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CHAPTER 5 SAR FUNCTION
218
(2) Setting registers for the ABR
The ABR service uses the APR, TBW, and AUB registers. The host must set values in these registers. In
addition, values must also be set in those registers that are responsible for internal congestion control (see
Section 5.8.6
).
APR register
The APR register is set with parameters for each port used for the ABR service. The parameters set
in the APR register are common to all ABR channels. Those parameters that are separately specified
for each channel (VC) are set in the transmit/receive VC table. The host sets, in the APR register, the
ABR parameters obtained through negotiation.
31
0
CRM
- 0 -
16
15
Trm0
7
Nrm0
Mrm
3
2
5
6
8
Trm0
The Trm parameter is used to set the length of the period during which FRM cell
transmission is performed for the active source.
For the host, set Trm0 so that Trm is displayed in cell time units. (1 cell time = 2.8312
μ
s; the
μ
PD98405 ignores the SONET/SDH overhead and performs rate calculation
with the maximum rate fixed to 149.76 Mbps.)
Trm (milliseconds) = Trm0*2.8312/1,000
Default value after a reset (Trm0): 35,321 (89F9H)
CRM
Missing RM cell count.
The CRM parameter controls the number of FRM cells that can be transmitted before a
BRM cell is returned.
Default value after a reset: 255
Mrm
The Mrm parameter controls the assignment of the bandwidth (cell count) for BRM cells
or data cells during FRM cell transmission.
Default value after a reset: 2
Nrm0
The Nrm parameter sets the maximum number of cells that the source can transmit
during FRM cell transmission.
Nrm is expressed as follows.
Nrm = 2*2
Nrm0
Default value after a reset (Nrm0): 4