
IBM2520L8767
IBM Processor for ATM Resources
Receive AAL Processing (RAAL)
Page 276 of 553
atmrm.chapt05.01
08/27/99
OAM F5 Blocking Support
If enabled, RAALL maintains OAM F5 blocking statistics on an LC basis. The following statistics are kept:
Total User Cells Received - TUC
16-bit Interleaved Parity - BIP-16
Both are 16-bit values.
Blocking can be enabled on a LC basis by turning on the blocking enable bit in the LC. Blocking can be
globally enabled/disabled across all LC’s by setting the appropriate bit in the RAALL mode register. The
global enable/disable overrides all LC enables, and the global disable overrides the global enable.
When an OAM F5 flow cell is received, the current receive TUC and BIP-16 are appended in the first full
eight-byte word after the cell data (depends on what offset is set to in the LC). This information can then be
used along with the values in the cell to complete the reporting/monitoring process. The BIP-16 is reset to
zero and the TUC takes the value from each PM cell. By doing this, the software does not need to maintain
any temporary copies of these fields. The PM processing does not affect the LC statistics fields.
Note:
If OAM blocking is enabled, you might as well turn on statistics because you get them for free.
Bad Cell Support (Bad HEC, VP/VC Out of Range, and VC Index Equal Zero)
If reception of bad cells is enabled in REASM, then bad cells are received as 53-byte cells using the non-user
data registers to select the receive queue, offset, and POOL ID. The LC pointer in the packet header is
zeroed. These cells are only received if receive bad frame mode has been turned on in RXQUE. This function
may be desirable for network tracing tools.
Raw Cell Routing Support
Raw Cells (53, 52, or 48 bytes) can be routed back out the transmit interface. Normally, when a cell is
received, the receive LCD is written into the packet header and the buffer is surfaced to the user. When
routing is enabled, by turning on the MSB of the LCD state field, the second word or the receive LCD is used
as the data to fill in the packet header LCD field. The buffer is then sent to the scheduler and rescheduled for
transmission. This allows cells to be routed out the transmit interface with the same or different VP/VC. When
routing cells, the default is to surface non-user data cells to the user. By turning on bit two of the LCD state
field, all non-user data cells will be routed the same way as user data cells for that LCD. The user should be
sure to turn on the Free On Transmit bit in the second word of the LCD so the cell buffers are freed when they
are re-transmitted. The original CLP bit from the inbound cell is always written to the LSB of LCD field in the
packet header.
General Packet/Cell Buffer Layout
When not using FIFOs, all cells and packets are assembled in packet buffers. These buffers have a packet
header followed by the data section. The following figure shows the general layout of AAL5 packets and
AAL0 cells: