S/UNI®-ATLAS-3200 Telecom Standard Product Data Sheet
Preliminary
Table 38 Backwards Cell Interface Cell Format
Bit 15 Bit 0
User Prepend/Postpend Bytes 1 and 2
User Prepend/Postpend Bytes 3 and 4
Cell Information Field (9 bits)
VC Record Address (16 bits)
16 LSBs of UL3 UDF field
VPI (12 bits)
PHYID (6 bits)
Reserved(1)
4 MSBs of VCI
12 LSBs of VCI
HEC field
PTI (3)
8 MSBs of UDF
CLP (1)
Payload 1
…
Payload 24
The User prepend/postpend bytes, along with the HEC and UDF fields, are the same as the
respective bytes on the UL3 interfaces. In the case of cells that are looped back, they contain
whatever data was already in these fields; in the case of generated cells (RDI, Bwd PM, and Rtd
LB) the contents are undefined. It is expected that the cell will be header translated
(Xlate_From_IBCIF = 1) bit in the reverse direction if the contents of the prepend or HEC/UDF
fields are to be used. If the optional Xlate_To_OBCIF bit is logic 1, then the VPI, VCI,
prepend/postpend, HEC, and UDF fields may contain data from the VC table as configured by the
Cell_Info_to_OCIF, XVPIVCI, XGFC, XPREPO, XHEC, and XUDF bits.
The insertion of the PHYID, Backwards VCRA, and Cell Information fields are controlled by the
OBCIF_PHYID, OBCIF_Bwd_VCRA, and OBCIF_Cell_Info register bits. However, if the
PHYID is not inserted, cells from the BCIF cannot be correctly reinserted in the reverse flow. If
the Backwards VCRA is not inserted, then the cell contents (as modified by the Xlate_To_OBCIF
in conjunction with the XVPIVCI etc. bits) must be able to be searched correctly, and the
Search_From_IBCIF bit must be set to logic 1.
The Cell Info field is purely for the convenience of an ASIC or tester, to assist in identifying the
cell and the connection from which it came. The BCIF Cell Info field is very similar to part of
the Microprocessor Cell Info Field, and is defined as follows:
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990553, Issue 4
136
PMC [ PMC-SIERRA, INC ]
