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2. Demo Description2.1. About the Demo
The IP Gateway (Global Call) demo is a host-based application that demonstrates
using the Global Call API to build a PSTN−IP gateway. The demo source code
can be used as sample code for those who want to begin developing an
application from a working application. The demo is not designed to implement a
complete gateway, lacking features such as least-cost routing, etc.
The IP Gateway (Global Call) demo is a cross-OS demo, running under the
Windows* or Linux* environments. Most of the differences in the environments
are handled directly by the programming interface and are transparent to the user.
Other differences, due to inherent differences in the operating systems, are
handled by the Platform Dependency Library (PDL).
For more information about the PDL refer to the source code in the pdl_win or
pdl_linux directories.
2.2. Choosing Channels
When a call comes from the PSTN, the call is answered by a PSTN line device.
During initialization, the PSTN channel was associated with a specific IP line
device, so the call is connected to the IP line device that is associated with this
PSTN line device.
When a call arrives from the IP network, there is no direct association of a
channel, since there are no individual physical connections for the IP channels.
The call is answered by a line device. During initialization, the line device was
associated with a specific PSTN line device. The Global Call API tells the IP
Gateway (Global Call) demo which PSTN channel is associated with this IP
channel. The application then connects the IP call to the appropriate PSTN
channel.