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Chapter 1

Introduction

1.1 Introduction

: 1.2.1 DPNSS Protocols and Protocol Layering
: 1.2.2 DPNSS Carriers

1.3 DPNSS Service Software

1.4 DPNSS Service Software Components

: 1.4.1 readme File
: 1.4.2 Driver Files
: 1.4.3 Downloadable Object Module
: 1.4.4 Server Task
: 1.4.5 DPNSS Server Control Panel Applet
: 1.4.6 DPNSS Function Libraries
: 1.4.7 Header Files
: 1.4.8 Demonstration Program
: 1.4.9 Switching DLL

1.5 Other Components

: 1.5.1 BX 3000 Boards
: 1.5.2 CT Access

1.6 Developing a DPNSS Application

1.1 Introduction

This chapter: Provides a brief introduction to DPNSS. Provides an overview of the NMS DPNSS service, and its role in an application. Lists and describes the DPNSS software components. Lists and describes the other hardware and software components required in an application. Outlines the application development process.

1.2 DPNSS

Digital Private Network Signaling System No. 1(DPNSS) is a set of codified standards that describe a signaling system for establishing and maintaining simple telephony and data calls. DPNSS is derived from British Telecom's Digital Access Signaling System (DASS).
DPNSS also describes a wide range of optional supplementary features, including Call Diversion operations, Call Transfer operations, and others. The range of available supplementary features depends upon the capabilities of the customer's Private Branch Exchange (PBX), and upon customer requirements.
A DPNSS 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). In this aspect, it can be compared with ISDN. However, DPNSS and ISDN differ in that DPNSS implements a complete set of features and allows access to virtual channels. Virtual channels allow exchanges between DPNSS nodes without allocating voice channels.

1.2.1 DPNSS Protocols and Protocol Layering

DPNSS 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 Interconnection (OSI) model for communication. DPNSS is based on this model. In OSI, seven separate levels, or layers, of communication are defined. The first three layers, called the chained layers, are the lowest levels. The chained layers are:
The physical layer (layer 1). This is 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.
The data link layer (layer 2). This is the layer above the physical layer. Protocols for this layer describe methods for error-free communication between devices across the physical link.
The network layer (layer 3). This is 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.
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, applications, etc.
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). Figure 1. OSI Protocol Layering Model

1.2.2 DPNSS Carriers

DPNSS is transmitted over standard E1 carriers. These are typically four-wire digital transmission links.
Data on an E1 trunk is transmitted in 32 separate channels. Each channel carries information digitized at 64 kbits per second (kbit/s).
E1 carries 32 channels. The channels are usually used as follows: 30 of the 32 channels carry data: voice, audio, data and/or video signals. These channels are called bearer channels (B channels). One channel carries signaling information for all B channels. This is called the D channel. One channel carries synchronization patterns and alarms.

1.3 DPNSS Service Software

The DPNSS API allows you to create powerful CT Access applications that communicate with E1 trunks to perform call control using a DPNSS protocol. The DPNSS API is implemented as a CT Access service. The DPNSS software is available under Windows NT only.
The service requires one or more BX 3000-1E or BX 3000-2E boards as the physical interface to DPNSS trunk lines. To perform voice processing and other DSP functions, you will need other NMS software and hardware such as AG or QX boards with ADI or VCE services. The BX 3000 boards and other hardware communicate using the MVIP bus, as shown in Figure 2. Figure 2. DPNSS Application Architecture
The DPNSS service software makes the D channel transparent to the application. The application addresses only real and virtual channels: A real channel consists of one B channel and its associated signaling. A virtual channel consists of a logical signaling channel without any associated traffic channel. Virtual channels are used to exchange DPNSS protocol messages without allocating supplementary B channels.
Using the DPNSS service, an application can access up to 30 real channels and 30 virtual channels simultaneously.
The DPNSS software is structured using a client/server model. Each process has access to the unique DPNSS server task through a DPNSS service instance mapped in the process space. The exchanges between DPNSS clients and server are performed through Windows sockets transporting a channel-based internal protocol. The DPNSS server is able to manage the full set of lines available on the BX 3000 boards installed in the host computer. All the available channels can be used by one single process. Each process can use only one channel. There are no constraints regarding which process is using which channel. Figure 3 depicts the DPNSS client/server architecture components: Figure 3. DPNSS Software Architecture

1.4 DPNSS Service Software Components

The DPNSS package contains the following: A readme file. Driver files for the BX 3000 boards. A downloadable object module containing the DPNSS protocol firmware. A DPNSS server task, implemented as a Windows NT Service. A Windows NT Control Panel applet which allows you to configure BX 3000 boards and interact with the DPNSS Server. An DPNSS function library for CT Access. Header files. A demonstration program, with its source code files and Visual C++ project files. A dynamic link library (DLL) file for switching.
The sections that follow briefly describe each of these components.

