Page 298 - 5G Basics - Core Network Aspects

1 Core network aspects

4) Energy efficiency and management

In the transport layer, congestion control and traffic transmission adjustment are related to the
issue of energy consumption. According to the network performance and traffic load information
(such as the Cwnd) of each path, policies to reduce energy consumption are required to be
considered as well as in multi-path transmission control. If it is unnecessary to maintain too many
paths, sub-transmission flows can be adjusted or transferred to fewer paths for energy savings, and
the idle connections can be released.
For example, if a user listens to online music through 3G access and browses the web using WLAN,
the audio stream can be adjusted to go through WLAN, and the 3G connection can be released to
save energy.

7 A multi-path transmission mechanism

7.1 Overview

As described in [ITU-T Y.2027], an MUE can maintain more than one access network connection
simultaneously. A multi-path transmission enhanced MUE (MPT-enhanced MUE) can distribute the service
flows into different connections, based on the service requirements and the network conditions. The MPT-
enhanced MUE may also divide a service flow into several sub-transmission flows and transmit them in
different paths for higher aggregated bandwidth if necessary. Different IP addresses are configured by each
access network, thus there exists one or several transmission paths simultaneously over a terminal device.

In order to avoid or relieve congestion in the multi-path transmission, specific congestion control
mechanisms are required. Multi-path transmission control is required to take all paths' performance into
account when a service flow is transmitted through several paths simultaneously in the NGN network. In
addition, parallel transmissions through multiple paths removes the restriction of a single network not
meeting the requirements of the high-bandwidth service. The packets of a service transmitted through
multiple paths simultaneously may lead to out-of-order packets at the receiving end; packet scheduling is
imperative for in-order delivery. At the same time, multi-path transmission control is required to take energy
efficiency into consideration.
In the NGN network, users within the paths acting as direct initiators of the paths can obtain information
about the end-to-end transmissions of current paths. The network can obtain and control the overall
performance of the related accesses. Multi-path transmission control can be initiated by either the user side
or the network side.

Connection information, access network performance parameters and policies are required to be sent to the
related functional entity for performing multi-path transmission control. In order to complete the multi-path
transmission control, the following enhancements are required to be supported in the multi-connection
architecture:

1) MUE can optionally be enhanced for the multi-path transmission support, such as comprehensive
path assessment, path status maintenance, adjustment decision and implementation (e.g.,
retransmission path selection, transmission rate adjustment, service separation/aggregation and
sub-transmission flow mobility);
2) Multi-connection policy control function entity (MPC-FE) is required to support a specific multi-path
transmission policy decision algorithm to provide adaptive decisions, such as decomposed service
transmission adjustment and service separation decision. The MPC-FE is required to provide the
information and adjustment policies of the end hosts to the multi-path transmission proxy (i.e.,
service control function (SCF));
3) SCF is required to be enhanced as a multi-path transmission proxy to transparently provide multi-
path capability to multi-path unaware hosts, such as the multi-path transmission traffic
separation/aggregation and path status maintenance. It may interact with the MPT-enhanced MUE
by the multi-path transmissions and interact with the MUE/user equipment (UE) by single-path
transmissions when necessary.

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