5.6.14 Support of Framed Routing

Framed Routing is only defined for PDU Sessions of the IP type (IPv4, IPv6, IPv4v6) and allows to support an IP network behind a UE, such that a range of IPv4 addresses or IPv6 prefixes is reachable over a single PDU Session, e.g. for enterprise connectivity. Framed Routes are IP routes behind the UE.

A PDU Session may be associated with multiple Framed Routes. Each Framed Route refers to a range of IPv4 addresses (i.e. an IPv4 address and an IPv4 address mask) or a range of IPv6 Prefixes (i.e. an IPv6 Prefix and an IPv6 Prefix length). The set of one or more Framed Routes associated to a PDU Session is contained in the Framed Route information. The network does not send Framed Route information to the UE: devices in the network(s) behind the UE get their IP address by mechanisms out of the scope of 3GPP specifications. See RFC 2865 [73], RFC 3162 [74].

Framed Route information is provided by the SMF to the UPF (acting as PSA) as part of Packet Detection Rule (PDR, see clause 5.8.5.3) related with the network side (N6) of the UPF.

NOTE: SMF can take the UPF capabilities into account when selecting PSA UPF, to ensure that the SMF chooses PSA UPF(s) that support Framed Routing for PDU Sessions to DNN and/or slices deemed to support Framed Routing e.g. DNN and/or slices intended to support RG or if Framed Route information has been received as part of Session Management Subscription data.

The Framed Route information may be provided to the SMF by:

• the DN-AAA server as part of PDU Session Establishment authentication/authorization by a DN-AAA server (as defined in clause 5.6.6); or by
• Session Management Subscription data associated with DNN and S-NSSAI sent by UDM (as defined in clause 5.2.3.3.1 of TS 23.502 [3]).

If the SMF receives Framed Route information both from DN-AAA and from UDM, the information received from DN-AAA takes precedence and supersedes the information received from UDM.

The IPv4 address / IPv6 Prefix allocated to the UE as part of the PDU Session establishment (e.g. delivered in NAS PDU Session Establishment Accept) may belong to one of the Framed Routes associated with the PDU Session or may be dynamically allocated outside of such Framed Routes.

If PCC applies to the PDU Session, at PDU Session establishment the SMF reports to the PCF the Framed Route information corresponding to the PDU Session (as described in clause 6.1.3.5 of TS 23.503 [45]). In this case, in order to support session binding, the PCF may further report to the BSF the Framed Route information corresponding to the PDU Session (as described in clause 6.1.2.2 of TS 23.503 [45]).

If the UDM or DN-AAA updates the Framed Route information during the lifetime of the PDU Session, the SMF releases the PDU Session and may include in the release request an indication for the UE to re-establish the PDU Session.