Motorola PowerQUICC II MPC8280 Series Reference Manual page 1217

IMA accomplishes these goals by the periodic insertion of special OAM cells, which
(among other things) define M-cell frame boundaries, provide frame sequence numbers,
and provide stuffing information. This framing information is used by the receiver to
correlate the received cell streams and extract cells in-order from the links of the IMA
group, thereby reconstructing the original cell stream.
Cell n Cell 4 Cell 3
ATM
TX
Function
Links 1 - N make up an IMA group
Cell 1 Cell 2 Cell 3 Cell 4 Cell n
ATM
RX
Function
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
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Link ID #1
Cell 2
Cell 1
IMA TX
Function
acting as a
Virtual PHY
Link ID #N
IMA RX
Function
acting as a
Virtual PHY
Figure 34-3. IMA Microcode Overview
Chapter 34. Inverse Multiplexing for ATM (IMA)
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Cell 1
Cell n+1
Fast
Communication
Cell 2
Controller
Cell n
Cell 1 Cell n+1
Fast
Communication
Cell 2
Controller
Cell n
IMA Protocol Overview
Phy 1
Phy 2
Phy n
Phy 1
Phy 2
Phy n
34-7