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CHAPTER 5 SAR FUNCTION
216
5.8.4 ABR Parameters
The following table lists the ABR parameters defined by the ATM Forum. Their initial values are also defined
by the ATM Forum.
Table 5-9. ABR Parameters
Label
Function
Unit and range
Initial value
PCR
Peak cell rate
Unit: cells/s
Range: (
Note
)
Unit: cells/s
Range: (
Note
)
Unit: cell/s
Range: (
Note
)
Power of 2
Range: 1/32,768 to 1
Power of 2
Range: 2 to 256
Constant: 2
MCR
Minimum cell rate
ICR
Initial cell rate, which is valid at initialization and in the idle
state
Rate increase factor, which is used to control the way the cell
is increased at RM cell reception
Maximum number of cells that can be transmitted between
FRM cell transmission sessions
The number (minimum number) of cells that are transmitted
between FRM cell transmission sessions is controlled.
Rate decrease factor, which is used to control the way the
transmission cell rate is decreased
Allowed cell rate, which is the current cell rate that can be
applied to transmission from the source
Missing RM cell count, which is used to control the number of
FRM cells that can be transmitted before a BRM cell is sent
back
ACR decrease time factor, that is, time limit between FRM
transmission sessions. If no FRM is transmitted even after
this time interval has elapsed, the rate is decreased to the
ICR.
Time between FRM cell transmission sessions for the active
source
RIF
1
Nrm
32
Mrm
2
RDF
Power of 2
Range: 1/32,768 to 1
Unit: cells/s
Range: (
Note
)
Unit: cells:
Integer
1/32,768
ACR
ICR
CRM
ADTF
Unit: seconds
Range: 0.01 to 10.23
(in 10 ms steps)
0.5
Trm
Unit: milliseconds
100 times power of 2
Range: 100*2
-7
to 100*2
0
Unit: microseconds
Range: 0 to 16.7 s
Unit: cells
Range: 0 to 16,777,215
100
FRTT
Fixed round trip time, which is the total propagation delay from
the source to the destination
Transient buffer exposure, which is a parameter used by the
network to limit the number of cells that can be transmitted
from the source within the start-up period before the first RM
cell is returned
Cut-off decrease factor, which is used to control the way the
ACR and the CRM are decreased
Tagged cell rate, at which the source can transmit out-of-rate
FRM cells
TBE
16,777,215
CDF
0 or power of 2
Range: 0, 1/64 to 1
Constant: 10 cells/s
1/16
TCR
10
Note
The rate field is represented as shown below:
Rate = 2
e
*(1 + m/512)*nz cells/s
14
0
m
15
Re-
served
9
8
nz
e
13