PM7340 S/UNI-IMA-8
PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
DATA SHEET
PMC-2001723
ISSUE 3
INVERSE MULTIPLEXING OVER ATM
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-8 should
be terminated prior to de-activating the group in order to prevent stale data from
being stored in the group FIFO.
10.2.3.3.1
IMA Service
For each IMA group-service request, a cell is transferred from the group FIFO to
one of the link FIFOs. If no cell is available from the group FIFO, an IMA filler cell
is generated and placed in the link FIFO. The link FIFOs within a group are
serviced in a round-robin fashion, with the round-robin order determined by the
LID. If the next link in the round robin is due to receive an ICP cell, the ICP cell is
generated using the link and group state information from the Transmit IMA
Group Context Record, and the LID and LSI from the link. If a stuff event is
scheduled, the stuff ICP cell is also inserted. Whenever an ICP cell is inserted,
the IMA group servicing proceeds to the next link in the round robin without
waiting for another service request. The IMA group service is complete when
either: (1) a cell is transferred from the group FIFO or (2) an ATM filler cell is
generated. When links are in the process of being added, but are not yet
available for carrying data traffic, IMA frames consisting of filler cells and ICP
cells are generated. Such links are not scheduled by the TxIDCC scheduler, but
will be processed with the currently active links.
During group start-up, even with all of the transmit links in the unusable state, the
TxIDCC scheduler is started and IMA frames are generated. During group start-
up (i.e. links are not yet in the active state), a group can be configured such that
received via the UTOPIA L2 / Any-PHY bus can be dropped to avoid the
accumulation of stale data or to drop stale data in the group FIFO left over from a
previous use of the VPHY ID. . During link additions, IMA frames are generated
on new links when they are added to the group.
10.2.3.3.2
TC Only Service
For TC-only mode groups, servicing is also initiated by group service requests
from the TxIDCC. However, servicing a group FIFO simply entails transferring a
cell from the group FIFO to the proper link FIFO. If a cell is not present in the
group FIFO, no cells are transferred and the servicing of the request is complete.
In TC mode, no other cells are inserted into the data stream by the IMA sub-layer
(physical layer idle cells are generated by the physical layer).
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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PMC [ PMC-SIERRA, INC ]
