# Enhanced Multistream Fast TCP: Rapid Bandwidth Utilization after Fast-Recovery Phase
## 1 Introduction  
Most of the internet applications are being deployed on long-range, high-speed, and high-bandwidth networks. Fast-paced data transfer over high-speed communication systems is the primary issue raised in long-range and high-bandwidth networks. Transmission Control Protocol (TCP) [1] transmits enormous data traffic globally [2]. Although, TCP provides reliable data transmission over the network at its inception, it was not capable of handling network blockage. [PERSON] proposed a congestion management scheme in 1988 [3] to overcome this limitation. Researchers improved the [PERSON]'s congestion management scheme through several enhancements [4; 5; 6; 7; 8; 9], but still, it can be further improved. TCP demonstrated exceptional performance over internet with the increase in size, speed, load, and connectivity. But loss-based congestion control schemes degrade TCP's performance in high-bandwidth-delay product networks. Delay-based congestion control schemes solved the limitation of loss-based congestion control schemes in high-bandwidth-delay product (BDP) networks [10]. TCP Vegas [11] and Fast TCP [12; 10] are examples of delay-based transport protocols. All TCP variants serialize the applications' independent messages over a single byte stream for data transmission across the network. This phenomenon becomes the reason of the head-of-line blocking [13]. Multistream Fast TCP (MFast TCP) provides a separate stream for each independent message of the application and interleaves each stream's segments over a single TCP connection to fix the head-of-line blocking problem [14]. This procedure alleviates the head-of-line blocking but does not affect the end-to-end throughput which can be increased through optimization of the congestion management scheme. Congestion management schemes [15] maintain smooth data flow, but do not provide assurance that data segments will not be lost during the data transmission across the network. The segment loss degrades TCP's performance. Therefore, the research community is still improving TCP congestion control schemes by focusing on its four intertwined phases that are: slow start phase, congestion avoidance phase, and fast-retransmit and fast-recovery phases [8; 9; 16]. Congestion control schemes increase the size of the congestion window (cwnd) after fast-recovery mode. This change should neither be too slow nor be too fast. In case of slow change in the congestion window, TCP does not use the available bandwidth efficiently and the fast change may create network congestion. Different TCP versions use different techniques to set the congestion window size after fast-recovery mode. The precise change as per the availability of bandwidth in the congestion window size after fast-recovery mode can increase the end-to-end throughput. MFast TCP and Fast TCP use their conventional approach to adjust their congestion windows. The approach is to re-compute the congestion window size on each round trip time (RTT) during congestion avoidance and also after fast-recovery mode. This approach takes significant time to consume the vacant network bandwidth after fast-recovery mode. This study proposes an algorithm to adjust the congestion window on each acknowledgment (ACK) after the fast-recovery phase until it consumes the available space of the network link. The algorithm performs the task in significantly less time. Consequently, the performance of MFast TCP is improved due to the decrease in convergence time after fast recovery and increase in end-to-end throughput and goodput. Simulation results showed that Enhanced Multistream Fast TCP (EMFast TCP) after fast recovery consumes available bandwidth in 29% less time compared to Fast TCP and MFast TCP and 52% less time compared to a Stream Control Transmission Protocol (SCTP), which follows additive-increase multiplicative-decrease (AIMD) behavior. The remaining research paper is arranged as follows. In Section 2, we discuss the background for this research study.