6.2 Tips for Programming Drop and Insert Applications

To the Global Call application, signaling is made available to the application as follows:

• Signaling information is passed to the Global Call application in the form of call control events; for example, line answer is passed as a GCEV_ANSWERED event.
• Signaling, such as line busy, is available to the application as an EGC_BUSY error code or a GCRV_BUSY result value; line no answer is available as an EGC_NOANSWER error code or GCRV_NOANSWER result value.
• Signaling such as a protocol error, an alerting event, a fast busy, an undefined telephone number, or network congestion are all returned to the application as an EGC_BUSY error code or a GCRV_BUSY result value.
• Protocols without acknowledgement, for example, non-backward CAS signaling protocols, generate a GCEV_DISCONNECTED event with an EGC_BUSY error code or a GCRV_BUSY result value when timeout or protocol errors occur during dialing.

For a drop and insert application in which the calling party needs to be notified of the exact status of the called party's line, the following approach may be used:

• Upon receipt of an incoming call from a calling party, issue a gc_MakeCall( ) function on the outbound line to the called party.
• After dialing completes on the outbound line, the application should drop the dialing resource, turn off call progress, and connect the inbound line to the outbound line so that the calling party can hear the tones returned on the outbound line. These tones provide positive feedback to the calling party as to the status of the called party's line.
• If the status of the called party's line is such that the call cannot be completed, the calling party hangs up and the application can then drop the call and release the resources used. Otherwise, when the call is answered, a GCEV_CONNECTED event will be received.

When call progress is being used, after dialing completes, the call progress software looks for ringback or voice on the outbound line. When ringback is detected, a GCEV_ALERTING event is generated. When voice is detected, a GCEV_ANSWERED event is generated. An unacceptable amount of time may lapse before either of these events is generated while the calling party is waiting for a response that indicates the status of the call. Thus, for drop and insert applications, call progress should be disabled as soon as dialing completes and the inbound and outbound lines connected so as to provide the calling party with immediate outbound line status and voice cut-through.

For a drop and insert application in which a call cannot be completed, the application can simulate and return a busy tone or a fast busy (redial) tone to the calling party. Typically, this condition occurs when a GCEV_DISCONNECTED event is generated due to a timeout or a protocol error during dialing or due to R2 backward signaling indicating a busy called party's line, equipment failure, network congestion or an invalid telephone number.

When a call cannot be completed because the called party's line is busy:

1. Use a tone or voice resource to generate a busy tone [60 ipm (impulses per minute)] or to record a busy tone.
2. Connect the busy tone to the calling party's line or play back the recorded busy tone file.
3. Drop and release the calling party's line when a GCEV_DISCONNECTED event is received.

When a call cannot be completed because of equipment failure, network congestion or an invalid telephone number:

1. Use a tone or voice resource to generate a fast busy tone (120 ipm) or to record a fast busy tone.
2. Connect the fast busy tone to the calling party's line or play back the recorded fast busy tone file.
3. Drop and release the calling party's line when a GCEV_DISCONNECTED event is received.

For voice function information, see the Voice API Library Reference for your operating system.

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