PM7340 S/UNI-IMA-8
PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
DATA SHEET
PMC-2001723
ISSUE 3
INVERSE MULTIPLEXING OVER ATM
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
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
54
PMC [ PMC-SIERRA, INC ]
