S/UNI®-JET Data Sheet
Released
When in frame, the SPLR extracts the path overhead octets and outputs them bit serially on
output RPOH, along with the RPOHCLK and RPOHFP outputs. Framing octet errors and path
overhead identifier octet errors are indicated as frame errors. Bit interleaved parity errors and
FEBEs are indicated. The yellow signal bit is extracted and accumulated to indicate yellow
alarms. Yellow alarms are declared when 10 consecutive yellow signal bits are set to logic one. It
is removed when 10 consecutive received yellow signal bits are set to logic zero. The C1 octet is
examined to maintain nibble alignment with the incoming transmission system sublayer bit
stream.
10.8 ATMF ATM Cell Delineator
The ATM Cell Delineator (ATMF) Block integrates circuitry to support HCS-based cell
delineation for non-PLCP based transmission formats. The ATMF block accepts a bit serial cell
stream from an upstream transmission system sublayer entity (such as the T3-FRMR, E3-FRMR,
or J2-FRMR Block) and performs cell delineation to locate the cell boundaries. For PLCP
applications, ATM cell positions are fixed relative to the PLCP frame, but the ATMF still
performs cell delineation to locate the cell boundaries.
Cell delineation is the process of framing to ATM cell boundaries using the HCS field found in
the ATM cell header. The HCS is a CRC-8 calculation over the first four octets of the ATM cell
header. When performing delineation, correct HCS calculations are assumed to indicate cell
boundaries.
The ATMF performs a sequential bit-by-bit, a nibble-by-nibble (DS-3 direct mapped), or a byte-
by-byte (J2 and E3 direct-mapped) hunt for a correct HCS sequence. This state is referred to as
the HUNT state. When receiving a bit serial cell stream from an upstream transmission-system
sublayer entity, the bit, nibble, or byte boundaries are determined from the location of the
overhead.
When a correct HCS is found, the ATMF locks on the particular cell boundary and assumes the
PRESYNC state. This state verifies that the previously detected HCS pattern was not a false
indication. If the HCS pattern was a false indication then an incorrect HCS should be received
within the next DELTA cells. At that point a transition back to the HUNT state is executed. If an
incorrect HCS is not found in this PRESYNC period then a transition to the SYNC state is made.
In this state synchronization is not relinquished until ALPHA consecutive incorrect HCS patterns
are found. In such an event a transition is made back to the HUNT state. The state diagram of the
cell delineation process is shown in Figure 6.
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990267, Issue 3
64
PMC [ PMC-SIERRA, INC ]
