S/UNI-IMA-4 Telecom Standard Product Data Sheet
Released
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.
Data Flow
The TIMA can support up to 4 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). Regardless of the
setting of the TCAEN bits, the VPHY ID may only be programmed in the TIMA between values
of 0 and 3. The Any-PHY/UTOPIA Interface will convert all incoming addresses down to
values in this range, depending on TCAEN.
The TIMA performs cell transfers from the group FIFOs to the link FIFOs in response to service
requests from the Tx IDCC. The Tx IDCC 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 Tx
IDCC will not suffer request congestion provided the ICP cells are spread throughout the frame
on IMA groups. If there is no service request pending, the TIMA remains idle. If a group is
unused, no cells will be pulled from the respective group FIFO. Therefore, when de-activating
groups, ATM cell flow to the S/UNI-IMA-4 should be terminated prior to de-activating the
group in order to prevent stale data from being stored in the group FIFO.
Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC-2020889, Issue 2
55
PMC [ PMC-SIERRA, INC ]
