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Chapter 1

Introduction

1.1 Introduction

1.2 ISDN

: 1.2.1 ISDN Protocols and Protocol Layering
: 1.2.2 ISDN Carriers
: 1.2.3 Specificity of BRI Boards

1.3 BRI Service and BX 2000 Boards

: 1.3.1 BX 2000 Boards
: 1.3.2 BRI Service Configuration
: 1.3.3 Typical Environment Configuration

1.4 BRI Service Software Components

: 1.4.1 readme File
: 1.4.2 BRI Service Function Libraries
: 1.4.3 Header Files
: 1.4.4 ISDN Protocol Stack Downloadable Object Modules
: 1.4.5 QX or AG Configuration File
: 1.4.6 Demonstration Program

1.5 Other Components

: 1.5.1 CT Access

1.6 Developing a BRI Service Application

1.1 Introduction

The BRI service allows you to create applications that interact with ISDN services in a variety of ways, using: The NMS CT Access application programming interfaces (APIs) One or more BX 2000 boards AG boards or QX boards (optional)
The BX 2000 boards are BRI trunk interface boards. These boards have four BRI trunks (i.e., 8 B channels). The BX 2000 boards do not offer DSP resources for media functions such as voice, DTMF, fax, etc. Therefore, if your application requires media functions, you need to add AG boards or QX boards to execute the media functions.
The BX 2000 boards, controlled by the BRI service, handle call control services at Layer 4, similar to the ADI service. The BRI service does not provide any access to low-level ISDN services (e.g., Layer 3 or Layer 2). BRI service functions, data structures, code, etc. have been modeled from the ADI service.
The BRI service is available under Windows NT.
This chapter: Provides an overview of ISDN Discusses the BRI service and its role in an application Lists and describes the BRI service components Lists and describes the other hardware and software components required in an application Outlines the application development process

1.2 ISDN

Integrated Services Digital Network (ISDN) is a continually evolving international standard for networking a wide range of services, including voice and non-voice services. The network is completely digital, from one end to the other: voice information is digitized and sent in digital form. Signaling information is sent separately from voice information, using a method called common channel signaling (CCS).

1.2.1 ISDN Protocols and Protocol Layering

ISDN communications can be described at many levels, from the way bits are transferred from machine to machine to the sets of messages computers pass to one another. A scheme for communication at a certain level is called a protocol.
In the late 1970's, the International Standards Organization (ISO) established the Open Systems Interconnect (OSI) model for communication. ISDN is based on this model. In OSI, seven separate levels, or layers, of communication are defined (refer to Figure 1). The first three layers, called the chained layers, are the lowest levels. The chained layers are: Layer Description 1 - Physical The electrical and mechanical layer. Protocols for this layer describe, on an electrical and mechanical basis, the methods used to transfer bits from one device to another. One protocol used at this layer is CCITT recommendation I.430/I.431. 2 - Data Link The layer above the physical layer. Protocols for this layer describe methods for error-free communication between devices across the physical link. One protocol used at this layer is CCITT recommendation Q.921, also known as Link Access Procedures on the D Channel (LAPD). 3 - Network The layer above the data link layer. Protocols for this layer describe methods for transferring information between computers. They also describe how data is routed within and between networks. One protocol used at this layer is CCITT recommendation Q.931.
Layers higher than these are end-to-end layers. They describe how information is exchanged and delivered end-to-end. They also define process-to-process communication, and describe application-independent user services, user interfaces and applications, etc. Figure 1. OSI Protocol Layering Model
The functionality provided by a layer includes the services and functions of all of the layers below it. A Service Access Point (SAP) is the point at which a layer provides services to the layer directly above it. With each SAP is associated a unique Service Access Point Identifier (SAPI).
The Layer 3 protocol is not a symmetric protocol, there is a network side and a terminal side. Typically, applications which act as a network node must use ISDN Network side stacks. Applications which act as a terminal (for example, IVR, or any application which is connected on the PSTN) must use ISDN Terminal side stacks.

Layer	Description
1 - Physical	The electrical and mechanical layer. Protocols for this layer describe, on an electrical and mechanical basis, the methods used to transfer bits from one device to another. One protocol used at this layer is CCITT recommendation I.430/I.431.
2 - Data Link	The layer above the physical layer. Protocols for this layer describe methods for error-free communication between devices across the physical link. One protocol used at this layer is CCITT recommendation Q.921, also known as Link Access Procedures on the D Channel (LAPD).
3 - Network	The layer above the data link layer. Protocols for this layer describe methods for transferring information between computers. They also describe how data is routed within and between networks. One protocol used at this layer is CCITT recommendation Q.931.

