TCP-PCP: A Transport Control Protocol Based on the Prediction of ...

More documents

Recommendations

Info

Recv( ACK[i] ): CP[i] → CP[i − 1]; calculate CP[i]; CP[i]-CP[i − 1] →△CP ; if newACK then if ACK[i].CE=1 ecn-action() SS() or CA() else SS() or CA() //Same as Newreno endif; else then if △CP > 0 Rate<strong>Control</strong>() //Same as Westwood Retransmit() else Retransmit() endif; Fig. 2: Pseudo code of <strong>TCP</strong>-<strong>PCP</strong>’s sender receiving procedure Time t1 Time t2 Ack[ 7] ecnecho Ack[ 0] ecnecho Time t3 A 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 Time t3 B 0 1 0 0 0 1 1 1 Fig. 3: The first scenario current ACK is duplicate and △CP ≤ 0, <strong>TCP</strong>-<strong>PCP</strong> sender only retransmits the data packet. <strong>TCP</strong>-<strong>PCP</strong> modified sender’s behavior by △CP when there are packet losses. This is the important distinguishing feature of <strong>TCP</strong>-<strong>PCP</strong> with respect to other <strong>TCP</strong> variants. For example, the sender of <strong>TCP</strong> Westwood will trigger Rate<strong>Control</strong> without care about the situation of mid routers, and that of Jersey will decide whether to do Rate<strong>Control</strong> just by single ECN signal. Additionally, <strong>TCP</strong>-<strong>PCP</strong>’s sender estimates the eligible bandwidth based on ACK packets arriving interval and adjusts the ssthresh (slow star thresh) and cwnd appropriately. This method to do Rate<strong>Control</strong> procedure is the same as <strong>TCP</strong> Westwood, which can be described as follows. ssthresh =(BWE∗RT Tmin)/seg size; if(cwnd > ssthresh) cwnd = ssthresh; Like <strong>TCP</strong> Jersey, <strong>TCP</strong>-<strong>PCP</strong> also employs threshold marking method in ECN. Concretely, the router marks all the packets when the EWMA-averaged queue length exceeds a given threshold, which is set to 1/3 of the link buffer capacity in experiments. B. Analysis of <strong>TCP</strong>-<strong>PCP</strong> In this section, we give two scenarios to show how <strong>TCP</strong>- <strong>PCP</strong> works in hybrid networks. As shown in Fig 3, the CE lists at t1, t2 and t3 are given, where t2 is the time when the sender receives the first ACK packet after t1, and t3 is after t2. Att1, the CE list of the latest 8 ACK packets is 00011111. At t2, the sender Time t1 Time t2 Time t3 Time t4 A Time t4 B Ack[ 7] ecnecho Ack[ 0] ecnecho 0 0 0 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 1 1 Fig. 4: The second scenario receives a duplicate ACK in which CE=1. So the CE list of the latest 8 ACK packets is 10001111 at t2. In some protocols, for example, <strong>TCP</strong> Jersey, the sender will trigger congestion control. However, In <strong>TCP</strong>-<strong>PCP</strong>, calculating result of CP[1] = CP[2] = 0.4 means that probability of congestion occurred in time t2 is not increased. So <strong>TCP</strong>-<strong>PCP</strong> sender does not invoke Rate<strong>Control</strong> procedure at t2. At t3, if <strong>TCP</strong>-<strong>PCP</strong>’s sender receives a duplicate ACK in which CE=1 and gets CP[3] = 0.55. DuetoCP[3] >CP[2], <strong>TCP</strong>-<strong>PCP</strong>’s sender predicts that congestion would occur soon and triggers the congestion control mechanism at the moment. On the contrary, if <strong>TCP</strong>-<strong>PCP</strong>’s sender receives a duplicate ACK in which CE=0 and gets CP[3] = 0.35. Due to CP[3] CP[3]. On the contrary, as long as CP[4] is less than CP[3], <strong>TCP</strong>-<strong>PCP</strong>’s sender will not decrease the sending rate. It is obvious that in <strong>TCP</strong>-<strong>PCP</strong> protocol, even if the sender received duplicate ACKs caused by several errors, as long as the queue length does not exceed the threshold or the congestion probability does not increase, the sender will not decrease its sending rate. Contrarily, even if there is only one duplicate packet arrival, the sending rate might decline because of CP value being increased. As a whole, <strong>TCP</strong>-<strong>PCP</strong> is based on ECN mark. By deducing a congestion probability, <strong>TCP</strong>-<strong>PCP</strong> can protect <strong>TCP</strong> connection from short-term, recoverable, non-congestive packet losses, and enhance its performance in hybrid network eventually. IV. PERFORMANCE EVALUATION We have done the necessary code modification in NS2 [11] to simulate <strong>TCP</strong>-<strong>PCP</strong>. The modification includes overwriting 978-1-4244-2324-8/08/$25.00 © 2008 IEEE. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE "GLOBECOM" 2008 proceedings. 1 1
