Cisco SPA1112 Provisioning Manual page 139

Voice Parameters
<Referral_Services_Code>s
Provisioning Guide for Cisco SPA100 and SPA200 Series Analog Telephone Adapters
These codes tell the ATA what to do when the user places the
current call on hold and is listening to the second dial tone.
One or more *codes can be configured into this parameter,
such as *98, or *97|*98|*123, etc. The maximum length is 79
characters. This parameter applies when the user places the
current call on hold by pressing the hook flash button. Each
*code (and the following valid target number according to
current dial plan) triggers the ATA to perform a blind transfer
to a target number that is prepended by the service *code.
For example, after the user dials *98, the ATA plays a special
dial tone called the Prompt Tone while waiting for the user the
enter a target number (which is checked according to dial
plan as in normal dialing). When a complete number is
entered, the ATA sends a blind REFER to the holding party
with the Refer-To target equal to *98 target_number. This
feature allows the ATA to hand off a call to an application
server to perform further processing, such as call park.
The *codes should not conflict with any of the other vertical
service codes internally processed by the ATA. You can
empty the corresponding *code that you do not want the ATA
to process.
Default setting: blank
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