I. Framed Routing is one of the basic functions supported by the 5G system; however, it is only applicable to PDU sessions of IP type (IPv4, IPv6, IPv4v6); it allows the IP network behind the terminal (UE) to access a series of IPv4 addresses or IPv6 prefixes through a single PDU session (e.g., for enterprise connections) – framed routing is the IP routing behind the UE.
II. Framed Routing and PDU: In the 5G system, a PDU session can be associated with multiple framed routes; each framed route points to an IPv4 address range (i.e., IPv4 address and IPv4 address mask) or an IPv6 prefix range (i.e., IPv6 prefix and IPv6 prefix length). The set of one or more framed routes associated with a PDU session is included in the framed routing information. The network does not send framed routing information to the terminal (UE); devices in the network behind the terminal (UE) obtain their IP addresses through mechanisms outside the scope of 3GPP specifications. – See RFC 2865 [73] and RFC 3162 [74] for details.
III. In 5G, framed routing information is provided by the SMF to the UPF (PSA function) as part of the packet detection rule (PDR) (see TS 23.501 section 5.8.2.11.3), and the rule is related to the UPF network side (N6); the SMF needs to consider the UPF's capabilities when selecting a UPF as a PSA to ensure that the SMF selects a PSA (UPF) that supports framed routing for the PDU session to the DNN and/or slice that is considered to support framed routing, for example, a DNN and/or slice intended to support RG, or if the framed routing information has been received as part of the session management subscription data.
IV. Framed routing information can be provided to the SMF in the following ways:
If the SMF receives frame routing information from both DN-AAA and UDM simultaneously, the information received from DN-AAA takes precedence and overrides the information received from UDM.
V. The IPv4 address/IPv6 prefix assigned to the UE as part of PDU session establishment (e.g., passed in the NAS PDU session establishment acceptance) may belong to one of the frame routes associated with that PDU session, or it may be dynamically assigned outside of these frame routes.
VI. If PCC is applied to the PDU session, the SMF reports the frame routing information corresponding to that PDU session to the PCF during PDU session establishment (as described in Section 6.1.3.5 of TS 23.503 [45]). In this case, to support session binding, the PCF may also report the frame routing information corresponding to that PDU session to the BSF (as described in Section 6.1.2.2 of TS 23.503 [45]).
----If the UDM or DN-AAA updates the frame routing information during the lifetime of the PDU session, the SMF will release the PDU session and may include an instruction in the release request indicating that the UE should re-establish the PDU session.