1.4.1 readme File

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

1.4.2 Driver Files

The driver files are copied into the winnt\system32\drivers\bx3000 directory during the installation. The installer creates one directory for each board and copies the driver into each directory.

1.4.3 Downloadable Object Module

The downloadable object module file contains the basic low-level software which an BX 3000 board requires to support DPNSS. The module is transferred from the host into on-board memory at launch time when the DPNSS server task is initialized.

1.4.4 Server Task

This component runs on the host PC. It is used by the DPNSS function library to interact with the board. One or several processes using the DPNSS library can access the server simultaneously.

1.4.5 DPNSS Server Control Panel Applet

This component is located in the Windows NT's Control Panel. When you start the NMS DPNSS Server, a panel appears. It allows you to perform basic operations such as starting or stopping the DPNSS channel activity. It also allows you to obtain information and statistics about the DPNSS channel in use.

1.4.6 DPNSS Function Libraries

This component runs on the host PC. It is used by the application program to interact with the DPNSS server.
The library is supplied as an extension to the CT Access software. It is a dynamic link library (DLL) named dpnapi.dll. This DLL is implicitly used by the library dpnapi.lib, that must be included in your project.

1.4.7 Header Files

One header file named dpndef.h is supplied with DPNSS software. It contains every declaration related to DPNSS service functions, structures, event codes, identifier values, and error codes.

1.4.8 Demonstration Program

A demonstration program is included, with its source code files and Microsoft Visual C++ project files. For details, see Chapter 9.

1.4.9 Switching DLL

The switching DLL (bx3sw.dll) manages the switching matrix located on the BX 3000 board. This DLL is used by the standard CT Access SWI service located in the CT Access manager SWIMGR.

1.5 Other Components

In addition to the DPNSS software, you need the following components to build an application implementing call control on a DPNSS network: One or more BX 3000-1E or BX 3000-2E boards to provide interfaces to DPNSS E1 trunks. CT Access version 2.1 or later.

1.5.1 BX 3000 Boards

Two versions of BX 3000 boards are currently available: BX 3000-1E boards each provide an interface to one DPNSS E1 trunk. BX 3000-2E boards each provide an interface to two DPNSS E1 trunks.
Each BX 3000 board occupies a single ISA slot in the host computer. A computer can be equipped with four boards in a standard configuration giving a total amount of 240 channels.
BX 3000 boards connect to other boards via the MVIP bus. The MVIP bus allows the BX 3000 boards to share B channels with other boards on the MVIP bus. For example, you can connect a BX 3000 with one or more AG Quad boards for applications that perform trunk-to-trunk switching. You can add additional DSP resources, analog station interfaces, or loop start line interfaces on other AG boards. You can also use compatible products from other manufacturers with AG and BX 3000 boards.

1.5.2 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, tone and DTMF tone generation and detection, and voice playing and recording.
CT Access includes a service which controls switching on MVIP-compliant devices. You can use this service to make or break connections, send patterns, sample data, etc. This service supports both MVIP-95 and MVIP-90 specifications. Alternatively, you can use the swish standalone utility to control switching interactively or in a batch mode.
For general information about installing and using CT Access, see the CT Access documentation.

1.6 Developing a DPNSS Application

To create a DPNSS application: Step Where Step is Documented 1. Install CT Access 2.1. CT Access Installation Manual 2. Install a BX-3000 board. BX-3000 Installation and Developer's Manual 3. Install the DPNSS software. BX-3000 Installation and Developer's Manual 4. Test your hardware installation. BX-3000 Installation and Developer's Manual 5. Write your application. This manual and the CT Access documentation set.

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