S/UNI-IMA-4 Telecom Standard Product Data Sheet
Released
Figure 21 IMA Error/Maintenance State Diagram
Persistence of non-IMA Sync
Leaving IMA
Sync state
ꢀ
( +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.
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, which is cleared by the ICP cell
processing procedure. Cells received while the LCD latched status bit is set will be written to
the DCB as filler cells, and the write pointers will be incremented. After an LCD condition is
exited, the delay synchronization of the link must be rechecked and resynchronized.
Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC-2020889, Issue 2
66
PMC [ PMC-SIERRA, INC ]
