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 ...
A complete layered view of various components of the OSU scheme is shown in Figure 5.9. The minimum that we need for correct operation is the fairness algorithm. The aggressive fairness option allows fairness to be achieved faster. The precise fair share computation option allows both fairness and e ciency to be achieved quickly but requires the switches to use all declared OCRs in computing the fair share. The BECN option helps reduce the feedback delay in large WAN cases. As shown in Figure 5.9, these options can be used individually or inalayered manner. Figure 5.9: Alayered view of various components and options of the OSU scheme 5.4 Other Simple Variants of the OSU Scheme are: Some variations that do not materially change the performance of the OSU scheme 121
1. The source o ered average cell rate is measured at the entry switch rather than at the source. This option may be preferable for policing and for operation in public network environments, where a sources' measurements cannot be trusted. 2. The o ered average cell rate of a VC is measured at every switch. This is unnecessary since the average rate of a VC should not change from switch to switch. This may be used only if the VC crosses many ATM networks under di erent administrative domains. 3. Use multiplicative load adjustment factors instead of divisors. In OSU scheme, divisors are used for rates. However, for the inter-cell transmission time, the same factor is used as amultiplier. 4. Use dynamic averaging intervals. The averaging interval at the switch and the source are kept constant in the OSU scheme. It is possible to use regeneration intervals as the averaging interval as was done in the DECbit scheme [46]. However, our experience with DECbit scheme was that implementors didn't like the the regeneration interval and queue length averaging because of the number of instructions required in the packet forwarding path. 5. Use cell counts rather than cell rates. Since the averaging interval is constant, the cell rates are proportional to the counts. 5.5 Simulation Results In this section, we present simulation results for several con gurations. These con gurations have been specially chosen to test a particular aspect of the scheme. In general, we prefer to use simple con gurations that test various aspects of the 122
- 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
- Page 105 and 106: the bandwidth allocations to satis
- Page 107 and 108: 4.10 DMRCA scheme The Dynamic Max R
- Page 109 and 110: on its CCR. Further MAX times out i
- Page 111 and 112: other words, a di erent set of para
- Page 113 and 114: A combination of several ideas in a
- Page 115 and 116: 4.13 SP-EPRCA scheme The SP-EPRCA s
- Page 117 and 118: RTD and shuts o the source (for sta
- Page 119 and 120: 4.14.1 Common Drawbacks Though the
- Page 121 and 122: The ATM Tra c Management standard a
- Page 123 and 124: 5.1.1 Control-Cell Format The contr
- Page 125 and 126: The last two elds are used in the b
- Page 127 and 128: Figure 5.3: Flow chart for updating
- Page 129 and 130: LAF in cell Max(LAF in cell, z) The
- Page 131 and 132: the time of departure (instant mark
- Page 133 and 134: the steady state. The system operat
- Page 135 and 136: 5.2.3 Use Measured Rather Than Decl
- Page 137 and 138: said about the maximum queue length
- Page 139 and 140: The key problem with some unipolar
- Page 141 and 142: Figure 5.6: Space time diagram show
- Page 143 and 144: As noted, these heuristics do not g
- Page 145 and 146: Transmitted Cell Rate ABR Queue Len
- Page 147: 4. The RM cell contains a timestamp
- Page 151 and 152: Transmitted Cell Rate Link Utilizat
- Page 153 and 154: Transmitted Cell Rate Link Utilizat
- Page 155 and 156: Transmitted Cell Rate Link Utilizat
- Page 157 and 158: Figure 5.17: The parking lot fairne
- Page 159 and 160: Figure 5.19: Network con guration w
- Page 161 and 162: Transmitted Cell Rate Link Utilizat
- Page 163 and 164: Transmitted Cell Rate Link Utilizat
- Page 165 and 166: 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
- Page 189 and 190: the CCR value may not be an accurat
- 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
1. The source o ered average cell rate is measured at <strong>the</strong> entry switch ra<strong>the</strong>r than<br />
at <strong>the</strong> source. This option may be preferable <strong>for</strong> polic<strong>in</strong>g and <strong>for</strong> operation <strong>in</strong><br />
public network environments, where a sources' measurements cannot be trusted.<br />
2. The o ered average cell rate of a VC is measured at every switch. This is<br />
unnecessary s<strong>in</strong>ce <strong>the</strong> average rate of a VC should not change from switch to<br />
switch. This may be used only if <strong>the</strong> VC crosses many ATM networks under<br />
di erent adm<strong>in</strong>istrative doma<strong>in</strong>s.<br />
3. Use multiplicative load adjustment factors <strong>in</strong>stead of divisors. In OSU scheme,<br />
divisors are used <strong>for</strong> rates. However, <strong>for</strong> <strong>the</strong> <strong>in</strong>ter-cell transmission time, <strong>the</strong><br />
same factor is used as amultiplier.<br />
4. Use dynamic averag<strong>in</strong>g <strong>in</strong>tervals. The averag<strong>in</strong>g <strong>in</strong>terval at <strong>the</strong> switch and <strong>the</strong><br />
source are kept constant <strong>in</strong> <strong>the</strong> OSU scheme. It is possible to use regeneration<br />
<strong>in</strong>tervals as <strong>the</strong> averag<strong>in</strong>g <strong>in</strong>terval as was done <strong>in</strong> <strong>the</strong> DECbit scheme [46].<br />
However, our experience with DECbit scheme was that implementors didn't<br />
like <strong>the</strong> <strong>the</strong> regeneration <strong>in</strong>terval and queue length averag<strong>in</strong>g because of <strong>the</strong><br />
number of <strong>in</strong>structions required <strong>in</strong> <strong>the</strong> packet <strong>for</strong>ward<strong>in</strong>g path.<br />
5. Use cell counts ra<strong>the</strong>r than cell rates. S<strong>in</strong>ce <strong>the</strong> averag<strong>in</strong>g <strong>in</strong>terval is constant,<br />
<strong>the</strong> cell rates are proportional to <strong>the</strong> counts.<br />
5.5 Simulation Results<br />
In this section, we present simulation results <strong>for</strong> several con gurations. These<br />
con gurations have been specially chosen to test a particular aspect of <strong>the</strong> scheme.<br />
In general, we prefer to use simple con gurations that test various aspects of <strong>the</strong><br />
122
Change language