CPSC 538A1 Dynamic Behavior of Slowly- Responsive Congestion Control Algorithms Deepak Bansal, Hari BalaKrishna, Sally Floyd and Scott Shenker Presented By : Dinu (P. Subbaiah)

CPSC 538A2 Congestion Control in TCP AIMD- Additive Increase and Multiplicative Decrease 1% packet loss rate may cause 50-75% decrease in throughput.

CPSC 538A3 TCP Compatible Paradigm for congestion control Characteristics of TCP –Roughly equal bandwidth for similarly situated (same RTT) flows with same packet size –Bandwidth is proportional to 1/sqrt(p), p is packet loss rate Compatibility –Another protocol should have the same characteristics, in the presence of a constant loss rate

CPSC 538A4 TCP Compatible Algorithms

CPSC 538A5 Binomial Binomial algorithms – nonlinear generalization of AIMD Upon congestion : W->W-b(W^l) no congestion : W->W+a/(w^k) IIAD: Inverse Increase-Additive Decrease(k = 1, l = 0) SQRT : (k = l = 0.5) a and b are increase and decrease parameters of the algorithm.

CPSC 538A6 TEAR: TCP Emulation At Receivers Instead of reporting congestion signals, process them immediately at receivers. The sender sets its transmission rate to R Sender Emulate TCP window adjustment Receiver Report rate R.

CPSC 538A7 TFRC: TCP Friendly Rate Control The receiver measures the loss event rate and feeds this information back to the sender. The sender also uses these feedback messages to measure the RTT. The loss event rate and RTT are then fed into TFRC's throughput equation, giving the acceptable transmit rate. The sender then adjusts its transmit rate to match the calculated rate.

CPSC 538A8 Dynamic Scenario The congestion Control algorithms are defined and tested in a static scenario. This paper tests the behavior of slow responsive algorithms in a dynamic environment by changing the bottleneck bandwidth. The goal is to evaluate any potential dangers in the deployment of slowCC.

CPSC 538A9 Tests and Results Abrupt reduction in available bandwidth. High packet loss rates can be reduced by packet conservation

CPSC 538A10 Tests and Results Long Term Fairness. –Note the relative fairness between TCP and TFRC

CPSC 538A11 Tests and Results Loss in throughput with sudden increase in Bandwidth f(k) is average link utilization where k is number of RTTs. Tested for bandwidth of 10 Mbps and a RTT of 50 ms.

CPSC 538A12 Tests and Results Smoothness in bursty loss patterns. TFRC Smoothness: Largest ratio between two consecutive sending rates

CPSC 538A13 Conclusion Safe for deployment –SlowCC mechanisms lose bandwidth, relative to TCP in dynamic environments. –SlowCC mechanisms (TFRC) achieve smooth data rates even in bursty loss rates. Significant contribution –Incorporating a Self Clocking mechanism based on packet preservation in slowCC algorithms prevent overload or persistent loss rates.