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 ...
Label Expansion Default Value PCR Peak Cell Rate - MCR Minimum Cell Rate 0 ACR Allowed Cell Rate - ICR Initial Cell Rate PCR TCR Tagged Cell Rate 10 cells/s Nrm Number of cells between FRM cells 32 Mrm Controls bandwidth allocation 2 between FRM, BRM and data cells Trm Upper Bound on Inter-FRM Time 100 ms RIF Rate Increase Factor 1/16 RDF Rate Decrease Factor 1/16 ADTF ACR Decrease Time Factor 0.5 ms TBE Transient Bu er Exposure 16,777,215 CRM Missing RM-cell Count d TBE/Nrm e CDF Cuto Decrease Factor 1/16 FRTT Fixed Round-Trip Time - Table 2.1: List of ABR Parameters exceed the ACR of the source. Such RM cells are called \in-rate" RM cells. Under exceptional circumstances, switches, destinations, or even sources can generate extra RM cells. These \out-of-rate" RM cells are not counted in the ACR of the source and are distinguished by having their cell loss priority (CLP) bit set, which means that the network will carry them only if there is plenty of bandwidth and can discard them if congested. The out-of-rate RM cells generated by the source and switch are limited to 10 RM cells per second per VC. One use of out-of-rate RM cells is for BECN from the switches. Another use is for a source, whose ACR has been set to zero by the network, to periodically sense the state of the network. Out-of-rate RM cells are also used by destinations of VCs whose reverse direction ACR is either zero or not su cient to return all RM cells received in the forward direction. 17
Note that in-rate and out-of-rate distinction applies only to RM cells. All data cells in ABR should have CLP set to 0 and must always be within the rate allowed by the network. 2.3 Forward and Backward RM cells Resource Management cells traveling from the source to the destination are called \forward RM" (FRM) cells. The destination turns around these RM cells and sends them back to the source on the same VC. Such RM cells traveling from the destination to the source are called Backward RM (BRM) cells. Forward and backward RM cells are illustrated in Figure 2.4. Note that when there is bi-directional tra c, there are FRMs and BRMs in both directions on the Virtual Channel (VC). A bit in the RM cell payload indicates whether it is an FRM or BRM. This direction bit (DIR) is changed from 0 to 1 by the destination. 2.4 RM Cell Format The complete format of the RM cells is shown in gure 2.5. Every RM cell has the regular ATM header of ve bytes. The payload type indicator (PTI) eld is set to 110 (binary) to indicate that the cell is an RM cell. The protocol id eld, which isone byte long, is set to one for ABR connections. The direction (DIR) bit distinguishes forward and backward RM cells. The backward noti cation (BN) bit is set only in switch generated BECN cells. The congestion indication (CI) bit is used by relative rate marking switches. It may also be used by explicit rate switches under extreme congestion as discussed later. The no increase (NI) bit is another bit available to explicit rate switches to indicate moderate congestion. The request/acknowledge, 18
- Page 1 and 2: Tra c Management for the Available
- 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: feedback from nearby switches to re
- 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 and 54: as the timeout value) which reduces
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- 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
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- Page 81 and 82: CHAPTER 4 SURVEY OF ATM SWITCH CONG
- Page 83 and 84: The adaptive FCVC algorithm [63] co
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- Page 87 and 88: networks like ATM can have complete
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Note that <strong>in</strong>-rate and out-of-rate dist<strong>in</strong>ction applies only to RM cells. All data<br />
cells <strong>in</strong> <strong>ABR</strong> should have CLP set to 0 and must always be with<strong>in</strong> <strong>the</strong> rate allowed<br />
by <strong>the</strong> network.<br />
2.3 Forward and Backward RM cells<br />
Resource <strong>Management</strong> cells travel<strong>in</strong>g from <strong>the</strong> source to <strong>the</strong> dest<strong>in</strong>ation are called<br />
\<strong>for</strong>ward RM" (FRM) cells. The dest<strong>in</strong>ation turns around <strong>the</strong>se RM cells and sends<br />
<strong>the</strong>m back to <strong>the</strong> source on <strong>the</strong> same VC. Such RM cells travel<strong>in</strong>g from <strong>the</strong> dest<strong>in</strong>ation<br />
to <strong>the</strong> source are called Backward RM (BRM) cells. Forward and backward RM cells<br />
are illustrated <strong>in</strong> Figure 2.4. Note that when <strong>the</strong>re is bi-directional tra c, <strong>the</strong>re are<br />
FRMs and BRMs <strong>in</strong> both directions on <strong>the</strong> Virtual Channel (VC). A bit <strong>in</strong> <strong>the</strong> RM<br />
cell payload <strong>in</strong>dicates whe<strong>the</strong>r it is an FRM or BRM. This direction bit (DIR) is<br />
changed from 0 to 1 by <strong>the</strong> dest<strong>in</strong>ation.<br />
2.4 RM Cell Format<br />
The complete <strong>for</strong>mat of <strong>the</strong> RM cells is shown <strong>in</strong> gure 2.5. Every RM cell has<br />
<strong>the</strong> regular ATM header of ve bytes. The payload type <strong>in</strong>dicator (PTI) eld is set to<br />
110 (b<strong>in</strong>ary) to <strong>in</strong>dicate that <strong>the</strong> cell is an RM cell. The protocol id eld, which isone<br />
byte long, is set to one <strong>for</strong> <strong>ABR</strong> connections. The direction (DIR) bit dist<strong>in</strong>guishes<br />
<strong>for</strong>ward and backward RM cells. The backward noti cation (BN) bit is set only <strong>in</strong><br />
switch generated BECN cells. The congestion <strong>in</strong>dication (CI) bit is used by relative<br />
rate mark<strong>in</strong>g switches. It may also be used by explicit rate switches under extreme<br />
congestion as discussed later. The no <strong>in</strong>crease (NI) bit is ano<strong>the</strong>r bit available to<br />
explicit rate switches to <strong>in</strong>dicate moderate congestion. The request/acknowledge,<br />
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