1. SCbus Introduction

SCbus Product Overview

The SCbus is a real-time, high-speed, time division multiplexed (TDM) communications bus that provides 1024 time slots for transmission of digital information between SCbus products. The SCbus allows high-density systems to efficiently share resources so that multiple technologies can be connected to each port as needed.

Each SCbus product consists of several devices. Each of these devices can communicate via the SCbus with any other device connected to the SCbus. For example:

• a D/41ESC board provides 4 on-board analog loop start interface devices and 4 voice devices, for a total of 8 devices communicating over the SCbus.
• a D/160SC-LS board provides 16 on-board analog loop start interface devices and 16 voice devices, for a total of 32 devices communicating over the SCbus.
• a D/240SC-T1 board provides a T-1/DSX-1 interface for processing 24 T-1 time slots/calls and 24 voice devices, for a total of 48 devices communicating over the SCbus.
• a D/300SC-E1 board provides an E-1 interface for processing 30 E-1 time slots/calls and 30 voice devices, for a total of 60 devices communicating over the SCbus.
• a VFX/40ESC board provides 4 on-board analog loop start interface devices and 4 fax/voice devices, for a total of 8 devices communicating over the SCbus.
• a MSI/240SC board provides 24 on board station devices, for a total of 24 devices communicating over the SCbus.

All devices connected to the SCbus have a transmit (TX) channel and a receive (RX) (listen) channel. At system initialization, each transmit channel is assigned to a specific and unique SCbus time slot. This transmit channel assignment cannot be changed by the application.

Since all transmit channels are pre-assigned, routing an SCbus device only requires connecting the receive (listen) channel of the device to an SCbus time slot. The connected device then listens to all data transmitted over that SCbus time slot. This receive channel can be moved (disconnected and connected) to a different SCbus time slot at any time by the application.

NOTE:

The SCbus routing functions only support SCbus configurations.

This guide provides an overview of SCbus routing and defines the nomenclature used to identify devices, channels and time slots in various SCbus configurations. These configurations may include combinations of resources such as voice devices, analog loop-start network interfaces (analog devices), digital network interfaces (T-1 or E-1 devices) and facsimile devices (fax devices).

Chapter 2 describes SCbus routing concepts for communicating with resources via the SCbus and provides a summary listing of the SCbus routing functions. See the companion volumes listed below for detailed information about each SCbus routing function.

Chapters 3 through 6 contain examples of routing resources using SCbus routing functions.

• Chapter 3 provides an overview of SCbus routing assignments after system initialization and routing resources using SCbus convenience functions or individual SCbus routing functions.
• Chapter 4 provides an example of SCbus routing and sample code for an analog inbound/outbound call application.
• Chapter 5 provides an example of SCbus routing and sample code for a digital service inbound/outbound call application.
• Chapter 6 provides an example of SCbus routing and sample code for sharing a fax resource.
• Chapter 7 describes special considerations to keep in mind when routing SCbus devices and when programming voice and analog loop-start device configurations.

The following companion volumes describe the network/resource (nr_) SCbus convenience functions, the individual SCbus routing functions and SCbus routing demo programs.

• SCbus Routing Software Reference for MS-DOS
• SCbus Routing Software Reference for OS/2
• SCbus Routing Software Reference for Linux and Windows

Appendices contain a summary list of the SCbus routing functions, a list of related publications and a glossary.

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