CompactPCI Unites Computer and Telephone

Author: Gerd Weking


The year 2000 will soon be upon us and with it the much-acclaimed knowledge and information society. The sheer quantity of information is growing continuously; available any time, any place, it in creasingly permeates both our work and our private life. Numerous intelligent telecommunications services are already a reality, for example guidance of telephone callers by synthetically generated voices and automatic routing to the relevant call centre.


It will not be long before other visions also become reality. The intelligent mobile phone sends your choice of evening meal to your home, where the intelligent refrigerator checks its contents and automatically orders any missing food items via the Internet. Mobile communication and the Internet are bringing forth new services. The growth in networking of intelligent communications equipment is also bringing together two sectors of industry which used to be clearly delineated - computers

and telecommunications.

Convergence of markets


Standards designed to ensure that the computer and telecommunications worlds grow together are summarised under the term, computer telephony (CT). In addition, CT is a synonym for new multimedia information technologies, with which transmission of speech, video signals and data can be combined. An example of this is telelearning, and another is telephone conversation via the Internet - both of which also illustrate how CT can produce cost savings. Even today, CT is already a sector of industry that is growing at a tremendous pace. New and better systems are appearing with evergreater regularity. At the same time, the compatibility problems familiar from current telephone systems are to be avoided from the outset by intensive standardisation efforts.

Standardisation of Software and Hardware

An important element in computer-based telecommunications equipment is the integration of a so-called telecom bus. When CT development began, bus systems developed in-house dominated, but before long the first steps towards standardisation were being taken. Since 1996, 140 manufacturers and telephone companies have joined together in the VoIP (Voice over Internet Protocol) Forum in order that the same level of reliable world-wide accessibility is achieved with Internet-supported voice data transmission as with conventional telephone networks.

Similarly, in the USA there is the ECT Forum (Enterprise Computer Telephony Forum), a grouping of leading industry representatives with the task of agreeing open standards for equipment interfaces and protocols (hardware and software). The ECTF initially restricted itself to PCI (Peripheral Component Interconnect) applications, for which the market is only now beginning to develop. The newly specified telecom bus was designed in such a way that existing CT standards, such as MVIP-90, H-MVIP or SCbus could be integrated.

Physical Layer specifications H.100 and H.110

The Physical Layer Specification H.100 describes the fundamental technical conditions for implementing the CT bus in a PCI system. The transmission protocol itself is based on TDM (Time Division Multiplex) technology. Now, PCs and their subsystems are not exactly renowned for extreme technical reliability. Furthermore, they do not offer various characteristics that are essential in telecommunications, for example expandability and the possibility of replacing defective modules while the system is running (hot swap).


For quite some time now, work has been conducted on optimising PCI-based systems for industrial measuring and control equipment. The PICMG (PCI Industrial Computer Manufacturers Group) carried out the studies and defined the CompactPCI bus (CPCI). Since CPCI had already brought significant improvements in mechanical design, it was a logical step for the ECTF to enhance the existing H.100 specification to include such requirements as hot swap. Thus, the new Physical Layer Specification H.110 for computer telephony on the CPCI bus came up.

Physical Layer Specification PICMG 2.5

Since the PICMG is responsible for all CPCI-relevant specifications, the H.110 recommendations of the ECTF were integrated into the Computer Telephony Specification PICMG 2.5.

The following important characteristics of the H.110 specification should be emphasised:


Protocol and interface based on H.100 Design with 19-inch rack system with 6U height module boards and backplanes with up to 20 slots Connectors from the <i>har-bus® HM</i> series in compliance with IEC 61076-4-101 Different plug-in levels for hot swap with leading and lagging contacts Part assembly of the contact blades and divided screen plates of the har-bus HM in the CT bus module P4/J4 give extended isolation between system voltage, stand-by voltage and the low voltages for the logic functions, in compliance with IEC 950

The 6SU standard board for computer telephony on the CompactPCI bus contains the following connectors:

  • P1/J1 carries the 32-bit PCI bus (the connector is Type A in compliance with IEC 61076-101)
  • P2/J2 contains the other connections for the 64-bit PCI bus (the connector is based on IEC Type B, but in a shorter version)
  • P3/J3 is not defined for CPCI-CT but can be used for additional input and output signals
  • P4/J4 carries the CT bus to H.110 (the connector is IEC Type A)
  • P5/J5 is reserved for input and output signals to other equipment in the network, which are fed from the rear of the equipment to the bus (the connector is based on IEC Type B, but in a shorter version)

Looking to the future

Blick in die Zukunft

Extremely rapid pace of development in communications and information technology will accelerate still further in the new millennium. Increasing bit rates and falling signal levels are leading to new requirements for signal integrity and screening in connection technology. For this reason, the decisive factor influencing the quality of a connector will be optimised signal transmissions, which depends on exact knowledge of the influencing factors. HARTING utilises Spice, IBIS and other models for close-to-real simulation of products. Consequently the har-bus® HM marks the beginning of a new generation of electronic connectors.