uing (FQ)-FQ has two main objectives: to provide fair access to bandwidth, resources, and routers and to ensure that no one flow receives more than its fair share. FQ assumes that queues are serviced in a bit-by-bit IP QoS round-robin fashion (see Figure 8.23). FQ transmits one bit from each queue, but bits from different queues are not interleaved. FQ computes when the packet would have left the router by using bit-by-bit round robin. Weighted Fair Queuing (WFQ)-The WFQ scheduler orders packets for departure based on their weights. For example, in Figure 8.24, source 1 gets 50%, source 2 gets 33%, and source 3 gets 17% of the bandwidth. WFQ pro- vides flow protection and can be used to bound delay. Weighted Round Robin (WRR)-WRR assigns a weight to each queue, and it then services each nonempty queue in proportion to its weight, in round- robin fashion (see Figure 8.25). WRR is optimal when using uniform packet sizes, a small number of flows, and long connections. Deficit Round Robin (DRR)-DRR does not need to know the mean packet size up front. It assigns a quantum to the queue scheduler and initializes a deficit counter to 0. DRR services each nonempty queue if the packet size is Source Queue 1 Queue 2 Source Scheduler Queue 3 Source Device Figure 8.23 IP QoS queue scheduling: Fair Queuing Source Queue 1-50% Queue 2-33% Source Scheduler Queue 3-17% Source Device Figure 8.24 IP QoS queue scheduling: Weighted Fair Queuing Chapter 8 The Internet and IP Infrastructures Queue 1-Priority 1 Source Queue 2-Priority 2 Source Scheduler Queue 3-Priority 3 Source Figure 8.25 IP QoS queue scheduling: Weighted Round Robin less than or equal to the quantum plus the deficit counter, and then it updates the deficit counter. Otherwise, it adds the quantum to the deficit counter and tries on the next pass. DRR is simple to implement. Like WRR, it is optimal with uniform packet sizes, a small number of flows, and long connections. Figure 8.26 illustrates how DRR works. This example shows a quantum value of 1,000 bytes and three d