Traffic Management for the Available Bit Rate (ABR) Service in ...
Traffic Management for the Available Bit Rate (ABR) Service in ... Traffic Management for the Available Bit Rate (ABR) Service in ...
Option # VC Rate Input Rate Link Allocated Method Measurement Congestion Rate point E ect Updated at A From FRM1 per-VC prev loop only FRM1 only B At per-class Q per-class both loops FRM1 only C From FRM1 per-VC both loops FRM1 only D At per-class Q per-class both loops FRM1 and BRM2 E From FRM1 per-VC both loops BRM2 only F At per-class Q per-class both loops BRM2 only Table 9.2: Summary of viable VS/VD design alternatives 9.5 Performance Evaluation of VS/VD Design Options 9.5.1 Metrics We use four metrics to evaluate the performance of these alternatives: Response Time: is the time taken to reach near optimal behavior on startup. Convergence Time: is the time for rate oscillations to decrease (time to reach the steady state). Throughput: Total data transferred per unit time. Maximum Queue: The maximum queue before convergence. The di erence between response time and convergence time is illustrated in Fig- ure 9.15. The following sections present simulation results with respect to the above metrics. Note that we have used greedy (in nite) tra c sources in our simulations. Wehave studied the algorithmic enhancements in non-VS/VD switches for non-greedy 357
sources in chapter 6. We expect the best implementation option (see below) to work well and produce consistent results when such (bursty) tra c is used. Response Time Figure 9.15: Response time vs Convergence time Without VS/VD all response times are close to the round-trip delay. With VS/VD, the response times are close to the feedback delay from the bottleneck. Since VS/VD reduces the response time during the rst round trip, it is good for long delay paths. The quick response time (10 ms in the parking lot con guration which has a 30 ms round trip time) is shown in Figure 9.13. Response time is also important for bursty tra c like TCP le transfer over ATM which \starts up" at the beginning of every active period (when the TCP window increases) after the corresponding idle period (see chapter 7). Throughput The number of cells received at the destination is a measure of the throughput achieved. These values are listed in Table 9.3. The top row is a list of the con guration codes (these codes are explained in Table 9.2. The nal column lists the throughput values for the case when a non-VS/VD switch is used. The 2 source+VBR and the parking lot con gurations have been introduced in earlier section. 358
- Page 333 and 334: hand, the frequency of the VBR is h
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- Page 355 and 356: Video Sources ABR Metrics # Avg Src
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- Page 365 and 366: call such a switch a \VS/VD switch"
- Page 367 and 368: Figure 9.2: Per-class queues in a n
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- Page 403 and 404: good transient performance. Since r
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- Page 407 and 408: APPENDIX A SOURCE, DESTINATION AND
- Page 409 and 410: 7. After following behaviors #5 and
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sources <strong>in</strong> chapter 6. We expect <strong>the</strong> best implementation option (see below) to work<br />
well and produce consistent results when such (bursty) tra c is used.<br />
Response Time<br />
Figure 9.15: Response time vs Convergence time<br />
Without VS/VD all response times are close to <strong>the</strong> round-trip delay. With<br />
VS/VD, <strong>the</strong> response times are close to <strong>the</strong> feedback delay from <strong>the</strong> bottleneck. S<strong>in</strong>ce<br />
VS/VD reduces <strong>the</strong> response time dur<strong>in</strong>g <strong>the</strong> rst round trip, it is good <strong>for</strong> long delay<br />
paths. The quick response time (10 ms <strong>in</strong> <strong>the</strong> park<strong>in</strong>g lot con guration which has a<br />
30 ms round trip time) is shown <strong>in</strong> Figure 9.13.<br />
Response time is also important <strong>for</strong> bursty tra c like TCP le transfer over ATM<br />
which \starts up" at <strong>the</strong> beg<strong>in</strong>n<strong>in</strong>g of every active period (when <strong>the</strong> TCP w<strong>in</strong>dow<br />
<strong>in</strong>creases) after <strong>the</strong> correspond<strong>in</strong>g idle period (see chapter 7).<br />
Throughput<br />
The number of cells received at <strong>the</strong> dest<strong>in</strong>ation is a measure of <strong>the</strong> throughput<br />
achieved. These values are listed <strong>in</strong> Table 9.3. The top row is a list of <strong>the</strong> con guration<br />
codes (<strong>the</strong>se codes are expla<strong>in</strong>ed <strong>in</strong> Table 9.2. The nal column lists <strong>the</strong> throughput<br />
values <strong>for</strong> <strong>the</strong> case when a non-VS/VD switch is used. The 2 source+VBR and <strong>the</strong><br />
park<strong>in</strong>g lot con gurations have been <strong>in</strong>troduced <strong>in</strong> earlier section.<br />
358
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