Traffic Shaping

Quality of Service (QoS) is a mechanism that allows you to manage network resources in order to guarantee a certain level of performance to data flows. Therefore, it is the best technology to use for traffic shaping to prioritize VoIP traffic across the network. The other options are not suitable for this task. Network Address Translation (NAT) is useful for converting private IP addresses into public IP addresses for Internet routing, but it does not prioritize traffic. Dynamic Host Configuration Protocol (DHCP) is handy for allocating IP addresses in a network, but it doesn't shape or prioritize traffic either. A Virtual Private Network (VPN) allows secure access over a public network, such as the Internet, but it doesn't offer prioritization of traffic.

In this particular scenario, 'Reserved Bandwidth' would be the best technique to ensure the continuous availability of bandwidth for video calls. This technique allows an IT administrator to allocate a certain amount of bandwidth specifically for video calls, thus ensuring that it is always available. This prevents other traffic from consuming all the bandwidth and hindering video conferencing. The other techniques might not be as effective because: 'Tail Drop' occurs when the network buffer is full and the network has to discard additional packets, which may disrupt the video conferencing; 'Empty Bucket' is a technique where the incoming rate exceeds the outgoing rate, causing overflow and resulting in packet loss, which might adversely affect the video conference; 'Time Division Multiplexing (TDM)' is a method that divides the transmission time into various slots for multiple signals but this does not necessarily reserve bandwidth for a specific type of traffic like video, hence not providing a guaranteed solution for continuous availability for video conference bandwidth.

Weighted Fair Queuing (WFQ) is the most effective traffic shaping technique for a network with high, medium, and low priority applications running simultaneously. It assigns a separate queue to each data flow and 'weights' each queue based on its priority. This ensures higher priority data flows are given more bandwidth and lower latency times than lower priority flows. In contrast, the 'First-In, First-Out (FIFO)' method doesn't consider the priority of data flows, meaning high priority data might wait behind lower priority data, which can result in sub-optimal network performance. The 'Leaky Bucket' method is a simple traffic shaping algorithm controls data transfer to a network by removing data from the bucket at a set rate. It doesn't prioritize traffic, which means it can't guarantee quality of service for priority applicationsThe 'Token Bucket' traffic shaping algorithm allows bursts of data, unlike the Leaky Bucket, and it fills the bucket with tokens at a set rate, but it also doesn't prioritize traffic. Hence, it can't guarantee that high-priority applications will get the network resources they need.