Nortel DMS-100 Series Maintenance Manual page 113

Functional overview 2-37
makes sure that internal processes have enough small memory blocks to finish
the current tasks. External messages that require SMBs are rejected when the
XLCM enters extremely heavy overload. The messages are rejected when the
total number of SMBs available is less than or equal to the size of the SMB
reserve. The exception is maintenance or monitor messages. At this point, the
XLCM sends an overload report to the computing module (CM).
The current overload protection system is static because the throttle levels are
constant and non-reactive. The overload protection system can be described
as distributed. This description occurs because a single place in which
overload is monitored or protective measures are initiated and controlled is not
present.
Figure 10 XLCM Overload Protection Systemxxx
No external messages received
BIC scanning stopped
Updates to mate unit stopped
XPM delays processing originations
100 Normal Operation 45 40 35 25 0
Total available small memory blocks
Early POTS models of the small memory LCM (64k) can be memory block
limited. In the past, the LCM used all the small memory blocks before
real-time usage. The design of the LCM depends on this characteristic.
Memory block limited is an LCM characteristic transferred to the XLCMs for
use.
The XLCM overload system works with POTS traffic. The current selection
for the number of SMBs (100) and the size of the SMB reserve (25) allows the
following condition. The processor is memory block limited with POTS
traffic. The processor runs out of SMBs before real-time use. A rough graph
of processor occupancy can demonstrate this condition. Real-time use
compared to memory block use demonstrates this condition as follows.
DMS-100 Family OPM Maintenance Manual ISN07 (TDM)/SN07 (DMS) and up