PM7340 datasheet(71/334 Pages) PMC

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PRELIMINARY

INVERSE MULTIPLEXING OVER ATM

PM7340 S/UNI-IMA-8

DATA SHEET

PMC-2001723

ISSUE 3

INVERSE MULTIPLEXING OVER ATM

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

In ITC mode, the stuff event may also be advertised in the ICP cell of the

preceding frame or in the 4 preceding frames. If the stuff event needs to be

advertised for 4 preceding frames, a DS1/E1 clock tolerance of +/- 50 ppm is

required. If a frequency tolerance greater than +/- 50 ppm is required between

the independent transmit clocks, the TIMA can provide the single frame

advertisement of stuff events.

To determine when a stuff cell is needed on ITC mode links (not the TRL), a link

stuff detection unit with rate counters is used to track the relative rate of data

being read from the link FIFOs within a group to the rate of data being read from

the TRL FIFO for the same group. When the relative rate counter indicates that

the rate differences have accounted for a slip of a cell, a stuff cell is inserted.

10.2.3.3

Data Flow

The TIMA can support up to 8 groups (IMA group or TC link). Each FIFO on the

ATM-layer interface side represents either an IMA group or a TC group. Each

group’s behavior is controlled by the internal memory tables and records.

For IMA groups, the following internal memory structures are used:

1) the Transmit IMA Group Configuration Record for configuring group

options and mapping to a port on the ATM interface (VPHY ID)

2) Transmit IMA Group Context Record contains statistics and the current

ICP cell image.

3) Transmit LID to the PHYsical Link Mapping Table is used to map

individual physical links into a group and assign the LIDs.

4) TIMA Physical Link Context Record contains per-link statistics, and

state information.

For TC links, only one record is used, the Transmit Physical Link Record, to

maintain statistics and to map the physical link to a port on the ATM interface

(VPHY ID).

The TIMA performs cell transfers from the group FIFOs to the link FIFOs in

response to service requests from the TxIDCC. The TxIDCC schedules both IMA

groups, as well as low rate TC-only connections. Groups are scheduled

according to their rates. Higher-rate groups are prioritized above the lower-rate

groups. The TIMA operates at a rate sufficient to ensure the TxIDCC will not

suffer request congestion provided the ICP cells are spread throughout the frame

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