Traffic Management for the Available Bit Rate (ABR) Service in ...

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which may be given as feedback to the source. If the overload factor (z) is underestimated, the VC share increases. The overload factor is usually not overestimated. However, if the interval length is small, the estimated values may have high variation. The overload factor (z) can suddenly change in an interval if the load or capacity in that interval changes due to the variation. The out-of-phase e ect of TCP may lead to no cells being seen in the forward direction (z = 0, a huge underestimate !), while BRM cells are seen in the reverse direction. The switch will then allocate a high rate in the feedback it writes to the BRM cell. We have designed two averaging schemes for the overload as described in chapter 6. Both schemes use an averaging parameter \ z". The rst scheme is similar to the technique of exponential averaging technique for a random variable. However, it di ers in that it resets the averaging mecha- nism whenever the instantaneous value of overload is measured to be zero or in nity. The second scheme does not ignore the outlier values (zero or in nity) of the overload factor. Further, it averages the overload by sepa- rately averaging the input rate and capacity, and then taking the ratio of the averages. It can be shown [49] that this is theoretically the right way to average a ratio quantity like overload. The number of active sources (Na) is used to calculate a minimum fairshare that is given to any source. If Na is underestimated, then the minimum fairshare is high leading to overallocation. If Na is overestimated, then the 309
minimum fairshare is low. This may result in slower transient response, but does not result in overallocation. The number of active sources can uctuate if some sources are not seen in an interval. Further, due to the clustering e ect of TCP, cells from just a few VCs may be seen in an interval leading to an underestimate of Na. In averaging Na, the scheme maintains an activity level for each source. The activity level of the source is set to one when any cell of the source is seen in the interval. However, when no cell from a source is seen in an interval, the scheme \decays" the activity level of the source by a factor, \ n"(also called DecayF actor). Hence, the source becomes inactive only after many intervals. A recommended value of n is 0.9. Roughly, the Na measured with this value of n is approximately equal to the Na measured without averaging over an averaging interval 8 or 9 times larger than the current averaging interval. 3. Third, we modify the response to boundary conditions of the scheme. This allows the scheme to handle the boundary conditions gracefully. Speci cally, the number of active sources is set to one if it is measured to be below one. The second method of overload factor averaging does not allow the overload factor be zero or in nity. However, outlier measurements are not ignored in the averaging method. The ERICA+ scheme with these modi cations controls the ABR queues without overly compromising on TCP throughput. Table 8.9 shows the results of representa- tive experiments using these features. 310
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Tra c Management for the Available
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ABSTRACT With the merger of telecom
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Tra c Management for the Available
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To my family iv
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VITA April 30, 1971 :::::::::::::::
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2.7 Switch Behavior . . . . . . . .
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5.8 Proof: Fairness Algorithm Impro
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8.15 Factors A ecting Bu ering Requ
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Bibliography . . . . . . . . . . .
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8.12 Maximum Queues for Satellite N
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5.1 Transmitted cell rate (instanta
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6.13 Results foratwo sources con gu
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7.11 E ect of UILI on Medium Bursts
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C.3 Flow Chart of Bi-Directional Co
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header information which limits the
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switches since a standard does not
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congestion control deals with the c
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hand side of the equation is the su
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analyses which are used to validate
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CHAPTER 2 THE ABR TRAFFIC MANAGEMEN
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time (RTT). As we explain later, AB
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feedback from nearby switches to re
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Note that in-rate and out-of-rate d
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Data cells also have an Explicit Fo
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opportunity the source may nd that
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Figure 2.7: Scheduling of forward R
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as the timeout value) which reduces
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It has been incorrectly believed th
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NI CI Action 0 0 ACR Min(ER, ACR +
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Source Rule 13: Sources can optiona
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Switch Rule 1: This rule speci es t
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Observe that the ABR tra c manageme
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complex method like per-VC queuing
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graphs have a steady state with con
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Figure 3.2: Operating point between
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The following example illustrates t
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mention this concept of fairness fo
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control problem was also simpler. S
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of such an occurrence is expected t
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y giving only one feedback per meas
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CHAPTER 4 SURVEY OF ATM SWITCH CONG
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The adaptive FCVC algorithm [63] co
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np. Thus, long path VCs have fewer
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networks like ATM can have complete
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scheme followed by a discussion of
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exibility of decoupling the enforce
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4.6.1 Key Techniques In EPRCA, the
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If the mean ACR is not a good estim
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is the ratio of the input rate to t
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which shares the link equally as al
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proportional to the the unused ABR
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The key technique in the scheme is
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the bandwidth allocations to satis
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4.10 DMRCA scheme The Dynamic Max R
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on its CCR. Further MAX times out i
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other words, a di erent set of para
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A combination of several ideas in a
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4.13 SP-EPRCA scheme The SP-EPRCA s
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RTD and shuts o the source (for sta
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4.14.1 Common Drawbacks Though the
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The ATM Tra c Management standard a
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5.1.1 Control-Cell Format The contr
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The last two elds are used in the b
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Figure 5.3: Flow chart for updating
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LAF in cell Max(LAF in cell, z) The
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the time of departure (instant mark
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the steady state. The system operat
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5.2.3 Use Measured Rather Than Decl
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said about the maximum queue length
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The key problem with some unipolar
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Figure 5.6: Space time diagram show
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As noted, these heuristics do not g
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Transmitted Cell Rate ABR Queue Len
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4. The RM cell contains a timestamp
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1. The source o ered average cell r
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Transmitted Cell Rate Link Utilizat
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Figure 5.17: The parking lot fairne
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Figure 5.19: Network con guration w
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5.8 Proof: Fairness Algorithm Impro
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Region 2: y s and x s and U(1 + ) x
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eing divided into eight non-overlap
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Proof for Region 2 Triangular regio
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have: and y 0 = y(1 ; ) z x + y 0 =
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The OSU scheme is, therefore, incom
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workloads, where input load and cap
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(a) Regions used to prove Claim C1
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6.1 The Basic ERICA Algorithm The s
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A ow chart of the basic algorithm i
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efore competing sources can receive
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that the latest CCR information is
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the CCR value may not be an accurat
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(Target Utilization) (Link Bandwidt
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ABR Capacity Input Rate Overload Fa
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of arithmetic averaging used above.
