ually BC CIR * Tc (assuming 2x burst) The amount of time it takes to send B Usually T=Bc/ = CIR (assuming 2x burst) Excess burst in bits (not bps!) (not normally required) To configure traffic shaping, we need to slow down the bits being sent to each branch (Figure 32-4). To accomplish this, we need to figure out how fast the DS3 is sending bits based on each branch's connection speed. Hang on, kids, here comes some math. DS3 = :44,737,000 bits per second 111111111111111111111111111111111111111111111111111111111111111111111111111111111 How fast can it send 128k, 265k, etc? Figure 32-4. DS3 speed versus 128k A DS3 sends data at 44,736,000 bits per second. Therefore, 128,000 bits (as in 128 Kbps) will be sent over a DS3 in .0029 seconds or 2.9 milliseconds (128,000 / 44,736,000 = 0.0028612). Let's apply this information to a sample link. For a 256 Kbps link with a 2x burst (512 Kbps), the values for traffic shaping will be as follows, as- suming the DS3 head-end link in our network: CIR: 256000 Bc: 1465 (256000* 1.0057) T..0057 Be: Not required I've gone ahead and done the math for all speeds T1 and under, for a DS3 head end incorporating common burst speeds. The values are given in Table 32-1. Chapter 32: Designing QoS Table 32-1. Traffic-shaping values for common T1 speeds Burst 128k (2x) .0029 sec [2.9 ms] 256k (2x) .0057 sec [5.7 ms] 384k (2x) .0086 sec [8.6 ms] 512k (2x) 1024k .0114 sec [11.4 ms] 640k (2x) 1280k .0143 sec [14.3 ms] 768k (2x) 1536k .0172 sec [17.2 ms] 13185 1536k .0200 sec [20.0 ms] 1024k 1536k .0229 sec [22.9 ms] 1152k 1536k .0258 sec [25.8 ms] 1280k 1536k .0286 sec [28.6 ms] 1408k 1536k .0315 sec [31.5 ms] 1536k 1536k .0343 sec [34.3 ms] You got all that? Good, because as much as you need to understand it, we don't need any of it for this exercise. Luckily, our requirements are simple. The router assumes a 2x burst, SO you don't need to configure a burst if that's what you've got in place. Here are the policy maps for four different speed links, all with 2x bursts (128 Kbps, 256 Kbps, 384 Kbp