RS8234EBGC Mindspeed Technologies, RS8234EBGC Datasheet - Page 184

• Manufacturer Part Number: RS8234EBGC
• Description: RS8234EBGC ATM XBR SAR
• Manufacturer: Mindspeed Technologies

6.0 Traffic Management
6.3 ABR Flow Control Manager
Figure 6-14. RS8234 ABR-ER Feedback Generation (Destination Behavior)
6.3.3 Source and Destination Behaviors
6.3.4 ABR VCC Parameters
6-24
6.3.2.3 Out-of-Rate
6.3.2.2 Destination
FORWARD_RM
BACKWARD_RM
Behavior
Cells
The RS8234 also responds to an incoming ABR cell stream as an ABR
Destination. The reassembly coprocessor processes received Forward RM cells. It
turns around this incoming information to the segmentation coprocessor via the
SCH_STATE part of the segmentation VCC Table entry. The segmentation
coprocessor then formats Backward RM cells containing this information and
inserts these turnaround RM cells into the transmit cell stream.
backpressure to the Source. The host notifies the RS8234 of internal system
congestion. The RS8234 passes this information to the Source via Backward RM
cells, to flow control the transmitting Source. The SAR also processes the EFCI
bit in the data cell header(s) per the rules in TM 4.1.
In addition to in-rate cell streams, the RS8234 can also generate out-of-rate
(CLP=1) cell streams. These CLP=1 streams compliment and enhance the
information flow contained in the in-rate cell streams. An example of the use of
this mechanism would be to send out-of-rate Forward RM cells on a channel if the
transmit rate on that channel has dropped below the schedule table minimum rate.
This provides a mechanism to restart scheduling of an ABR VCC whose rate has
dropped to zero or below the schedule table minimum rate.
ABR’s Source and Destination Behavior Definitions are each listed in the ATM
Forum’s TM 4.1 Specification. Refer to this specification for these definitions.
The state of each VCC is stored individually in its SEG VCC Table entry. The
ABR parameters are stored in the SCH_STATE portion of the segmentation VCC
Table entry. Due to the large number of ABR parameters, the SCH_STATE of
ABR VCCs requires an additional location in the SEG VCC Table.
The RS8234 also provides a mechanism for the Destination host to apply
This process is illustrated in
Mindspeed Technologies
Segmentation
Coprocessor
Reassembly
Coprocessor
(Backward RM Cell Formatting)
(Forward RM Cell Processing)
Turnaround
Information
ATM ServiceSAR Plus with xBR Traffic Management
Figure
SCH_STATE
Table Entry
Seg VCC
6-14.
™
Backpressure
Congestion
28234-DSH-001-B
Host
RS8234
100074_053