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

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Rule 6 unnecessarily and degrade performance. Hence, the Forum decided to use FRTT parameter instead of RTT. Note that it is possible to disable source Rule 6, by setting CDF to zero. Source Rule 7: When sending an FRM, the sources should indicate their current ACR in the CCR eld of the RM cells. Source Rules 8 and 9: Source Rule 8 and 9 describe how the source should re- act to network feedback. The feedback consists of explicit rate (ER), congestion indication bit (CI), and no-increase bit (NI). Normally, a source could simply change its ACR to the new ER value� but this could cause a few problems as discussed next. First, if the new ER is very high compared to current ACR, switching to the new ER will cause sudden queues in the network. Therefore, the amount of increase is limited. The rate increase factor (RIF) parameter determines the maximum allowed increase in any one step. The source cannot increase its ACR by more than RIF PCR. Second, if there are any EFCI switches in the path, they do not change the ER eld. Instead, they set EFCI bits in the cell headers. The destination monitors these bits and returns the last seen EFCI bit in the CI eld of a BRM. A CI of 1 means that the network is congested and that the source should reduce its rate. The decrease is determined by rate decrease factor (RDF) parameter. Unlike the increase, which is additive, the decrease is multiplicative inthe sense that ACR ACR(1 ; RDF) 29
NI CI Action 0 0 ACR Min(ER, ACR + RIF PCR, PCR) 0 1 ACR Min(ER, ACR ; ACR RDF) 1 0 ACR Min(ER, ACR) 1 1 ACR Min(ER, ACR ; ACR RDF) Table 2.2: Source End System actions upon CI and NI bits It has been shown that additive increase and multiplicative decrease is su - cient to achieve fairness [19]. Other combinations such as additive increase with additive decrease, multiplicative increase with multiplicative decrease, and multiplicative increase with additive increase are unfair. The no-increase (NI) bit was introduced to handle mild congestion cases. In such cases, a switch could specify an ER, but instruct that, if ACR is already below the speci ed ER, the source should not increase the rate. The actions corresponding to the various values of CI and NI bits are listed in Table 2.2. ACR Max(ACR,MCR) If there are no EFCI switches in a network, setting RIF to 1 allows ACRs to increase as fast as the network directs it. This allows the available bandwidth to be used quickly. For EFCI networks, or a combination of ER and EFCI networks, RIF should be set conservatively to avoid unnecessary oscillations. Once the ACR is updated, the subsequent cells sent from the source conform to the new ACR value. However, if the earlier ACR was very low, it is possible that the very next cell is scheduled a long time in the future. In such a situation, 30
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Tra c Management for the Available
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ABSTRACT With the merger of telecom
Page 5 and 6: Tra c Management for the Available
Page 7 and 8: To my family iv
Page 9 and 10: VITA April 30, 1971 :::::::::::::::
Page 11 and 12: 2.7 Switch Behavior . . . . . . . .
Page 13 and 14: 5.8 Proof: Fairness Algorithm Impro
Page 15 and 16: 8.15 Factors A ecting Bu ering Requ
Page 17 and 18: Bibliography . . . . . . . . . . .
Page 19 and 20: 8.12 Maximum Queues for Satellite N
Page 21 and 22: 5.1 Transmitted cell rate (instanta
Page 23 and 24: 6.13 Results foratwo sources con gu
Page 25 and 26: 7.11 E ect of UILI on Medium Bursts
Page 27 and 28: C.3 Flow Chart of Bi-Directional Co
Page 29 and 30: header information which limits the
Page 31 and 32: switches since a standard does not
Page 33 and 34: congestion control deals with the c
Page 35 and 36: hand side of the equation is the su
Page 37 and 38: analyses which are used to validate
Page 39 and 40: CHAPTER 2 THE ABR TRAFFIC MANAGEMEN
Page 41 and 42: time (RTT). As we explain later, AB
Page 43 and 44: feedback from nearby switches to re
Page 45 and 46: Note that in-rate and out-of-rate d
Page 47 and 48: Data cells also have an Explicit Fo
Page 49 and 50: opportunity the source may nd that
Page 51 and 52: Figure 2.7: Scheduling of forward R
Page 53 and 54: as the timeout value) which reduces
Page 55: It has been incorrectly believed th
Page 59 and 60: Source Rule 13: Sources can optiona
Page 61 and 62: Switch Rule 1: This rule speci es t
Page 63 and 64: Observe that the ABR tra c manageme
Page 65 and 66: complex method like per-VC queuing
Page 67 and 68: 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
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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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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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