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

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stringent test is required. We had observed that the original ERICA algorithm does not converge to max-min fairness in certain situations. Such situations arise when the ERICA algorithm is executed in a state where some of the sources cannot fully utilize their allocated bandwidth on a link (for example, because they are bottlenecked on another link), and the rest of the sources contending for bandwidth have unequal CCR values, which are greater than the fair share value ( rst term in the maximum formula). The ERICA algorithm does not converge to max-min fairness in these situations because, after z converges to one, the second term in the maximum formula becomes CCRi=1 =CCRi, and the rst term is constant. The maximum of the two terms for the contending sources is the second term, because there are sources that are not fully utilizing their allocated bandwidth. Hence, the sources do not change their rates. Figure 6.10: Upstream Con guration An example of this situation can be illustrated by an upstream con guration (see gure 6.10). The upstream con guration consists of three switches and 17 VCs. The second link is shared by VC 15, VC 16, and VC 17. Because there are 15 VCs on the 191
st link, VC 15 is limited to a throughput of less than 1/15 the link rate. VC 16 and VC 17 should, therefore, each converge to a little less than 7/15 of the second link rate. The con guration is called an upstream con guration because the bottleneck link is the rst link (upstream link). A WAN con guration (1000 Km links) is used in this situation to illustrate the scalability of ERICA to long distances. Figure 6.17 shows that the original ERICA algorithm was unfair in this situation, and gure 6.18 shows that ERICA, after the modi cation discussed in section 6.2, is fair. As seen in gure 6.18, the modi ed algorithm converges to max-min allocations. Regardless of the initial load factor value, after a short transient period, all sources contending for bandwidth are allocated equal rates, and the two curves in gure 6.18(b) (number of cells received at the destination) have the same slope (compare with gure 6.17(b)). The transient responseisslightly worse than the original ERICA algorithm due to the temporary over-allocation needed to equalize the shares, but the steady state performance is as good as with the original ERICA algorithm. 6.22.5 Transient and Steady State Performance To test the transient response of the system, we use a modi ed two source con- guration. The con guration is similar to the two source con guration because two sources share the same link, but one of the sources is only active from 10 ms to 20 ms while the other source is active throughout. Besides illustrating the transient response of the system, this con guration also illustrates the e ect of the \fairshare rst" algorithm discussed in section 6.3. That algorithm (see section 6.3) prevents a low rate VC to rise above F airShare. This VC takes an extra round trip compared to the basic ERICA because it rst comes to F airShare before rising further. The 192
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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
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 and 186: efore competing sources can receive
Page 187 and 188: that the latest CCR information is
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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
Page 215 and 216: espectively. The target delay T 0 i
Page 217: 6.22.4 Fairness Figure 6.9: Parking
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
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
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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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