ibm3206k0424 ETC-unknow, ibm3206k0424 Datasheet - Page 302

• Manufacturer Part Number: ibm3206k0424
• Description: Ibm Processor For Network Resources
• Manufacturer: ETC-unknow

IBM3206K0424
IBM Processor for Network Resources
Preliminary
Entity 11: ATM Transmit Buffer Segmentation (SEGBF)
The segmentation buffer entity (SEGBF) accepts frames from the cell scheduler (CSKED) or software, and
then generates ATM cells to send out over the external physical interface. This entity knows or cares nothing
about scheduling cells over time; it will simply construct a cell when it is provided an address of a logical
circuit descriptor to operate on. All rate and scheduling concerns must be addressed by the CSKED logic or
software prior to queueing a frame to SEGBF.
The SEGBF logic consists of four input LCD address latches, two specialized processors and the associated
ROM/RAM for each, a 16-cell array buffer, and various support logic. The input latches and cell buffers are
logically divided into four different drops, with each drop consisting of an input latch and four cell buffers.
Under normal operation (CSKED providing LCD), the drop is defined by the drop field in the transmit LCD.
When an LCD is enqueued by software, data bits five and six of the enqueued address define which drop the
enqueued LCD is associated with. The four logical drops in SEGBF can be mapped to any of the physical link
level addresses via registers in LINKC (LINKC Map Transmit Ports to Configuration). The processors fetch
instructions from ROM/RAM and handle normal segmentation activity such as LCD update operations and
cell generation functions. The type of cell that is generated by the segmentation logic is determined by the
initial instruction pointer that is contained in the LCD structure. For example, software can enqueue an LCD
that has the initial instruction pointer field set for normal AAL5 cells, and SEGBF will generate a single AAL5
cell as a result of the enqueue operation. If, however, software enqueues an LCD that has the initial instruc-
tion pointer field set for POS-PHY operation, then SEGBF will continue to generate buffers to pass to the link
level until all the data has been exhausted. For a more complete description of the segmentation entry points,
refer to the seg_prc_Entry_point field in the transmit LCD data structure section of this document. After the
buffers/cells are built in a 16-by-64 byte array, they are marked as available to the link level layer (LINKT) in
the IBM3206K0424. A simplified block diagram is shown in the SEGBF Block Diagram.
ATM Transmit Buffer Segmentation (SEGBF)
pnr25.chapt05.01
Page 302 of 676
August 14, 2000