1.1 Introduction

1.2 AG ISDN Supplementary Services and ISDN Variants

1.2.1 About The ETS 300 Variant

1.2.2 About The Q.SIG Variant

1.3 AG ISDN Implementation and Related Specifications

1.3.1 ETS 300 Variant

1.3.2 Q.SIG Variant

1.1 Introduction

The AG ISDN Supplementary Service Developer's Reference Manual describes ISDN supplementary services accessible by means of the Natural Microsystems AG ISDN software. This manual provides:

• Background information about each available service, as it is defined in European Telecommunications Standards Institute (ETSI) specifications, and/or in the specifications for the Q.SIG variant.

• A programming guide for AG ISDN Messaging API applications.

• Documentation of a demonstration program included with the software.

This document is targeted to developers of telephony and voice applications who are using CT Access. This document defines telephony terms where applicable, but assumes that the reader is familiar with basic telephony concepts. It also assumes that the user is familiar with the C programming language.

Although some introductory material is provided, this manual also assumes that the reader is familiar with the operation of basic ISDN supplementary services, as described in appropriate specifications.

ISDN supplementary services allow an AG ISDN application to implement powerful functionality beyond basic call control. These functions include:

• Call transfer operations: an application can reroute a call on hold to another user.

• Call forwarding operations: a network or ISDN stack can reroute a call destined for a user to another user.

• Call hold and retrieve services: an application can place a call on hold, and retrieve a held call.

• Advice of Charge services: an application can track the costs of a specific call, in real-time.

• Tandem services: an application can support a transit node (one that exists between two other nodes, and route messages from one node to the other).

• Identification services: called or calling parties can exchange information.

An AG ISDN application can access supplementary services using the standard AG ISDN Messaging API. Supplementary services messages are included in standard ACU messages sent to or received from the AG ISDN protocol stack. Each service specification and any associated data is stored in an extended data area appended to the ACU message buffer. Supplementary services can be invoked with any primitive passing over the ACU interface.

One primitive may contain multiple extended data structures. This allows the application to invoke multiple services with one primitive, or to receive multiple indications with one primitive coming up from the ACU interface. For details, see Chapter 2.

1.2 AG ISDN Supplementary Services and ISDN Variants

ISDN supplementary services are implemented differently under various variants. AG ISDN supports a subset of the supplementary services in two variants:

• The Digital Signaling System No. One (DSS1) European Telecommunications Standard (ETS) produced by the Signaling Protocols and Switching (SPS) Technical Committee of the European Telecommunications Standards Institute (ETSI). In this document, this variant is referred to as the ETS 300 variant.

• The Q.SIG signaling system for corporate networking. Q.SIG is standardized by a consortium of standards-producing bodies, including ETSI, the European Computer Manufacturer's Association (ECMA), and the International Organization for Standardization (ISO). The production effort is coordinated by the IPNS Forum. In this document, this variant is referred to as the Q.SIG variant.

1.2.1 About The ETS 300 Variant

ETS 300 specifications describe a protocol designed to access network services from an intelligent user terminal. The protocol is not symmetric. It requires two distinct roles, the user side and the network side. AG ISDN supports both sides for basic call control. Supplementary services, at this time, have been implemented only for the user side.

Figure 1 shows a sample network and the points where an AG ISDN ETS 300 supplementary service application can interface with the network. As shown in the figure, an AG ISDN application written for the ETS 300 variant interfaces with the network on the user side of the S/T reference point of a CEPT E1 PRI ISDN trunk.

Figure 1. Network Diagram Showing Position of ETSI Application

Supplementary services over the T reference point are generally requests by the application for the network to do something on behalf of a subscriber or interface (e.g. transfer a call).

1.2.2 About The Q.SIG Variant

Q.SIG specifications describe interactions between nodes in a private ISDN network (PISN). Each node is a Private ISDN Network Exchange (PINX). These nodes play identical roles in the network. Q.SIG is a symmetric protocol because there is no distinct user side and network side.

Figure 2 shows a sample Q.SIG network, and the reference points where an AG ISDN Q.SIG supplementary service application can join into the network. As shown in the figure, an AG ISDN application written for this variant interfaces with the network at the Q reference point. The role of the application is to implement call control, and control message exchanges at this point.

Figure 2. Network Diagram Showing Position of Q.SIG Application

Figure 3 shows the part of an AG ISDN application that is the Q reference point.

Note: Application code related to local access (analog lines, etc.) is not considered part of the Q reference point.

Figure 3. Q Reference Point

Supplementary services over the Q reference point are generally requests by the application for services from another node in the network, or notifications that the local node has performed various services.

Note: If you are building a Q.SIG application, the PINX node address must be specified in your initial call to isdnStartProtocol. For more information, see Section 3.10.

