CN8236EBGB Mindspeed Technologies, CN8236EBGB Datasheet - Page 205

• Manufacturer Part Number: CN8236EBGB
• Description: ATM SAR 155Mbps 3.3V ABR/CBR/GFR/UBR/VBR 388-Pin BGA
• Manufacturer: Mindspeed Technologies

Specifications of CN8236EBGB

• Package: 388BGA
• Traffic Class: ABR|CBR|GFR|UBR|VBR
• Utopia Type: Level 1|Level 2
• Host Interface: PCI
• Maximum Data Rate: 155 Mbps
• Typical Operating Supply Voltage: 3.3 V
• Minimum Operating Supply Voltage: 3 V

CN8236
ATM ServiceSAR Plus with xBR Traffic Management
6.3.7.4 Forward RM Cell
28236-DSH-001-B
Transmission Decisions
6.3.7.5 ACR Change
Notification
The CN8236 also adjusts the transmission rates of an ABR in-rate cell stream
before sending a Forward RM cell. This adjustment utilizes a Rate Decision
Vector selection process. As stated above, four of the eight ARDB vectors are
used for CI/NI rate adjustment. The other four are used for Forward RM cell rate
adjustments.
the ADTF timer and the CRM counter. These internal measures may force the
connection to decrease its rate when sending an RM cell.
table entry (FWD_ER). The normal value for FWD_ER is PCR. When this field
is initialized in the VCC table entry, it must be set to the rate specified by the
exponent table entries so that the resulting selected rate is PCR. This is because
when a Forward RM cell is eventually received as a Backward RM cell, the
CN8236 maps the available cell rate (ACR) to a rate specified by the exponent
table. If PCR falls between two exponent table rates and FWD_ER is set to PCR,
the ACR of the connection is limited to the lower of the two exponent table rates,
thereby lowering the rate below PCR.
An ACR change notification mechanism per ATM Forum AF-SAA-0108*
Appendix D is implemented for both source and destination. Five fields in the
SEG VCC table entry (S_EN_NCR, S_NCR_LO, S_NCR_HI, S_NCR_TRIG,
and S_NCR_DIR) are used for source ACR change notification. Six fields in the
RSM VCC table entry (D_EN_NCR, D_NCR_LO_, D_NCR_HI,
ND_CR_TRIG, D_NCR_DIR, and ACR_NOT_ER) are used for destination
ACR/ER change notification. x_EN_NCR enables the ACR change notification
mechanism. x_NCR_LO is the low threshold value, and x_NCR_HI is the high
threshold value. x_NCR_TRIG indicates that a notification has been triggered.
x_NCR_DIR indicates which threshold was crossed last, logic high for HI, logic
low for LO. Finally, ACR_NOT_ER allows the user to choose between
destination ACR or ER change notification. A special status queue entry is
written when the following conditions occur:
NOTE:
current ACR value and is indicated by the NCR bit set to a logic 1. The
SRC_NOT_DEST bit indicates whether the notification is source- or
destination-generated. In the case of a destination change notification the current
ER value (TA_ER) is also provided.
Instead of the CI/NI bits, the Forward RM cell vector selection is based upon
The ER for Forward RM cells on any channel is set in word 18 of the VCC
• x_NCR_LO triggers a notification when
• x_NCR_HI triggers a notification when
The special segmentation status queue (see
– The new value of ACR
– Either this is the first notification OR the last notification was triggered
– The new value of ACR
– Either this is the first notification or the last notification was triggered
(1)
depending on ACR_NOT_ER value.
For the destination change notification, this can be either ACR or ER
Mindspeed Technologies
from NCR_HI.
from NCR_LO.
(1)
(1)
is less than or equal to NCR_LO, AND
is greater than or equal to NCR_HI, AND
™
Section
6.3 ABR Flow Control Manager
4.3.6) containing the
6.0 Traffic Management
6-37