Congestion Control

 

This appendix describes the Congestion Control feature. It covers the following topics:

•

Overview

•	Configuring Congestion Control

Overview

Congestion Control monitors the system for conditions that could potentially degrade performance when the system is under heavy load. Typically, these conditions are temporary (for example, high CPU or memory utilization) and are quickly resolved. However, continuous or large numbers of these conditions within a specific time interval may impact the system’s ability to service subscriber sessions. Congestion control helps identify such conditions and invokes policies for addressing the situation.

Congestion control operation is based on configuring the following:

•

Congestion Condition Thresholds: Thresholds dictate the conditions for which congestion control is enabled and establishes limits for defining the state of the system (congested or clear). These thresholds function in a way similar to operation thresholds that are configured for the system as described in the Thresholding Configuration Guide. The primary difference is that when congestion thresholds are reached, a service congestion policy and an SNMP trap, starCongestion, are generated.

A threshold tolerance dictates the percentage under the configured threshold that must be reached in order for the condition to be cleared. An SNMP trap, starCongestionClear, is then triggered.

•	Port Utilization Thresholds: If you set a port utilization threshold, when the average utilization of all ports in the system reaches the specified threshold, congestion control is enabled.

•	Port-specific Thresholds: If you set port-specific thresholds, when any individual port-specific threshold is reached, congestion control is enabled system-wide.

•	Service Congestion Policies: Congestion policies are configurable for each service. These policies dictate how services respond when the system detects that a congestion condition threshold has been crossed.

Important: This section provides the minimum instruction set for configuring congestion control. Commands that configure additional interface or port properties are provided in the Subscriber Configuration Mode chapter of the Command Line Interface Reference.

Configuring Congestion Control

To configure Congestion Control functionality:

Step 1

Configure congestion control thresholds as described in the Configuring the Congestion Control Threshold section.

Step 2

Configure service congestion policies as described in the Configuring Service Congestion Policies section.

Step 3

Enable redirect overload policies as described in the Enabling Congestion Control Redirect Overload Policy section.

Step 4

Configure disconnecting subscribers based on call or inactivity time as described in the Disconnecting Subscribers Based on Call or Inactivity Time section.

Step 5

Save your configuration as described in the Saving and Verifying Your Configuration chapter in this guide.

Configuring the Congestion Control Threshold

To configure congestion control threshold, apply the following example configuration in the Global Configuration mode of the CLI:

configure

  congestion-control threshold max-sessions-per-service-utilization <percent>

  congestion-control threshold tolerance <percent>

  end

Notes:

•	There are several additional threshold parameters. See the Global Configuration Mode chapter of the Command Line Interface Reference for more information.

•	The tolerance is the percentage under a configured threshold that dictates the point at which the condition is cleared.

•	Repeat this configuration as needed for additional thresholds.

Configuring Service Congestion Policies

To create a congestion control policy, apply the following example configuration in the Global Configuration mode of the CLI:

configure

  congestion-control policy <service> action { drop | none | redirect | reject }

  end

Notes:

•	When the redirect action occurs for PDSN services, the PDSN responds to the PCF with a reply code of 136, “unknown PDSN address” along with the IP address of an alternate PDSN.

•	redirect is not available for PDIF.

•	The default action for PDIF is “none.”

•	When the redirect action occurs for HA services, the system responds to the FA with a reply code of 136, “unknown home agent address”.

•	redirect can not be used in conjunction with GGSN services.

•	redirect is not available for the LMA service.

•	When setting the action to reject, the reply code is 130, “insufficient resources”.

•	For the GGSN, the reply code is 199, “no resources available”.

•	For the MME, redirect is not available.

Configuring Overload Reporting on the MME

When an overload condition is detected on an MME and the report-overload keyword is enabled in the congestion-control policy command, the MME reports the condition to a specified percentage of eNodeBs and proceeds to take the configured action on incoming sessions. To create a congestion control policy with overload reporting, apply the following example configuration:

configure

   congestion-control policy mme-service action report-overload reject-new-sessions enodeb-percentage <percentage>

   end

Notes:

•	Other overload actions include permit-emergency-sessions and reject-non-emergency-sessions.

