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Design Considerations for CVP in Comprehensive mode with regard to RAI messaging

 

Introduction

The H.323 Service (VoiceBrowser) on the CallServer monitors the number of calls in progress and when this reaches a configured threshold, the H.323 service will send an RAI message to the Gatekeeper stating that it is out of resources. When the number of calls then drops below another configured threshold, the H.323 service will send another RAI message to the Gatekeeper stating that it can now accept calls again.

Problem Description

A problem can arise when using the default configuration for these thresholds. The H.323 Service monitors 2 different resources ( see below for Calculations), these are currentIVRCalls and CurrentTotalCalls. If the thresholds are not configured correctly you can enter a situation where one resource is above the Maximum Threshold and the other resource is below the Minimum Threshold. Thus causing the H.323 to constantly send RAI messages to the GateKeeper saying out-of-resource, in-resource, out-of-resource, etc..,

 

RAI Parameters and Calculations

There are 5 separate parameters used in the calculations to determine if an RAI indicator is sent to the Gatekeeper, to either stop routing further incoming calls to this H.323 Service or to resume routing calls to this H.323 Service. These parameters can be configured in the VBAdmin tool.

 

This information is taken from the CVP Configuration and Administration Guide

 

RAI Parameters

 

  • RAIMaxThreshold - A percentage of the active incoming calls. If the number of calls exceeds this value an RAI indicator is sent to the Gatekeeper to stop routing further incoming calls to this H.323 Service - Default value 80
  • RAIMinThreshold - A percentage of the active incoming calls. If the number of calls drops below this value an RAI indicator is sent to the Gatekeeper to resume routing further incoming calls to this H.323 Service - Default value 70
  • MaxIVRPorts - Maximum number of calls in the H.323 Service which are allowed to received IVR treatment at any given time - Default value 50
  • MaxTotalCalls - Maximum total number of calls allowed in the H.323 Service - Default value 135
  • TakebackPercentage - Percentage of currently transferred calls for which IVR ports should be reserved for queuing or other IVR treatment - Default value 0

 

RAI Calculations

 

The H.323 Service monitors both currentIVRCalls and CurrentTotalCalls and applies the following calculations

Max Threshold

If the number of currentTotalCalls exceeds (RAIMaxThreshold/100)*MaxTotalCalls

OR

the number of currentIVRCalls exceeds (RAIMaxThreshold/100)*maxIVRports – (currentTransferredCalls * (takebackPercentage/100))an RAI indicator is sent to the Gatekeeper to stop routing further incoming calls to this H.323 Service.

Min Threshold

If the number of currentTotalCalls drops below  (RAIMinThreshold/100)*MaxTotalCalls

OR

the number of currentIVRCalls drops below(RAIMinThreshold/100)*maxIVRports – (currentTransferredCalls * (takebackPercentage/100)) and RAI indicator is sent to the Gatekeeper to resume routing calls to this H.323 Service.

 

Design Considerations

Because the H.323 service is monitoring 2 separate resources, and is using an OR in the calculation then for certain numbers of incoming calls with the default parameter values you can exceed the Max Threshold on the number of currentTotalCalls but be below the Min Threshold on the number of currrentIVRCalls, thus causing the H.323 to constantly send RAI messages to the GateKeeper saying out-of-resource, in-resource.

See below for illustration of Thresholds with default values

RAIMinMax.JPG

 

When determining the correct value for these parameters use VB Admin and check the max values seen for currentTotalCalls and currentIVRCalls using the ShowStatus command.

 


CLI: Voice Browser Total Statistics -------

 Since Startup:
     Total Calls:                           589202
       Disconnect Disposition:
         Redirected:                        1189
         Caller Hangup:                     553424
         Called Party Hangup:               33535
         ICM Release:                       34482
         Critical Media:                    4705
     Max Simultaneous Calls:                136
     Max IVR Ports:                         7
     Total prompts not found:               0
     Total transfers not completed:         1141
        Busy:                               360
        Ring-no-answer:                     428
        Gatekeeper problem:                 308
        Destination problem:                45
        Other:                              0
     System Startup Time:                   May 12 2008, 23:10:32
     System UpTime:                         119 Days, 18 Hours, 32 Minutes, 16 Seconds
     Current State:                         In Service
     Packets Transmitted(approx):           2.358e+004


As a general rule of thumb the key parameter in a comprehensive CVP deployment is the takebackPercentage.

 

I would recommend that you use an Excel spreadsheet to model your values before deploying.

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‎08-29-2017 08:13 AM
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