y Figure 29-2. Overflow condition Now, imagine you decide to get a little crazy and pour three liters into the funnel in one minute's time. The hose will only allow one liter per minute to flow out of the funnel. So what happens to the other two liters? They pour over the top of the funnel all over the floor, literally creating an overflow condition. Our T1 is similar, but instead of water, we've got packets, which have the property of being discrete logical objects as opposed to being a fluid. A T1 can handle 1,500,000 packets per second. When the rate of packets being sent to the T1 exceeds this rate, the T1 interface on the router buffers as many of the packets as possible Chapter 29: Introduction to QoS (like the funnel does with the water), and then, when the buffer gets full, it over- flows. Instead of spilling water all over the floor, the interface drops the packets. At this point, the packets go into the proverbial "bit bucket." Sadly, that's just a fun term. There's no bucket-when packets are dropped, they are gone forever. Water is just water, but some types of packets may be more important than other types of packets. Packets are categorized in different ways: UDP, TCP, FTP, HTTP, and VoIP, to name a few. Not only can different packets have different priorities, but in many instances, they can be time-sensitive as well. Some protocols require that packets arrive in order. Other protocols may be sensitive to packet loss. Let's take a look at some of these protocols and see how they differ: TCP includes algorithms that alert the sending station of lost or damaged pack- ets SO they can be resent. Because of this, TCP-based applications are generally not sensitive to lost packets. TCP-based applications tend to be less time- sensitive than UDP-based applications. UDP does not do any error checking, and does not report on lost packets. Because of this, UDP-based applications may be sensitive to packet loss. HTTP is TCP-based. Generally, HTTP applications are not time-sensitive. When viewing a web page, hav