Page 303 - 5G Basics - Core Network Aspects
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Core network aspects                                            1


            If all available paths are uncongested, the retransmission traffic can be scheduled through the reserved path
            (e.g., RTX-SAME) or chose one retransmission path randomly (e.g., RTX-ASAP).

            If the path is in a state of congestion, some  indicators, such as the RTO occurs, are used to trigger the
            retransmission scheme. In multi-path transmission control, the following retransmission aspects are required
            to be considered:
            –       In  order  to  ensure  the  timely  delivery  of  retransmitted  packets,  retransmitted  traffic  from  the
                    sending end can be scheduled through a path that has Cwnd space available at that time (e.g., RTX-
                    ASAP), or a path that has the largest Cwnd (e.g., RTX-CWND). In order to guarantee the reliable
                    delivery of retransmitted packets, the minimum packet loss or retransmission path is required to be
                    selected so that the retransmission traffic can be scheduled through the paths with the lowest PLR
                    (e.g., RTX-LOSSRATE) or the largest SSThresh (e.g., RTX-SSTHRESH).

            –       The receiving end can choose the shortest RTT path or the path with the highest reliability for packet
                    acknowledgement messages transmission. This may reduce the sending side's requirements  for
                    buffering, and prevent unnecessary retransmission from a different path.


            8       Capability requirements

            8.1     MPT-enhanced MUE requirements in the sending side
            In order to highlight the benefits of multi-path transmission, the following capabilities are required for the
            MPT-enhanced MUE at the sending end:
            1)      identify and maintain all the paths' information, e.g., path failure detection;
            2)      provide service separation for bandwidth aggregation, if necessary;

            3)      properly select and timely adjust the path(s) for service transmission in a multi-path transmission
                    control;
            4)      analyse the path performance parameters, e.g., PLR, RTT, SSThresh and the available bandwidth;

            5)      adjust the congestion control parameters of each path, e.g., Cwnd and RTO;
            6)      adopt an appropriate manner to improve the network transmission efficiency, e.g., network coding
                    technology or retransmission policy;
            7)      address verification before adding a new path;
            8)      maintain the mapping information between a service and its path(s);
            9)      provide path failure detection and path recovery;
            10)     provide packet delivery mechanisms for service separation.

            8.2     MPT-enhanced MUE requirements in the receiving side

            In order to highlight the benefits of the multi-path transmission, the following capabilities are required for
            the MPT-enhanced MUE in the receiving end:

            1)      analyse the path performance parameters, e.g., PLR, RTT;
            2)      select an appropriate path for ACK transmission;
            3)      provide packet caching and reordering for the separated service and delivery to the upper layer;
            4)      provide network decoding and lost packet recovery if possible;

            5)      ensure data confidentiality and integrity verification;
            6)      maintain the mapping information between a service and its path(s);
            7)      provide packet delivery mechanisms for service aggregation.








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