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 ...
CHAPTER 9 THE VIRTUAL SOURCE/VIRTUAL DESTINATION (VS/VD) FEATURE: DESIGN CONSIDERATIONS Oneofthearchitectural features in the ABR speci cation is the Virtual Source/Virtual Destination (VS/VD) option. This option allows a switch to divide an end-to-end ABR connection into separately controlled ABR segments by actinglike a destination on one segment, and like a source on the other. The coupling in the VS/VD switch between the two ABR control segments is implementation speci c. In this section, we model a VS/VD ATM switch and study the issues in designing coupling between ABR segments. Weidentify a number of implementation options for the coupling. We show thatagoodchoice signi cantly improves the stability and transient performance of the system and reduces the bu er requirements at the switches. As mentioned, the VS/VD option allows a switch to divide an ABR connection into separately controlled ABR segments. On one segment, the switch behaves as a destination end system, i.e., it receives data and turns around resource management (RM) cells (which carry rate feedback) to the source end system. On the other segment the switch behaves as a source end system, i.e., it controls the transmission rate of every virtual circuit (VC) and schedules the sending of data and RM cells. We 337
call such a switch a \VS/VD switch". In e ect, the end-to-end control is replaced by segment-by-segment control as shown in Figure 9.1. Figure 9.1: End-to-End Control vs VS/VD Control One advantage of the segment-by-segment control is that it isolates di erent net- works from each other. One example is a proprietary network like frame-relay or circuit-switched network between two ABR segments, which allows end-to-end ABR connection setup across the proprietary network and forwards ATM packets between the ABR segments (signaling support for this possibility is yet to be considered by the ATM Forum). Another example is the interface point between a satellite network and a LAN. The gateway switches at the edge of a satellite network can implement VS/VD to isolate downstream workgroup switches from the e ects of the long delay satellite paths (like long queues). A second advantage of segment-by-segment control is that the segments have shorter feedback loops which can potentially improve per- formance because feedback is given faster to the sources whenever new tra c bursts are seen. The VS/VD option requires the implementation of per-VC queueing and scheduling at the switch. The goal of this study is nd answers to the following questions: 338
- Page 313 and 314: queue length is less susceptible to
- Page 315 and 316: to equalize rates for fairness, and
- Page 317 and 318: QB = Link bandwidth (RT T ; T ) and
- Page 319 and 320: u ered at the end-system, and not i
- Page 321 and 322: Part b): When ABR load goes away, t
- Page 323 and 324: All our simulations presented use t
- Page 325 and 326: Averaging RTT(ms) Feedback Max Q Th
- Page 327 and 328: a modi ed version of the ERICA algo
- Page 329 and 330: ABR is better than UBR in these (en
- Page 331 and 332: problems. During the ON time, the V
- Page 333 and 334: hand, the frequency of the VBR is h
- Page 335 and 336: like ERICA+ which uses the queueing
- Page 337 and 338: minimum fairshare is low. This may
- Page 339 and 340: 8.17 E ect of Long-Range Dependent
- Page 341 and 342: terminology) are called \Presentati
- Page 343 and 344: The key point is that the MPEG-2 ra
- Page 345 and 346: the MPEG-2 Transport Stream, and st
- Page 347 and 348: 8.17.4 Observations on the Long-Ran
- Page 349 and 350: For the video sources, we choose me
- Page 351 and 352: Video Sources ABR Metrics # Mean St
- Page 353 and 354: However, with modi cations to ERICA
- Page 355 and 356: Video Sources ABR Metrics # Avg Src
- Page 357 and 358: Video Sources ABR Metrics # Avg Src
- Page 359 and 360: On the other hand, if the applicati
- Page 361 and 362: of managing bu ers, queueing, sched
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- Page 367 and 368: Figure 9.2: Per-class queues in a n
- Page 369 and 370: which arises is where the rate calc
- Page 371 and 372: 9.2 The ERICA Switch Scheme: Renota
- Page 373 and 374: The unknowns in the above equations
- Page 375 and 376: Figure 9.9: Two methods to measure
- Page 377 and 378: 9.4 VS/VD Switch Design Options 9.4
- Page 379 and 380: # VC Rate VC Input Rate Input Rate
- Page 381 and 382: 8 uses source rate measurement, we
- Page 383 and 384: The allocated rate update and the e
- Page 385 and 386: sources in chapter 6. We expect the
- Page 387 and 388: con guration mentioned in the table
- Page 389 and 390: can be very di erent for di erent V
- Page 391 and 392: CHAPTER 10 IMPLEMENTATION ISSUES At
- Page 393 and 394: With an enhanced UBR service, appli
- Page 395 and 396: 2. Some switch schemes have a proce
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- Page 403 and 404: good transient performance. Since r
- Page 405 and 406: variant background tra c conditions
- Page 407 and 408: APPENDIX A SOURCE, DESTINATION AND
- Page 409 and 410: 7. After following behaviors #5 and
- Page 411 and 412: set the QL and SN elds to zero, pre
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call such a switch a \VS/VD switch". In e ect, <strong>the</strong> end-to-end control is replaced by<br />
segment-by-segment control as shown <strong>in</strong> Figure 9.1.<br />
Figure 9.1: End-to-End Control vs VS/VD Control<br />
One advantage of <strong>the</strong> segment-by-segment control is that it isolates di erent net-<br />
works from each o<strong>the</strong>r. One example is a proprietary network like frame-relay or<br />
circuit-switched network between two <strong>ABR</strong> segments, which allows end-to-end <strong>ABR</strong><br />
connection setup across <strong>the</strong> proprietary network and <strong>for</strong>wards ATM packets between<br />
<strong>the</strong> <strong>ABR</strong> segments (signal<strong>in</strong>g support <strong>for</strong> this possibility is yet to be considered by<br />
<strong>the</strong> ATM Forum). Ano<strong>the</strong>r example is <strong>the</strong> <strong>in</strong>terface po<strong>in</strong>t between a satellite network<br />
and a LAN. The gateway switches at <strong>the</strong> edge of a satellite network can implement<br />
VS/VD to isolate downstream workgroup switches from <strong>the</strong> e ects of <strong>the</strong> long delay<br />
satellite paths (like long queues). A second advantage of segment-by-segment control<br />
is that <strong>the</strong> segments have shorter feedback loops which can potentially improve per-<br />
<strong>for</strong>mance because feedback is given faster to <strong>the</strong> sources whenever new tra c bursts<br />
are seen. The VS/VD option requires <strong>the</strong> implementation of per-VC queue<strong>in</strong>g and<br />
schedul<strong>in</strong>g at <strong>the</strong> switch.<br />
The goal of this study is nd answers to <strong>the</strong> follow<strong>in</strong>g questions:<br />
338
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