Content

| 8.5 |  | Scheduling |
| 8.5.4 |  | WFQ and IP precedence |

Title WFQ is IP precedence-aware. It can detect higher priority packets marked with precedence by the IP Forwarder and can schedule them faster, providing superior response time for this traffic. Therefore, as the precedence increases, WFQ allocates more bandwidth to the conversation during periods of congestion. WFQ assigns a weight to each flow, which determines the transmit order for queued packets. In this scheme, lower weights are served first. For standard Cisco IOS WFQ, the IP precedence serves as a divisor to this weighting factor. For each cycle through all flows, WFQ effectively services queues such that the proportion of bandwidth given to any IP precedence level is the IP Precedence plus 1. For example, if there is one flow at each precedence level, each flow will get precedence + 1 parts of the link:

> 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = 36

Therefore, precedence 0 traffic will get 1/36 of the bandwidth, precedence 1 traffic will get 2/36, and precedence 7 traffic will get 8/36.

However, for 18 precedence-1 flows and one of each of the rest, the total is now:

> 1 + 2(18) + 3 + 4 + 5 + 6 + 7 + 8 = 70

So an individual precedence 1 flow will receive 2/70 or 1/35 of the bandwidth.

As flows are added or ended, the actual allocated bandwidth will continuously change.