You are here: CSP Developer’s Guide: Common Channel Signaling > 5 TUP, BT IUP & SSUTR2 > Enabling Congestion Control for BT IUP

Enabling Congestion Control for BT IUP

Purpose

Congestion Control is enabled for BT IUP by turning on specific configuration bytes that are outlined in this section.

Enabling Congestion Control

To enable the congestion management features you must:

Step | Action
1 | Enable L3 BT IUP Config Byte 0x03 for incoming congestion detection.
2 | Enable L3P BT IUP Config Byte 0x35 for outgoing congestion detection.
3 | Enable Level 2 congestion detection in the MTP3 component 0x2B Config Byte 0x11 by setting the value to 0x01.

Switch Response to 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.

BT IUP Incoming Calls

If Congestion Level 1 is reached, a CNA message is sent to the call originator. The Return Cause reason is indicated as 0x07, meaning there is congestion.

Outgoing Calls

If Congestion Level 1 is reached, L3P IUP sends an Access Denied indication to the host with a Cause Code of 0x59, which means outseize failed and blocked.

Switch Response to Congestion Level 2

If Congestion Level 2 is reached, all new call MSUs (IAM, IFAM) 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.

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

Congestion Control Implementation Can be Changed

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

Message Transfer Part level 3 - network level
See Signaling System Number Seven.
See Integrated Services Digital Network User Part.
Telephone User Part
See Programmable Protocol Language.