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CHAPTER 5 SAR FUNCTION
213
15. When a period at least equal to ADTF has elapsed since the latest in-rate FRM cell transmission, and
neither a data cell nor BRM cell is waiting:
a) If ACR
≥
ICR, the
μ
PD98405 sets the ACR with ICR, and removes the relevant channel from the
ABR scheduler.
b) If ACR < ICR, the
μ
PD98405 keeps the ACR as is, and removes the relevant channel from the ABR
scheduler.
Remarks 1
.
Nrm, Trm, Mrm, and CRM are specified for individual ports. (These parameters are set in
indirect address registers.)
2
.
PCR, MCR, ICR, RIF, CDF, RDF, and ADTF are specified for individual VCs. (These
parameters are set in the VC table.)
3
.
In-rate FRM and BRM cell transmission is included in the source rate assigned to the relevant
VC.
4
.
The ABR scheduler is a module for controlling the transmit cell time interval determined by
the ACR.
(2) Destination behavior
1.
Upon receiving a data cell, the
μ
PD98405 saves the EFCI of the data cell as the EFCI state of the
connection.
2.
Upon receiving an FRM cell, the
μ
PD98405 transmits a turn-around BRM cell to send back an RM cell
to the source. The DIR bit of the RM cell to be sent back is changed from forward (DIR = 0) to
backward (DIR = 1). The BN bit is reset to 0. The CCR, MCR, ER, CI, and NI fields are not changed
except in the following cases.
a) If the preserved EFCI state is set to 1, the
μ
PD98405 sets the CI bit of the RM cell to 1, and resets
the preserved EFCI state.
b) Upon receiving an internal congestion command (Set_Rx_Congestion command) from the host, the
μ
PD98405 sets the CI and/or NI of all BRM cells to 1.
c) If the number of cells in the receive FIFO becomes greater than the threshold value, the
μ
PD98405
sets the CI of all BRM cells to 1. (Internal congestion control: see
Section 5.8.6
.)
d) If there is no remaining capacity of the receive pool, the
μ
PD98405 sets the CI of those BRM cells
returned from the VC that belongs to this receive pool to 1.
3.
If an FRM cell is received before a turn-around BRM cell is scheduled for in-rate transmission (at the
relevant connection), the
μ
PD98405 schedules the turn-around BRM cell for in-rate transmission.
4.
If the
μ
PD98405 receives an FRM cell when another turn-around BRM cell is being scheduled for in-
rate transmission (at the relevant connection):
a) The contents of a BRM cell that has already been scheduled are overwritten with the contents of the
new BRM cell.