1.2.2 ISDN Carriers

ISDN is transmitted over T1 carriers, E1 carriers, and BRI (Basic Rate) carriers. These are typically four-wire digital transmission links.
With basic-rate ISDN, the channels are usually used as follows: Two channels carry data digitized at 64 Kbps: voice, audio, data and/or video signals. These channels are called bearer channels (B channels). One channel carries signaling information for the two B channels. This is called the D channel. Figure 2. BX 2000 Configuration

1.2.3 Specificity of BRI Boards

The BX 2000 board is designed to work with two types of CCITT I.430 BRI configuration, generally known as S-bus.
Figure 3 shows the first type of S-bus configuration which is called point-to-point configuration. The BX 2000 board is a terminal equipment connected to the network. Figure 3. Point-to-Point Configuration
Figure 4 shows the second type of S-bus configuration which is called point-to-multipoint configuration. One of the four BRI trunks of the BX 2000 board shares the S-bus with other Terminal Equipments (other BX 2000 board's trunks or ISDN phones, fax machines, PC for data transfer, etc.). The S-bus supports up to eight terminal equipments.
When several terminals share the S-bus, they share the 2 B channels available on the S-bus. Only two calls can be handled simultaneously. When calls arrive from the network, the terminals will be notified but only one will establish the incoming call. In point-to-multipoint configurations, bus contention issues must be addressed. Note: Each BRI trunk of a BX 2000 board is terminal equipment. It provides a standardized plug called S interface as a connection to the network. Since the S-bus is standard, all terminal equipment providing an S-interface (standardized plug to connect to the network), can be connected to any PBX or network. Figure 4. Point-to-Multipoint Configuration Note: BX 2000 boards can only act as terminals on the S-bus or in point-to-point configurations. BX 2000 boards never act as the network side on the S-bus or in point-to-point configurations.

1.3 BRI Service and BX 2000 Boards

The BRI service software allows you to write CT Access applications that communicate with BRI trunks of BX 2000 boards to perform call control using ISDN Common Channel Signaling protocols.
The BRI service is designed to use up to four BX 2000 boards as the physical interface to trunk lines. Note: The BRI service is only supported on BX 2000 boards.

1.3.1 BX 2000 Boards

BX 2000 boards have four BRI trunk interfaces, but they do not have an on-board DSP. Each BX 2000 board occupies only one PCI slot in the host computer.
BX 2000 boards connect to other boards via the MVIP bus. The MVIP bus allows the boards to share data, signaling, and switching information with other boards on the MVIP bus. Depending upon the application type, you may require DSP resources from QX boards or AG boards.
For detailed information on BX 2000 boards, refer to the BX 2000 Installation and Developer's Manual.

1.3.2 BRI Service Configuration

The BRI service allows you to access ISDN call control services.
The configuration shown in Figure 5 contains the following components: The ISDN protocol stack runs on the board. The stack implements all ISDN layer 2 and layer 3 functionality. Only the terminal side stacks are provided on BX 2000 boards. The BRI Service runs on the host. It serves as the interface between the CT Access application and a B channel on a trunk. At initialization, the application creates a CTA context instance for each B channel (voice channel). It communicates with the BRI service via the CTA context. The BRI service for a B channel routes BRI call control commands to the resource attached to that channel, and routes call control events from the resource back to the CTA context. In addition, it translates CT Access commands involving signaling into ISDN messages, and sends them to the ISDN protocol stack, which controls the D channel. It interprets ISDN messages coming from the ISDN protocol stack, translates them into appropriate BRI events and sends them to the application via the CTA context.
B channel information can be routed to DSP resources (on AG boards or QX boards) through the BX 2000 board's MVIP switch. The switch can be controlled using the CT Access Switching service. Figure 5. BRI Service Application Architecture (Using BRI Call Control)

1.3.3 Typical Environment Configuration

BX 2000 boards do not have DSP resources; they are line interface boards. This is why the BRI service provides only call control functions.
If your application requires media functions such as voice, DTMF, fax, speech recognition, etc., use AG boards or QX boards with the ADI Service or any other service available under CT Access.
The B channel data is routed to the DSP boards via the MVIP bus.
Call establishment is done by the BX 2000 board through the BRI service. Then, using the Switching service, the B channel of the BRI trunk is connected to DSP resources on AG boards or QX boards so that media functions are available. Figure 6 shows the data flow of this type of configuration. Figure 6. BRI Service Environment Configuration

1.4 BRI Service Software Components

The BRI service with the BX 2000 board implements the Euro-ISDN standard.
The BRI service package contains: A readme file BRI service function libraries for CT Access A header file The BX 2000 board Control Panel Applet The BX 2000 board drivers and a downloadable object module containing the ISDN stacks software which run on-board Sample configuration files for using AG boards and QX boards with BX 2000 boards (optional) A demonstration program with source code A tool to help you configure the MVIP bus clocks in mixed configurations (when BX 2000 boards are used with AG boards or QX boards)
The sections that follow briefly describe each of these components.

