Free Trial

Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.

Share this Page URL
Help

CHAPTER 14 Scheduling Packets > 14.7 SCHEDULERS THAT PROVIDE DELAY GUARANTEES - Pg. 354

354 CHAPTER 14 Scheduling Packets Organization A (70%) Organization B (30%) Web traffic (40%) Other (60%) Web traffic (50%) Other (50%) F I G U R E 14.14 Example of a class-based queuing specification for bandwidth sharing. 1 2 3 1 2 3 1 1 2 3 1 Strict priority or 1 1 2 3 Alternate priority 2 1 3 1 Up to 8 queues selected by IP precedence F I G U R E 14.15 Cisco's modified DRR (MDRR) scheme. D EFICIT R OUND -R OBIN P LUS P RIORITY A simple idea implemented by Cisco systems (and called Modified DRR, or MDRR) is to combine DRR with priority to allow minimal delay for voice over IP. The idea, depicted in Figure 14.15, allows up to eight flow queues for a router. A packet is placed in a queue based on bits in the IP TOS fields called the IP precedence bits. However, queue 1 is a special queue