Content for  TS 29.502  Word version:  18.5.0

As specified in clause 4.3.1 of TS 23.502, for Home Routed PDU sessions, there is NAS SM information that the V-SMF and H-SMF need to interpret, and NAS SM information that the V-SMF only needs to transfer between the UE and H-SMF but which it does not need to interpret. NAS SM information that only needs to be transferred between the UE and H-SMF by the V-SMF can be extended in later versions or releases of the NAS specification, e.g. defining new fields or values within existing IEs, and the extensions should not impact the V-SMF. Besides, in HR roaming scenarios, the V-SMF and H-SMF can comply to different versions or releases of the NAS specification. It should be possible to support new SM features only requiring support from the H-SMF without impacting the V-SMF, when the H-SMF complies with a more recent release than the V-SMF, e.g. defining new NAS SM IEs in signalling from the UE to the H-SMF and/or signalling from the H-SMF to the UE.

The V-SMF shall transfer NAS SM information that it only needs to transfer to the H-SMF (i.e. known IEs, and IEs that have an unknown value not set to "reserved" according to the release to which the V-SMF complies, that only need to be forwarded by the V-SMF) in n1SmInfoFromUe binary data within the HTTP content. This carries N1 SM IE(s), encoded as specified in TS 24.501, including the Type field and, for TLV or TLV-E IEs, the Length field. The V-SMF shall transfer NAS SM information that it does not comprehend (i.e. unknown IEs, or known IEs to be interpreted by the V-SMF that have an unknown value not set to "reserved" according to the release to which the V-SMF complies) in unknownN1SmInfo binary data within the HTTP content. This carries N1 SM IE(s), encoded as specified in TS 24.501, including the Type field and, for TLV or TLV-E IEs, the Length field. When receiving n1SmInfoToUe binary data in the HTTP contentfrom the H-SMF, the V-SMF shall parse all the N1 SM IEs received in the binary data and construct the NAS SM message to the UE according to TS 24.501. The V-SMF shall append unknown NAS SM IEs received in the binary data at the end of the NAS SM message it sends to the UE. The V-SMF shall comprehend and be able to encode at their right place in a given NAS message, all the IEs of the version of the NAS specification it implements that do not need to be interpreted by the V-SMF and which precede the last interpreted IE that the V-SMF implements in a NAS message.

When receiving unknownN1SmInfo binary data in the HTTP content from the V-SMF, the H-SMF shall process any N1 SM IE received in this binary data that do not require to be interpreted by the V-SMF. Other N1 SM IEs shall be dropped, e.g. IEs that the H-SMF comprehends but which require to be interpreted by the V-SMF. The H-SMF shall transfer NAS SM information which the V-SMF does not need to interpret (i.e. that it only needs to transfer to the UE) in n1SmInfoToUe binary data within the HTTP content. This carries N1 SM IE(s), encoded as specified in TS 24.501, including the Type field and, for TLV or TLV-E IEs, the Length field. The NAS SM IEs in n1SmInfoToUe binary data shall be encoded in the same order as specified in TS 24.501. N1 SM information which does not require to be interpreted by the V-SMF is information that is not defined as specific IEs over N16.

The requirements specified in clause 5.2.3.1 shall also apply for the transfer of NAS SM information between the UE and the SMF for PDU sessions with an I-SMF, whereby the I-SMF and SMF shall take the role of the V-SMF and H-SMF respectively.