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Performance, Capacity, and Reliability
Performance, capacity, and reliability define the primary factors needed to support a high-quality voice portal platform. The implementation of these particular requirements is clearly outside the scope of the application designer. However, the designer would use these figures to help in determining the best deployment platform to meet his or her needs. The following list contains some of the parameters most important to the VoiceXML application designer with respect to the performance characterization of a voice portal:
Maximum calls per second, assuming various permutations of TTS, ASR, audio prompting, and DTMF input being active in the benchmark call model. Note that the language chosen for TTS and/or ASR affects the capacity of the portal. Because American English is typically the benchmark language, the benchmark results most likely will be presented for that language.
Maximum downloadable file sizes, which should include audio prompt files, VoiceXML pages, or grammar files. The larger the file, the longer the download time. Although caching greatly reduces the impact of the file sizes, the portal obviously has a limit on what it can process.
Maximum number of subscribers, which affects the number of callers who can access the application after it's deployed. The number of expected subscribers and their calling patterns will not only affect the calls-per-second capacity, but may result in the addition of more portals by the provider. Again, these concerns are transparent to the application designer; however, these particular issues may increase the deployment cost of the application for obvious reasons.
Prompt bargein latency, which is the amount of time that expires between interrupting a prompt and when the prompt actually stops. Because speech recognition is not needed to recognize DTMF tone input, the latency for DTMF bargein input should be the minimum latency. Human factors results show that the bargein latency should not be much more than 250 milliseconds.
Of the four performance characteristics just presented, the bargein latency is the most relevant because this directly affects the end-user's experience with your application. Hence, assuming that the provider can handle your expected call volume and subscriber size, and properly sizes the voice portal, the higher priority should be given to the bargein latency.