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1                                                Core network aspects


            The keywords "is not recommended" indicate a requirement which is not recommended but which is not
            specifically prohibited. Thus, conformance with this specification can still be claimed even if this requirement
            is present.
            The keywords "can optionally" indicate an optional requirement which is permissible, without implying any
            sense of being recommended. This term is not intended to imply that the vendor's implementation must
            provide the option and the feature can be optionally enabled by the network operator/service provider.
            Rather,  it  means  the  vendor  may  optionally  provide  the  feature  and  still  claim  conformance  with  the
            specification.


            6       Scenarios and requirements

            6.1     Scenarios
            In the multi-connection environment, the multi-connection user equipment (MUE) has more than one active
            connection  simultaneously,  it  can  send  and  receive  different  IP  flows  of  the  same  application  through
            different accesses. In the case where one of the accesses is lost or is no longer usable, a mechanism is
            provided to move the IP flows to another (target) access in order to minimise service disruption. When an
            access is recovered, a mechanism is provided to move the IP flow over to the recovered access. Precedence
            is given to those accesses associated with policies. The covered scenarios include an MUE-initiated flow-
            based service continuity (FSC) scenario and a network-initiated FSC scenario.
            6.1.1   MUE-initiated FSC scenario
            In the MUE-initiated FSC mode only the MUE controls the traffic routing for the associated multi-connections
            and applying policies for FSC rules.

            The MUE can request to move selected IP flows from an old access to a new access by sending one or more
            routing rules to the network. The routing rules specify the selected IP flows and the new access. The MUE
            determines the routing rules and provides them to the network. The network may either accept or reject the
            routing rules requested by the MUE, but it does not provide routing rules by itself.
            6.1.2   Network-initiated FSC scenario

            In the network-initiated FSC mode, the network controls the traffic routing within the multi-connections. The
            network determines the routing rules and provides them to the MUE. The MUE may either accept or reject
            the network's request for routing rules (e.g., based on the suitability of the access link conditions), but the
            MUE does not provide routing rules by itself.

            6.2     Requirements

            6.2.1   General requirements
            In the multi-connection environment, the MUE may transfer one or multiple IP sub-flows seamlessly when
            the MUE moves out of coverage and the connection is lost, or when there is network congestion. This clause
            identifies requirements in order to provide service continuity to the user and the application during service
            transfer:
            1)      Data forwarding mechanism: A data forwarding mechanism is required to keep data integrity.

            2)      Mobility control mechanism: A mobility control mechanism is required to minimize the time during
                    the flow transfer and maintain flow service continuity.
            3)      Flow sequence numbers: sub-flow sequence numbers need to be added to each sub-flow. A flow
                    sequence number is used for transmission control and data recovery at the receiving end.
            4)      The  multi-connection  policy  control  functional  entity  (MPC-FE)  should  support  specific  policy
                    decision algorithms to provide adaptive decision making, such as decomposed service transmission
                    adjustment and service separation decisions.





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