Media Access

A telephony service provider can directly supply limited access to and control over media. With the addition of media service providers, a paired MSP becomes the preferred method for accessing and manipulating media. The following material relates to media support mechanisms available through a TSP.

The media type is the form in which data is transmitted on a line. The telephony service provider is responsible for filling out the dwMediaModes member of LINEDEVCAPS, which is used by an application and by TAPI to identify the media capabilities of a given device.

The service provider is also responsible for reporting media type changes when requested. This process is sometimes referred to as call classification. The mechanism used to determine the type of a media stream (such as voice, fax, data modem) is service-provider specific.

A service provider can filter the media stream for energy or tones that characterize the media type. Alternatively, the service provider can determine the type by messages exchanged over the network, by use of distinctive ringing, or by knowledge about the caller or called ID.

If a telephony service provider supports some media control, it must accept requests to carry out actions on the media stream when given events occur, such as on receiving a specific tone or DTMF digit in the media stream. For example, the service provider might receive a request to suspend the media stream when it detects a # DTMF digit, and resume the media stream when it detects a * DTMF digit.