Line Card Overload Logic Actions

When a 16-span line card reaches the Approaching Busy threshold, the CSP sends an Alarm to the host, and does nothing else. When the line card reaches the Real Busy threshold, it sends an alarm of Line Card Busy. All Idle channels are put into a new, well-defined PPL state in the Out Of Service protocol, and the response to all subsequent call requests is Access Denied.

When the resource usage falls back below the Safe Level threshold, the Real Busy condition has resolved. The card sends a message to clear the alarm and the channels are returned to Idle state. The line card generates a PPL Event indicating Line Card Not Busy and the Matrix Controller is informed about all of the channels that were taken out of service.

When Timer 1 detects that the card has reached the Approaching Busy threshold, it sends an Approaching Busy alarm to the host and sets a global flag. This state is handled in the ISUP and TUP call control modules as described below.

Atomic Function 140 tests for local or remote system overload conditions. It also tests for the flag, SS7 PQ Card Approaching Busy. If the flag is set, a PPL Event sends a Release for new calls to the network, and the network withholds additional traffic. Because the host has also been informed of the Approaching Busy condition, it stops setting up new calls.

Similar changes were made to Atomic Function 142. If the SS7 Card Approaching Busy flag is set, a PPL event is generated and an Overload Message is sent to the network.

When the Approaching Busy condition clears, the SS7 Card Approaching Busy flag is cleared and the SS7 Approaching Busy Clear alarm is sent. Both TUP and ISUP then start accepting new calls.

If the overload condition persists and the card reaches the Real Busy threshold, the Matrix Controller in turn sends the alarm, SS7 Real Busy, and all Idle CICs are taken out of service. The CSP sends one Grouped Channel Status message for each span, containing all the timeslots on the span that was taken out of service. The CICs taken out of service remain out of service until the Real Busy condition clears. Because the CICs are in the Out Of Service protocol, all Outseizures from the Matrix Controller are returned as "Access Denied."

When the overload condition resolves, the SS7 Real Busy Clear alarm is sent to the host. All CICs that were taken out of service are brought back in service, and the CSP sends one Grouped Channel Status message for each span to the Matrix Controller.

You must use the following API messages to implement Line Card Overload Logic. These messages are documented in the API Reference.

See Programmable Protocol Language.

A condition that, when met, drives a state machine from one state to another. A condition that drives a Component out of its current state by invoking an associated primitive.

See Signaling System Number Seven.

See Integrated Services Digital Network User Part.

American National Standards Institute. ANSI administers and coordinates the U.S. voluntary standardization and conformity assessment system for the
telecommunications industry. More details on these standards may be
viewed at www.ansi.org.

International Telecommunications Union (UN)

AF. A predefined PPL software routine that performs a single, simple task, such as "Transmit Line Signaling" or "Allocate Digit Buffer." It is composed of standard software interrupts, calls, and data formats used by applications. Each AF has two values named "Arguments." AFs 1-50 are generic, and apply to all PPL components. AFs 51 and above apply to specific components. An AF is called "Atomic" because it is the smallest useful unit in PPL.

In PPL, a condition that, when met, drives a state machine (PPL Component) from one state to another, by invoking an associated Primitive. In PPL files, an Event is marked by an arrow and text.