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

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The target utilization (U) and the TUB present afewtradeo s. During overload (transients), U a ects queue drain rate. Lower U increases drain rate during transients, but reduces utilization in steady state. Further, higher U also constrains the size of the TUB. Anarrow TUB slows down the convergence to fairness (since the formula depends on ) but has smaller oscillations in steady state. A wide TUB results in faster progress towards fairness, but has more oscillations in steady state. We nd that a TUB of 90%(1 0.1) used in our simulations is a good choice. The switch averaging interval a ects the stability of z. Shorter intervals cause more variation in the z and hence more oscillations. Larger intervals cause slow feedback and hence slow progress towards steady state. The OSU scheme parameters can be set relatively independent of the target work- load and network extent. Variance in measurement isthekey error factor in the OSU scheme, and a larger interval is desirable to smooth the e ect of such variance. Some schemes, on the other hand, are very sensitive totheworkload and network diameter in their choice of parameter values. An easy way to identify such schemes is that they recommend di erent parameter values for di erent network con gurations. For example, a switch parameter may be di erent for WAN con gurations than in a LAN con guration. A switch generally has some VCs travelling short distances while oth- ers travelling long distances. While it is ok to classify a VC as a local or wide area VC, it is often not correct to classify a switch as a LAN switch oraWAN switch. In a nationwide internet consisting of local networks, all switches could be classi ed as WAN switches. Note that the problem becomes more di cult when the scheme uses many parameters, and/or the parameters are not independent of each other. 107
5.2.3 Use Measured Rather Than Declared Loads Many schemes prior to OSU scheme, including the MIT scheme, used source declared rates for computing their allocation without taking into account the actual load at the switch. In the OSU scheme, we measure the current total load. All unused capacity is allocated to contending sources. We use the source's declared rate to compute a particular sources' allocation but use the switch's measured load to decide whether to increase or decrease. Thus, if the sources lie or if the source's information is out-of-date, our approach maynotachieve fairness but it still achieves e ciency. For example, suppose a personal computer connected to a 155 Mbps link is not be able to transmit more than 10 Mpbs because of its hardware/software limitation. The source declares a desired rate of 155 Mbps, but is granted 77.5 Mbps since there is another VC sharing the link going out from the switch. Now if the computer is unable to use any more than 10 Mbps, the remaining 67.5 Mbps is reserved for it and cannot be used by the second VC and the link bandwidth is wasted. The technique of measuring the total load has become minimum required part of most switch algorithms. Of course, some switches may measure each individual source's cell rate rather than relying on the information in the RM cell 5.2.4 Congestion Detection: Input Rate vs Queue Length Most congestion control schemes for packet networks in the past were window based. Most of these schemes use queue length as the indicator of congestion. When- ever the queue length (or its average) is more than a threshold, the link is considered congested. This is how initial rate-based scheme proposals were also being designed. 108
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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
Page 83 and 84: The adaptive FCVC algorithm [63] co
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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
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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 and 120: 4.14.1 Common Drawbacks Though the
Page 121 and 122: The ATM Tra c Management standard a
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: the steady state. The system operat
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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
Page 171 and 172: Proof for Region 2 Triangular regio
Page 173 and 174: have: and y 0 = y(1 ; ) z x + y 0 =
Page 175 and 176: The OSU scheme is, therefore, incom
Page 177 and 178: workloads, where input load and cap
Page 179 and 180: (a) Regions used to prove Claim C1
Page 181 and 182: 6.1 The Basic ERICA Algorithm The s
Page 183 and 184: 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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