This paper represents an accurate delay-based congestion avoidance (ADCA) algorithm. It eliminates the void components of round-trip time (RTT), which is used as main parameter in delay-based congestion avoidance (DCA) algorithm. ADCA improves TCP throughput and efficiency comparing to the normal DCA algorithm, such as TCP Vegas. Simulations show that ADCA detects network circumstance more exactly and enhances TCP efficiency obviously.
IntroductionInternet adopts TCP to deal with the network congestions. TCP starts timer when sends a packet, and waits for the respondent ACK. Once the ACK has not come before the timer ends, TCP considers the network congested and the sending packet lost, and accordingly reduces the congestion window and sending rate to eliminate the network congestion.Internet adopts TCP Reno [1][2] at present. Although TCP Reno can deal with congestions effectively, it manages the traffic conservatively and limits the throughput of the network.To increase the capability of TCP, researchers improve the algorithms in two ways. The first one is to fast recover congestion window size once the ACK timeout occurred. The other one is to detect the network situation in congestion avoid phase, and reduce the congestion window size actively before the network congestion would occur.The researches in first way have already achieved many excellent results [3][4][5][6][7][8][9]. They discussed the throughput-ineffective problems in slow start phase and represented many constructive solutions in several different application situations, such as in wireless network [6][7], in high-speed network torrent congestion [8], and in web application [9].The researches in the second way focus on DCA algorithms. TCP Vegas [10] and Dual [11] are the typical DCA algorithms. DCA detects RTT of the packet and adjusts congestion window size based on the change of the RTT to avoid network congestion in advance. The application facts show that DCA improves network throughput obviously. However, in some certain situations, there is only 7%-18% packet loss related to the increase of the RTT and it would decrease TCP throughput 7%-58% if using RTT to predict and avoid congestions beforehand [12].This paper represents an accurate DCA algorithm, which can eliminate congestion irrelative RTT component influences, predict network congestion accurately and improve the capability of TCP.
