Media File Options
This chapter covers the following topics:
•Deployment and Ongoing Management
•Bandwidth Calculation for Prompt Retrieval
•Best Practices for Prompt Management
•Configuring Caching on IOS
•Branch office implications
Deployment and Ongoing Management
Voice prompts can be stored in the following locations:
•In flash memory on each local gateway — In this way, gateways do not have to retrieve .wav files for prompts, so WAN bandwidth is not affected. However, if a prompt needs to change, you must change it on every gateway.
•On an HTTP media server — In this way, each local gateway (if properly configured) can cache many or all prompts, depending on the number and size of the prompts.
Bandwidth Calculation for Prompt Retrieval
When prompts are stored on an HTTP media server, the refresh period for the prompts is defined on that server. The bandwidth consumed by prompts consists of the initial loading of the prompts at each gateway and of the periodic updates at the expiration of the refresh interval.
As an example of determining the bandwidth consumed by prompts, assume that a deployment has 50 prompts with an average size of 50 kB (50,000 bytes) each. Also assume that the refresh period for the prompts is defined as 15 minutes (900 seconds) on the HTTP media server. The WAN bandwidth required for prompts in this deployment can be calculated as follows:
50 prompts 50,000 bytes 8 bits = 20,000,000 bits
20,000,000 bits / 900 seconds = 22.2 kbps per branch
Best Practices for Prompt Management
The following are best practices for managing prompts:
•If the prompts are changing frequently, you can ensure that the prompts are current by configuring the HTTP client cache refresh rate to be 30 minutes. This setting allows the voice gateway to cache prompts that will expire after 30 minutes. Upon the next request the prompt will be downloaded and cached again.
•The HTTP client cache memory file represents the largest prompt file (in kilobytes) that can be cached. In general, divide prompts larger than 500 kB (about a minute in length) into smaller, more manageable pieces to facilitate loading and caching. For example, queue music could be a repetitive loop of a 30-second prompt. Because the prompts are streamed, the prompt are not cached unless the whole prompt is played. Therefore, make prompts a manageable size.
•If prompts are going to be retrieved from flash, specify prompt URLs in the form: `flash:<filename>.wav'.
Configuring Caching on IOS
The Cisco MRCP client uses an HTTP client, which is a part of Cisco IOS. The client fetches VoiceXML documents, audio files, and other file resources. To optimize the fetching of the HTTP client, set the cache configurations.
For example, if a 1 MB audio file is being fetched, ensure the audio file is also cached. If there is not enough space configured on the router to hold the file, the HTTP client fetches the same audio file each time it is needed; this causes delays in processing.
There are two key HTTP client cache configurations:
•http client cache memory file size in kb 1 - 10,000
•http client cache memory pool size in kb 1 - 10,000
Note The upper range is the maximum space allowed for all cached files. The space available can not exceed 10 MB, otherwise subsequent files are not cached.
Branch office implications
In most cases, customers implementing CVP in Branch Office deployments expect a small footprint for hardware. In most scenarios, when a separate media server is not a preferred model, customers prefer deploying voice prompts on the gateway flash.
Typical prompt sizes when recorded in G711 MuLaw format of average duration are about 10-15K in size. When sizing gateways for such implementations, size the FLASH memory by factoring in the number of prompts and their sizes and also room on which to store the IOS image.