Page 296 - 5G Basics - Core Network Aspects

1 Core network aspects

5 Conventions

In this Recommendation:
The keyword "is required to" indicate a requirement which must be strictly followed and from which no
deviation is permitted if conformance to this document is to be claimed.
The keyword "is prohibited from" indicate a requirement which must be strictly followed and from which no
deviation is permitted if conformance to this document is to be claimed.
The keyword "is recommended" indicate a requirement which is recommended but which is not absolutely
required. Thus this requirement is not present to claim conformance.
The keyword "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 keyword "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

The general scenarios in [b-ITU-T Y Suppl.9] are required to be taken into consideration in multi-path
transmission control. Typical scenarios are derived based on scenario C of [b-ITU T Y Suppl.9] where a multi-
connection user equipment (MUE) can establish multiple connections to heterogeneous access networks
controlled by different access control functions, but the same service control function for a specific service.
According to the relationship among the multiple service flows, these scenarios can be further classified into:

1) Scenario I
In scenario I, an MUE establishes multiple connections to heterogeneous access networks, for
example, in a video conference: voice is transmitted by 2G, 3G or long term evolution (LTE) to assure
real-time service, and video is transmitted by wireless local area network (WLAN) which has higher
bandwidth and may be cost efficient for a large number of network flows. In the transport layer, the
flows can be transported in multiple paths.
In this scenario, the multiple service data flows may have a native coupled relationship, but some
mechanisms are required to guarantee the aggregation of the service. Cache and synchronization
are the necessary mechanisms for service aggregation.
2) Scenario II
In scenario II, an MUE is required for access to heterogeneous access networks simultaneously, such
as 2G, 3G or WLAN. For example, to achieve greater bandwidth when downloading a multimedia
file with a large volume of data, the MUE chooses a WLAN connection for download. When time is
limited, to achieve a higher transmission rate, the multimedia file will be split and transferred to
both the WLAN and 3G paths in the transport layer.
In this scenario, the multiple data flows are split and aggregation is simply based on the service
separation policy and data scheduling mechanism.

6.2 Requirements
In [ITU-T Y.2251] IP flows are identified and bound to the proper connections. Because the connection status
and service flows change dynamically, some connections may become overloaded and the lost data packets
will be retransmitted frequently, thus reducing data transmission efficiency. Occasionally, data transmission
through a single path cannot meet a user's service requirements such as real-time demand for large amounts

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