![](http://datasheet.mmic.net.cn/380000/-PD98405_datasheet_16745025/-PD98405_219.png)
CHAPTER 5 SAR FUNCTION
219
TBW register
The host sets, in the TBW register, all the bands that can be used by the
μ
PD98405, such as 155.52
and 25.6 Mbps. Obtain each band to be specified, using the following expression, and express it in
cells/s.
Band = 2
e
*(1 + m/2,048) cells/s
31
0
e
- 0 -
16
15
11
m
10
A band specified in the TBW register must be one that can be used by the ATM layer, that is, a band
that does not include the SONET/SDH overhead. The following table lists examples of the settings
made for the 155.52-Mbps SONET/SDH framer or 25.6-Mbps PHY device.
155.52 Mbps (149.76 Mbps)
e = 18, m = 711
25.6 Mbps (25.126 Mbps)
e = 15, m = 1,656
Because 149.76 Mbps (e = 18 and m = 711) is specified initially, it need not be specified if the built-in
PHY layer is used.
AUB register
The host sets, in the AUB register, a band that is exclusively used for the ABR or UBR service. If the
UBR service is not being used, the value set in the register will correspond to the band used for the
ABR service. The host can change this value at any time. When ABR and UBR are used
simultaneously, the total of C_ABR (band for ABR) and C_UBR (band for UBR) is C_ABR+UBR. See
Section 5.9
for details.
The AUB register is used with the source internal congestion control. See
Section 5.8.6
for details.
31
0
C_ABR+UBR
- 0 -
14
15
C_ABR+UBR: ABR and UBR bands. Bands used exclusively for the ABR and/or UBR service are
specified using the rate expression described below:
Rate = 2
e
*(1 + m/512)*nz cells/s
14
0
m
9
8
nz
e
13
Remark
The
μ
PD98405 performs rate adjustment based on the band that can be used in the ATM
layer (excluding the overhead incurred by SONET/SDH). Make the rate settings for the
AUB register, PCR, MCR, and ICR in that band of the ATM layer (excluding the overhead)
that can be used. When the 155.52-Mbps SONET/SDH framer is being used, the
maximum rate that can be set is 149.76 Mbps.