CTI Plug & Play Protocols

Every major telephony and computer vendor has invested heavily in contributing towards interoperability. Each industry group that has tackled these challenges has moved the industry closer to fully satisfying the requirements; each group has built upon and added to previous efforts. These industry efforts have included the following:

1. Telephone Manager (Apple and partners),
2. TAPI (Microsoft and partners),
3. CSTA (ECMA),
4. TSAPI (AT&T, Novell, and partners), and the
5. CTI Encyclopedia (Versit and partners).

Of these, the efforts of ECMA, ECTF, and Versit have included establishing standardized CTI protocols. A team working for Versit spent nearly three years preparing the Versit CTI Encyclopedia. The six volume CTI encyclopedia was based directly on ECMA's CSTA phase I and phase II specifications, and incorpoated support for all these other industry initiatives. It is the first and only complete specification for CTI Plug & Play interoperability. It forms the basis for ECMA CSTA Phase III and ECTF C.001.

CTI Interfaces and Messages

A CTI interface is a telephony resource that creates a portal through which interoperable telephony components communicate with one another. A CTI interface operates by generating, sending, receiving, and interpreting messages containing status information and requests for services to be performed.

CTI Protocols

CTI protocols are specifications of the structure, contents, use, and flow of CTI control and status messages that travel between CTI system components over well-defined communication paths. CTI protocols are high-level protocols, like the protocols used to send electronic mail, print to a printer, retrieve files from a file server or, browse the World Wide Web. Like these other protocols, they are designed to be transmitted over any type of reliable communication path. Three standard CTI protocols have been defined. They are:

1. CTI Protocol 1
   CTI Protocol 1 is optimized for use between a switch and a CTI server. It uses ASN.1 encoding that is optimized for compatibility with CSTA implementations.
2. CTI Protocol 2
   CTI Protocol 2 is optimized for use between client computers and CTI servers. It uses ASN.1 encoding but is optimized to minimize decoding overhead on client computers.
3. CTI Protocol 3
   CTI Protocol 3 is optimized for use between telephone stations, PDAs, and client computers. It is optimized to use buffers as small as 80 bytes and minimizes the computing power required for encoding and decoding--necessary attributes for implementing CTI components such as CTI-enabled pay phones, cellular phones, desk phones, and PDAs.

These protocols all represent the same application layer CTI protocol but the encoding, or presentation layer protocol, specified for each is optimized for a different type of product implementation. This means that each CTI protocol is capable of carrying the same CTI messages and while each can be used in any context, each is intended for use with specific types of CTI system components. For example, CTI Protocol 3 is optimized to use buffers as small as 80 bytes whereas, CTI Protocol 1 (intended for a dedicated link between the CTI interface on a switch and a CTI server) uses ISO's ASN.1 encoding and requires buffers that may need to be as large as 2000 bytes or more.

CT Plug & Play

CT Plug & Play interoperability is made possible through the use of standard CT protocols. CT Plug & Play means that no software specific to a particular logical server needs to be installed on a logical client. This type of interoperability between any two CT components is achieved when each CT component implements both:

• Standardized CT protocol(s)
• Standard communication path(s)

A CT component that does not satisfy both of these requirements requires special software to be installed and thus is not CT Plug & Play.