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

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Figure 7.10 shows the e ect of UILI on the source rate of small bursts. The network feedback rst arrives when the source is idle, asking it to increase its ACR. The source uses its ACR to almost send the full burst. The rst RM cell sent reduces its source rate back to ICR. The source rate goes back to zero when the source is idle. Now, the time-based and count-based proposals di er in the way they respond to subsequent network feedback. In the time-based proposal, the feedback brought by the next RM cell is ignored because of rule 5b. Now there is no RM cell of the source in the network and at least two bursts are sent at ICR before the next RM cell is sent which results in an ACR increase. Note that the sending of this second RM cell does not decrease the ACR further because ACR is already at ICR. Therefore, on the average one out of every three bursts is sent at a higher rate. In the count-based proposal, the rate-increase feedbacks are always ignored because the system is in region B (Figure 7.3). The ACR slowly reduces to ICR and then remains at ICR. Over the long term, all short bursts are sent out at ICR only. This can be improved by using a leaky bucket or GCRA [32] type burst tolerance mechanism where small bursts can be sent at link rate irrespective of ACR or ICR. Other alternatives include choosing a small TDF or a larger ICR. An ICR of 10 Mbps allows LANE tra c (the source of small bursts) to go through at full speed. On the other hand, since the burst is very short, there is not a signi cant time di erence in transmitting the burst at ACR and transmitting it at ICR (assuming ICR is not very small). In such a case, the emphasis then shifts to supporting medium bursts and large bursts e ciently. 249
Medium Bursts Medium bursts are expected in ATM backbone tra c or in native mode ATM applications. Medium bursts contain more than Nrm (32) cells, but the active time is shorter than the round trip time. Though multiple RM cells are sent in a single burst, the network feedback for the burst arrives only after the burst has already been transmitted. Figure 7.11: E ect of UILI on Medium Bursts As shown in Figure 7.11, the UILI mechanism triggers once when the rst RM cell is sent. In the time-based proposal, the amount of decrease is proportional to the idle time prior to the burst, while in the count-based UILI, the decrease is a constant amount. In the time-based proposal, if the idle time is large, almost the entire burst may be transmitted at ICR. Since, the count-based proposal sends the burst almost at ACR (1 ; TDF), it provides better burst response. Accordingly, simulation results in reference [60] show that the average source rate experienced by the bursts is higher for the count-based option (120 Mbps) compared to the time-based option (68 Mbps). 250
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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
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
Page 251 and 252: RM cells. In this chapter, we devot
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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
Page 275: The algorithm measures the load and
Page 279 and 280: count-based technique may be insu c
Page 281 and 282: Figure 7.13: An event trace illustr
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
Page 297 and 298: the performance is fair. Also, the
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
Page 309 and 310: on a link, two cells are expected a
Page 311 and 312: state only after the switch algorit
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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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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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