Section: 6.5 UE requested ESM procedures 6.5.0 General
Content: The UE's maximum number of active EPS bearer contexts in a PLMN is determined by whichever is the lowest of the maximum number of EPS bearer identities allowed by the protocol (as specified in 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [12] clause 11.2.3.1.5), the PLMN's maximum number of EPS bearer contexts in S1 mode and the UE's implementation-specific maximum number of EPS bearer contexts. NOTE 1: Clauses 6.5.1.4 and 6.5.3.4 specify how the UE determines the PLMN's maximum number of EPS bearer contexts in S1 mode. In earlier versions of the protocol, the maximum number of simultaneously active EPS bearer contexts was limited by lower layer protocols to 8. In the present version of the protocol, the UE and the network may support a maximum number of 15 EPS bearer contexts. A UE supporting signalling for a maximum number of 15 EPS bearer contexts shall support the extended range or EPS bearer identities from 0 to 15 (as specified in 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [12] clause 11.2.3.1.5). The UE indicates support of signalling for a maximum number of 15 EPS bearer contexts by setting the 15 bearers bit in the UE Network Capability IE. A network supporting signalling for a maximum number of 15 EPS bearer contexts shall support the extended range or EPS bearer identities from 0 to 15 (as specified in 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [12] clause 11.2.3.1.5). The network indicates support of signalling for a maximum number of 15 EPS bearer contexts by setting the 15 bearers bit in the EPS network feature support IE. NOTE 2: A UE and a network not supporting signalling for a maximum number of 15 EPS bearer contexts will treat the EPS bearer identity values 1 to 4 as 'reserved' values. For a UE in NB-S1 mode, the UE's implementation-specific maximum number of active user plane radio bearers is 2 (as defined in 3GPP TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [20]) when the UE sets the Multiple DRB support bit to "Multiple DRB supported" during attach or tracking area updating procedures, and 1 otherwise. Upon an inter-system change from N1 mode to NB-S1 mode in EMM-IDLE mode for the UE operating in single-registration mode, if: a) the number of active default EPS bearer contexts in the UE is larger than the UE's implementation-specific maximum number of active user plane radio bearers; and b) the UE is using user plane CIoT EPS optimization; the UE shall locally deactivate at least one default EPS bearer context such that the total number of active default EPS bearer contexts that remained does not exceed the UE's implementation-specific maximum number of active user plane radio bearers. In this case, choosing which EPS bearer context to deactivate is implementation specific. The UE shall then include the EPS bearer context status IE in the TRACKING AREA UPDATE REQUEST message. Upon the inter-system change from A/Gb mode or Iu mode to S1 mode, for any PDN connection that has been transferred, if the PDN connection is not associated with a PDU session ID and the UE supporting N1 mode decides to enable the transfer of the PDN connection from S1 mode to N1 mode, the UE may first initiate the UE requested PDN disconnection procedure and then the UE requested PDN connectivity procedure for such PDN connection(s). As an implementation option, the UE may deactivate all EPS bearer contexts for such PDN connection(s) locally, and if the last PDN connection is not deactivated or the UE supports EMM-REGISTERED without PDN connection, the UE shall include the EPS bearer context status IE in the TRACKING AREA UPDATE REQUEST message of the tracking area updating procedure upon inter-system change from A/Gb mode or Iu mode to S1 mode, and then initiate UE requested PDN connectivity procedure for such PDN connection(s). NOTE 3: Upon the inter-system change from A/Gb mode or Iu mode to S1 mode, if a PDN connection does not support interworking with 5GS and the UE determines that the PLMN or the APN cannot support interworking with 5GS, it is recommended that a UE does not release and re-establish the PDN connection in order to enable interworking with 5GS for the PDN connection. Whether and how the UE determines the PLMN or the APN can support interworking with 5GS is implementation specific.