The reason is that there would be no way for the UE to acknowledge the network-provided Routing Rules during the addition of an access. Instead, Routing Rules need to be provided from the network using a separate IP flow mobility procedure.

NBIFOM is not supported for Transparent Single Connection Mode. Therefore only scenario (A) in Figure 6.2.3.1-1 is applicable to NBIFOM.

6.2.3.2 Multi-connection mode

This procedure is used to add trusted WLAN access in multi-connection mode to an existing PDN Connection. The decision to use the multi-connection mode is made during authentication as described in clause 16.2.

Figure 6.2.3.2-1: UE-Initiated Connectivity to PDN in WLAN on GTP S2a

It is assumed that the UE has established a PDN connection over a 3GPP access and has received from the network an indication that NBIFOM is supported for to this PDN connection.

It is also assumed that the UE has made initial attach in trusted WLAN access and negotiated MCM during EAP authentication, as described in clause 16.2.1 in TS 23.402 [2].

In order to use the TWAN access with MCM for the same PDN connection simultaneously, the UE now performs the procedure TS 23.402 [2] clause 16.8.1 (PDN Connection establishment) with the following additions:

Step 1: In the WLCP PDN Connection Request, the UE indicates handover and the same APN as for the PDN connection established over the 3GPP access. The UE also includes an indication in the PCO that the procedure is for addition of an access for the PDN connection.

If UE-initiated NBIFOM mode was selected at initial PDN Connection establishment, the UE may include Routing Rules in the WLCP PDN Connection Request, as well as an indication for default access for the PDN Connection.

Step 2: Since the handover indication is included, the TWAN selects the same PDN GW as is already allocated for the PDN Connection. The TWAN includes an NBIFOM capability indication in the Create Session Request. The TWAN also includes Routing Rules(s) and the indication for default access if provided by the UE in step 2.

When the PDN GW receives the Create Session Request indication, the PDN GW does not remove the bearers over 3GPP access for the corresponding PDN connection. The same IP address is allocated for the PDN connection as the one used in 3GPP access network

Step 3: Instead of an IP-CAN Session Establishment procedure, the PDN GW performs an IP-CAN Session Modification procedure. The PDN GW indicates to the PCRF of addition of an access for the PDN connection and informs the PCRF about the additional RAT type. The PCRF may reject the addition of the access if the multi-access IP-CAN session would correspond to an invalid combination of IP-CAN and RAT Types or is not allowed by the subscription.

If network-initiated NBIFOM mode was selected at initial PDN Connection establishment, the PCRF shall indicate the default access for the PDN Connection to the PDN GW.

If UE-initiated NBIFOM mode was selected at initial PDN Connection establishment and the UE included an indication for default access for the PDN Connection, the PDN GW provides the indication to the PCRF. The PCRF takes a final decision on the default access based on the subscription, and indicate the default access for the PDN Connection to the PDN GW. The default access replied by the network may be different than the default access requested by the UE.

Step 5: The PDN GW indicates the default access for the PDN Connection to the TWAG via S2a.

Step 7: The TWAG indicates the new default access to the UE as part of the WLCP PDN Connection Response. If the TWAN and the PDN GW support NBIFOM and the addition of an access is accepted by the PCRF, the PDN GW generates a Charging Id for the Default Bearer and includes the Charging Ids for the PDN Connection and the Default Bearer in the Create Session Response to the TWAN. The PDN GW indicates the support of NBIFOM in the PCO included in WLCP PDN Connectivity Accept to be sent to the UE.

In network-initiated NBIFOM mode, the network does not provide any routing rules to the UE during this procedure.

Step 8: In UE-initiated NBIFOM mode, if the UE provided Routing Rules to the network when adding trusted WLAN access to the PDN Connection, the PDN GW executes appropriate 3GPP resource release procedures for the resources associated with the flows that were moved away from the 3GPP source access, based on the routing rules provided by the UE, as specified in TS 23.402 [2].

6.2.4 Addition of an access using S2b

6.2.4.1 Addition of Untrusted WLAN access

This procedure is used to add untrusted WLAN access to an existing PDN Connection.

