Transport Assistants to Enhance TCP Performance: Analysis of the Packet Delivery Delay

As of today, TCP remains the de-facto transport protocol in the Internet. However, TCP may incur high delays, especially when retransmitting lost packets as they have to be retransmitted only by the source and after a timeout that is roughly equal to a round trip time. To reduce such delay, recent work [1]-[3] proposed to deploy a special network function, called Transport Assistant (TA), that is able to detect and retransmit lost TCP packets from inside the network rather than the source, and thereby, reduces retransmission delays. Unfortunately, there is no study so far on the impact of the placement of the TA on its performance benefits in terms of packet delivery delayIn this paper, we focus on the TA placement problem. We discuss the trade-offs and parameters to be considered to select the best placement for the TA. We mathematically model the TCP packet delivery delay, i.e., the time needed to deliver TCP packets when the TA is deployed, using different parameters like the location of the TA, the loss probabilities and the propagation delays of the network links. Thanks to this model, we study the impact of these parameters on the performance and efficiency of the TA.