1. A CTIVE Q UEUE M ANAGEMENT Comparing RED and BLUE Presentation held at: Telia Prosoft AB, Farsta, Sweden 2001-May-18 Thesis worker:Bartók István bartoki@hpn.telialabs.net Consultant:Imre Juhász Imre.I.Juhasz@telia.se

2. A CTIVE Q UEUE M ANAGEMENT Introduction n Demand for short Round Trip Time n Wish for low packet loss rate n All this with best effort traffic n “Guaranteed minimum + fair share” broadband package customers will saturate any backbone

3. A CTIVE Q UEUE M ANAGEMENT The Challenge n Drop-tail is not adequate n Random Early Detection is not perfect n What about Explicit Congestion Notification? n Many proposed algorithms to replace RED n Is BLUE the right one? n Add BLUE to the Linux kernel n Compare by measurements

4. A CTIVE Q UEUE M ANAGEMENT Drop-tail n Signals congestion only when the queue is already saturated n Likely to drop more packets from the same flow n Unfair with bursty flows

5. A CTIVE Q UEUE M ANAGEMENT Random Early Detection - RED

6. A CTIVE Q UEUE M ANAGEMENT Explicit Congestion Notification

7. A CTIVE Q UEUE M ANAGEMENT The problems with RED n The queue length either oscillates, n Or it cannot control the congestion

8. A CTIVE Q UEUE M ANAGEMENT Other Algorithms n Adaptive RED n P-I Controller n Adaptive Virtual Queue n BLUE n...

9. A CTIVE Q UEUE M ANAGEMENT BLUE n Tail drop happens?Increase Pdrop n Queue empy?Decrease Pdrop n Freeze Pdrop after change n Its author’s simulations are promising:

10. A CTIVE Q UEUE M ANAGEMENT Linux kernel Traffic Control n Nice Framework n Part of the standard Linux kernel n But written by a Real Programmer TM Bare documentation

11. A CTIVE Q UEUE M ANAGEMENT Real Life n ECN problems u Retransmits u SYN n High bias towards ECN when naive n Standardization problems - Linux & FreeBSD ECN breaks the RFC n Take the BLUE pill?

12. A CTIVE Q UEUE M ANAGEMENT Conclusion n The perfect mechanism still has not been arrived n Design for Nonlinear n Include Arrival & Departure Rate

13. A CTIVE Q UEUE M ANAGEMENT Future Work n Measure & Simulate n Improve some of the algorithms, or n Design The One n Good background is provided in the thesis doc: u Guide to TCP Congestion Control u Guide to Linux kernel Traffic Control Framework u Evaluation of some Queue Management algorithms