1.6 Global Call API versus DTI API

The standard R4 Digital Network Interface (DTI) API presents several functions, for example, time-division multiplexing (TDM) bus routing, network interface alarms, and time slot signaling control. The standard Global Call API presents a higher level of call control abstraction than the DTI API.

There are numerous digital interface telephony protocols in use worldwide. To name some, there are robbed-bit T-1, CAS E-1, ISDN, SS7, IP, and ATM. They all have one thing in common: they all try to solve the problem of connecting two or more people or machines anywhere in the world in direct conversation. Once the connection has been established, various data and voice streaming mechanisms can be used, such as digitized human voice, IP packets, or any other digital data.

Those protocols mentioned above all use a similar high level layer 3 protocol. The end result is that one end can initiate a call (make call), be informed of an incoming call, or drop the call. The Global Call API presents the developer with a similar level of abstraction at the API level, hiding the internals of the specific protocol. That is, in order to make a call under a T-1 robbed-bit trunk, the protocol indicates that one must flip the A & B signaling bits, while to do the same under an ISDN PRI protocol, one must send a specific HDLC packet over the ISDN data channel. All of these complicated operations are hidden from the Global Call developer.

It is technically possible to design a Global Call application in such a way that the same application can run with an E-1 CAS trunk or an E-1 ISDN trunk without requiring changes.

Global Call is the API of choice for a number of reasons. The following are some of the most obvious:

• Global Call presents the right level of abstraction for rapid digital interface telephony application deployment.
• The existing DM3 architecture with the TSC resource does not provide access to low-level channel associated signaling (CAS, robbed-bit), hence most of the DTI API cannot be provided.
• Global Call also enables easier digital network interface to analog network interface portability, where analog network interface is supported.

One of the challenges of migrating an application that used Springware boards and the DTI API is the lack of support for much of the DTI API functionality when using DM3 boards. However, Global Call more than makes up for this shortcoming and simplifies the life of the CTI application developer by providing a level of abstraction that allows seamless support for any telephony interface, including T-1, E-1, ISDN or even analog. Once an application has been designed to use Global Call, minimum changes (if any) are required for the same application to run on various Intel® Dialogic hardware, including Springware and DM3 boards.

It is a good architectural decision to use Global Call because of the greater flexibility and portability provided by Global Call. This is true, not just for applications that use DM3 boards, but for any CTI application that uses Intel® Dialogic hardware.

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