PM7340 S/UNI-IMA-8
PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
DATA SHEET
PMC-2001723
ISSUE 3
INVERSE MULTIPLEXING OVER ATM
Figure 19
- IMA Error/Maintenance State Diagram
Persistence of non-IMA Sync
Leaving IMA
Sync state
γ
( +2) IMA frames
Out of IMA
Frame (OIF)
Anomaly
State
IMA
LIF
Working State
Defect
Entering IMA
Sync state
Persistence of IMA SYNC for at least 2 IMA frames
The IMA Working state enables the RDAT to write user cells to the DCB. If the
IFSM leaves the IMA Sync state, the IESM state machine will transition to the
OIF Anomaly state, and the OIF anomaly counter will be incremented.
In the OIF Anomaly state, incoming user cells are written as filler cells to the
DCB, and write pointers are incremented. If the IFSM does not return to the IMA
Sync state within gamma + 2 frames, the IESM state will transition to the LIF
Defect state. (Gamma is programmable, and is the same gamma used in the
IFSM). If the IMA Sync state is entered prior to gamma + 2 frames, the IESM
state will transition back to the IMA Working State. This is considered a “fast
recovery” from the OIF Anomaly.
In the LIF Defect state, incoming user cells are written as filler cells to the DCB,
and write pointers are incremented. The LIF-latched status bit will be set in the
link-context memory. The IESM state machine will transition to the IMA Working
state when IMA Sync has been detected for two consecutive IMA frames. If the
IMA Sync state is entered and then exited during LIF, then the OIF anomaly
counter will be incremented. When the IESM enters the working state, user cells
may be forwarded once again if an overrun (with respect to the configured depth
for the link) is not detected. The overrun detection provides the necessary
differential-delay checking required after a defect.
10.2.4.3.2
Loss of Cell Delineation Status (LCD)
LCD is detected by the TC layer and the information is passed to the RDAT.
When a link is in LCD, a LCD-latched status bit is set in link context memory,
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67
PMC [ PMC-SIERRA, INC ]
