Of the choices provided, low latency queuing (LLQ) is the most appropriate for handling voice, video, mission-critical, and lower-priority traffic. LLQ supports the creation of up to 64 user defined traffic classes as well as one or more strict priority queues that can be used specifically for delay sensitive traffic, such as voice and video traffic. Each strict-priority queue can use as much bandwidth as possible but can only use its guaranteed minimum bandwidth when other queues have traffic to send, thereby avoiding bandwidth starvation. You can also implement weighted random early detection (WRED) on each of the user defined traffic classes to mitigate packet loss? WRED is particularly useful for networks with a large amount of Transmission Control Protocol (TCP) traffic.

On voice networks, you can implement LLQ to help reduce jitter. Additionally, you can configure the voice class with a smaller queue size. Although a smaller queue size could result in dropped packets, voice traffic is more tolerant of dropped packets than of delayed packets. A small amount of packet loss is not noticeable to the human ear. Additionally, some codecs can correct small amounts of packet loss. Therefore, a smaller queue size combined with the use of LLQ could reduce delay and jitter.

Class based weighted fair queuing (CBWFQ) provides bandwidth guarantees, so it can be used for voice, video, mission-critical, and lower-priority traffic. However, CBWFQ does not provide the delay guarantees provided by LLQ, because CBWFQ does not provide support for strict priority queues. CBWFQ improves upon weighted fair queuing (WFQ) by enabling the creation of up to 64 custom traffic classes, each with a guaranteed minimum bandwidth.

Although WFQ can be used for voice, video, and mission-critical traffic, it does not provide the bandwidth guarantees or the strict-priority queues that are provided by LLQ. WFQ is used by default on Cisco routers for serial interfaces at 2.048 Mbps or lower. Traffic flows are identified by WFQ based on source and destination IP address, port number, protocol number, and Type of Service (ToS). Although WFQ is easy to configure, it is not supported on high speed links. First-in-first-out (FIFO) queuing is the least appropriate for voice, video, and mission-criticaltraffic. By default, Cisco uses FIFO queuing for interfaces faster than 2.048 Mbps. FIFO queuing requires no configuration, because all packets are arranged into a single queue. As the name implies, the first packet received is the first packet transmitted, without regard for packet type, protocol, or priority.