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1                                                Core network aspects


            1       Scope
            This  Recommendation  describes  the  flow-based  service  continuity  mechanism  in  a  multi-connection
            environment. This Recommendation also describes scenarios, requirements, information flow mechanisms
            and security of flow-based service continuity in a multi-connection environment. For information on other
            aspects outside of the scope of this Recommendation, such as security and charging for flow-based service
            continuity in a multi-connection environment, see [ITU-T Y.2251].


            2       References

            The following ITU-T Recommendations and other references contain provisions which, through reference in
            this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated
            were valid. All Recommendations and other references are subject to revision; users of this Recommendation
            are  therefore  encouraged  to  investigate  the  possibility  of  applying  the  most  recent  edition  of  the
            Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is
            regularly published. The reference to a document within this Recommendation does not give it, as a stand-
            alone document, the status of a Recommendation.
            [ITU-T Y.2027]         Recommendation ITU-T Y.2027 (2012), Functional architecture of multi-connection.
            [ITU-T Y.2028]         Recommendation  ITU-T  Y.2028  (2015),  Intelligent  access  selection  in
                                   multi-connection.

            [ITU-T Y.2029]         Recommendation  ITU-T  Y.2029  (2015),  A  multi-path  transmission  control  in
                                   multi-connection.

            [ITU-T Y.2251]         Recommendation ITU-T Y.2251 (2011), Multi-connection requirements.


            3       Definitions

            3.1     Terms defined elsewhere
            This Recommendation uses the following terms defined elsewhere:

            3.1.1   connection  [b-ITU-T  X.200]:  A  connection  is  an  association  established  for  the  transfer  of  data
            between two or more peer-(N)-entities. This association binds the peer-(N)-entities together with the (N-1)-
            entities in the next lower layer.
            3.1.2   multi-connection [b-ITU-T Y.2252]: The collection of several connections between two or more
            peer-(N)-entities  simultaneously.  At  least  one  of  the  connections  is  associated  with  a  physical  layer
            connectivity different from the rest of the connections. All connections are coordinated with each other to
            provide service to higher layer entities.
            3.1.3   multi-connection user equipment (MUE) [ITU-T Y.2027]: A user equipment which can support two
            or more network connections simultaneously under the control of a network enhanced for multi-connection
            capability.

            3.1.4   service continuity [b-ITU-T Q.1706]: The ability for a moving object to maintain ongoing service
            including over current states, such as user's network environment and session for a service.

            3.1.5   service  transfer  [ITU-T  Y.2251]:  Act  of  moving,  one  or  more  services  or  service  components
            belonging to a single multi-connection UE, from one access network associated with one interface of the
            multi-connection UE to another access network(s) associated with other interface(s) of the multi-connection
            UE.
            3.1.6   IP flow [b-RFC 3917]: A flow is defined as a set of IP packets passing an observation point in the
            network during a certain time interval. All packets belonging to a particular flow have a set of common
            properties. Each property is defined as the result of applying a function to the values of:





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