MPC8280 datasheet(1154/1386 Pages) FREESCALE

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Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

34-8

Freescale Semiconductor

Figure 34-4. IMA Frame and ICP Cell Formats

The IMA protocol must compensate for potential differences in delay between the different links of the

IMA group. The allowable delay differential for DS1/E1 links is 25ms, which at E1 rates is equivalent to

approximately 118 cells.

34.2.3.2

IMA Filler Cells

At the transmitting end, cells are transmitted continuously. If there are no ATM layer cells to be sent

between ICP cells within an IMA frame, then the IMA transmitter sends filler cells to maintain a

continuous stream of cells at the physical layer. The insertion of Filler cells provides cell rate decoupling

at the IMA sublayer. The Filler cells should be discarded by the IMA receiver.

34.3

IMA Microcode Architecture

This chapter explains the architecture of the receive and transmit IMA microcode tasks.

34.3.1

IMA Function Partitioning

The IMA microcode performs only those functions with regular, critical real-time demands. The other

functions of IMA (e.g. control and management) are the responsibility of host software. As such, the IMA

microcode corresponds primarily to the user plane functions defined in the IMA specification, and

software must provide the layer management and plane management functionality. The IMA microcode

provides interrupts when interaction with layer management and plane management is required.

Cell 1

Cell 2

Cell 3

Cell 4

Cell n

IMA Frame

ICP Cell

.....

ICP Cell offset should be different for each link.

ICP cell offset is determined at start-up.

FSN

IMA

Link

ICP

Cell

Cell ID

ICP Cell

Header

OAM

Label

PTI/CLP = b1011

HEC = 0x64

Link ID

IMA

cell

offset

Stat. &

Ctrl CI

Grp.

Ctrl.

Stat. &

timing

info

test

ctrl

test

ptrn.

test

ptrn

Link

info.

end to

end

ch.

CRC

1-5

17 18-49 50

52-53

Link information for links 0-31

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