More Ideas on Traffic Management Improve TCP Stay with end-point only architecture Enhance routers to help tcP Random Early Discard Enhance routers to control traffic Rate limiting Fair Queueing Provide Qos by limiting congestion
6 More Ideas on Traffic Management • Improve TCP • Stay with end-point only architecture • Enhance routers to help TCP • Random Early Discard • Enhance routers to control traffic • Rate limiting • Fair Queueing • Provide QoS by limiting congestion
Router mechanisms Buffer management: when and which packet to drop? Scheduling: which packet to transmit next? classifie flow 2 Scheduler Buffer management 7
7 Router Mechanisms • Buffer management: when and which packet to drop? • Scheduling: which packet to transmit next? 1 2 Scheduler flow 1 flow 2 flow n Classifier Buffer management
Typical Internet Queuing FIFO drop-tail Simplest choice Used widely in the Internet FIFo (first-in-first-ou Implies single class of traffic Drop-tail Arriving packets get dropped when queue is full regardless of flow or importance Important distinction FIFO: scheduling discipline Drop-tail: drop policy
8 Typical Internet Queuing • FIFO + drop-tail • Simplest choice • Used widely in the Internet • FIFO (first-in-first-out) • Implies single class of traffic • Drop-tail • Arriving packets get dropped when queue is full regardless of flow or importance • Important distinction: • FIFO: scheduling discipline • Drop-tail: drop policy
FIFO Drop-tail Problems Leaves responsibility of congestion control completely to the edges(e.g, TCP) Does not separate between different flows No policing: send more packets> get more service Synchronization end hosts react to same events
9 FIFO + Drop-tail Problems • Leaves responsibility of congestion control completely to the edges (e.g., TCP) • Does not separate between different flows • No policing: send more packets → get more service • Synchronization: end hosts react to same events
FIFO Drop-tail Problems Full queues Routers are forced to havehave large queues to maintain high utilizations TCP detects congestion from loss Forces network to have long standing queues in steady-state Lock-out problem Drop-tail routers treat bursty traffic poorly Traffic gets synchronized easily With old TCP, caused very low tput Can be very unfair in b/w between flows
10 FIFO + Drop-tail Problems • Full queues • Routers are forced to have have large queues to maintain high utilizations • TCP detects congestion from loss • Forces network to have long standing queues in steady-state • Lock-out problem • Drop-tail routers treat bursty traffic poorly • Traffic gets synchronized easily • With old TCP, caused very low tput • Can be very unfair in b/w between flows