1.4.1 readme File

This ASCII text file contains release information that does not appear in other documentation. The file is named readme.txt. Refer to this file to learn where the BRI service software components are located after installation.

1.4.2 BRI Service Function Libraries

The libraries are dynamic-link libraries (DLLs) under Windows NT. They are brimgr.dll (BRI service manager) and briapi.dll (BRI API). briapi.lib is also provided for the application to link with.

1.4.3 Header Files

bridef.h is the header file that is supplied with the BRI service. This file contains defines, BRI API function prototypes, and BRI service parameter structures.

1.4.4 ISDN Protocol Stack Downloadable Object Modules

A downloadable object module file contains the basic low-level software which a BX 2000 board requires to support ISDN and communicate with the host PC.
The BX 2000 boards are fully plug-and-play. When installing the BX 2000 boards, the Control Panel Applet configures them and creates Windows NT services for the different drivers. These Windows NT services are started automatically when the PC boots. At that time, they download the object module into on-board memory.
Therefore, the BX 2000 boards do not require any configuration file to specify the interrupt, files to download, etc.

1.4.5 QX or AG Configuration File

If your applications requires media functions, you must add AG boards or QX boards in your system and configure them to work with BX 2000 boards. The main issue implies the MVIP switching and clock configuration of the boards.
Sample ag.cfg files are provided to show how to configure the AG boards (these files are also applicable to QX boards). For more information, refer to the BX 2000 Installation and Developer's Manual.

1.4.6 Demonstration Program

A BRI service demonstration program is included, with source code files and makefiles. Refer to Chapter 7 for more information.

1.5 Other Components

In addition to the BRI service and the BX 2000 board, you will need the following components to build a BRI service application: CT Access version 2.1 or later. Optionally, one or more AG boards or QX boards with DSP resources if you want to use media functions in your applications. For more information, refer to the appropriate AG or QX installation and developer's manual.

1.5.1 CT Access

CT Access is a complete development environment for telephony applications. It provides a standard set of telephony functions grouped into logical services, each of which has a standard API. CT Access provides functions for telephony-related tasks such as call control, DTMF generation and detection, tone generation and detection, and voice playing and recording.
CT Access includes a Switching service which controls switching on MVIP-compliant devices. You can use this service to make or break connections, send patterns, sample data, etc. The BX 2000 board has an MVIP-compliant driver.
For general information about installing and using CT Access, refer to the CT Access documentation.

1.6 Developing a BRI Service Application

To create a BRI service application: Step Where Step is Documented 1. Install BX 2000 boards in a system, and any other boards you will need in your application. The BX 2000 Installation and Developer's Manual and, if needed, the installation manuals for the other boards installed. 2. Install CT Access. CT Access Installation Manual. 3. Optionally, if there are AG boards or QX boards in your system, edit the AG configuration file or the QX configuration file so it describes all AG boards or QX boards in your system. The installation manuals for your AG boards and QX boards, and the AG Runtime Configuration and Developer's Manual. 4. Test your hardware configuration. The BX 2000 Installation and Developer's Manual and, if needed, the installation manuals for the other boards installed. 5. Write your application. This manual and the CT Access documentation set.

Step	Where Step is Documented
1. Install BX 2000 boards in a system, and any other boards you will need in your application.	The BX 2000 Installation and Developer's Manual and, if needed, the installation manuals for the other boards installed.
2. Install CT Access.	CT Access Installation Manual.
3. Optionally, if there are AG boards or QX boards in your system, edit the AG configuration file or the QX configuration file so it describes all AG boards or QX boards in your system.	The installation manuals for your AG boards and QX boards, and the AG Runtime Configuration and Developer's Manual.
4. Test your hardware configuration.	The BX 2000 Installation and Developer's Manual and, if needed, the installation manuals for the other boards installed.
5. Write your application.	This manual and the CT Access documentation set.

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