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
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- Page 327 and 328: a modi ed version of the ERICA algo
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- Page 335 and 336: like ERICA+ which uses the queueing
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- Page 351 and 352: Video Sources ABR Metrics # Mean St
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- Page 355 and 356: Video Sources ABR Metrics # Avg Src
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- Page 371 and 372: 9.2 The ERICA Switch Scheme: Renota
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- Page 375 and 376: Figure 9.9: Two methods to measure
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- Page 379 and 380: # VC Rate VC Input Rate Input Rate
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- Page 409 and 410: 7. After following behaviors #5 and
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CHAPTER 9<br />
THE VIRTUAL SOURCE/VIRTUAL DESTINATION<br />
(VS/VD) FEATURE: DESIGN CONSIDERATIONS<br />
Oneof<strong>the</strong>architectural features <strong>in</strong> <strong>the</strong> <strong>ABR</strong> speci cation is <strong>the</strong> Virtual Source/Virtual<br />
Dest<strong>in</strong>ation (VS/VD) option. This option allows a switch to divide an end-to-end<br />
<strong>ABR</strong> connection <strong>in</strong>to separately controlled <strong>ABR</strong> segments by act<strong>in</strong>glike a dest<strong>in</strong>ation<br />
on one segment, and like a source on <strong>the</strong> o<strong>the</strong>r. The coupl<strong>in</strong>g <strong>in</strong> <strong>the</strong> VS/VD switch<br />
between <strong>the</strong> two <strong>ABR</strong> control segments is implementation speci c. In this section,<br />
we model a VS/VD ATM switch and study <strong>the</strong> issues <strong>in</strong> design<strong>in</strong>g coupl<strong>in</strong>g between<br />
<strong>ABR</strong> segments. Weidentify a number of implementation options <strong>for</strong> <strong>the</strong> coupl<strong>in</strong>g. We<br />
show thatagoodchoice signi cantly improves <strong>the</strong> stability and transient per<strong>for</strong>mance<br />
of <strong>the</strong> system and reduces <strong>the</strong> bu er requirements at <strong>the</strong> switches.<br />
As mentioned, <strong>the</strong> VS/VD option allows a switch to divide an <strong>ABR</strong> connection<br />
<strong>in</strong>to separately controlled <strong>ABR</strong> segments. On one segment, <strong>the</strong> switch behaves as a<br />
dest<strong>in</strong>ation end system, i.e., it receives data and turns around resource management<br />
(RM) cells (which carry rate feedback) to <strong>the</strong> source end system. On <strong>the</strong> o<strong>the</strong>r<br />
segment <strong>the</strong> switch behaves as a source end system, i.e., it controls <strong>the</strong> transmission<br />
rate of every virtual circuit (VC) and schedules <strong>the</strong> send<strong>in</strong>g of data and RM cells. We<br />
337
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