PM7341 datasheet(86/413 Pages) PMC

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PRELIMINARY

INVERSE MULTIPLEXING OVER ATM

PM7341 S/UNI-IMA-84

DATASHEET

PMC-2000223

ISSUE 4

INVERSE MULTIPLEXING OVER ATM

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

Figure 10

- Max Differential Delay Tolerance vs. SDRAM Size

# of T1/E1

Links

Cells of

Buffering

Delay (T1)

in ms

Delay (E1) in

SDRAM

size

32 T1/ 32 E1

1024

279 ms

226 ms 1Mbit x16

84 T1/ 63 E1

256

69 ms

56 ms 1Mbit x16

84 T1 / 63 E

1024

279 ms

226 ms 4Mbit x16

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. In

order to support DS3 rates, the Synchronous Payload Envelope (SPE) concept is

carried over from the SBI Interface. The link FIFOs are divided into 3 groups

where each group is given 1/3 of the bandwidth. The RDAT arbitrates between

links requiring service within each group. If a group does not use its priority

bandwidth, it is made available to the next group. This arbitration also works with

the Clock/Data interface since all links should be close in rate.

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 its 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.

10.2.4.2

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 11.

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