Page 320 - 5G Basics - Core Network Aspects

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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