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CSP Response to Congestion

Overview

This section describes the CSP response when the congestion level reaches Level 1 or Level 2 on an SS7 card.

Congestion Level 1

If congestion Level 1 is reached, an Alarm message is sent to the host and action is taken on the congested stack.

The Alarm message in response to congestion Level 1 includes the following information:

Severity: Major (0x01)

Entity: General (0x01)

Alarm Number: SS7 Signaling Stack Congestion (0x16)

Data[0] Stack ID

Data[1] Direction

0x00 | Incoming
0x01 | Outgoing

Data[2] Status

0x01 | Congestion Level 1
0x02 | Congestion Level 2

The action the CSP takes in response to congestion depends on whether the call is incoming or outgoing and whether the stack is configured for ITU or ANSI and ISUP or TUP.

ITU/ANSI Incoming Calls

If congestion Level 1 is reached, the call is not processed and a Release message is sent to the call originator with a cause of Congestion. An optional parameter of Automatic Congestion Control is included, with the congestion level as defined in the protocol.

TUP Incoming Calls

If congestion Level 1 is reached, a Backward SETUP Indication message is sent to the call originator. The Return Cause reason (Congestion Type) is configurable with Config Byte 20 of the TUP CPC component.

When the originator receives this message it sends a Clear Forward message. After receiving Clear Forward message, the CSP experiencing congestion will send an Automatic Congestion Control message followed by a Release Guard message.

Outgoing Calls

If congestion Level 1 is reached, L3P or L3P TUP sends an Access Denied indication to the host with a Cause Code of 0x0C.

Congestion Level 2

If congestion Level 2 is reached, all new call MSUs (IAM, IAI, SAM, SAO) are discarded by MTP3. The host is sent an Alarm message indicating the change in Congestion Status to Level 2 (0x02). All new call MSUs are discarded until the congestion cleared threshold is reached and the stack returns to a No Congestion status.

From congestion Level 2, you can only go to a No Congestion status. The Congestion Status cannot go from Level 2 to Level 1. When the Congestion Cleared threshold is reached and maintained for n number of probes, the host is sent an Alarm Cleared message and normal call processing resumes. See Congestion Cleared for more information.

Important! Congestion Level 2 can only be reached for incoming calls. Outgoing call requests are rejected if congestion Level 1 is reached.

Congestion Cleared

When the congestion condition is reduced below the Congestion Cleared threshold and remains below that level for a specified number of probes, an Alarm Cleared message is sent to the host and normal call processing resumes on the stack.

The Alarm Cleared message includes the following information:

Severity: Major (0x01)

Entity: General (0x01)

Alarm Number: SS7 Signaling Stack Congestion (0x16)

Data[0] Stack ID

Data[1] Direction

0x00 | Incoming
0x01 | Outgoing

Data[2] Congestion Status

0x00 | Congestion Cleared

Modifying Congestion Control

This section describes modifications you can make to the default Congestion Control implementation. Congestion levels are monitored by the ISUP SPRC (0x13) or TUP SPRC (0x53) components. To change the default implementation of congestion control, modify the following PPL Config Bytes or Timers as required:

• Congestion Level 1 Probe Delay Threshold - Incoming Calls

PPL Config Byte 0x29

• Congestion Level 1 Probe Delay Threshold - Outgoing Calls

PPL Config Byte 0x2D

See for default values

• Congestion Level 1 Average Delay Threshold - Incoming Calls

PPL Config Byte 0x2A

• Congestion Level 1 Average Delay Threshold - Outgoing Calls

PPL Config Byte 0x2E

• Amount of time between probes

PPL Timer 2

• The number of probes used to calculate the Average Delay

PPL Config Byte 0x28

• Congestion Cleared Threshold - Incoming Calls

PPL Config Byte 0x2B

Number of probes to determine Incoming Congestion Cleared

PPL Config Byte 0x2C

• Congestion Cleared Threshold - Outgoing Calls

PPL Config Byte 0x2F

Number of probes to determine Outgoing Congestion Cleared

PPL Config Byte 0x30

See Signaling System Number Seven.
International Telecommunications Union (UN)
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.
See Integrated Services Digital Network User Part.
Telephone User Part
Message Transfer Part level 3 - network level
See Programmable Protocol Language.