IPv6 Quality of Service (QoS)

Correct Answer: Weighted Fair Queuing (WFQ)

Weighted Fair Queuing (WFQ) is the correct answer. WFQ is a network traffic scheduling method that assigns a priority to each flow of traffic. It is highly beneficial in congested networks as it guarantees bandwidth for critical applications, thus reducing latency selectively. Round Robin Queuing (RRQ) and First-Come, First-Serve (FCFS) do not factor in traffic priority and so won't be as effective in reducing latency for specific critical applications. Priority Queuing (PQ) could lead to lower priority traffic being continually ignored during heavy traffic leading to possible starvation, hence is not as efficient as WFQ.

Correct Answer: Differentiated Services (DiffServ)

Differentiated Services (DiffServ) is the correct answer. DiffServ is a protocol used for handling bandwidth on a network. It allows the network to prioritize certain data packets over others by classifying them into different service classes. This makes it a suitable mechanism for managing real-time applications using Quality of Service (QoS) services on a network with increased jitter and latency. On the other hand, Integrated Services (IntServ) does provide QoS functionalities but it's more resource-intensive, making it less suitable for larger networks. Best Effort Delivery (BE) does not prioritize certain types of traffic or provide any QoS, which makes it an inaccurate response in this context. Lastly, Multicast Listener Discovery (MLD) is unrelated to QoS or application prioritization; it is a protocol used for devices to report their multicast group membership to neighboring routers.

Correct Answer: Low Latency Queuing (LLQ)

Low Latency Queuing (LLQ) is the most appropriate queuing mechanism in this scenario. This is because LLQ provides priority to specific traffic identified by the administrator. In this case, the video calling application can be given priority to reduce the latency. On the other hand, Random Early Detection (RED) is not ideal as it drops packets when the buffer starts to fill, leading to a possible increase in latency for the video calling application. First-Come, First-Serve (FCFS) is not suitable either as it treats all packets equally and does not prioritize the video calling application. Round Robin Queuing (RRQ) also doesn't serve the purpose as it only circulates through the queues and picks out a packet from each, not providing any specific priority to the video calling application, which is what the scenario requires.