4 Architecture model and concepts

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

4.1 General concepts

A PDN connection supporting NBIFOM provides simultaneous access to a single PDN via different access networks: a 3GPP access network and a WLAN access network. It is used by multi-radio (i.e. 3GPP and WLAN) capable UEs that are able to simultaneously connect to a given PDN via different access systems (3GPP and WLAN).

In order to enable NBIFOM, the UE can establish and maintain a PDN connection over both 3GPP access and WLAN access simultaneously. This is supported for both S2b and S2a connectivity. The UE can add an access to a PDN connection even if traffic is not immediately routed over the added access. When a PDN connection is established over both 3GPP access and WLAN access simultaneously there is one default bearer for each access.

On a PDN connection established over both 3GPP access and WLAN access, it is possible to move individual IP flows from one access network to another, when policies determine that flows should be moved and the target access is available for the UE.

The PDN GW performs IP flow routing of downlink traffic. The UE performs IP flow routing of uplink traffic.

A mechanism is defined for the UE and the network to discover whether the network and the UE respectively support NBIFOM and to decide whether NBIFOM will be applied for a given PDN connection. This mechanism works on a per-PDN connection basis.

The UE and the PDN GW shall always be aware of which access IP flows of the PDN connection shall use.

For NBIFOM, the UE and the PDN GW exchange Routing Rules (RR). Routing Rules (RR) describe the mapping between a set of IP flows (identified by a Routing filter) and a Routing access type (e.g. 3GPP or WLAN) over which to route these IP flows.

Routing rules are exchanged over control plane protocols (NAS over a 3GPP access, WLCP / IKE over WLAN access, S2a/S2b/S5/S8 control protocol).

The following NBIFOM modes are supported:

– UE-initiated NBIFOM: In the UE-initiated NBIFOM mode only the UE controls the traffic routing within the multi-access PDN connection. The UE determines the Routing rules and provides them to the PDN GW. The network may either accept or reject the Routing Rules requested by the UE, but does not provide Routing rules itself.

– Network-initiated NBIFOM: In the Network-initiated NBIFOM mode, the network controls the traffic routing within the multi-access PDN connection The PDN GW determines the Routing rules and provides them to the UE. The UE may either accept or reject the network’s request for Routing rules (e.g. based on the suitability of the WLAN link conditions), but does not provide Routing Rules itself.

The NBIFOM mode that applies to a PDN connection is determined during the PDN connection establishment.

Routing Rule installation is possible at any time during the lifetime of a PDN connection. Routing Rules can be installed even if there is no IP flow currently matching the routing filter in the Routing Rule.

For a UE with active flows on both 3GPP access and WLAN access, in case one of the accesses is lost or no longer usable, a mechanism is provided to move the IP Flows to the other (target) access in order to minimise service disruption. When an access is recovered, a mechanism is provided to move over this recovered access the IP Flows which are associated with policies giving precedence to this access. For UE-initiated NBIFOM mode, the UE-initiated IP flow mobility procedures described in clause 6.3.3 are used. For network-initiated NBIFOM mode, the procedures described in clause 6.6 are used.

When PCC is deployed and supports NBIFOM, the PCRF provides the PDN GW with Access information which is part of PCC rules. The Access information controls the access over which the traffic that matches the Service data Flow template of this PCC rule should be sent.

When PCC is not deployed or active for a PDN Connection, the PDN GW may apply static NBIFOM related policies. The PCEF static policy and control functionality is not based on subscription / user quota information.

The PDN GW translates Access information received in PCC rules into Routing Rules to be used between the UE and the PDN GW. In case UE initiated NBIFOM is applied and PCC is deployed for this PDN connection, the PDN GW provides, upon subscription of the PCRF, the PCRF with notifications of UE requests for IP flow mapping to an Access Type. In that case, the PCRF analyses the received information (requested IP flow mapping to an Access Type), makes a policy decision and provides PCC rules to the PDN GW with corresponding Access Type values.

In a PLMN all MME(s), SGSN(s) and SGW(s) are assumed to have the same level of support of NBIFOM. If the PDN GW detects a change in the support of NBIFOM on the 3GPP access of a PDN connection, it removes the 3GPP access from the multi-access PDN connection.

NOTE 1: This may happen in the case of inter PLMN mobility.

For S2a case, NBIFOM applies in both Multi-Connection Mode (MCM) and Single-Connection Mode (SCM) modes but not in Transparent Single-Connection Mode (TSCM). In SCM mode:

– Routing Rules are exchanged only on the 3GPP access. Delivery of Routing Rules delivery is further described in clause 5.3.

– No dedicated bearers are supported on the S2a access of the PDN connection.

– There is no way to indicate the loss of 3GPP access to the PGW in SCM. There is no support for the indication of loss of 3GPP access in SCM.

NOTE 2: Following features are not supported in this release of the specification:

– The support of Routing rules referring to an Application Id,

– The support of Network Based Mobility based on PMIP.

4.2 Architecture reference model

The same architecture than defined in TS 23.402 [2] clause 4.2 (S2b case) and clause 16 (S2a case) applies. No new functional entity or reference point is defined for NBIFOM.

More details on the NBIFOM impacts on the various network functions are provided in clause 5.10.