Nortel DMS-100 Series Maintenance Manual page 65

BIC, queries of the BIC prevent incoming work from the P-side. The
queries of the BIC are in the output buffers of the BIC. When the buffers are
full, work is not accepted, and the results are partial dials or ignored keys on
business sets.
Display of overload state
When the RLCM overloads, the LCM status display of the RLCM changes
to in-service trouble (ISTb) while the two units indicate INSV. When a user
enters the QUERYPM FLT command at the LCM level, the response
includes the phrase
LCM Overloaded
Log reports PM128 and PM181 indicate the overload condition in the
RLCM. When call processing resumes, the system generates log PM128
with the phrase
LCM out of Overload
Current extended memory LCM (XLCM) overload controls
The XLCM has 256 kbytes of memory and a specified number of small,
medium, and large memory blocks of a fixed size. Domestic LCMs and
XLCMs use small and large memory blocks to receive external messages
and to send messages. Small memory blocks (SMB) are also used for utility
purposes like timer control blocks. Medium memory blocks (MMB) are
used for call data blocks (CDB) which hold data for active lines.
In the current XLCM application, overload is reported when the XLCM
cannot receive an external message, DMSX or Inter-Unit Communication
(IUC). The XLCM cannot receive an external message because of a lack of
small or large memory blocks. Some service degradation is clear before
overload is entered.
Currently, the XLCM has four levels of throttling to prevent overload. The
number of available SMBs determines three of these levels. These levels
conserve SMBs. The levels are weighted to give terminating calls priority
over originations.
The following paragraphs describe the four levels of throttling.
1 The XPM throttles messages to the XLCM a maximum of two every 50
ms. This limit helps control small peaks of heavy traffic. Sustained
messaging at this rate can drive the XLCM to overload.
2 The XLCM appends the number of SMBs the XLCM has available. The
XLCM requires SMBs for external messages to each POTS origination
message. The XLCM also requires messages that originate from
P-phones. This number equals total available SMBs minus the number
of SMB in reserve. When this number is less than 20, the XPM delays
processing the origination until this number returns to 20 or higher.
DMS-100 Family RLCM Maintenance Manual XPM12 and up
Maintenance overview 1-49
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