Page 301 - 5G Basics - Core Network Aspects

Core network aspects 1

2) Select single-path transmission

If only a single specific path can meet the service requirements, it is unnecessary to split the service
among several paths. In this case, although using multi-path to transfer the service packets can
possibly improve throughput or accelerate the transmission speed, it may lead to operational
complexity, high energy consumption or low resource utilization. Considering the processing
overhead, if only a single path can meet the requirements of the service, parallel transmission is
unnecessary.
A multi-path transmission can also be used for concurrent multi-service transmissions. For two
concurrent download services, belonging to the same application or different applications, the
traffic of each service can be transferred through different paths and do not have to be split. At the
same time, the paths’ energy consumption cannot be ignored for longer battery life. For energy
savings, low energy consumption path(s) would be selected with higher priority.

7.3.2.2 Path management mechanism
A multi-path transmission control is required to have the abilities to automatically adjust the paths according
to the current available paths' abilities and services requirements. For example, a path(s) is required to be
added or deleted based on the received reachability state of destination transport addresses and service
requirements. For energy savings, paths in multi-path transmission are required to be properly suspended or
activated. At the same time, the mechanism of path failure detection and recovery is also essential.
In multi-path transmission, the following mechanisms are required to be considered:
1) Path update
In the communication process, path state is required to be updated in real time. There are many
factors that can lead to path addition or deletion, such as the reachability state of destination
transport addresses, service requirements and the possibility of unused path(s) with better
performance than the current path(s) in use.

2) Path failure detection and recovery
Network failure may lead to path interruption or unavailability in a multi-path transmission. Hence,
the mechanism of path failure detection and recovery is necessary in a multi-path transmission
control. For instance, SCTP uses heartbeat messages to monitor the reachability of peer addresses,
and judges whether the path has failed or not. The MPTCP sender will declare a path failed after a
predefined upper bound on retransmissions is reached, or on the receipt of an ICMP error. If the
predefined time installed for the failure path is exceeded, the failed path will be deleted. When a
path has failed, the sub-transmission traffic transmitted on the failed path should be transferred to
other paths.
3) Path suspending and path activation
If fewer paths meet the requirements of the services, part of the available paths can be kept in an
idle state. In this case, a path suspending mechanism can save energy, since it can reduce the
number of the transmission paths used simultaneously. When the used path(s) cannot satisfy the
requirements of the current service, a path activation mechanism to increase the available path(s)
is required.
7.3.3 Congestion control and traffic transmission adjustment mechanism

7.3.3.1 Load balance mechanism with fairness consideration
In multi-path transmission control, MPT-enhanced MUE attaches to the Internet through several interfaces
simultaneously for higher aggregated bandwidth, while MPT-enhanced MUE and MUE/UE share the network
resources. Multi-path transmission improves the service experience, but it is required that the service using
only a single-path for transmission dose not compromise the performance. The multi-path transmission is
required to be fair to the existing single-path transmission.
To ensure fairness to a single-path transmission, multi-path transmission control is required to determine
which sub-transmission flows share a point of congestion and which sub-transmission flows do not. Sub-

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