Freescale Semiconductor MPC8250, Family Reference Manual

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Inverse Multiplexing for ATM (IMA)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 33-7
33.2.3 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.
33.2.3.1 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
RX
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
TX
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