2 Supplementary Services Overview

This chapter:

The following table summarizes the supplementary service operations available across the variants.

Three parties are identified in the activation or invocation of a supplementary service:

This section provides an overview of the supplementary services available with the ETS 300 variant, and how these services operate in the network architecture.

Under ETS 300, most supplementary services require subscription. Subscription services are optional services provided by the network operator on a provisioning basis. When the user requests network services from a provider, he/she also can optionally request one or more subscription services. The services are not available unless the interface is provisioned with them.

Note: Some supplementary services may not require subscription. For example, the Call Hold service may be generally available.

Under ETS 300, most supplementary services must be activated before they are used. Activation is the process of "turning on" the service at the network or stack level. Once a service is activated, the network, the stack and/or the application can invoke (use) the service when needed.

A supplementary service can be activated in at least one of the following ways:

The act of using an activated supplementary service is called invocation of the service. In some cases, an application can automatically activate an inactive supplementary service by invoking it: the activation and invocation occur simultaneously. The Explicit Call Transfer service is an example: the application can invoke this service on a call-by-call basis.

An application on the user side of the S/T reference point may invoke Hold and Retrieve services on the network. When a call (identified by its connection id) is placed on hold, the bearer channel (B channel) resource for the call is deallocated without losing the context of the call. The network side of the S/T reference point then reserves the B channel for allocation in a subsequent call offered by the user side.

The following hold and retrieve operations can be performed under ETS 300:

For more information, see Chapter 5.

Call Transfer services allow an application at the user side of the S/T reference point to cause two existing calls to be joined together on the network side.

The following call transfer operations can be performed under ETS 300:

Under ETS 300, two types of call forwarding services are available: Call Diversion and Call Deflection.

Call Diversion is activated by the served user application on the network for all calls for a specific user or trunk. With this service active, the network reroutes calls addressed to a specific user or trunk, without consulting the user side of the S/T reference point. Three types of call diversion are supported: Call Forwarding - Unconditional, Call Forwarding - Busy, and Call Forwarding - No Response.

The following Call Diversion operations can be performed under ETS 300:

Call Deflection can be activated for all calls, or activated on a call-by-call basis. When invoked, the served user stack (not the network) deflects (redirects) the call to a new destination. With this service, the user side can deflect a call to a different destination, without first answering it.

The following Call Deflection operations can be performed under ETS 300:

A special Remind Diversion service can also be activated for an ETS 300 application, on a subscription basis. When a served user initiates an outbound call, this service causes the network to remind the served user if Call Diversion has been activated for incoming calls.

Advice of Charge (AOC) provides the user with a way of tracking the costs of a specific call, in real time. Three separate AOC services are available, depending upon at what point the application requires AOC information:

The following Advice of Charge operations can be performed under ETS 300:

The following identification services are implemented in AG ISDN for the ETS 300 variant:

This section provides an overview of the supplementary services available with the Q.SIG variant, and how these services are implemented in the network architecture.

Q.SIG applications provide supplementary services as part of their basic duties: the "subscription" concept has no meaning at this level. All supported services are activated at all times: a Q.SIG application need only invoke a service in order to use it.

Tandem services support the transit node role. A transit node is an intermediate step in a call being set up through a network. A PINX may take on the responsibilities of a transit node during the call setup procedures, as a result of routing decisions, or it may happen as a result of supplementary service activation (e.g. call transfer). A transit node must maintain two separate basic calls, and additionally, interwork the events from one call into actions on the other call.

AG ISDN supports the Call Bridging tandem service. When this service is active, all notification and facility information elements are passed from one end to the other through the transit node. However, the application remains responsible for basic call control interaction. for example, the application must handle hanging up.

This service may be invoked in either of two ways:

AG ISDN supports transfer-by-join operations between Q.SIG nodes. In a transfer-by-join operation, the two separate calls are connected through the local node. The local node is still involved in the call (i.e. the call was not rerouted).

To transfer a call under Q.SIG, the application must perform the switching required to connect calls together, using standard calls to the CT Access Switching service. The application also invokes a Notify Transfer operation to notify each remote party that the transfer has taken place.

Under Q.SIG, Call Diversion supports Call Forwarding - Unconditional, Call Forwarding - Busy, and Call Forwarding - No Response.

The following Call Diversion operations are supported under Q.SIG:

All of the call identification services for the ETS 300 variant (see Section 2.4.6) are also implemented for Q.SIG. In addition, the following Q.SIG-only identification services are implemented in AG ISDN: