1. jinho Promoting the Use of End-To-End Congestion Control in the Internet IEEE/ACM Transaction on Networking Vol.7 No.4 August 1999 Sally Floyd and Kevin Fall

2. jinho Outline Introduction Problems Approaches Comparison between FCFS and the approach in this paper

3. jinho Abstract Potentially negative impacts of an increasing deployment of non-congestion- controlled best-effort traffic on the Internet These impacts range from extreme unfairness against competing TCP traffic to the potential for congestion collapse.

4. jinho Introduction Promote the end-to-end congestion control: –Router mechanisms –Restrict the bandwidth of selected high- bandwidth best-effort flows Approaches: –identify a high bnadwidth flow as Unresponsive –Not TCP-friendly –Using disproportionate bandwidth

5. jinho Possible Approaches 1.Involves the deployment of packet scheduling disciplines in routers that isolate each flow(per- flow scheduling mechanisms) 2.(in this paper)for routers to support the continued use of end-to-end congestion control to share scarce bandwidth 3.Rely on financial incentives or pricing mechanisms to control sharing

6. jinho TCP UDP Definition: GoodPut: A Flow as the bandwidth delivered to the recerver,excluding duplicate packets. Unresponsive flows: flows that do not use end-to-end congestion control,and do not reduce their load on the network when subjected to packet drops.

7. jinho 25% WRR:each flow assigned an equal weight in units of bytes/s

8. jinho Danger of Congestion Collapse Classical congestion collapse –Largely due to TCP connection unnecessarily retransmitting packets –Corrected by the timer improvements and congestion-control mechanism in modern implementations of TCP

9. jinho (cont’d) Congestion collapse from undelivered packets –Bandwidth is wasted by delivering packet through the network that are dropped before reaching their ultimate destination –(different from classical)the degraded condition is not stable,but returns to normal once the load is reduced

10. jinho Set bandwidth 128 kb/s, 9% Bandwidth wasted by the packets that never reach dest. UDP flow restricted to 25% of the link bandwidth

11. jinho 35% 10%

12. jinho

13. Prevent Congestion Collapse from undelivered packets 1.To Succeed,through incentives at routers,in maintaining an environment characterized by end-to-end congestion control 2.Maintain a virtual-circuit-style environment where packets are prevented from entering the network unless the network has sufficient reources to deliver

14. jinho Identify flow to regulate(A) TCP-friendly flows:if its arrival rate does not exceed the arrival of conformant TCP connection in the same circumstances. Assume a flow should not use more bandwidth than would the most aggressive conformant TCP implementation in the same circumstances.

15. jinho Maximum sending rate:T bytes/s Maximum packet size:B bytes Minimum round-trip time R Packet drop rate p Can Calculate the max arrival rate Limitations:Can only be applied to a flow at the level of granularity of a single TCP connection (hard to determine B,R)

16. jinho Identify flow to regulate(B) Unresponsive:its arrival rate decreases appropriately in response to an increased packet drop rate. If the packet drop rate of the connection increases by a factor of x, then the arrival rate from the source should decrease by a factor of roughly

17. jinho (Cont’d) If steady-state drop rate increases by a factor x and the presented load for a high- bandwidth flow does not decrease by a factor reasonably close to or more,then the flow can be deemed not to be using congestion control(unresponsive)

18. jinho Conclusion In this paper has argued on the need for end-to- end congestion control, and further,on the need for mechanisms in the network to detect and restrict unreoponsive or high bandwidth best-effort flows in times of congestion In this paper have not yet oulined a specific proposal for mechanisms for identifying and controlling unresponsive flows.

19. jinho Future Work The most important issue is not the precise functioning of the mechanisms to restrict the bandwidth of unresponsive best-effort flows,but simply that such mechanisms be deployed. Mechanisms such as these would go a long way to making concrete the essential role played by congestion control for best-effort traffic in the Internet.

20. jinho Characterize TCP-friendly flows

21. jinho