Enabling Congestion Control Redirect Overload Policy

To create a congestion control policy and configure a redirect overload policy for the service, apply the following example configuration:

Important: Redirect is not available on PDIF for this release.

configure

  congestion-control

  context <context_name>

      {service_configuration_mode}

         policy overload redirect address

         end

Notes:

•	Optional: If the congestion control policy action was configured to redirect, then a redirect overload policy must be configured for the service(s) that are affected.

•	There are several service configuration modes that you can configure. See the Command Line Interface Reference for a complete list of modes.

•	You can set various options for redirection. See the Command Line Interface Reference for more information.

•	Repeat this configuration example to configure overload policies for additional services configured in the same context.

Verify the Service Overload Policies

To verify that the service overload policies were properly configured enter the following command in the Exec Mode:

show service_type name service_name

This command lists the entire service configuration. Verify that the information displayed for the “Overload Policy” is accurate.

Repeat this configuration example to configure additional services in other contexts.

Verify the Congestion Control Configuration

To verify Congestion Control Configuration enter the show congestion-control configuration command in the Exec Mode.

The following output is a concise listing of all threshold and policy configurations:

Congestion-control: enabled

Congestion-control threshold parameters

system cpu utilization: 80%

service control cpu utilization: 80%

system memory utilization: 80%

message queue utilization: 80%

message queue wait time: 10 seconds

port rx utilization: 80%

port tx utilization: 80%

license utilization: 100%

max-session-per-service utilization: 100%

tolerence limit: 10%

Overload-disconnect: disabled

Overload-disconnect threshold parameters

   license utilization: 80%

   max-session-per-service utilization: 80%

   tolerance: 10%

   session disconnect percent: 5%

   iterations-per-stage: 8

Congestion-control Policy

   pdsn-service: none

   ha-service: none

   lma-service: none

   ggsn-service: none

   closedrp-service: none

   lns-service: none

   cscf-service: reject

   pdif-service: none

   fng-service: none

   sgsn-service: none

   mme-service: drop

   asngw-service: none

   asnpc-service: none

   phsgw-service: none

   phspc-service: none

   mipv6ha-service: none

   lma-service: none

   sgw-service: none

   pgw-service: none

   hnbgw-service: none

   pcc-policy-service: none

   pcc-quota-service: none

   pcc-af-service: none

The primary threshold to observe is license utilization. This threshold is defaulted to 80%. Overload controls on the system enables the Congestion-control Policy when the system has only 80% of the licenses used. The overload condition will not clear until the utilization drops below the tolerance limit setting. The tolerance limit is defaulted to 10%. If the system goes into overload due to license utilization (threshold at 80%), the overload condition will not clear until the license utilization reaches 70%.

The system may go into overload if threshold settings are set too low and congestion control is enabled. You will need to review all threshold values and become familiar with the settings.

Since the recommendation for license utilization overload threshold is 100%, you should enable a license threshold alarm at 80%. An alarm is then triggered when the license utilization hits 80%. When the congestion-control policy setting is set to drop, the system drops incoming packets containing new session requests.

Important: For additional information on configuring the alarm threshold, refer to the Threshold Configuration Guide.

Disconnecting Subscribers Based on Call or Inactivity Time

During periods of heavy system load, it may be necessary to disconnect subscribers in order to maintain an acceptable level of system performance. You can establish thresholds to select subscribers to disconnect based on the length of time that a call has been connected or inactive.

To enable overload disconnect for the currently selected subscriber, use the following configuration example:

configure

   context <context_name>

      subscriber name <subscriber_name>

         default overload-disconnect threshold inactivity-time <dur_thresh>

         default overload-disconnect threshold connect-time <dur_thresh>

         end

To disable the overload disconnect feature for this subscriber, use the following configuration example:

configure

   context <context_name>

      subscriber <subscriber_name>

      no overload-disconnect {[threshold inactivity-time] | [threshhold connect-time]}

      end

Notes:

•	overload-disconnect is not supported for the CSCF service.

 

 

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