
ABM-3G
PXF 4333 V1.1
Functional Description
Data Sheet
47
2001-12-17
will occur in that case. The CPU reads consecutive bytes from the cell
’
s payload chunks
that can be re-assembled immediately in the host memory while the AAL5 Assistant unit
checks the AAL5 trailer. The section
“AAL5 Packet Extraction” on Page 121
provides
programming details.
Refer to
“Scheduler Configuration Table Integer Transfer Registers” on Page 257
for the assignment of scheduler blocks to the AAL5 Assistant and the programming of
their rates.
For insertion, the CPU prepares the ATM cell header for the following packet and writes
packet payload chunks to the AAL5 Assistant unit which will generate the cells and the
AAL5 trailer for automatic completion of the last cell of the packet. Internally, the cells
are forwarded to either the downstream or upstream Cell Handler and processed in the
same way as cells received by an UTOPIA receive interface.
The section
“AAL5 Packet Insertion” on Page 121
provides the details.
3.2.4
Internal Address Reduction Unit
The ABM-3G requires an internal 16-bit Local Connection Identifier (LCI) to address its
resources. Two basic cell addressing schemes are supported to extract/generate an LCI
from the cell header:
LCI Mapping Modes
An external device generates an LCI and maps it into the ATM cell header. Three
different mapping modes are supported by the ABM-3G.
The LCI mapping modes are described as part of the UTOPIA interface description in
chapters
“UTOPIA L2 Interfaces (PHY side)” on Page 124
and
“UTOPIA L2
Interface (Backplane side)” on Page 134
.
Internal Address Reduction Mode
The ABM-3G generates its own internal LCI as a programmable combination of the
cell header fields VPI, VCI and the Port Number (PN). The port number is taken either
from the UTOPIA port number or the UDF1 cell header byte.
Internal Address Reduction
Two parameters in
Register 111 "MODE2" on Page 315
determine the building
function of the internal LCI value:
PNUM(2:0)
Determines the number of bits taken from the port number field.
MNUM(3:0)
Determines the VCI and VPI ranges depending on the cell header VPI value.
Two translation functions are effective, depending on the cell header VPI(11:0) value
compared to the configured parameter MNUM.