PM7341 datasheet(115/413 Pages) PMC

115 / 413 page

PRELIMINARY

INVERSE MULTIPLEXING OVER ATM

PM7341 S/UNI-IMA-84

DATASHEET

PMC-2000223

ISSUE 4

INVERSE MULTIPLEXING OVER ATM

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

117

Figure 24

- Cell delineation State Diagram

The values of ALPHA and DELTA determine the robustness of the cell delineation

method. ALPHA determines the robustness against false misalignments due to

bit errors. DELTA determines the robustness against false delineation in the

synchronization process. ALPHA is chosen to be 7 and DELTA is chosen to be 6.

The loss of cell delineation (LCD) alarm is declared after a programmable

threshold of incorrect cells occurs while in the HUNT state. The threshold is set

by the LCD Count Threshold register. The threshold has a default value of 104,

which translates to 28 ms at 1.55 Mbps. All idle cells may be filtered out and not

passed to the IMA sub-layer. They are identified as cells containing all-zero VPI

and VCI fields and a one in the CLP bit. Optionally, unassigned cells (like idle

cells except CLP is a zero) may also be filtered. Note that these should not be

filtered for IMA links..

All cells with an incorrect HCS octet may optionally be dropped. These cells can

also be preserved and tagged as errored. Preservation of HEC errored cells is

required for correct operation of IMA. Failure to preserve the cells will lead to

increased numbers of OIF violations and data misordering. Header correction is

not implemented.

For IMA operation, there are two unique features: the first is optionally passing

cells with errored HEC; the second results in passing cells during OCD and LCD.

PM7341 Datasheet(PDF) 115 Page - PMC-Sierra, Inc