Abstract
In today’s data networks, the main protocol used to ensure reliable communications is the transmission control protocol (TCP). The TCP performance is largely determined by the used congestion control (CC) algorithm. TCP CC algorithms have evolved over the past three decades and a large number of CC algorithm variations have been developed to accommodate various network environments. The fifth-generation (5G) mobile network presents a new challenge for the implementation of the TCP CC mechanism, since networks will operate in environments with huge user device density and vast traffic flows. In contrast to the pre-5G networks that operate in the sub-6 GHz bands, the implementation of TCP CC algorithms in 5G mmWave communications will be further compromised with high variations in channel quality and susceptibility to blockages due to high penetration losses and atmospheric absorptions. These challenges will be particularly present in environments such as sensor networks and Internet of Things (IoT) applications. To alleviate these challenges, this paper provides an overview of the most popular single-flow and multy-flow TCP CC algorithms used in pre-5G networks. The related work on the previous examinations of TCP CC algorithm performance in 5G networks is further presented. A possible implementation of TCP CC algorithms is thoroughly analysed with respect to the specificities of 5G networks, such as the usage of high frequencies in the mmWave spectrum, the frequent horizontal and vertical handovers, the implementation of the 5G core network, the usage of beamforming and data buffering, the exploitation of edge computing, and the constantly transmitted always-on signals. Moreover, the capabilities of machine learning technique implementations for the improvement of TCPs CC performance have been presented last, with a discussion on future research opportunities that can contribute to the improvement of TCP CC implementation in 5G networks. This survey paper can serve as the basis for the development of novel solutions that will ensure the reliable implementation of TCP CC in different usage scenarios of 5G networks.
Highlights
For every new generation of mobile network, the demand for new services and use cases increases
MP-transmission control protocol (TCP) has been introduced as a TCP variant for multipath data communication and Quick user datagram protocol (UDP) Internet Connection (QUIC) is a UDP-based TCP alternative initially developed for hypertext transfer protocol (HTTP) traffic (Figure 4)
Regardless of the method used for congestion detection, from the analysis of the presented works, we have addressed the three main challenges to TCP congestion control (CC) when operating in the mmWave mobile network:
Summary
Congestion avoidance and a fast retransmit mechanism. Introduced fast recovery mechanism. The algorithm uses the modified congestion avoidance mechanism of of TCP Vegas [38] Another modification of TCP Vegas has been developed, TCP Vegas to address issues such as fairness against TCP New Reno flows, rerouting iscalled TCP Vegas-A (Figure 4). The algorithm uses the modified congestion avoidance sues, bias against high bandwidth connections and fairness issues between old and new mechanism of TCP Vegas to address issues such as fairness against TCP New Reno flows, connections in wired and satellite networks [39]. If the number of buffered packets is far from the defined scaling parameter, the FAST TCP algorithm increases or decreases the cwnd size, effectively utilising the network capacity. On the other hand, when the number of buffered packets reaches the target scaling parameter, the FAST TCP algorithm adjusts its cwnd by a small amount, ensuring the networks’ stability [47]
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