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

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world wide web (which use TCP/IP) running over ABR and UBR. In this disser- tation, we concentrate on the performance of TCP/IP over ATM-ABR. ATM-UBR performance has been examined in several recent studies [29, 28, 67, 35]. The afore- mentioned TCP studies also compare UBR performance with ABR using either EFCI switches [28] or explicit rate (ER) switches in local area network (LAN) topologies. Since LANs have short feedback loops, some properties of the ABR control mechanisms may not be clearly observed in LAN con gurations. In this chapter, we provide a more detailed study of the dynamics and performance of TCP over ABR. In the UBR service class, the only degree of freedom to control tra c is through scheduling, bu er allocation and cell drop policies. ABR has additional degrees of freedom in terms of switch schemes and source parameters. The ABR service requires network switches to constantly monitor their load and feed the information backtothe sources, which in turn dynamically adjust their input into the network. The Transport Control Protocol (TCP), at the same time, uses packet loss in the subnetwork as an implicit feedback indicating network congestion and reduces its data load on the network. This mechanism is called the "Slow Start" congestion avoidance mechanism [40]. There is currently a debate in the networking community about the need for ABR service particularly in light of TCP's built-in congestion control facilities. We address some of these issues in this chapter. We rst study the dynamics of TCP tra c over ATM, the e ect of cell loss, and the interaction of TCP with the ABR congestion control mechanisms. We nd that TCP performs best when it does not experience packet loss. For the ABR service, we quantify the amount of bu ering required at the ATM switches to avoid TCP packet loss. Speci cally, we nd that ABR is scalable over TCP in the sense that it requires 257
u ering which does not depend upon the number of connections. The amount of bu ering depends upon factors such as the switch congestion control scheme used, and the maximum round trip time (RTT) of all virtual circuits (VCs) through the link. On the other hand, the UBR service is not scalable in the sense that it requires bu ering proportional to the sum of the TCP receiver windows of all sources. The above observations are true for applications like le transfer which have per- sistant demand characteristics. We verify that the requirements hold even in the presence of highly VBR background tra c (including multiplexed MPEG-2 video tra c). However, when TCP applications are bursty (i.e., have active and idle peri- ods), it is possible that the network is overloaded by a burst of data from a number of TCP sources simultaneously. While there can be little guarantees under such patho- logical workloads, we nd that our observations about bu er requirements hold for a large number of World Web Web (real-life bursty) applications running over TCP. 8.1 TCP control mechanisms TCP is one of the few transport protocols that has its own congestion control mechanisms. The key TCP congestion mechanism is the so called \Slow start." TCP connections use an end-to-end ow control window to limit the number of packets that the source sends. The sender window is the minimum of the receiver window (Wrcvr) and a congestion window variable (CWND). Whenever a TCP connection loses a packet, the source does not receive an ac- knowledgment and it times out. The source remembers the congestion window (CWND) value at which it lost the packet by setting a threshold variable SSTHRESH 258
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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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Page 233 and 234: (a) Transmitted Cell Rate (basic ER
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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
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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
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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
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Page 281 and 282: Figure 7.13: An event trace illustr
Page 283: CHAPTER 8 SUPPORTING INTERNET APPLI
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
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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
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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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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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