GDK Subsystem
Dialogic has developed a fax subsystem optimized for mission critical, high volume, fax applications. CP Fax hardware channels are integrated through direct connection to the Public Switched Telephone Network (PSTN) or as a shared resource in a telephony bus environment such as Pulse Code Modulation Expansion Bus (PEB) or Signal Computing Bus (SCbus). All the details, critical timings, fax machine compatibility, on-line image conversions, High-Level Data-Link Control (HDLC) and signal quality measurements occur on-card via field upgradable, soft loadable firmware.
Architecturally, a GDK channel functions as a client-server to the host computer. Communication between the fax channel server and the host application client is through an operating-system dependent driver (the GDK system service dispatcher) and a GDK API messaging interface. This method differs greatly from traditional (Class 1 or Class 2) fax-data modems.
The GDK APIs provide fax communications in two ways - passive batch mode and runtime interactive mode. These two modes are described in more detail later in this chapter.
During fax transactions, the Dispatcher is a server to the fax channels executing proprietary remote procedure call requests for files, data, system time, or other host services. The application can participate in fax communication through event monitoring using the run-time API, or can ignore the details of the fax protocols by using the batch-programming model.
The GDK architecture shields the application from critical protocol timings, allowing the development of very high-density systems with inexpensive host chassis hardware. A fax transaction can withstand up to 30-second delay in host service. This delay can occur in Local Area Networks (LANs) and Wide Area Networks (WANs) used to connect mission critical, integrated fax solutions in businesses and service bureaus.
This architecture also protects the T.30 protocol from misuse in foreign countries where the fax protocol may be restricted by government approval requirements. Dialogic CP Fax products are approved for many countries.
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