MPC8280 datasheet(1153/1386 Pages) FREESCALE

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Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

34-7

Figure 34-3. IMA Microcode Overview

34.2.3

Overview of IMA Cells

An IMA frame consists of M number of cells (M = 32, 64, 128, or 256 cells). Each frame consists of ATM

data cells and IMA control cells. Two types of IMA control cells are defined by and used by the IMA

protocol; IMA Control Protocol (ICP) cells and filler cells.

34.2.3.1

IMA Control Cells

There is at least one control cell (IMA Control Protocol) in each frame. An additional ICP cell may be

included in a frame to compensate for timing differences between the links in an IMA group (e.g., one link

is slightly faster than the other). The insertion of additional ICP cells to compensate for timing differences

between links is called a “stuff event”. The transmitter is responsible for inserting “stuff” ICP (SICP) cells

and the receiver will monitor for stuff indication and discard SICP cells. The location of the ICP cell in an

IMA frame is determined during the IMA start-up sequence.

ATM

Function

Cell 1 Cell 2 Cell 3

Cell 4

Cell n

IMA RX

Function

Fast

Communication

Controller

acting as a

Virtual PHY

Cell 1

Cell n

Cell 2

Phy 1

Phy 2

Phy n

Cell n+1

ATM

Function

Cell 1

Cell 2

Cell 3

Cell 4

Cell n

IMA TX

Function

Fast

Communication

Controller

acting as a

Virtual PHY

Cell 1

Cell n

Cell 2

Phy 1

Phy 2

Phy n

Cell n+1

Link ID #1

Link ID #N

Links 1 - N make up an IMA group

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