1.3 AG ISDN Implementation and Related Specifications

This section describes the relationship of the AG ISDN supplementary service implementation to ETSI specifications.

1.3.1 ETS 300 Variant

The NMS ETS 300 variant implementation is a reference to the Digital Subscriber Signaling System No. One (DSS1) European Telecommunications Standard (ETS) produced by the Signaling Protocols and Switching (SPS) Technical Committee of the European Telecommunications Standards Institute (ETSI). The standard can be catagorized as a basic Q.931 protocol with the addition of ASN.1 facilities to support ISDN supplementary services.

Following is a partial list of the documents describing supplementary services as they are implemented in the NMS ETSI supplementary service package:

• ETS 300 102-1 (1990): "Integrated Services Digital Network (ISDN) User- network interface layer 3; Specifications for basic call control."

• ETS 300 195-1: "Integrated Services Digital Network (ISDN); Supplementary service interactions; Digital Subscriber Signaling System No. One (DSS1) protocol; Part 1: Protocol specification."

• ETS 300 196-1 (1993): "Integrated Services Digital Network (ISDN); Generic functional protocol for the support of supplementary services; Digital Subscriber Signaling System No. One (DSS1) protocol; Part 1: Protocol Specification."

• ETS 300 207-1 (1994): "Integrated Services Digital Network (ISDN); Diversion supplementary services; Digital Subscriber Signaling System No. One (DSS1) protocol; Part 1: Protocol Specification."

1.3.2 Q.SIG Variant

Q.SIG specifications are produced by a consortium of standards-producing bodies, including ETSI, the European Computer Manufacturer's Association (ECMA), and the International Organization for Standardization (ISO). The production effort is coordinated by the IPNS Forum.

The AG ISDN Q.SIG implementation is based on ETSI second-edition specifications. These were produced after ECMA-created standards (based on CCITT standards and enhanced by ECMA after a European Commission mandate to produce such standards) were submitted to the ISO/IEC.

Following is a partial list of standards documents relevant to the AG ISDN implementation. Where two standards are listed, the first is the stage 1/stage 2 standard and the second is the stage 3 (Q.SIG) standard.

Q.SIG Service Name	ECMA Standard and Publication Date	ETSI Standard and Publication Date	ISO/IEC Standard and Publication Date
Basic Call (64kb/s unrestricted, 3.1kHz audio and speech bearer services)	ECMA-142/143, June 1990	ETS300 171/172, January 1993	IS 11574/11572 1994
Calling Line Identification Presentation	ECMA-148, June 19901	ETS300 173, December 1992*	IS 14136 1995*
Connection Line Identification Presentation	ECMA-148, June 1990*	ETS300 173, December 1992*	IS 14136 1995*
Calling/Connected Line Identification Restriction	ECMA-148, June 1990*	ETS300 173, December 1992*	IS 14136 1995*
Calling Name Identification Presentation	ECMA 163/164, March 1992	ETS300 237/238, June 1993	IS 13864/13868 1995
Connected Name Identification Presentation	ECMA 163/164, March 1992	ETS300 237/238, June 1993	IS 13864/13868 1995
Calling/Connected Name Identification Restriction	ECMA 163/164, March 1992	ETS300 237/238, June 1993	IS 13864/13868 1995
Generic Functional Procedures	ECMA 165, March 1992	ETS300 239, June 1993	IS 11582 1995
Call Forwarding Unconditional	ECMA 173/174, June 1992	ETS300 256/257, November 1993	IS 13872/13873 1995
Call Forwarding Busy	ECMA 173/174, June 1992	ETS300 256/257, November 1993	IS 13872/13873 1995
Call Forwarding No Reply	ECMA 173/174, June 1992	ETS300 256/257, November 1993	IS 13872/13873 1995
Call Transfer	ECMA 177/178, June 1992	ETS300 260/261, November 1993	IS 13865/13869 1995
Advice of Charge, Start of Call	ECMA 211/212, December 1994
Advice of Charge, During Call	ECMA 211/212, December 1994
Advice of Charge, End of Call	ECMA 211/212, December 1994

1 There is no stage 3 standard for this supplementary service. Q.SIG support for this supplementary service is covered by the basic call stage 3 standard.

In the ISO specifications, Q.SIG is referred to as Private Signaling System No. One.

The Q.SIG specifications identify different types of Private ISDN Network Exchanges (PINXs), and different supplementary services. This creates a conformance "matrix."

Q Reference Points

The Q reference point is different than typical reference points, in that it describes the functions of a part of the network, rather than describing a point of interface to the network. The reference point location also implies that there is no user or network side of a connection. Rather, all Q.SIG signaling is symmetric between adjacent nodes.