Improving TCP Performance via Enhanced PDCP Reordering in 5G and Beyond Networks

Radio Access Network (RAN) data plane systems in 5G are expected to support multiple user traffic flows demanding high throughput and low latency. With increased usage of available services and applications, a single user will tend to have multiple streams of Internet Protocol (IP) flow and applications supported over a single Protocol Data Unit (PDU) session. Applications of similar Quality of Service (QoS) requirements get mapped to a single Data Radio Bearer (DRB) over the RAN. Several studies have found that over 90 % of total Internet traffic is Transmission Control Protocol (TCP) traffic. Single DRB can have multiple TCP flows in it. New Radio (NR) Packet Data Convergence Protocol (PDCP) layer delivers packets in-order to the upper layers for the configured DRB. When out-of-order packets are received, the reordering timer is triggered at PDCP and packets will wait in the reordering window until missing packets are received or the reorder timer expires. So a packet loss in one flow in the DRB can affect all the flows in the DRB and can lead to increased latency and reduced throughput in other TCP flows without loss. We propose a novel method to segregate TCP flows at a DRB in PDCP and handle data loss specific to each flow, so that flows without data loss are not impacted. When tested with multiple TCP flows under diverse loss conditions, the proposed solution yields a 4–9 % reduction in average latency and round-trip time (RTT) while boosting throughput when compared to NR PDCP.