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Automatic Congestion Control

Overview

Automatic Congestion Control (ACC) allows the CSP to handle the following:

• local overloads

• remote overloads

Local overload is the condition where the local SS7 stack on the CSP is overloaded. All incoming calls from the network and all Outseize Control requests from Layer 4 are throttled (rejected) and the CSP comes back to a load level to process steady call traffic.

Remote overload is the condition where a remote node is overloaded or there is a network congestion to the remote node. All Outseize Control requests from Layer 4 get throttled which brings that node to a lower load level.

In either case, for Outseize Control requests, Layer 4 receives an Access Denied Reason of 0x51 when the SS7 is overloaded locally or there is a remote overload at the destination of the call. Layer 4 releases the incoming side with the cause code of Congestion with ACL2.

Configuration

PPL Components

You use the following PPL Components to implement this feature:

• ACC 0xA8 - Configuration Bytes and PPL Timers

• SPRC 0x13 - Configuration Bytes and PPL Timers

In most cases, the parameter’s default value is appropriate but depending on the network, you might have to change some parameters.

Refer to ISUP SPRC (0x0013) for configuration information.

Acceptance Rate and Automatic Congestion Level Values

The Automatic Congestion Level (ACL) values define the two overload levels that you can assign to a destination. For example you would assign a destination to have ACL Level 1 or ACL Level 2 overload.

The Acceptance Rate defines how many calls per second each ACL can handle before the calls are throttled.

You include the Acceptance Rate TLV (0x4E24) in the PPL Event Request (0x0044) API message to change the Acceptance Rate for each destination for either ACL levels. The Acceptance Rate is the number of call per second associated with the ACL.

Refer to the TLV Chapter in the API Reference.

Alarms

Refer to the Alarm (0x00B9) API message for information on four general alarms associated with this feature:

• SS7 Signaling Network Congestion (0x0E)

• ISDN/SS7 Signaling Stack Congestion (0x16)

• Signaling Destination Congestion (0x3A)

• Signaling Link Congestion (0x3B)

See Signaling System Number Seven.
Outgoing call setup during real-time call processing on a specific channel.
Call processing layer of the CSP.
See Programmable Protocol Language.
Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.
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 Integrated Services Digital Network.