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level of control. These parameters
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6.14 ERICA+: Queue Length as a Seco
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6.16 ERICA+: Maintain a \Pocket" of
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hence, introduces a new parameter,
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Figure 6.4: Linear functions for ER
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and Figure 6.6: The queue control f
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small averaging intervals. If the a
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The maximum value of T 0 also depen
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6.22 Performance Evaluation of the
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espectively. The target delay T 0 i
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6.22.4 Fairness Figure 6.9: Parking
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st link, VC 15 is limited to a thro
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From the gures, it is clear that ER
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counts the bursty source as active
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6.23 Summary of the ERICA and ERICA
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(a) Transmitted Cell Rate (c) Link
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(a) Transmitted Cell Rate (basic ER
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RM cells. In this chapter, we devot
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low. This tradeo was discovered and
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in the speci cation. b) ACR shall n
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7.1.6 December 1995 Proposals There
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Figure 7.2: Multiplicative vsAdditi
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is never triggered. However, the PR
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simulation results of bursty source
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1. The time-based proposal also ind
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The switch maintains a local alloca
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PNI = f0, 1g : f1 ) No rule 5b, 0 )
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after reaching the goal. The time-b
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Figure 7.8: Closed-Loop Bursty Tra
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The algorithm measures the load and
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Medium Bursts Medium bursts are exp
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count-based technique may be insu c
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Figure 7.13: An event trace illustr
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CHAPTER 8 SUPPORTING INTERNET APPLI
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Page 287 and 288: 4 make it to the destination are ar
Page 289 and 290: Figure 8.3: At the ATM layer, the T
Page 291 and 292: issues and e ect of bursty applicat
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Page 295 and 296: 8.8 Performance Metrics We measure
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Page 299 and 300: Figure 8.7(b) shows the rates (ACRs
Page 301 and 302: Window Size in bytes vfive-tcp/opti
Page 303 and 304: The e ect of large bu ers on CLR is
Page 305 and 306: 8.13 Summary of TCP/IP performance
Page 307 and 308: Feedback delay: Twice the delay fro
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Page 311 and 312: state only after the switch algorit
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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
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Page 331 and 332: problems. During the ON time, the V
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Page 335: like ERICA+ which uses the queueing
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
Page 363 and 364: hence control the total load on the
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
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
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Page 385 and 386: sources in chapter 6. We expect the
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con guration mentioned in the table
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can be very di erent for di erent V
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CHAPTER 10 IMPLEMENTATION ISSUES At
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With an enhanced UBR service, appli
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2. Some switch schemes have a proce
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4. Large legacy switches have a pro
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section 9. Further, WAN switches wo
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CHAPTER 11 SUMMARY AND FUTURE WORK
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good transient performance. Since r
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variant background tra c conditions
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APPENDIX A SOURCE, DESTINATION AND
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7. After following behaviors #5 and
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set the QL and SN elds to zero, pre
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d) VS/VD Control: The switch may se
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5. Setting of other parameters at V
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4. The averaging interval timer exp
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1. Initialization: Target Cell Rate
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THEN IF (OCR In Cell Fair Share Rat
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APPENDIX C ERICA SWITCH ALGORITHM:
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Number Active VCs In Last Interval
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IF (NOT(Averaging VCs Option)) THEN
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IF (Load Factor = In nity) THEN Loa
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; (Contribution[VC] = Decay Factor)
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Name Explanation Flow Chart (FC) or
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Figure C.2: Flow Chart for Achievin
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Figure C.4: Flow Chart of averaging
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Figure C.6: Flow chart of averaging
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C.3 Pseudocode for VS/VD Design Opt
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(* | Bottleneck rate of next loop |
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Follow SESRules 1-4 (see appendix A
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CRM - Missing RM-cell Count DIR bit
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TUB -Target Utilization Band Trm -
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[12] J. Bennett and G. Tom Des Jard
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[38] M. Grossglauser, S.Keshav, and
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[64] H. T. Kung. Flow Controlled Vi
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