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The Congestion objects provide a facility for managing the call congestion for SBC application. Following system congestion levels are defined in this section, with each level representing an increasing severity of congestion within the SBC:

  • adaptive – The congestion level at which the adaptive congestion control algorithm activates. The adaptive algorithm iteratively adjusts the call acceptance rate up or down to maximize call throughput while maintaining target performance metrics throughout the overload event. The algorithm is self-tuning to automatically adjust to nominal capacity (and to non-call-rate related events consuming unpredictable amounts of CPU) and is independent of call scenario mix, signaling types, and user retry behavior. There is a single default configuration for all system configurations. Emergency calls may optionally be given preference over non-priority calls.
  • levelMC1 – Limited congestion level. By default, no calls are rejected due to congestion in this level.
  • levelMC2 – Moderate congestion level. By default, the adaptive congestion controls activate when this level of congestion is reached.
  • levelMC3 – Critical congestion level. By default, this level is disabled since the adaptive congestion controls (which activate at levelMC2) prevent the box from reaching this level.
  • mode – Mode for the system congestion control.
  • policer – System congestion Call Rate Policer configuration.

In levels MC1 and MC2, the SBC software will attempt to balance traffic by assigning H.323 and SIP calls to non-congested modules. In levels MC1, MC2, and MC3, all INFO event log messages are suppressed.

These congestion levels only apply to the packet calls. You define the threshold at which these congestion levels are trigger by associating each level with an Overload Profile. CPU utilization congestion criteria thresholds and durations are specified in the Overload Profile. By configuring the Overload Profile appropriately, some of the congestion criteria can trigger a change in the congestion level.

During a sustained system load, the SBC accepts calls at a smooth rate, avoiding behavior such as accepting all calls for a short period of time, and then rejecting all calls for the remaining sampling period. This is accomplished with system-level policers. Unlike IP Traffic Policers--which control the allowed rate of incoming IP packets, congestion policers control the allowed rate of incoming calls in a system. Individually configurable bucket sizes (POLICER BUCKETSIZE) control the call burst handling capability. The policer fill rate controls the sustained rate (the rate at which tokens are added to the bucket). In this case, the fill rate is the sustained call rate allowed at calls per second (CPS). Fill rates are not configurable when using congestion policers; instead, they are dynamically adjusted based on resource usage, to maximize those resources.

Command Syntax

% set system congestion
    adaptive
        MCLevel <mc1 | mc2 | mc3>
% set system congestion
    levelMC1
        mode <inService | outOfService>
        overloadProfileName <defaultMC1 | defaultMC2 | defaultMC3>
    levelMC2
        mode <inService | outOfService>
        overloadProfileName <defaultMC1 | defaultMC2 | defaultMC3>
    levelMC3
        mode <inService | outOfService>
        overloadProfileName <defaultMC1 | defaultMC2 | defaultMC3>
% set system congestion
    mode <adaptive>
    policer preference
        call <0-3>
        emergencyCall <0-3>
        initialSipRegister <0-3>
        initialSipSubscribe <0-3>

Command Parameters

Table : Congestion Parameters

Parameter

Description

adaptive

Adaptive overload configuration.

  • MCLevel – Sets the system machine congestion level at which the system adaptive algorithm activates:
    • mc1 – Adaptive congestion control is activated at system congestion level mc1.
    • mc2 – Adaptive congestion control is activated at system congestion level mc2.
    • mc3 – Adaptive congestion control is activated at system congestion level mc3.

levelMC1

The operational state of machine congestion level 1, or MC1.

  • mode – The Maintenance mode for MC1.
    • inService – (default) The most recently assigned Overload Profile is validated and activated.
    • outOfService – Congestion control processing for machine level 1 is suspended. A new Overload Profile can be assigned.
  • overloadProfileName – The Overload Profile name for MC1.
    • defaultMC1(default) The name of the Overload Profile defined for Machine Congestion Level 1 (MC1).
    • defaultMC2 – The name of the Overload Profile defined for Machine Congestion Level 2 (MC2).
    • defaultMC3 – The name of the Overload Profile defined for Machine Congestion Level 3 (MC3).

See MC Level Thresholds table below for Set and Clear thresholds.

levelMC2

The operational state of machine congestion level 2, or MC2.

  • mode – The Maintenance mode of MC2.
    • inService – (default) The most recently assigned Overload Profile is validated and activated.
    • outOfService – Congestion control processing for machine level 2 is suspended. A new Overload Profile can be assigned.
  • overloadProfileName – The Overload Profile name for MC2.
    • defaultMC1 – The name of the Overload Profile defined for Machine Congestion Level 1 (MC1).
    • defaultMC2(default) The name of the Overload Profile defined for Machine Congestion Level 2 (MC2).
    • defaultMC3 – The name of the Overload Profile defined for Machine Congestion Level 3 (MC3).

See MC Level Thresholds table below for Set and Clear thresholds.

levelMC3

The operational state of machine congestion level 3, or MC3.

  • mode – The Maintenance mode of MC3.
    • inService – (default) The most recently assigned Overload Profile is validated and activated.
    • outOfService – Congestion control processing for machine level 3 is suspended. A new Overload Profile can be assigned.
  • overloadProfileName – The Overload Profile name for MC3.
    • defaultMC1 – The name of the Overload Profile defined for Machine Congestion Level 1 (MC1).
    • defaultMC2 – The name of the Overload Profile defined for Machine Congestion Level 2 (MC2).
    • defaultMC3(default) The name of the Overload Profile defined for Machine Congestion Level 3 (MC3).

See MC Level Thresholds table below for Set and Clear thresholds.

mode

The system overload control mode.

  • adaptive – (default) Adaptive overload control mechanism is applied.

policer  preference

The system congestion Call Rate Policer configuration.  Use this control to assign a preference value (0 to 3) to the call types below, where 0 is the highest and 3 is the lowest preference value.

  • call – Preference value applied during normal call admission (default = 1).
  • emergencyCall – Preference value that is applied during emergency call admission (default = 0).
  • initialSipRegister – Preference value that is applied during initial SIP registration admission (default = 2).
  •  initialSipSubscribe – Preference value to apply to initial SIP Subscribe requests during initial SIP Subscribe admission (default = 2).

Table : Default Overload Profile Settings

Overload ProfileSet Threshold (%)Clear Threshold (%)Set Duration (seconds)Clear Duration (seconds)
defaultMC185801010
defaultMC2908636
defaultMC3989533

 

Command Example

To display congestion configuration information:

% set system congestion adaptive MCLevel mc1
% set system congestion levelMC1 mode inService overloadProfileName defaultMC1
% set system congestion levelMC2 mode inService overloadProfileName defaultMC2
% set system congestion levelMC2 mode outOfService overloadProfileName defaultMC3
% set system congestion mode adaptive
% set system congestion policer preference call 0
 
% show system congestion
levelMC1 {
    mode                inService;
    overloadProfileName defaultMC1;
}
levelMC2 {
    mode                inService;
    overloadProfileName defaultMC2;
}
levelMC3 {
    mode                outOfService;
    overloadProfileName defaultMC3;
}
mode adaptive;
adaptive {
    MCLevel mc1;
}
policer {
    preference {
        call 0;
    }
}

  

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