# Enhanced Multistream Fast TCP: Rapid Bandwidth Utilization after Fast-Recovery Phase
## 5 Results and Discussion
### Convergence Time  
Figure 6 shows the congestion window variation of Fast TCP, MFast TCP, EMFast TCP, TCP New Reno, and SCTP during the simulation period. SCTP and TCP New Reno due to their loss-based congestion control algorithm drop multiple packets during the transmission, whereas ast TCP, MFast TCP, and EMFast TCP maintain their congestion window during the simulation period. The size of their congestion window is reduced due to the packet loss. This packet loss is introduced by the error model. The congestion windows of SCTP and TCP New Reno fluctuate during the simulation period. This fluctuation is due to the loss-based congestion control algorithm. Fast TCP, MFast TCP, and EMFast  
Figure 6: Congestion window graph, without any competing flow during the simulation period. TCP maintain their congestion windows because of the delay-based congestion control algorithm. The protocols reduce the congestion window at the time packet of loss. Fast TCP and MFast TCP showed exactly the same behavior. Therefore, the lines in the graph representing these protocols overlap each other. In the absence of competing flows, the protocols consume all available bandwidth of the network and provide maximum throughput as allowed by their algorithms. Four flows are introduced with each individual flow of the protocol under study to further observe the behavior of the protocols in the presence of competing flows. The protocols accommodate the additional flows and adjust their own congestion windows accordingly. Fast TCP, MFast TCP, and EMFast TCP are sensitive to network delay. Therefore, they adjust their congestion windows considering the network state. These protocols are not so greedy toward network queues; therefore, they easily accommodate new data flows by adjusting their data transfer rate. This phenomenon can be seen in Figure 7.  
In order to get a closer view, a portion of the congestion window graph from Figures 6 and 7 is extracted in Figures 8 and 9, respectively. Figure 8: Congestion window graph during the interval of packet drop and after fast-recovery stage (without any competitive flow). Figure 7: Congestion window graph, with four competing flows during the simulation period. The figures show the portion of the congestion window graphs, to highlight the interval in which the packet is lost and how the protocols consume the available bandwidth of network link after the fast recovery. We overlapped the congestion window graphs (during the period of packet loss) of all the protocols within a same time interval for better analysis. Figures 8 and 9 show that EMFast TCP consumes the available network link after the fast recovery more rapidly than Fast TCP, MFast TCP, TCP New Reno, and SCTP. EMFast TCP provides better performance compared to the rest of the protocols under study in the presence or absence of competing flows. It consumes the available network bandwidth in a minimum convergence time compare to rest of the protocols. EMFast TCP consumed the available network link in 9 RTT, as shown in Figure 10; whereas MFast TCP and Fast TCP were performing the same task in 17 RTTs as shown in Figure 4.  
Convergence time (T) is the time taken by the flow to gain a fair share of the available bandwidth of network link. Our focus is on the convergence time after the fast-recovery phase. Convergence time is calculated by using Equation (3). Where T\({}_{\text{PD}}\) represents the time of receiving the third duplicate  
Figure 10: Inter-packet delay jitter during and after fast-retransmit and -recovery phases of Enhanced Multistream Fast Transmission Control Protocol (EMFast TCP). Figure 9: Congestion window graph during the interval of packet drop and after fast-recovery stage (with four competing flows). acknowledgment and T\({}_{\text{LF}}\) represents the time when the protocol regains the fair share of the available bandwidth of network link after fast-recovery phase.