ng (WFQ) Weighted fair queuing is the default queuing mechanism on 2 Mbps and slower serial links. For most implementations, the default configuration works fine. WFQ can be configured very specifically, but it usually isn't configured at all. When VoIP is involved, low-latency queuing is typically used in place of WFQ. Class-based weighted fair queuing (CBWFQ) Class-based weighted fair queuing allows you to configure classes of traffic and assign them to priorities and queues. CBWFQ is the basis for low-latency queuing. Priority queuing Priority queuing works just how it sounds: queues are created, and each class of packet is assigned to an appropriate queue based on priorities you design. Custom queuing Custom queuing is one of those features that you probably won't see much. You'll see it on Cisco exams, and you may see it on networks that had specific problems to be solved where voice was not a concern at the time of the resolu- tion. That's not to say that custom queuing is not suitable for voice, but again, low-latency queuing is the QoS method of choice for voice-enabled networks. Low-latency queuing (LLQ) Low-latency queuing is class-based weighted fair queuing with a strict priority queue. A strict priority queue is one in which hardware is used to send packets that need to be sent with the lowest latency possible. This is especially useful for voice and video, where any latency or delay causes problems. LLQ is the pre- ferred method of QoS for voice networks, and is the QoS method I focus on in this book. Traffic shaping Traffic shaping is slightly different from queuing. Traffic shaping monitors traf- fic, and, when it reaches a threshold, instead of discarding packets, keeps them until a point where bandwidth has lowered and they can be sent. The benefits are a smoother use of bandwidth (Figure 29-7) and the fact that packets are buff- ered and not just dropped. The downside is that traffic shaping requires memory to function because it buffers packets. Also, if the configured buffer overflows, packet