PM5342 Datasheet, PDF (146/558 Pages) PMC-Sierra, Inc – SONET/SDH Payload Extractor/Aligner

DATA SHEET
PMC-970133
ISSUE 4
PM5342 SPECTRA-155
SONET/SDH PAYLOAD EXTRACTOR/ALIGNER
The RTAL may optionally insert the tributary multiframe sequence and clear the
fixed stuff columns. The tributary multiframe sequence is a four byte pattern
('hFC, 'hFD, 'hFE, 'hFF) applied to the H4 byte. The H4 byte of the frame
containing the tributary V1 bytes is set to 'hFD. The fixed stuff columns of a
synchronous payload envelope (virtual container) may optionally be over-written
all-zeros in the fixed stuff bytes.
9.9.1 Elastic Store
The Elastic Store perform rate adaptation between the receive data stream and
the DROP bus. The entire received payload, including path overhead bytes, is
written into in a first-in-first-out (FIFO) buffer at the receive byte rate. Each FIFO
word stores a payload data byte and a one bit tag labeling the J1 byte. Receive
pointer justifications are accommodated by writing into the FIFO during the
negative stuff opportunity byte or by not writing during the positive stuff
opportunity byte. Data is read out of the FIFO in the Elastic Store block at the
DROP bus rate by the Pointer Generator. Analogously, pointer justifications on
the DROP bus are accommodated by reading from the FIFO during the negative
stuff opportunity byte or by not reading during the positive stuff opportunity byte.
The FIFO read and write addresses are monitored. Pointer justification requests
will be made to the Pointer Generator based on the proximity of the addresses
relative to programmable thresholds. The Pointer Generator schedules a pointer
increment event if the FIFO depth is below the lower threshold and a pointer
decrement event if the depth is above the upper threshold. FIFO underflow and
overflow events are detected and path AIS is optionally inserted in the DROP bus
for three frames to alert downstream elements of data corruption.
9.9.2 Pointer Generator
The Pointer Generator generates the DROP bus pointer (H1, H2) as specified in
the references. The pointer value is used to determine the location of the path
overhead (the J1 byte) in the DROP bus STS-3 (STM-1/AU3) or STS-1
(STM-0/AU3) stream. The algorithm can be modeled by a finite state machine.
Within the pointer generator algorithm, five states are defined as shown below:
NORM_state (NORM)
AIS_state (AIS)
NDF_state (NDF)
INC_state (INC)
DEC_state (DEC)
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE 124