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1、Dynamic-CBT,Better Performing Active Queue Management for Multimedia Networking,Jae Chung and Mark Claypool,Computer Science Department Worcester Polytechnic Institute Worcester, Massachusetts, USA,http:/perform.wpi.edu/,Outline,Introduction CBT D-CBT Evaluation Issues,Internet Routers Today,Volume
2、of traffic increasing More simultaneous active flows Increase in multimedia flows Tight timing constraints Different flow-control mechanism than TCP Emphasis on Congestion Control and Fairness among active flows,Current Router Queue Mgmt,Drop Tail (FIFO),Resource Reservation,.,(Lin, Morris 97),FRED,
3、Active Queue Mgmt,.,Class-Based Threshold (CBT),( Floyd, Jacobson 95),CBQ,( Floyd, Jacobson 93),RED,(Parris, Jeffay, Smith 99),CBT Design,CBT - Pros and Cons,Pros: RED + Class-Based Isolation Early congestion notification Protect TCP and protect Tagged UDP (MM) Different classes of flows coexist wit
4、h predefined fairness Cons: CBQ function w/o admission control Fairness for changing traffic mixes Utilization on outgoing link Changes “Best-Effort” nature of Internet,Dynamic-CBT (D-CBT),Drop Tail (FIFO),Resource Reservation,.,CBQ,RED,FRED,Active Queue Mgmt,.,Class-Based Threshold (CBT),Dynamic-CB
5、T,D-CBT Design,RED,TCP,Untagged UDP,Tagged UDP (MM),Early Drop Test,Queue Manager,* Threshold Test is activated when red_avg red_min,Classify,Evaluation using NS,Developed a flow-controlled Multimedia Application (for tagged UDP class) AIMD Media Scaling (5 discrete rates) “MPEG-1 like” transmission
6、 rates Implemented and validated CBT Implemented D-CBT and measured congestion time fairness RED vs. CBT vs. D-CBT,Simulation (RED, CBT, D-CBT),Fairness: RED,Fairness: CBT,Fairness: D-CBT,D-CBT Issues,Tagging UDP packets Who tags packets? (End Host? ISP?) Which field of IP header to use? IPv4: Unuse
7、d Bit in Type-Of-Service Field IPv4: Another Protocol in Protocol Field IPv6: Use Priority Field Define a flow IPv4: Source-Destination Address IPv6: Plus Flow-ID,D-CBT Issues,Active Flow Counting (Overhead) For every incoming packet, insert or update info and update count Hash Table - O(1) Every ms
8、, delete old flows and update count Hash Table - O(n) Measure Active Flow Counting overheads: Linux implementation Processing Time and Memory Usage,D-CBT Issues,Test D-CBT with other (available) flow-controlled MM Applications Effect of the thresholds on MM quality Sensitivity of D-CBT to RED parameters How many different classes are needed? Example 1 class is RED 1 class per flow is FRED Overhead per class,
