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

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6.4 Forward CCR Used for Reverse Direction Feedback Earlier schemes [43] provided their feedback to the RM cells going in the forward direction. This ensured that the CCR in the RM cell was correlated to the load level measured by the switch during that interval. However, the time taken by the forward going RM cell to travel back to the source was long and this slowed down the response of the system. Figure 6.1: Reverse direction feedback Switches can indicate their feedback to the sources in the reverse path of the RM cell. The backward going RM (BRM) cell takes less time to reach the source than the forward going RM (FRM) cell which has to reach the destination rst. Thus, the system responds faster to changes in the load level. However, the CCR carried by the BRM cell no longer re ects the load level in the system. To maintain the most current CCR value, the switch copies the CCR eld from FRM cells, and uses this information to compute the ER value to be inserted in the BRM cells. This ensures 159
that the latest CCR information is used in the ER calculation and that the feedback path is as short as possible. Figure 6.1 shows that the rst RM cell carries (in its backward path), the feedback calculated from the information in the most recent FRM cell. The CCR table update and read operations still preserve the O(1) time complexity ofthealgorithm. 6.5 Single Feedback in a Switch Interval The switch measures the overload, the number of active sources and the ABR capacity periodically (at the end of every switch averaging interval). The source also sends RM cells periodically. These RM cells may contain di erent rates in their CCR elds. If the switch encounters more than one RM cell from the same VC during the same switch interval, then it uses thesamevalue of overload for computing feedback in both cases. For example, if two RM cells from the same VC carried di erent CCR values, then the feedback in one of them will not accurately re ect the overload. As a result, the switch feedback will be erroneous and may result in unwanted rate oscillations. The switch thus needs to give only one feedback value per VC in a single switch interval. The above example illustrates a fundamental principle in control theory, which says that the system is unstable when the control is faster than feedback. But the system is unresponsive if the control is slower than feedback. Ideally, thecontrol rate should be matched to the feedback rate. In our system, the delay between successive feedbacks should not be greater than the delay between successive measurements (controls). 160
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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
Page 135 and 136: 5.2.3 Use Measured Rather Than Decl
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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
Page 185: efore competing sources can receive
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Page 191 and 192: (Target Utilization) (Link Bandwidt
Page 193 and 194: ABR Capacity Input Rate Overload Fa
Page 195 and 196: of arithmetic averaging used above.
Page 197 and 198: level of control. These parameters
Page 199 and 200: 6.14 ERICA+: Queue Length as a Seco
Page 201 and 202: 6.16 ERICA+: Maintain a \Pocket" of
Page 203 and 204: hence, introduces a new parameter,
Page 205 and 206: Figure 6.4: Linear functions for ER
Page 207 and 208: and Figure 6.6: The queue control f
Page 209 and 210: small averaging intervals. If the a
Page 211 and 212: The maximum value of T 0 also depen
Page 213 and 214: 6.22 Performance Evaluation of the
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Page 217 and 218: 6.22.4 Fairness Figure 6.9: Parking
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Page 221 and 222: From the gures, it is clear that ER
Page 223 and 224: counts the bursty source as active
Page 225 and 226: 6.23 Summary of the ERICA and ERICA
Page 227 and 228: (a) Transmitted Cell Rate (c) Link
Page 233 and 234: (a) Transmitted Cell Rate (basic ER
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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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