Nortel Meridian SuperNode SL-100 Reference Manual page 97

6-10 Feature implementation
in the IPE. On the other hand, the XPM does not have these two deficiencies.
The XPM is limited by real time rather than address space.
In addition, a sophisticated flow control system in the XPM already exists for
manipulating call processing messages according to call priorities. The flow
control system automatically provides progress message favoring, a system in
which preference is given to calls in progress over new calls.
Therefore, by knowing whether an IPE is overloaded together with the existing
knowledge of the call processing state of each terminal, the XPM can control
the flow of work from and to the IPE intelligently. The origination shedding
is, therefore, also called origination flow control.
The IPE is responsible for informing the host XPM when the origination flow
control needs to be applied. Each origination message that is sent to the host
XPM contains a load state indicator. This indicator is filled in with the
information on the current load state. After receiving the flow task message,
the XPM examines and interprets the load state indicator to determine the
available call processing data store left in the IPE.
If the load state indicator of an IPE reaches or goes beyond the predefined
overload level, the following actions are carried out in its host XPM:
•
•
•
These line origination messages are not handled until the corresponding IPE
load is reduced.
When the IPE is no longer in a high load condition, the next message sent from
the IPE to its host XPM indicates normal traffic condition in the load state
indicator fields. However, the IPE may not transfer any flow task message
after it comes out of overload. In this case, the GDT audit in the XPM, which
runs every three seconds, returns an overload IPE back to In-Service (INSV)
state (the internal state only) if there have been no messages from the IPE for
the past 3 seconds.
At times of high peak traffic load, the overload control for IPEs regulates the
flow of messages between the overloaded IPE and its host XPM. The IPE is
555-4001-129 Standard 08.01 November 2000
The IPE is overloaded and its internal state is set to In-Service Trouble
(ISTB).
The host XPM does not immediately process any new incoming line
origination messages conveyed from the overloaded IPE. The XPM
queues up these new messages.
The host XPM places the queued line origination messages to another
appropriate queue under the Guaranteed Dial Tone (GDT) system of the
flow control. These messages are placed continuously at the back of the
queue until the IPE is out of overload state.