PM7346 datasheet(89/419 Pages) PMC

89 / 419 page

PM7346 S/UNI-QJET

DATASHEET

PMC-960835

ISSUE 6

SATURN QUAD USER NETWORK INTERFACE FOR J2, E3, T3

PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA INC., AND ITS CUSTOMERS’ INTERNAL USE 68

CRC-8 calculation over the first 4 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 10.

Figure 10

- Cell delineation State Diagram

HU NT

PR ES YN C

SY NC

Corr ec t H C S

(bit b y bit)

In c o rr ec t H C S

(c ell b y ce ll)

D E LT A c o nse c u t ive

co r rec t H C S 's

(c ell b y ce ll)

ALP H A c o ns ec u tive

in c o rr ec t H C S 's

(c ell b y ce ll)

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

method. ALPHA determines the robustness against false misalignments due to

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

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