S 10Mbps 45ms BS 2Mbps 1ms Fig. 5: Network Topology 1 Fig. 6: Comparison of throughput on network topology 1 droptail, downloading Westwood [13] and Jersey [12], appending <strong>TCP</strong>-<strong>PCP</strong> and so on. A. Throughput analysis on topology 1 The simulation environment is the same with that used in Ref. [12]. As shown in Fig.5, the source connects to a base station via a 10 Mb/s wired link with 45 ms oneway delay. The base station is linked to the destination, a wireless mobile node, via a 2 Mb/s loss channel with 1 ms delay. A single <strong>TCP</strong> connection running a long-lived FTP application delivers data from the source to the destination. We run the simulation for <strong>TCP</strong>-<strong>PCP</strong>, Westwood, and Jersey respectively. In our experiments, the random link error rate at the wireless bottleneck link varies from 0.001 to 0.1, which creates by a simple union error model. The simulation time is 100 seconds. The throughput of different protocols are shown in Fig.6. Throughput of Westwood falls behind that of Jersey and <strong>TCP</strong>-<strong>PCP</strong> because Westwood handles corruption by estimate available bandwidth only. For link error rate smaller than 0.005, Jersey and <strong>TCP</strong>-<strong>PCP</strong> perform closely to each other. Beyond that point, <strong>TCP</strong>-<strong>PCP</strong> starts to outperform Jersey. Especially when the loss rate increases to 0.01, the throughput of <strong>TCP</strong>-<strong>PCP</strong> outperforms Jersey by 23% and Westwood by 50%. B. Throughput analysis on topology 2 Simulations of this section are based on the topology shown in Fig.7,which is the same as that used in Ref. [13]. As shown in Fig.7, one <strong>TCP</strong> flow is sent from R0 to R3, link R1-R2 emulates a long delay pipe of Internet, and the last hop is a wireless link with error model. Concretely, the bandwidth of access link is 100 Mbps with 3 ms delay, the bandwidth of wireless link is 10 Mbps with 3 ms delay. The bandwidth of bottleneck is 5 Mbps with 40 ms delay. The buffer is set to be 100 packets. The simulation lasts for 100 s. Fig.8 gives the throughput comparison of the three algorithms under different link. As shown in Fig.8, Jersey’s throughput is close to Westwood’s, which is different from D R0 100 Mbps 3 ms R1 5 Mbps 40 ms R2 10 Mbps 3 ms Fig. 7: Network topology 2 Fig. 8: Comparison of throughput on network topology 2 the simulation results in topology 1. The reason is that there is an obvious bottleneck in topology 2, which results in more congestion losses. It is observed that Jersey experiences performance degradation in the case that congestion losses and error losses coexist. It is clear that <strong>TCP</strong>-<strong>PCP</strong> can get higher throughput in this case. Especially, when the packet loss rate is 0.01, Jersey’s throughput is 1300Kbps and Westwood’s throughput is 1340Kbps, but <strong>TCP</strong>-<strong>PCP</strong> can get 1444Kbps throughput. Then we introduce exponential distributed ON/OFF flow in topology 2. Its sending rate is 5 Mbps, and there are 25 ms to be “on” state in 100 ms period. Throughput under such situation are shown in Table I. TABLE I: Comparison of throughput with ON/OFF flow in network topology 2 Loss rate: 0.001 Loss rate: 0.005 Loss rate: 0.01 <strong>Protocol</strong> <strong>TCP</strong> UDP <strong>TCP</strong> UDP <strong>TCP</strong> UDP (kbps) (kbps) (kbps) (kbps) (kbps) (kbps) Westwood 1694 936 1457 971 1346 970 Jersey 1437 1114 1393 1041 1359 1039 <strong>TCP</strong>-<strong>PCP</strong> 1679 994 1618 1039 1482 1055 As shown in Table I, the throughput of the three algorithms are decreasing with the increasing of loss rate. Westwood’s throughput decreases by 20% when link loss rate varies from 0.001 to 0.01, but <strong>TCP</strong>-<strong>PCP</strong>’s throughput only decreases by 11%. Moreover, the total throughput of <strong>TCP</strong>-<strong>PCP</strong> is the highest in the three algorithms. It is anticipated that <strong>TCP</strong>-<strong>PCP</strong> can cope with error losses better than the other <strong>TCP</strong> variants by using congestion probability. C. Fairness analysis Fairness is an important metric for evaluating <strong>TCP</strong> protocol. Multiple connections of the same <strong>TCP</strong> scheme must cooperate fairly. Network topology 3 shown in Fig.9 is used to test this 978-1-4244-2324-8/08/$25.00 © 2008 IEEE. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE "GLOBECOM" 2008 proceedings. R3
Page 1 and 2: TCP-PCP</s
Page 3: ECN feedback. On the contrary, if t

TCP-PCP: A Transport Control Protocol Based on the Prediction of ...

Create successful ePaper yourself

Delete template?

Save as template?