Figure 6.2.4.1-1: Addition of WLAN access to the PDN connection

Figure 6.2.4.1-1 shows the particular case when the UE is first connected to a 3GPP access and then it requests addition of a WLAN access.

It is assumed that the UE has successfully attached to 3GPP access and established a PDN connection over 3GPP access using GTP as described in clause 6.1.1 and that the UE has received from the network an indication that NBIFOM is supported for this PDN connection.

Subsequently the UE performs the untrusted WLAN attachment, and requests to establish a PDN connection using the same APN, and attempts to use both accesses for the same PDN connection simultaneously.

1. The UE discovers a WLAN and performs the authentication and authorization procedure with 3GPP EPC via the WLAN access as specified in TS 23.402 [2] clause 7.2.1 step 1.

2. IKEv2 authentication and tunnel setup procedure are performed via the WLAN access between the UE, ePDG and 3GPP AAA Server/HSS as specified in TS 33.402 [6]. For IP address preservation, the UE includes the same address (IPv4 address or IPv6 prefix/address or both) that was allocated during its attachment to 3GPP access. A new access can be added to a multi-access PDN connection without an associated routing rule.

If UE-initiated NBIFOM mode was selected at initial PDN Connection establishment, the UE may include Routing Rules in this step, as well as an indication for default access for the PDN Connection.

3. Since the handover indication is included, the TWAN selects the same PDN GW as is already allocated for the PDN Connection. The ePDG includes an NBIFOM indication in the Create Session Request message to the PDN GW. The ePDG also includes Routing Rules(s) and the indication for default access if provided by the UE in step 2.

4. When the PDN GW receives the Create Session Request with NBIFOM indication, the PDN GW does not remove the bearers over 3GPP access for the corresponding PDN connection. The same IP address is allocated for the PDN connection as the one used in 3GPP access network. If dynamic PCC is applied, the PDN GW initiates the IP-CAN Session Modification Procedure with the PCRF. The PDN GW indicates to the PCRF the addition of an access for the PDN connection and informs the PCRF about the additional RAT type. The PCRF may reject the addition of the access if the multi-access IP-CAN session would correspond to an invalid combination of IP-CAN and RAT Types or is not allowed by the subscription.

If routing rules were received, the PDN GW provides the PCRF with notification of the UE requested IP flow mapping to an Access Type. The PCRF may accept or reject the routing rules. . If network-initiated NBIFOM mode was selected at initial PDN Connection establishment, the PCRF shall indicate the default access for the PDN Connection to the PDN GW.

If UE-initiated NBIFOM mode was selected at initial PDN Connection establishment, the UE indicates the default access to the PCRF via PDN GW during this procedure. The PCRF takes a final decision on the default access based on the subscription, and indicate the default access for the PDN Connection to the PDN GW. The default access replied by the network may be different than the default access requested by the UE.

5. The PDN GW sends a Create Session Response message to the ePDG that includes the routing rules. The PDN GW generates a Charging Id for the Default Bearer and includes the Charging Ids for the PDN Connection and the Default Bearer in the Create Session Response to the ePDG. The PDN GW also indicates the default access for the PDN Connection to the ePDG.

6. The ePDG indicates to the UE that the authentication and authorization with the external AAA server is successful.

7. If routing rules were included in step 2 above, the ePDG notifies the UE whether the routing rules were accepted or rejected. In network-initiated NBIFOM procedure, the network does not provide any routing rules to the UE during this procedure. The ePDG indicates the default access to the UE as part of the IKEv2 signalling.

8. IP connectivity from the UE to the PDN GW is now setup. Any packet in the uplink direction complying with the routing rules is tunnelled to the ePDG by the UE using the IPSec tunnel. The ePDG then tunnels the packet to the PDN GW. From the PDN GW normal IP-based routing takes place. In the downlink direction, the packet for UE arrives at the PDN GW. The PDN GW tunnels the packet to the ePDG based on the routing rules. The ePDG then tunnels the packet to the UE via the IPsec tunnel.

9. If routing rules were included in step 2 above, the appropriate 3GPP resource release procedures are executed for the resources associated with the flows that were moved onto the WLAN access as specified in TS 23.402 [2].