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.
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.
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
The H.323 Service monitors both currentIVRCalls and CurrentTotalCalls and applies the following calculations
If the number of currentTotalCalls exceeds (RAIMaxThreshold/100)*MaxTotalCalls
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.
If the number of currentTotalCalls drops below (RAIMinThreshold/100)*MaxTotalCalls
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.
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
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.