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

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We observe that there is a drastic reduction of TCP throughput which is not proportional to the increase in CLR. The throughput drops by 36% while the CLR is only 0.18%. Figure 8.7 shows graphs of window size, sequence numbers, and ACR for the two sources. Figure 8.7(a) shows that there is one loss around t=200 ms. No acks are received for the next 300 ms and therefore, the window remains constant and nally drops to 1 at t=500 ms. The packets are retransmitted and window rises ex- ponentially upto the half of the value before the drop. Subsequently, the window rise linearly. Note that the linear rise is very slow. The source window is much below its maximum. In other words, the sources are window limited. The congestion windows of both sources are approximately equal, and so the operation is fair. However, the throughput in this experiment is only 64% of the maximum throughput. The measured cell loss ratio in this case was only 0.18%. Note that the CLR and throughput loss are one order of magnitude apart. Window Size in bytes two-tcp/option=1/optionb=295/optiont=6/sw_qsize=2048/tbe=512/granularity=100/wnd_scale_factor=4/epd_thresh=2045/icr=10.0/air=1/xdf=0.5/tdf=0/headroom=1.0 t_threshold=900000.0/maxsrcrate=10.0/ontime=100000/offtime=100000/vbrrate=124.41/t0v=120/a=1.15/b=1.05/qlt=0.8/time_int=1000.0/sw_int=100/dist=1000 / Date:02/03/96 300000 250000 200000 150000 100000 50000 ICR: 10.00 10.00 10.00 10.00 / XRM: 16.00 16.00 16.00 16.00 / Graph: 1 Two TCP : Cwnds Cwnd Size for S1 Cwnd Size for S2 0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Time in milliseconds (a) Congestion Window Rates two-tcp/option=1/optionb=295/optiont=6/sw_qsize=2048/tbe=512/granularity=100/wnd_scale_factor=4/epd_thresh=2045/icr=10.0/air=1/xdf=0.5/tdf=0/headroom=1.0 t_threshold=900000.0/maxsrcrate=10.0/ontime=100000/offtime=100000/vbrrate=124.41/t0v=120/a=1.15/b=1.05/qlt=0.8/time_int=1000.0/sw_int=100/dist=1000 / Date:02/03/96 180 160 140 120 100 80 60 40 20 ICR: 10.00 10.00 10.00 10.00 / XRM: 16.00 16.00 16.00 16.00 / Graph: 1 Two TCP : ACRs ACR for S1 ACR for S2 0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Time in milliseconds (b) ACR Figure 8.7: Two TCP Source Con guration, Bu er=2048 cells, TBE=512 271
Figure 8.7(b) shows the rates (ACRs) allocated to the two sources. Notice that the curves for the two sources and are at the maximum possible value (90% of the link rate) and so the sources have a large ACR. The reason for throughput being less than maximum possible is not the sources' ACRs but their windows. That is,the sources are not rate-limited but are window-limited. Also, notice that the two curves overlap. This shows that the ABR rate allocation mechanism is fair. The main reason for the large drop in throughput is that cells (packets) are dropped. Each cell loss results in a signi cant loss of time and throughput. In this case, this happens before the ABR control loop is set up (open-loop period). The TBE in this case was 512. For two sources, one would assume that having 1024 bu ers in the switch would be su cient. But this case shows that cells are lost even when there are twice as many (2048) bu ers in the switch. Thus, TBE is not a good mechanism to control or allocate bu ers. This observation was also made in our earlier work on non-TCP bursty tra c [53, 27]. 8.11 E ect of Finite Bu ers and Varying ABR Capacity Next we studied the e ect of varying ABR capacity. For this purpose, weintroduce a VBR tra c in the background. We conducted several experiments with two and ve ABR sources. Since VBR takes up 40% of the link bandwidth, we expect the maximum ABR throughput to be 60% of the case without VBR. Figures 8.8 and 8.9 show the window graphs for the two- and ve-source source con gurations, respectively. Four di erent TBE and bu er size combinations are used. The graphs clearly show the instants when cells are lost and the TCP windows 272
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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
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(a) Transmitted Cell Rate (basic ER
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(a) Transmitted Cell Rate (basic ER
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Page 247 and 248: (a) Transmitted Cell Rate (c) Link
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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
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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 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: the performance is fair. Also, the
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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Page 331 and 332: problems. During the ON time, the V
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Page 335 and 336: like ERICA+ which uses the queueing
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Page 339 and 340: 8.17 E ect of Long-Range Dependent
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Page 343 and 344: The key point is that the MPEG-2 ra
Page 345 and 346: the MPEG-2 Transport Stream, and st
Page 347 and 348: 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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