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

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specifying where and when exactly the measurements should be made, and feedback should be given. Several schemes (with the notable exceptions of the Phantom and, to some extent, the DMRCA scheme) do not attempt to address these concerns. Several switch algorithms require the source to restrict its rise by lim- iting the Rate Increase Factor (RIF) parameter to avoid oscillations. But, this a ects the transient performance of the scheme. Other switch algorithms require setting multiple parameters, and may sometimes be sensitive to parameters. Another issue with respect to parameters is control-feedback correlation. Switch algorithms use several control parameters (available capacity, source's rate, the aggregate input rate, the number of active sources etc) to calculate the feedback quantities. Typically,control parameters values are measured asynchronously with respect to when feedback isgiven. One important responsibility of the switch algorithm is to ensure that the feedback is correlated with the control. Lack ofsuch correlation will lead to perpetual oscillations at best, and queue divergence and collapse at worst. Most schemes do not specify in detail how the correlation is maintained (especially when there is high variation in the network tra c). Many schemes change from one policy to another for small changes in system state. This introduces discontinuities in the feedback rate calculation function. If the system state is oscillating around the places where discontinuity is introduced, the scheme would exhibit undesirable oscillations. However, the presence of discontinuities in the feedback function alone does not mean that the scheme is bad. If the number of discontinuities are many (like the use of several queuing thresholds) the scope for undesirable oscillations increases. 93
The ATM Tra c Management standard also mention the Use-it or Lose-it problem where sources may retain allocations and use it later when the allocations are invalid. The standard provides minimal support from the source end systems. The switch needs to be able to tolerate transient queuing, and recover quickly from such uncontrollable circumstances. In this dissertation, we address all these issues and present the design, performance analysis of the switch scheme, and several other aspects of ABR tra c management. 94
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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
Page 69 and 70: Figure 3.2: Operating point between
Page 71 and 72: The following example illustrates t
Page 73 and 74: mention this concept of fairness fo
Page 75 and 76: control problem was also simpler. S
Page 77 and 78: of such an occurrence is expected t
Page 79 and 80: y giving only one feedback per meas
Page 81 and 82: CHAPTER 4 SURVEY OF ATM SWITCH CONG
Page 83 and 84: The adaptive FCVC algorithm [63] co
Page 85 and 86: np. Thus, long path VCs have fewer
Page 87 and 88: networks like ATM can have complete
Page 89 and 90: scheme followed by a discussion of
Page 91 and 92: exibility of decoupling the enforce
Page 93 and 94: 4.6.1 Key Techniques In EPRCA, the
Page 95 and 96: If the mean ACR is not a good estim
Page 97 and 98: is the ratio of the input rate to t
Page 99 and 100: which shares the link equally as al
Page 101 and 102: proportional to the the unused ABR
Page 103 and 104: The key technique in the scheme is
Page 105 and 106: the bandwidth allocations to satis
Page 107 and 108: 4.10 DMRCA scheme The Dynamic Max R
Page 109 and 110: on its CCR. Further MAX times out i
Page 111 and 112: other words, a di erent set of para
Page 113 and 114: A combination of several ideas in a
Page 115 and 116: 4.13 SP-EPRCA scheme The SP-EPRCA s
Page 117 and 118: RTD and shuts o the source (for sta
Page 119: 4.14.1 Common Drawbacks Though the
Page 123 and 124: 5.1.1 Control-Cell Format The contr
Page 125 and 126: The last two elds are used in the b
Page 127 and 128: Figure 5.3: Flow chart for updating
Page 129 and 130: LAF in cell Max(LAF in cell, z) The
Page 131 and 132: the time of departure (instant mark
Page 133 and 134: the steady state. The system operat
Page 135 and 136: 5.2.3 Use Measured Rather Than Decl
Page 137 and 138: said about the maximum queue length
Page 139 and 140: The key problem with some unipolar
Page 141 and 142: Figure 5.6: Space time diagram show
Page 143 and 144: As noted, these heuristics do not g
Page 145 and 146: Transmitted Cell Rate ABR Queue Len
Page 147 and 148: 4. The RM cell contains a timestamp
Page 149 and 150: 1. The source o ered average cell r
Page 151 and 152: Transmitted Cell Rate Link Utilizat
Page 157 and 158: Figure 5.17: The parking lot fairne
Page 159 and 160: Figure 5.19: Network con guration w
Page 165 and 166: 5.8 Proof: Fairness Algorithm Impro
Page 167 and 168: Region 2: y s and x s and U(1 + ) x
Page 169 and 170: 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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u ering which does not depend upon
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4 make it to the destination are ar
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Figure 8.3: At the ATM layer, the T
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issues and e ect of bursty applicat
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from the loss and they trigger the
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8.8 Performance Metrics We measure
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the performance is fair. Also, the
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Figure 8.7(b) shows the rates (ACRs
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Window Size in bytes vfive-tcp/opti
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The e ect of large bu ers on CLR is
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8.13 Summary of TCP/IP performance
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Feedback delay: Twice the delay fro
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on a link, two cells are expected a
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state only after the switch algorit
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queue length is less susceptible to
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to equalize rates for fairness, and
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QB = Link bandwidth (RT T ; T ) and
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u ered at the end-system, and not i
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Part b): When ABR load goes away, t
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All our simulations presented use t
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Averaging RTT(ms) Feedback Max Q Th
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a modi ed version of the ERICA algo
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ABR is better than UBR in these (en
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problems. During the ON time, the V
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hand, the frequency of the VBR is h
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like ERICA+ which uses the queueing
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minimum fairshare is low. This may
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8.17 E ect of Long-Range Dependent
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terminology) are called \Presentati
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The key point is that the MPEG-2 ra
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the MPEG-2 Transport Stream, and st
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8.17.4 Observations on the Long-Ran
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For the video sources, we choose me
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Video Sources ABR Metrics # Mean St
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However, with modi cations to ERICA
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Video Sources ABR Metrics # Avg Src
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Video Sources ABR Metrics # Avg Src
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On the other hand, if the applicati
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of managing bu ers, queueing, sched
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hence control the total load on the
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call such a switch a \VS/VD switch"
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Figure 9.2: Per-class queues in a n
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which arises is where the rate calc
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9.2 The ERICA Switch Scheme: Renota
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The unknowns in the above equations
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Figure 9.9: Two methods to measure
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9.4 VS/VD Switch Design Options 9.4
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# VC Rate VC Input Rate Input Rate
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8 uses source rate measurement, we
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The allocated rate update and the e
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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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