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IADIS International Conference WWW/Internet 20102.2 Compound TCPMicrosoft has proposed a new variant of TCP called Compound TCP (CTCP). CTCP is part of WindowsVista, Windows 7 and Windows 2008 Server and modifies standard TCP's loss-based congestion avoidancealgorithm, incorporating a scalable delay-based component (Tan et al., 2006). To do so, a new state variableis introduced in current TCP Control Block (TCB), namely dwnd (Delay Window), which controls thedelay-based component in CTCP. The conventional congestion window ( cwnd ) remains untouched, whichcontrols the loss-based component. Thus, the CTCP sending window now is controlled byboth cwnd and dwnd . Specifically, the TCP sending window ( wnd ) is now calculated as follows:1cwnd = cwnd +cwnd + dwnd( cwnd dwnd awnd )(1)wnd = min + ,(2)CTCP increments the congestion window upon receiving an ACK, using Equation 1. Using Equation 2,CTCP computes the transmission window ( wnd ) based on the Delay Window ( dwnd ), the congestionwindow ( cwnd ), and the reported receiver window ( awnd ).2.3 CUBICCUBIC is a modification to the congestion control mechanism of standard TCP, in particular, to the windowincrease function of standard TCP senders, to remedy the low utilization problem of TCP in fast longdistancenetworks. It uses a cubic increase function in terms of the elapsed time from the last congestionevent. Unlike most TCP variants use a convex increase function after a packet loss event, CUBIC uses boththe concave and convex profiles of a cubic function for window growth. After a window reduction followinga loss event, CUBIC records the window size where it got the loss event asW_ max and performs amultiplicative decrease of congestion window, and following the standard fast recovery and retransmit ofTCP. Once it enters congestion avoidance after fast recovery, it starts to increase the transmission windowusing the concave profile of the cubic function. The cubic function is set to have its plateau at W _ max , sothat the concave growth continues until the window size becomes W _ max . After that, the cubic functionturns into a convex profile and the convex window growth begins. This style of window adjustment(concave and then convex) improves protocol and network stability while maintaining high networkutilization. This is because the window size remains almost constant, forming a plateauaroundW_ max where network utilization is deemed highest. Under steady state, most CUBIC window sizesamples are close toW_ max ; thus promoting high network utilization and protocol stability. The TCPsending window (W ) is now calculated as shown in Equation 3, where C is a CUBIC parameter, t is theelapsed time from the last window reduction, and K is the time period that the above function takes toincreaseW toW_ max when there is no further loss event and it is calculated by Equation 4, where β is themultiplication decrease factor:W ( t)= C(t − K)³+ W _ max(3)3W _ max βK = (4)C3. COMPARING DCCP, CTCP, AND CUBIC WITH VOIP TRAFFICWe perform discrete event simulations on Network Simulator 2 (Fall & Varadhan, 2007) to carryperformance comparisons of the following transport protocols: (i) DCCP CCID2, (ii) DCCP CCID3, (iii)CTCP, and (iv) CUBIC using VoIP traffic patterns. Additionally, we include CBR traffic in the comparison213