Traffic Management for the Available Bit Rate (ABR) Service in ...
Traffic Management for the Available Bit Rate (ABR) Service in ... Traffic Management for the Available Bit Rate (ABR) Service in ...
suddenly appear at the switch during the rst round trip before the closed-loop phase of the control takes e ect. During this time, the source will have sent TBE/Nrm RM cells. Hence, CRM = d TBE Nrm e The xed part of the round-trip time (FRTT) is computed during connection setup. This is the minimum delay along the path and does not include any queuing delay. During this time, a source may send as many as ICR FRTT cells into the network. Since this number is negotiated separately as TBE, the following relationship exists between ICR and TBE: or ICR FRTT TBE ICR TBE=FRTT The sources are required to use the ICR value computed above if it is less than the ICR negotiated with the network. In other words: ICR used by the source = MinfICR negotiated with the network� TBE/FRTTg In negotiating TBE, the switches have to consider their bu er availability. As the name indicates, the switch may be suddenly exposed to TBE cells during the rst round trip (and also after long idle periods). For small bu ers, TBE should be small and vice versa. On the other hand, TBE should also be large enough to prevent unnecessary triggering of rule 6 on long delay paths. 27
It has been incorrectly believed that cell loss could be avoided by simply ne- gotiating a TBE value below the number of available bu ers in the switches. We have shown [53] that it is possible to construct workloads where queue sizes could be unreasonably high even when TBE is very small. For example, if the FRM input rate is x times the BRM output rate (see Figure 2.8), where x is less than CRM, rule 6 will not trigger but the queues in the network will keep building up at the rate of (x ; 1) ACR leading to large queues. The only reliable way to protect a switch from large queues is to build it in the switch allocation algorithm. The ERICA+ algorithm presented in this dissertation is an example of one such algorithm. Figure 2.8: Source Rule 6 does not trigger if BRM ow is maintained Observe that the FRTT parameter which is the sum of xed delays on the path is used in the formula for ICR. During the development of this rule, an estimate of round trip time (RTT), including the xed and variable delays was being used instead of FRTT in the ICR calculation. We argued that RTT estimated at connection setup is a random quantity bearing little relation to the round trip delays during actual operation [55]. Such parameter setting could trigger source 28
- Page 3 and 4: ABSTRACT With the merger of telecom
- Page 5 and 6: Tra c Management for the Available
- Page 7 and 8: To my family iv
- Page 9 and 10: VITA April 30, 1971 :::::::::::::::
- Page 11 and 12: 2.7 Switch Behavior . . . . . . . .
- Page 13 and 14: 5.8 Proof: Fairness Algorithm Impro
- Page 15 and 16: 8.15 Factors A ecting Bu ering Requ
- Page 17 and 18: Bibliography . . . . . . . . . . .
- Page 19 and 20: 8.12 Maximum Queues for Satellite N
- Page 21 and 22: 5.1 Transmitted cell rate (instanta
- Page 23 and 24: 6.13 Results foratwo sources con gu
- Page 25 and 26: 7.11 E ect of UILI on Medium Bursts
- Page 27 and 28: C.3 Flow Chart of Bi-Directional Co
- Page 29 and 30: header information which limits the
- Page 31 and 32: switches since a standard does not
- Page 33 and 34: congestion control deals with the c
- Page 35 and 36: hand side of the equation is the su
- Page 37 and 38: analyses which are used to validate
- Page 39 and 40: CHAPTER 2 THE ABR TRAFFIC MANAGEMEN
- Page 41 and 42: time (RTT). As we explain later, AB
- Page 43 and 44: feedback from nearby switches to re
- Page 45 and 46: Note that in-rate and out-of-rate d
- Page 47 and 48: Data cells also have an Explicit Fo
- Page 49 and 50: opportunity the source may nd that
- Page 51 and 52: Figure 2.7: Scheduling of forward R
- Page 53: as the timeout value) which reduces
- Page 57 and 58: NI CI Action 0 0 ACR Min(ER, ACR +
- Page 59 and 60: Source Rule 13: Sources can optiona
- Page 61 and 62: Switch Rule 1: This rule speci es t
- Page 63 and 64: Observe that the ABR tra c manageme
- Page 65 and 66: complex method like per-VC queuing
- Page 67 and 68: graphs have a steady state with con
- Page 69 and 70: Figure 3.2: Operating point between
- Page 71 and 72: The following example illustrates t
- Page 73 and 74: mention this concept of fairness fo
- Page 75 and 76: control problem was also simpler. S
- Page 77 and 78: of such an occurrence is expected t
- Page 79 and 80: y giving only one feedback per meas
- Page 81 and 82: CHAPTER 4 SURVEY OF ATM SWITCH CONG
- Page 83 and 84: The adaptive FCVC algorithm [63] co
- Page 85 and 86: np. Thus, long path VCs have fewer
- Page 87 and 88: networks like ATM can have complete
- Page 89 and 90: scheme followed by a discussion of
- Page 91 and 92: exibility of decoupling the enforce
- Page 93 and 94: 4.6.1 Key Techniques In EPRCA, the
- Page 95 and 96: If the mean ACR is not a good estim
- Page 97 and 98: is the ratio of the input rate to t
- Page 99 and 100: which shares the link equally as al
- Page 101 and 102: proportional to the the unused ABR
- Page 103 and 104: The key technique in the scheme is
suddenly appear at <strong>the</strong> switch dur<strong>in</strong>g <strong>the</strong> rst round trip be<strong>for</strong>e <strong>the</strong> closed-loop<br />
phase of <strong>the</strong> control takes e ect. Dur<strong>in</strong>g this time, <strong>the</strong> source will have sent<br />
TBE/Nrm RM cells. Hence,<br />
CRM = d TBE<br />
Nrm e<br />
The xed part of <strong>the</strong> round-trip time (FRTT) is computed dur<strong>in</strong>g connection<br />
setup. This is <strong>the</strong> m<strong>in</strong>imum delay along <strong>the</strong> path and does not <strong>in</strong>clude any<br />
queu<strong>in</strong>g delay. Dur<strong>in</strong>g this time, a source may send as many as ICR FRTT<br />
cells <strong>in</strong>to <strong>the</strong> network. S<strong>in</strong>ce this number is negotiated separately as TBE, <strong>the</strong><br />
follow<strong>in</strong>g relationship exists between ICR and TBE:<br />
or<br />
ICR FRTT TBE<br />
ICR TBE=FRTT<br />
The sources are required to use <strong>the</strong> ICR value computed above if it is less than<br />
<strong>the</strong> ICR negotiated with <strong>the</strong> network. In o<strong>the</strong>r words:<br />
ICR used by <strong>the</strong> source =<br />
M<strong>in</strong>fICR negotiated with <strong>the</strong> network�<br />
TBE/FRTTg<br />
In negotiat<strong>in</strong>g TBE, <strong>the</strong> switches have to consider <strong>the</strong>ir bu er availability. As<br />
<strong>the</strong> name <strong>in</strong>dicates, <strong>the</strong> switch may be suddenly exposed to TBE cells dur<strong>in</strong>g<br />
<strong>the</strong> rst round trip (and also after long idle periods). For small bu ers, TBE<br />
should be small and vice versa. On <strong>the</strong> o<strong>the</strong>r hand, TBE should also be large<br />
enough to prevent unnecessary trigger<strong>in</strong>g of rule 6 on long delay paths.<br />
27
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