PM7340 S/UNI-IMA-8
PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
DATA SHEET
PMC-2001723
ISSUE 3
INVERSE MULTIPLEXING OVER ATM
10.2.4.1
Writing data to the Delay Compensation Buffers (DCB)
When there is a full cell of data in the RX Link FIFOs, the link requests service.
The RDAT arbitrates between links requiring service in a round-robin fashion
When a link is chosen for service, if it is not an IMA link, the cells are stored in
external memory in a per link FIFO.
For IMA links, the IFSM is performed to locate the IMA Frame. Once the IMA
frame is located, the RDAT calculates the location to store the cells. The cells are
stored in a time-based FIFO structure. The buffer address for a cell is created
from the cell number in the IMA frame concatenated with the lower x (depends
upon M) bits of the IMA frame sequence number. Each link has it’s own reserved
FIFO. The cells are stored in this manner such that they are aligned in time in the
external memory and the differential-delay removal is simplified.
During periods in which the link is in a defect state, incoming cells will be
replaced with filler cells prior to being written to the DCB.
10.2.4.1.1
IMA Frame Synchronization Mechanism (IFSM)
For IMA links, the RDAT performs the IFSM. The IFSM is based upon the cell
delineation mechanism in I.432. The details of the IFSM can be found in AF-PHY-
0086.001 “Inverse Multiplexing for ATM (IMA) Specification Version 1.1”, March
1999. The state Machine is shown in Figure 10.
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