PM7340 S/UNI-IMA-8
PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
DATA SHEET
PMC-2001723
ISSUE 3
INVERSE MULTIPLEXING OVER ATM
IMA links. Idle cells will be treated as user cells by the RDAT for IMA processing
and will not be dropped at the IMA sub-layer.
10.2.4.4
DCB Playout
The IDCC scheduler provides the rate for data to be played out to the ATM layer
for an IMA group. For each cell to be played out, the IDCC generates a service
request. Upon the IDCC service request, the RDAT plays out data from the
FIFOs in a round-robin fashion. For each service request, the RDAT runs the
round robin servicing until it processes either a filler cell or user cell. If ICP cells
are encountered, the ICP cell is dropped and the servicing continues until a user
or filler cell is found. If a user cell is found, it is transferred from the external
memory to the appropriate group FIFO. If a filler cell is found, it is dropped.
The RDAT is not sensitive to the alignment of ICP cells within a group. There is
no performance degradation even if all of the ICP cells in a group have the same
offset.
If the device is in Any-PHY mode or UTOPIA L2 Single Port mode, there is only a
single FIFO shared among all of the groups. The RDAT ensures that no more
than 16 cells are stored in the shared FIFO for a single group. If the S/UNI-IMA-8
is in UTOPIA L2 Multi-port mode, each group has it’s own FIFO.
If the group FIFO is not emptied in a timely fashion, data is dropped; this is
similar to the procedure used by any other PHY level device. The IDCC service
request FIFO will always be serviced regardless of the state of the Group FIFO.
For multi-port mode, if the respective Group FIFO is full, the cell will be dropped.
In Any-PHY mode and UTOPIA L2 Single Port mode, if either the shared FIFO is
full or there are already 16 cells for the current group in the FIFO, the cell will be
dropped.
10.2.5 Link/Group State Machines
The Receive IMA Protocol Processor (RIPP) block is responsible for maintaining
and controlling the link and group state machines. The RIPP can accept
commands from the management plane to initiate group and link state machine
actions. The RIPP then controls the contents of ICP cells generated for the
transmit data path, as well as analyzes the link and group states received within
the ICP cells. The receive link and group states are utilized to maintain and
update the link and group states. The RIPP coordinates group wide state
transactions and performs the group wide procedures such as the Synchronized
Link activation during Group Start-up Procedure and the Link Addition and Slow
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
69
PMC [ PMC-SIERRA, INC ]
