The increasing performance requirements of today's Internet applications demand a reliable mechanism to transfer data. Many applications rely on the Transmission Control Protocol (TCP) as the transport protocol, due to its ability to adapt to properties of the network and to be robust in the face of many kinds of failures. However, improving the performance of applications that rely on TCP has been limited by the closed nature of legacy switches, which do not provide accurate visibility of network events. With the emergence of P4 programmable devices, developers can rapidly implement and test customized solutions that use fine-grained telemetry, provide sub round-trip time feedback to end devices to enhance congestion control, precisely isolate traffic to offer better Quality of Service (QoS), quickly detect congestion and re-route traffic via alternate paths, and optimize server resources by offloading protocols.This paper first surveys recent works on P4-programmable devices, focusing on schemes aimed at enhancing TCP performance. It provides a taxonomy classifying the aspects that impact TCP's behavior, such as congestion control, Active Queue Management (AQM) algorithms, TCP offloading, and network measurement schemes. Then, it compares the P4-based solutions, and contrasts those solutions with legacy implementations. Lastly, the paper presents challenges and future trends.
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