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

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7.2 Issues with Low Rate Sources Normally, the RM cells sent by the source or turned around by the destination are counted in the source's rate (ACR). However, SES Rule 11 of the tra c managemenet speci cation allows sources to send RM cells \out-of-rate" i.e., these RM cells are not counted towards the rate of the source. Out-of-rate RM cells are tagged with the CLP bit being set to one at the point of origination. The rate of such tra c is limited by the parameter TCR, which is 10 cells/s in all standard vectors. The text of the rule does not mandate the implementation of the out-of-rate RM cell policy. We noted that if sources can set their ACRs to zero and switches can give azero ACR feedback, then the out-of-rate mechanism is the only means to get out of the ACR = 0 situation. Further, for unidirectional VCs the reverse direction has no data to send and may be initialized with a rate of zero. Under such conditions, the out of rate mechanism is required to either obtain a non-zero rate for sending BRM cells, or for sending the BRM cell itself as an out-of-rate cell. In general, the out-of-rate mechanism can be selectively used to improve transient performance. Another related issue for low-rate sources is the source scheduling policy. Consider the event trace (from an actual simulation) shown in gure 7.13. Prior to the rst event (at 42.2 ms), the bottleneck link capacity had been grabbed by VBR tra c, leading to ACR = 0 allocation from the switch. At 42.2 ms, the out-of-rate RM policy triggers and an RM cell is sent, and the next opportunity to send is scheduled at 142.2 ms (due to the fact that ACR is currently zero, and the TCR value is 10 cells/s). Now new non-zero feedback is received from 43.2 ms (the switch uses the RM cells remaining in the network, including the out-of-rate RM cell). However, since the next send opportunity was scheduled at 142.2 ms, the rate allocations are ine ective 253
Figure 7.13: An event trace illustrating need forarescheduling mechanism till 142.2 ms, resulting in an unnecessary idle interval. In other words, the source once stopped is unable to use bandwidth for 100 ms even if it becomes available. The bandwidth is left unused not because there are no RM cells, but because the network feedback is ignored. Figure 7.14: The Rescheduling Mechanism To tackle this situation, we proposed that the sources may optionally \reschedule" their cell transmission opportunities based upon feedback. Speci cally, the source 254
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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
Page 229 and 230: (a) Transmitted Cell Rate (c) Link
Page 233 and 234: (a) Transmitted Cell Rate (basic ER
Page 251 and 252: RM cells. In this chapter, we devot
Page 253 and 254: low. This tradeo was discovered and
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Page 257 and 258: 7.1.6 December 1995 Proposals There
Page 259 and 260: Figure 7.2: Multiplicative vsAdditi
Page 261 and 262: is never triggered. However, the PR
Page 263 and 264: simulation results of bursty source
Page 265 and 266: 1. The time-based proposal also ind
Page 267 and 268: The switch maintains a local alloca
Page 269 and 270: PNI = f0, 1g : f1 ) No rule 5b, 0 )
Page 271 and 272: after reaching the goal. The time-b
Page 273 and 274: Figure 7.8: Closed-Loop Bursty Tra
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Page 277 and 278: Medium Bursts Medium bursts are exp
Page 279: count-based technique may be insu c
Page 283 and 284: CHAPTER 8 SUPPORTING INTERNET APPLI
Page 285 and 286: u ering which does not depend upon
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 317 and 318: QB = Link bandwidth (RT T ; T ) and
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Page 321 and 322: Part b): When ABR load goes away, t
Page 323 and 324: All our simulations presented use t
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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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