-world environments I've seen, and im- plementing it will illustrate how to mark different types of traffic in different ways. Determine Bandwidth Requirements To illustrate how to determine the bandwidth requirements for the various protocols, we'll use the sample network from the previous chapter, shown here in Figure 32-1. Building A Building B Figure 32-1. Two-building network with a single T1 Low-latency queuing is the preferred QoS method for VoIP. When using this method, you create a single high-priority queue for data streams that cannot suffer dropped packets (voice, video, etc.), and the remaining data is queued according to a hierarchy of priorities. The priority queue may be assigned a percentage of the available bandwidth (15 per- cent, for example), or a finite amount of bandwidth (300 Kbps, for example). The priority queue should not consume more than three-quarters of the available band- width. In fact, the Cisco IOS prevents you from allocating more than 75 percent to the priority queue, though this value can be altered with the max-reserved-bandwidth in- terface command: Config-if# max-reserved-bandwidth 80 Chapter 32: Designing QoS WAN links should never be built with more than 75 percent planned utilization. You should always leave 25 percent for overhead, routing protocols, administration, etc. Because of the way the scheduler works, if you assign an unusually large value to the priority queue, none of the other queues will ever get serviced. This will result in apparent outages, because only the priority queue's traffic will get through. We're going to assign voice RTP to the strict priority queue. For our purposes, let's say we'll need to allocate space for four G.729a CODEC VoIP calls (50 packets per second) at any given time. Some quick research shows that each call should take no more than 37 Kbps. Four calls at 37 Kbps equals 148 Kbps, which is the amount we'll assign to the priority queue: Voice RTP-priority queue-148 Kbps Call control requires very minimal bandwidth. Some Cisco docume