Media Event Timers - Telephony API Programmer's Reference

Custom Search

Media Event Timers

Many applications depend on the timing relationship between media events (for example, DTMF digits received) in order to determine the nature of a requested operation. For example, in a voice mail application, two consecutive DTMF "1" digits may mean "back up two segments" or "replay from beginning of message", depending on how much time elapsed between the two digits. In a client/server environment, if the DTMF detection is being performed on a separate processor from the one on which the application is running, latency in the local area network makes it very likely that the timing relationship between media events will be skewed, with the result that these timing-based differences could be lost or become unreliable.

To resolve this issue, several TAPI messages can be timestamped. Because it is the relative timing between these events that is important, the "clock time" of the event is not important, and sub-second timing is involved, these timestamps use the millisecond-resolution "time since Windows started" returned by the GetTickCount function. Applications must be aware that this is the tick count on the server (or machine where the service provider directly managing the hardware is running), and is not necessarily the same machine on which the application is executing; thus, the timestamps in these TAPI messages can only be compared to each other, and not to the value returned by GetTickCount on the processor on which the application is running.

The TAPI messages which can be timestamped are: LINE_GATHERDIGITS, LINE_GENERATE, LINE_MONITORDIGITS, LINE_MONITORMEDIA, and LINE_MONITORTONE. The tick count will be inserted into dwParam3 of these messages. If timestamping is not supported by the service provider (which is indicated by the service provider setting dwParam3 in these messages to 0), then TAPI itself will insert the tick count into dwParam3 of all of these messages (it can be skewed somewhat, but less than if the application did the same after the messages had traversed an interprocess communication scheme).

Last news from Greatis Software

    Nostalgia .Net     .Net is powerful, but not all-powerful, so sometimes we need to use Win32 API for our .Net applications. It's simple enough with Platform Invoke if you have Win32 skill, but we do not always have time to dig the ancient documentation, declare the special types that are compatible with Win32, find the values of the Win32's constants and so on. Nostalgia .Net offers several simple-to-use classes, and components that will allow you to forget about the headache of Win32 and just use the power of Win32 in your application the same way as you use the native. Net classes. More »

Recommended software for developers

    Ultimate Pack     Component pack for Delphi and C++ Builder that contains runtime form designer, runtime object inspector, print suite and much more for the very special price. More »

    Form Designer .Net     Unique runtime form design solution that allows to edit any form in .Net WinForms application at runtime with full source codes for only 300 euro! More »

    Print Suite .Net     Print Suite .Net is a set of components for easy printing texts, images and grids from your WinForms applications. Full C# source codes are available More »

    Gradient Controls .Net     Gradient Controls .Net offers controls with gradient background feature. Labels, panels and so on... Full C# source codes are available More »

    Greatis iGrid     iGrid plots drawing grid right over your desktop, so you can use it everywhere, with any drawing application without any special plugins for different graphic editors. More »

All the contacts and projects

Dmitry Vasiliev (just.dmitry)

More Online Helps

Win32 Programmer's Reference
Win32 Multimedia Programmer's Reference
OLE Programmer's Reference
Microsoft Windows Pen API Programmer's Reference
Microsoft Windows Sockets 2 Reference
Microsoft Windows Telephony API (TAPI) Programmer's Reference
Unix Manual Pages

greatis just4fun network