CN8236EBGB Mindspeed Technologies, CN8236EBGB Datasheet - Page 200

• 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

6.0 Traffic Management
6.3 ABR Flow Control Manager
6.3.7 Rate Decisions and Updates
6-32
6.3.7.2 Rate Adjustment
6.3.7.3 Backward RM
6.3.7.1 ABR Traffic
Cell Flow Control
Overview
Shaping
The CN8236 schedules ABR VCCs as a single leaky bucket GCRA channel, but
the rate is subject to continual adjustment. At initialization, the host assigns
flow-controlled VCCs I and L parameters corresponding to the negotiated ICR. The
Cell Scheduler rate-shapes the initial traffic according to these GCRA parameters.
This shaped cell stream includes in-rate Forward and Backward RM cells.
ABR Flow Control Manager overwrites the I and L parameters in the
SCH_STATE of the VCC. The updated rates fall within the range of MCR and
PCR, which are specified on a per-connection basis.
The CN8236 dynamically adjusts the rate of transmission for ABR VCCs based upon
network feedback, individual VCC parameters, and the current transmission rate. The
ABR Flow Control Manager uses all of these inputs to calculate the ACR of the
connection. This ACR corresponds to I and L GCRA parameters. The CN8236
updates the I and L parameters of the VCC with the new ACR I and L values.
types of events—the reception of a Backward RM cell or the transmission of a
Forward RM cell. The decision process is unique for each event type.
NOTE:
The ABR Rate Decision table consists of many indexed entries. Each of these
entries is called an ABR Rate Decision Block or ARDB. Each ARDB represents a
possible transmission rate for an ABR VCC. The rate of an ARDB is a
monotonically increasing function of the index of the block.
storing its current ARDB index in the RATE_INDEX field of the SCH_STATE VCC
structure. This RATE_INDEX uniquely identifies the current transmission rate of the
VCC.
When feedback from the network results in flow control rate adjustments, the
The Flow Control Manager updates the transmission rate in response to two
The CN8236 tracks the state of each ABR connection’s transmission rate by
Figure 6-18
Both of these event types may occur in one cell slot. In this case, the
CN8236 makes both decisions before updating ACR.
Mindspeed Technologies
illustrates a block diagram of Backward RM flow control.
ATM ServiceSAR Plus with xBR Traffic Management
™
28236-DSH-001-B
CN8236